,transcriber's ,notes ,text between underscores1 equal signs and tildes represents text printed in italics1 bold face and sans-serif1 respectively4 ,small capitals have been replaced with ,,all ,,capitals4 ,more ,transcriber's ,notes may be found at the end of this text4 ,,tunneling3 ,a ,,practical ,,treatise ,,by ,,charles ,,prelini1 ,c4 ,e4 ,,author ,,of 8,,earth ,,and ,,rock ,,excavation10 8,,dredges ,,and ,,dredging10 8,,earth ,,slopes1 ,,retaining ,,walls ,,and ,,dams10 ,,etc4 ,,professor ,,of ,,civil ,,engineering ,,in ,,manhattan ,,college1 ,,new ,,york #afg ,,illustrations ,,sixth ,,edition1 ,,revised ,,and ,,enlarged ,illustration ,,new ,,york ,d4 ,,van ,,nostrand ,,company ,,twenty-,,five ,,park ,,place #aiab ,,copyright1 #aiab1 ,,by ,d4 ,,van ,,nostrand ,,company ,,new ,,york ,stanhope ,press ,f4 ,h4 ,,gilson ,,company ,,boston1 ,u4,s4,a4 ,,preface ,,to ,,the ,,sixth ,,edition ,during the few years that have elapsed since the publication of the first edition of this work1 the art of tunneling through different soils and especially under large bodies of water1 has made considerable progress4 ,during the last ten years1 no less than eight subaqueous tunnels involving the construction of sixteen tubes have been constructed for the service of the city of ,new ,york alone4 ,the reader will1 no doubt1 also recall the tunnels under the ,boston ,harbor1 the ,st4 ,clair1 the ,charles and ,detroit ,rivers in our own country as well as the tunnels under the ,thames and the ,seine in ,europe4 ,engineers1 contractors and workmen have acquired such experience in these difficult underground and under-river construction that the work is now undertaken without any of the fear and hesitation that were associated with the earlier enterprises4 ,as entirely new methods have been introduced by professional men1 it was found necessary to arrange the presentation of the subject in this sixth edition so as to give due prominence to these recent methods4 ,besides this1 other changes have been made in order to give greater attention to ,american method of excavating tunnels through rock and loose soil4 ,this will explain the treatment of the crown-bar and also the extensive illustration of the heading and bench method as well as the drift method of driving tunnels which is followed in the ,united ,states4 ,space has also been given to important tunnels recently built mainly for the purpose of illustrating the various methods discussed in the text and also to bring out more clearly the characteristics of the different methods of tunnel excavation4 ,the author hopes that these added features will meet the present requirements of engineers and students4 ,,charles ,,prelini4 ,,manhattan ,,college1 ,,new ,,york ,,city4 ,,contents ,,page ,,introductory--,,the ,,historical ,,development ,,of ,,tunnel ,,building xiii ,,chapter ,i4 ,,preliminary ,,considerations2 ,,choice ,,between ,a ,,tunnel ,,and ,,an ,,open ,,cut2 ,,geological ,,surveys #a ,,ii4 ,,methods ,,of ,,determining ,,the ,,center ,,line ,,and ,,forms ,,and ,,dimensions ,,of ,,cross-,,section #i ,,iii4 ,,excavating ,,machines ,,and ,,rock ,,drills2 ,,explosives ,,and ,,blasting #bb ,,iv4 ,,general ,,methods ,,of ,,excavation2 ,,shafts2 ,,classification ,,of ,,tunnels #cf ,v4 ,,methods ,,of ,,timbering ,,or ,,strutting ,,tunnels #dg ,,vi4 ,,methods ,,of ,,hauling ,,in ,,tunnels #ei ,,vii4 ,,types ,,of ,,centers ,,and ,,molds ,,employed ,,in ,,constructing ,,tunnel ,,linings ,,of ,,masonry #ff ,,viii4 ,,methods ,,of ,,lining ,,tunnels #gb ,,ix4 ,,tunnels ,,through ,,hard ,,rock2 ,,general ,,discussion2 ,,representative ,,mechanical ,,installations ,,for ,,tunnel ,,work #hd ,x4 ,,tunnels ,,through ,,hard ,,rock 7continued72 ,,excavation ,,by ,,drifts2 ,,the ,,simplon ,,and ,,murray ,,hill ,,tunnels #ajb ,,xi4 ,,tunnels ,,through ,,hard ,,rock 7continued72 ,,excavation ,,by ,,headings #acj ,,xii4 ,,excavating ,,tunnels ,,through ,,soft ,,ground2 ,,general ,,discussion2 ,,the ,,belgian ,,method #adc ,,xiii4 ,,the ,,german ,,method--,,excavating ,,tunnels ,,through ,,soft ,,ground 7continued72 ,,baltimore ,,belt ,,line ,,tunnel #aee ,,xiv4 ,,the ,,full ,,section ,,method ,,of ,,tunneling2 ,,english ,,method2 ,,american ,,method2 ,,austrian ,,method #aff ,,xv4 ,,special ,,treacherous ,,ground ,,method2 ,,italian ,,method2 ,,quicksand ,,tunneling2 ,,pilot ,,method #ahb ,,xvi4 ,,open-,,cut ,,tunneling ,,methods2 ,,tunnels ,,under ,,city ,,streets2 ,,boston ,,subway ,,and ,,new ,,york ,,rapid ,,transit #aie ,,xvii4 ,,submarine ,,tunneling2 ,,general ,,discussion2 ,,the ,,severn ,,tunnel #bah ,,xviii4 ,,submarine ,,tunneling 7continued72 ,,the ,,compressed ,,air ,,method2 ,,the ,,milwaukee ,,water-,,works ,,tunnel #bbe ,,xix4 ,,submarine ,,tunneling 7continued72 ,,the ,,shield ,,system #bch ,,xx4 ,,submarine ,,tunneling 7continued72 ,,the ,,shield ,,and ,,compressed ,,air ,,method2 ,,the ,,hudson ,,river ,,tunnel ,,of ,,the ,,pennsylvania ,,railroad #bfc ,,xxi4 ,,submarine ,,tunneling 7continued72 ,,tunnels ,,at ,,very ,,shallow ,,depth2 ,,the ,,cofferdam ,,method2 ,,the ,,pneumatic ,,caisson ,,method2 ,,the ,,joining ,,together ,,sections ,,of ,,tunnels ,,built ,,on ,,land #bha ,,xxii4 ,,accidents ,,and ,,repairs ,,in ,,tunnels ,,during ,,and ,,after ,,construction #cja ,,xxiii4 ,,relining ,,timber-,,lined ,,tunnels ,,with ,,masonry #cae ,,xxiv4 ,,the ,,ventilation ,,and ,,lighting ,,of ,,tunnels ,,during ,,construction #cbe ,,xxv4 ,,the ,,cost ,,of ,,tunnel ,,excavation ,,and ,,the ,,time ,,required ,,for ,,work #ccf ,,list ,,of ,,illustrations ,,figure ,,page #a4 ,diagram ,showing ,manner of ,lining in ,rectilinear ,tunnels #aj #b4 ,b4 ,r4 ,value's ,device for ,locating the ,center ,line ,inside of a ,tunnel #aa #c4 ,triangulation ,system for ,establishing the ,center ,line of the ,st4 ,gothard ,tunnel #ab #d4 ,method of ,transferring the ,center ,line down ,center ,shafts #ac #e4 ,method of ,transferring the ,center ,line down the ,side ,shafts #ad #f4 ,method of ,laying out the ,center ,line of ,curvilinear ,tunnels #ae #g4 ,diagram of ,polycentric ,sectional ,profile #ai #h1 #i and #aj4 ,typical ,sectional ,profiles for ,tunnel #bj #aa4 ,soft ,ground ,bucket ,excavating ,machine2 ,central ,london ,underground ,railway #bb #ab4 ,column ,mounting for ,percussion ,drill2 ,ingersoll ,sargent ,drill ,co4 #bf #ac4 ,sketch of ,diamond ,drill ,bit #bg #ad4 ,diagram ,showing ,sequence of ,excavation for ,st4 ,gothard ,tunnel #cf #ae4 ,diagram ,showing ,manner of ,determining ,correspondence of ,excavation to ,sectional ,profile #ch #af4 ,polar ,protractor for ,determining ,profile of ,excavated ,cross- ,section #ci #ag4 ,joining ,tunnel ,struts by ,halving #dh #ah4 ,round ,timber ,post and ,cap ,bearing #dh #ai4 ,ceiling ,strutting for ,tunnel ,roofs #di #bj4 ,ceiling ,strutting with ,side ,post ,supports #di #ba4 ,sill1 ,side ,post and ,cap ,cross ,frame ,strutting #di #bb4 ,reinforced ,cross ,frame ,strutting for ,treacherous ,materials #di #bc4 ,longitudinal ,poling-,board ,system of ,roof ,strutting #ej #bd4 ,transverse ,poling-,board ,system of ,roof ,strutting #ej #be4 ,shaft with ,single ,transverse ,strutting #eb #bf4 ,rectangular ,frame ,strutting for ,shafts #ec #bg4 ,reinforced ,rectangular ,frame ,strutting for ,shafts in ,treacherous ,materials #ec #bh4 ,strutting of ,timber ,posts and ,railway ,rail ,caps #ef #bi4 ,strutting ,made ,entirely of ,railway ,rails #ef #cj4 ,rziha's ,combined ,strutting and ,centering of ,cast ,iron #eg #ca4 ,cast-,iron ,segment of ,rziha's ,strutting and ,centering #eg #cb4 ,cast-,iron ,segmental ,strutting for ,shafts #eh #cc4 ,platform ,car for ,tunnel ,work #ei #cd4 ,iron ,dump-,car for ,tunnel ,work #fj #ce4 ,wooden ,dump-,car for ,tunnel ,work #fj #cf4 ,box-,car for ,tunnel ,work #fa #cg4 ,elevator ,car for ,tunnel ,shafts #fe #ch4 ,ground ,mold for ,constructing ,tunnel ,invert ,masonry #fg #ci4 ,combined ,ground ,mold and ,leading ,frame for ,invert and ,side ,wall ,masonry #fg #dj4 ,leading ,frame for ,constructing ,side ,wall ,masonry #fh #da4 ,plank ,center for ,constructing the ,roof ,arch #fi #db4 ,trussed ,center for ,constructing the ,roof ,arch #gj #dc and #dd4 ,a ,typical ,form of ,timber ,lining for ,tunnels #gc #de4 ,diagram ,showing ,forms adopted for ,side-,wall ,foundations #gf #df and #dg4 ,transverse ,sections of ,tunnels ,showing ,methods for ,increasing the ,thickness of the ,lining at ,different ,points #gi #dh4 ,refuge ,niche in ,st4 ,gothard ,tunnel #ha #di4 ,east ,portal of ,hoosac ,tunnel #hb #ej1 #ea and #eb4 ,arrangement of ,drill ,holes in the ,heading of ,turchino ,tunnel #ia #ec and #ed4 ,arrangement of ,drill ,holes in the ,heading of the ,fort ,george ,tunnel #ia #ee4 ,diagram ,showing ,sequence of ,excavations in ,drift ,method of ,tunneling ,rock #ajb #ef4 ,sketches ,showing ,sequence of ,work in ,excavating and ,lining the ,simplon ,tunnel #aaa #eg4 ,general ,details of the ,brandt ,rotary ,drills ,employed at the ,simplon ,tunnel #aab #eh4 ,sequence of ,excavation in the ,murray ,hill ,tunnel #abd #ei4 ,traveling ,platform for the ,excavation of the ,upper ,side of the ,murray ,hill ,tunnel #abe #fj4 ,timbering ,used in the ,murray ,hill ,tunnel #abf #fa4 ,diagram ,showing ,sequence of ,excavation in ,heading ,method of ,tunneling ,rock #acb #fb4 ,method of ,strutting ,roof1 ,st4 ,gothard ,tunnel #ace #fc4 ,sketch ,showing ,arrangement of ,tracks1 ,st4 ,gothard ,tunnel #ace #fd4 ,arrangement of ,drill ,holes in the ,fort ,george ,tunnel #acg #fe4 ,longitudinal ,section of the ,heading and ,bench ,excavation at the ,fort ,george ,tunnel #acg #ff4 ,diagram ,showing the ,arrangement of ,drill ,holes in the ,heading and ,bench of the ,gallitsin ,tunnel #adj #fg4 ,diagram ,showing ,modification of the ,heading and ,bench ,method #adj #fh and #fh;,a4 ,diagrams ,showing ,sequence of ,excavation in the ,belgian ,method #ade #fi4 ,sketch ,showing ,radial ,roof ,strutting1 ,belgian ,method #adg #gj4 ,sketch ,showing ,roof ,arch ,center1 ,belgian ,method #adg #ga4 ,sketch ,showing ,method of ,underpinning ,roof ,arch with the ,side ,wall ,masonry #adi #gb4 ,longitudinal ,section ,showing ,construction by the ,belgian ,method #adi #gc4 ,diagram ,showing ,sequence of ,excavation in ,modified ,belgian ,method #aeb #gd4 ,sketch ,showing ,failure of ,roof ,arch by ,opening at ,crown #aec #ge4 ,sketch ,showing ,methods of ,repairing ,roof ,arch ,failures #aed #gf4 ,diagrams ,showing ,sequence of ,excavation in ,german ,method of ,tunneling #aee #gg4 ,diagram ,showing ,sequence of ,excavation in ,water ,bearing ,material1 ,german ,method #aef #gh4 ,sketch ,showing ,work of ,excavating and ,timbering ,drifts and ,headings #aeg #gi4 ,sketch ,showing ,method of ,roof ,strutting #aeg #hj4 ,sketch ,showing ,roof ,arch ,centers and ,arch ,construction #aeh #ha4 ,sketch ,showing ,method of ,excavating and ,strutting ,baltimore ,belt ,line ,tunnel #afb #hb4 ,roof ,arch ,construction with ,timber ,centers1 ,baltimore ,belt ,line ,tunnel #afc #hc4 ,roof ,arch ,construction with ,iron ,centers1 ,baltimore ,belt ,line ,tunnel #afd #hd4 ,diagram ,showing ,sequence of ,excavation in ,english ,method of ,tunneling #afg #he4 ,sketches ,showing ,construction of ,strutting1 ,english ,method #afh #hf and #hg4 ,sketches of ,typical ,timber ,roof-,arch ,centers1 ,english ,method #afi #hh4 ,sequence of ,excavation in the ,american ,method #agb #hi4 ,strutting the ,heading in the ,american ,method #agb #ij4 ,temporary ,timbering of the ,roof in the ,american ,method #agc #ia4 ,showing ,crown ,bars ,supported by ,segmental ,arches #agc #ib4 ,transversal and ,longitudinal ,section of a ,tunnel ,excavated and ,strutted ,according to the ,american ,method #agd #ic and #id4 ,diagrams ,showing ,sequence of ,excavation in ,austrian ,method of ,tunneling #agg #ie1 #if and #ig4 ,sketches ,showing ,construction of ,strutting1 ,austrian ,method #agh #ih4 ,sketch ,showing ,manner of ,constructing the ,lining ,masonry1 ,austrian ,method #agi #ii4 ,diagram ,showing ,sequence of ,excavation in ,italian ,method of ,tunneling #ahc #ajj4 ,sketch ,showing ,strutting for ,lower ,part of ,section #ahc #aja and #aja;,a4 ,sketches ,showing ,construction of ,centers1 ,italian ,method #ahd #ajb4 ,sketch ,showing ,invert and ,foundation ,masonry1 ,italian ,method4 #ahe #ajc4 ,sketch ,showing ,longitudinal ,section of a ,tunnel under ,construction1 ,italian ,method #ahf #ajd4 ,sketch ,showing ,sequence of ,excavation1 ,stazza ,tunnel #ahf #aje4 ,sketch ,showing ,method of ,strutting ,first ,drift1 ,stazza ,tunnel #ahg #ajf and #ajg4 ,sketches ,showing ,temporary ,strutting ,arch ,construction1 ,stazza ,tunnel #ahg #ajh4 ,sketch ,showing ,preliminary ,drainage ,galleries1 ,quicksand ,method #aij #aji4 ,sketch ,showing ,construction of ,roof ,strutting1 ,quicksand ,method #aij #aaj4 ,sketch ,showing ,construction of ,masonry ,lining1 ,quicksand ,method #aia #aaa4 ,sketch ,showing ,pilot ,method of ,tunneling #aic #aab4 ,diagram ,showing ,sequence of ,construction in ,open-,cut ,tunnels #aig #aac4 ,sketch ,showing ,method of ,timbering ,open-,cut ,tunnels1 ,double ,parallel ,trench ,method #aih #aad4 ,side-,wall ,foundation ,construction ,open-,cut ,tunnels #aih #aae4 ,wide-,arch ,section1 ,boston ,subway #bjd #aaf4 ,double-,barrel ,section1 ,boston ,subway #bje #aag4 ,four-,track ,rectangular ,section1 ,boston ,subway #bjf #aah4 ,section ,showing ,slice ,method of ,construction1 ,boston ,subway #bjf #aai4 ,double-,track ,section1 ,new ,york ,rapid ,transit ,railway #bab #abj4 ,park ,avenue ,deep ,tunnel ,construction1 ,new ,york ,rapid ,transit ,railway #bad #aba4 ,harlem ,river ,tunnel1 ,new ,york ,rapid ,transit ,railway #bae #abb4 ,sketch ,showing ,underground ,stream1 ,milwaukee ,water-,works ,tunnel #bbi #abc4 ,sketch ,showing ,methods of ,lining1 ,milwaukee ,water-,works ,tunnel #bcb #abd4 ,longitudinal ,section of ,brunel's ,shield1 ,first ,thames ,tunnel #bda #abe4 ,first ,shield ,invented by ,barlow #bdb #abf4 ,second ,shield ,invented by ,barlow #bdc #abg4 ,shield ,suggested by ,greathead for the ,proposed ,north and ,south ,woolwich ,subway #bde #abh4 ,beach's ,shield ,used on ,broadway ,pneumatic ,railway ,tunnel #bde #abi4 ,shield for ,city and ,south ,london ,railway #bdf #acj4 ,shield for ,st4 ,clair ,river ,tunnel #bdg #aca4 ,shield for ,blackwall ,tunnel #bdh #acb4 ,elliptical ,shield for ,clichy ,sewer ,tunnel1 ,paris #bdi #acc4 ,semi-,elliptical ,shield for ,clichy ,sewer ,tunnel #bej #acd4 ,roof ,shield for ,boston ,subway #bea #ace4 ,transversal and ,longitudinal ,section of ,prelini's ,shield #beb #acf4 ,elevation and ,section of ,hydraulic ,jack1 ,east ,river ,gas ,tunnel #bfj #acg4 ,cast-,iron ,lining1 ,st4 ,clair ,river ,tunnel #bfb #ach4 ,general ,elevations and ,sections of ,shields #bgj #aci4 ,plan and ,elevation of ,first ,bulkhead ,wall in ,south ,tube1 ,manhattan #bgc #adj4 ,typical ,cross-,sections of ,one ,tube of ,pennsylvania ,railroad ,tunnel under the ,hudson ,river #bgh #ada4 ,sections of ,cofferdam1 ,van ,buren ,st4 ,tunnel1 ,chicago #bhc #adb4 ,showing ,working ,platforms and ,piles ,sunk in ,dredged ,channel #bhf #adc4 ,showing ,sheeting-,piles for the ,sides of the ,caisson and ,trussed ,beam for the ,roof #bhg #add4 ,showing the ,caisson with the ,working-,chamber #bhg #ade4 ,showing the ,tunnel ,constructed within the ,caisson #bhi #adf4 ,showing ,sides of the ,caisson and ,supports for the ,roof #bij #adg4 ,showing the ,roof of the ,caisson ,formed by the ,upper ,half of the ,tunnel #bia #adh4 ,showing the ,tunnel ,completed by ,building the ,lower ,half within the ,caisson #bib #adi4 ,transversal ,section of the ,caissons for the ,tunnel under the ,seine ,river #bid #aej4 ,showing the ,joining of the ,caissons at the ,pont ,mirabeau ,tunnel under the ,seine ,river #bie #aea4 ,cross-,sections and ,plans of the ,detroit ,river ,tunnel #bih #aeb4 ,tunneling through ,caved ,material by ,heading #cjf #aec4 ,tunneling through ,caved ,material by ,drifts #cjg #aed and #aee4 ,filling in ,roof ,cavity ,formed by ,falling ,material #cjg #aef4 ,timbering to ,prevent ,landslides at ,portal #cjh #aeg4 ,shortening ,tunnel ,crushed by ,landslide at ,portal #cjh #aeh4 ,extending ,tunnel through ,landslide at ,portal #cji #aei and #afj4 ,relining ,timber-,lined ,tunnel #caf #afa4 ,relining ,timber-,lined ,tunnel1 ,great ,northern ,ry #cag #afb4 ,relining ,timber-,lined ,tunnel1 ,great ,northern ,ry #cah #afc4 ,relining ,timber-,lined ,tunnel1 ,great ,northern ,ry #cai #afd4 ,construction of ,centering ,mullan ,tunnel #cbj #afe4 ,centering ,mullan ,tunnel #cba #aff4 ,relining ,timber-,lined ,tunnel1 ,norfolk ,western ,ry #cbb #afg4 ,relining ,timber-,lined ,tunnel1 ,norfolk ,western ,ry #cbc ,,introduction ,,the ,,historical ,,development ,,of ,,tunnel ,,building4 ,a tunnel1 defined as an engineering structure1 is an artificial gallery1 passage1 or roadway beneath the ground1 under the bed of a stream1 or through a hill or mountain4 ,the art of tunneling has been known to man since very ancient times4 ,a ,theban king on ascending the throne began at once to drive the long1 narrow passage or tunnel leading to the inner chamber or sepulcher of the rock-cut tomb which was to form his final resting-place4 ,some of these rock-cut galleries of the ancient ,egyptian kings were over #gej ft4 long4 ,similar rock-cut tunneling work was performed by the ,nubians and ,indians in building their temples1 by the ,aztecs in ,america1 and in fact by most of the ancient civilized peoples4 ,the first built-up tunnels of which there are any existing records were those constructed by the ,assyrians4 ,the vaulted drain or passage under the southeast palace of ,nimrud1 built by ,shalmaneser ,,ii4 7#hfj-hbd ,b4,c471 is in all essentials a true soft-ground tunnel1 with a masonry lining4 ,a much better example1 however1 is the tunnel under the ,euphrates ,river1 which may quite accurately be claimed as the first submarine tunnel of which there exists any record4 ,it was1 however1 built under the dry bed of the river1 the waters of which were temporarily diverted1 and then turned back into their normal channel after the tunnel work was completed1 thus making it a true submarine tunnel only when finished4 ,the ,euphrates ,river tunnel was built through soft ground1 and was lined with brick masonry1 having interior dimensions of #ab ft4 in width and #ae ft4 in height4 ,only hand labor was employed by these ancient peoples in their tunnel work4 ,in soft ground the tools used were the pick and shovels1 or scoops4 ,for rock work they possessed a greater range of appliances4 ,research has shown that among the ,egyptians1 by whom the art of quarrying was highly developed1 use was made of tube drills and saws provided with cutting edges of corundum or other hard1 gritty material4 ,the usual tools for rock work were1 however1 the hammer1 the chisel1 and wedges2 and the excellence and magnitude of the works accomplished by these limited appliances attest the unlimited time and labor which must have been available for their accomplishment4 ,the ,romans should doubtless rank as the greatest tunnel builders of antiquity1 in the number1 magnitude1 and useful character of their works1 and in the improvements which they devised in the methods of tunnel building4 ,they introduced fire as an agent for hastening the breaking down of the rock1 and also developed the familiar principle of prosecuting the work at several points at once by means of shafts4 ,in their use of fire the ,romans simply took practical advantage of the familiar fact that when a heated rock is suddenly cooled it cracks and breaks so that its excavation becomes comparatively easy4 ,their method of operation was simply to build large fires in front of the rock to be broken down1 and when it had reached a high temperature to cool it suddenly by throwing water upon the hot surface4 ,the ,romans were also aware that vinegar affected calcareous rock1 and in excavating tunnels through this material it was a common practice with them to substitute vinegar for water as the cooling agent1 and thus to attack the rock both chemically and mechanically4 ,it is hardly necessary to say that this method of excavation was very severe on the workmen because of the heat and foul gases generated4 ,this was1 however1 a matter of small concern to the builders1 since the work was usually performed by slaves and prisoners of war1 who perished by thousands4 ,to be sentenced to labor on ,roman tunnel works was thus one of the severest penalties to which a slave or prisoner could be condemned4 ,they were places of suffering and death as are to-day the ,spanish mercury mines4 ,besides their use of fire as an excavating agent1 the ,romans possessed a very perfect knowledge of the use of vertical shafts in order to prosecute the excavation at several different points simultaneously4 ,pliny is authority#a for the statement that in the excavation of the tunnel for the drainage of ,lake ,fucino forty shafts and a number of inclined galleries were sunk along its length of #c miles1 some of the shafts being #djj ft4 in depth4 ,the spoil was hoisted out of these shafts in copper pails of about ten gallons' capacity by windlasses4 #a 8,tunneling10 ,encly4 ,brit41 #ahhi1 vol4 xxiii41 p4 #fbc4 ,the ,roman tunnels were designed for public utility4 ,among those which are most notable in this respect1 as well as for being fine examples of tunnel work1 may be mentioned the numerous conduits driven through the calcareous rock between ,subiaco and ,tivoli to carry to ,rome the pure water from the mountains above ,subiaco4 ,this work was done under the ,consul ,marcius4 ,the longest of the ,roman tunnels is the one built to drain ,lake ,fucino1 as mentioned above4 ,this tunnel was designed to have a section of #f ft4 #aj ft42 but its actual dimensions are not uniform4 ,it was driven through calcareous rock1 and it is stated that #cj1jjj men were employed for eleven years in its construction4 ,the tunnels which have been mentioned1 being designed for conduits1 were of small section2 but the ,romans also built tunnels of larger sections at numerous points along their magnificent roads4 ,one of the most notable of these is that which gives the road between ,naples and ,pozzuoli passage through the ,posilipo hills4 ,it is excavated through volcanic tufa1 and is about #cjjj ft4 long and #be ft4 wide1 with a section of the form of a pointed arch4 ,in order to facilitate the illumination of this tunnel1 its floor and roof were made gradually converging from the ends toward the middle2 at the entrances the section was #ge ft4 high1 while at the center it was only #bb ft4 high4 ,this double funnel-like construction caused the rays of light entering the tunnel to concentrate as they approached the center1 and thus to improve the natural illumination4 ,the tunnel is on a grade4 ,it was probably excavated during the time of ,augustus1 although some authorities place its construction at an earlier date4 ,during the ,middle ,ages the art of tunnel building was practiced for military purposes1 but seldom for the public need and comfort4 ,mention is made of the fact that in #adej ,anne of ,lusignan commenced the construction of a road tunnel under the ,col di ,tenda in the ,piedmontese ,alps to afford better communication between ,nice and ,genoa2 but on account of its many difficulties the work was never completed1 although it was several times abandoned and resumed4 ,for the most part1 therefore1 the tunnel work of the ,middle ,ages was intended for the purposes and necessities of war4 ,every castle had its private underground passage from the central tower or keep to some distant concealed place to permit the escape of the family and its retainers in case of the victory of the enemy1 and1 during the defense1 to allow of sorties and the entrance of supplies4 ,the tunnel builders of the ,middle ,ages added little to the knowledge of their art4 ,indeed1 until the #agth century and the invention of gunpowder no practical improvement was made in the tunneling methods of the ,romans4 ,engravings of mining operations in that century show that underground excavation was accomplished by the pick or the hammer and chisel1 and that wood fires were lighted at the ends of the headings to split and soften the rocks in advance4 ,although gunpowder had been previously employed in mining1 the first important use of it in tunnel work was at ,malpas1 ,france1 in #afgi-ha1 in the tunnel for the ,languedoc ,canal4 ,this tunnel was #eaj ft4 long1 #bb ft4 wide1 and #bi ft4 high1 and was excavated through tufa4 ,it was left unlined for seven years1 and then was lined with masonry4 ,with the advent of gunpowder and canal building the first strong impetus was given to tunnel building1 in its modern sense1 as a commercial and public utilitarian construction1 since the days of the ,roman ,empire4 ,canal tunnels of notable size were excavated in ,france and ,england during the last half of the #agth century4 ,these were all rock or hard-ground tunnels4 ,indeed1 previous to #ahjj the soft-ground tunnel was beyond the courage of engineer except in sections of such small size that the work better deserves to be called a drift or heading than a tunnel4 ,in #ahjc1 however1 a tunnel #bd ft4 wide was excavated through soft soil for the ,st4 ,quentin ,canal in ,france4 ,timbering or strutting was employed to support the walls and roof of the excavation as fast as the earth was removed1 and the masonry lining was built closely following it4 ,from the experience gained in this tunnel were developed the various systems of soft-ground subterranean tunneling since employed4 ,it was by the development of the steam railway1 however1 that the art of tunneling was to be brought into its present prominence4 ,in #ahbj-bf two tunnels were built on the ,liverpool ,manchester ,ry4 in ,england4 ,this was the beginning of the rapid development which has made the tunnel one of the most familiar of engineering structures4 ,the first railway tunnel in the ,united ,states was built on the ,alleghany ,portage ,r4 ,r4 in ,pennsylvania in #ahca-cc2 and the first canal tunnel had been completed about #ac years previously 7#ahah-ba7 by the ,schuylkill ,navigation ,co41 near ,auburn1 ,pa4 ,it would be interesting and instructive in many respects to follow the rise and progress of tunnel construction in detail since the construction of these earlier examples1 but all that may be said here is that it was identical with that of the railway4 ,the art of tunneling entered its last and greatest phase with the construction of the ,mont ,cenis tunnel in ,europe and the ,hoosac tunnel in ,america1 which works established the utility of machine rock-drills and high explosives4 ,the ,mont ,cenis tunnel was built to facilitate railway communication between ,italy and ,france1 or more properly between ,piedmont and ,savoy1 the two parts of the kingdom of ,victor ,emmanuel ,,ii41 separated by the ,alps4 ,it is #g4f miles long1 and passes under the ,col di ,frjus near ,mont ,cenis4 ,sommeiller1 ,grattoni1 and ,grandis were the engineers of this great undertaking1 which was begun in #aheg1 and finished in #ahgb4 ,it was from the close study of the various difficulties1 the great length of the tunnel1 and the desire of the engineers to finish it quickly1 that all the different improvements were developed which marked this work as a notable step in the advance of the art of tunneling4 ,thus the first power-drill ever used in tunnel work was devised by ,sommeiller4 ,in addition1 compressed air as a motive power for drills1 aspirators to suck the foul air from the excavation1 air compressors1 turbines1 etc41 found at ,mont ,cenis their first application to tunnel construction4 ,this important rle played by the ,mont ,cenis tunnel in ,europe in introducing modern methods had its counterpart in ,america in the ,hoosac tunnel completed in #ahge4 ,in this work there were used for the first time in ,america power rock-drills1 air compressors1 nitro-glycerine1 electricity for firing blasts1 etc4 ,there remains now to be noted only the final development in the art of soft-ground submarine tunneling1 namely1 the use of the shield and metal lining4 ,the shield was invented and first used by ,sir ,isambard ,brunel in excavating the tunnel under the ,river ,thames at ,london1 which was begun in #ahbe1 and finished in #ahda4 ,in #ahfi ,peter ,william ,barlow used an iron lining in connection with a shield in driving the second tunnel under the ,thames at ,london4 ,from these inventions has grown up one of the most notable systems of tunneling now practiced1 which is commonly known as the shield system4 ,in closing this brief review of the development of modern methods of tunneling1 to the presentation of which the remainder of this book is devoted1 mention should be made of a form of motive power which promises many opportunities for development in tunnel construction4 ,electricity has long been employed for blasting and illuminating purposes in tunnel work4 ,it remains to be extended to other uses4 ,for hauling and for operating certain classes of hoisting and excavating machinery it is one of the most convenient forms of power available to the engineer4 ,its successful application to rock-drills is another promising field4 ,for operating ventilating fans it promises unusual usefulness4 ,,tunneling ,,chapter ,i4 ,,preliminary ,,considerations4 ,,choice ,,between ,a ,,tunnel ,,and ,,open ,,cut4 ,,geological ,,surveys4 ,,choice ,,between ,a ,,tunnel ,,and ,,an ,,open ,,cut4 ,when a railway line is to be carried across a range of mountains or hills1 the first question which arises is whether it is better to construct a tunnel or to make such a dtour as will enable the obstruction to be passed with ordinary surface construction4 ,the answer to this question depends upon the comparative cost of construction and maintenance1 and upon the relative commercial and structural advantages and disadvantages of the two methods4 ,in favor of the open road there are its smaller cost and the decreased time required in its construction4 ,these mean that less capital will be required1 and that the road will sooner be able to earn something for its builders4 ,against the open road there are3 its greater length and consequently its heavier running expenses2 the greater amount of rolling-stock required to operate it2 the heavy expense of maintaining a mountain road2 and the necessity of employing larger locomotives1 with the increased expenses which they entail4 ,in favor of the tunnel there are3 the shortening of the road1 with the consequent decrease in the operating expenses and amount of rolling-stock required2 the smaller cost of maintenance1 owing to the protection of the track from snow and rain and other natural influences causing deterioration2 and the decreased cost of hauling due to the lighter grades4 ,against the tunnel1 there are its enormous cost as compared with an open road and the great length of time required to construct it4 ,to determine in any particular case whether a tunnel or an open road is best1 requires a careful integration of all the factors mentioned4 ,it may be asserted in a general way1 however1 that the enormous advance made in the art of tunnel building has done much to lessen the strength of the principal objections to tunnels1 namely1 their great cost and the length of time required for their construction4 ,where the choice lies between a tunnel or a long dtour with heavy grades it is sooner or later almost always decided in favor of a tunnel4 ,when1 however1 the conditions are such that the choice lies between a tunnel or a heavy open cut with the same grades the problem of deciding between the two solutions is a more difficult one4 ,it is generally assumed that when the cut required will have a vertical depth exceeding #fj ft4 it is less expensive to build a tunnel unless the excavated material is needed for a nearby embankment or fill4 ,this rule is not absolute1 but varies according to local conditions4 ,for instance1 in materials of rigid and unyielding character1 such as rock1 the practical limit to the depth of a cut goes far beyond that point at which a tunnel would be more economical according to the above rule4 ,in soils of a yielding character1 on the other hand1 the very flat slope required for stability adds greatly to the cost of making a cut4 ,it may be noted in closing that the same rule may be employed in determining the location of the ends of the tunnel1 for assuming that it is more convenient to excavate a tunnel than an open cut when the depth exceeds #fj ft41 then the open cut approaches should extend into the mountain- or hill-sides only to the points where the surface is #fj ft4 above grade1 and there the tunnel should begin4 ,if1 therefore1 we draw on the longitudinal profile of the tunnel a line parallel to the plane of the tracks1 and #fj ft4 above it1 this line will cut the surface at the points where the open-cut approaches should cease and the tunnel begin4 ,this is a rule-of-thumb determination at the best1 and requires judgment in its use4 ,should the ground surface1 for example1 rise only a few feet above the #fj ft4 line for any distance1 it is obviously better to continue the open cut than to tunnel4 ,,the ,,method ,,and ,,purpose ,,of ,,geological ,,surveys4 ,when it has been decided to build a tunnel1 the first duty of the engineer is to make an accurate geological survey of the locality4 ,from this survey the material penetrated1 the form of section and kind of strutting to be used1 the best form of lining to be adopted1 the cost of excavation1 and various other facts1 are to be deduced4 ,in small tunnels the geological knowledge of the engineer should enable him to construct a geological map of the locality1 or this knowledge may be had in many cases by consulting the geological maps issued by the ,state or general government surveys4 ,when1 however1 the tunnel is to be of great length1 it may be necessary to call in the assistance of a professional geologist in order to reconstruct accurately the interior of the mountain and thereby to ascertain beforehand the different strata and materials to be excavated1 thus obtaining the data for calculating both the time and cost of excavating the tunnel4 ,the geological survey should enable the engineer to determine1 7#a7 the character of the material and its force of cohesion1 7#b7 the inclination of the different strata1 and 7#c7 the presence of water4 ,character of ,material4--,the character of the material through which the proposed tunnel will penetrate is best ascertained by means of diamond rock-drills4 ,these machines bore an annular hole1 and take away a core for the whole depth of the boring1 thus giving a perfect geological section showing the character1 succession1 and exact thickness of the strata4 ,by making such borings at different points along the center line of the projected tunnel1 and comparing the relative sequence and thickness of the different strata shown by the cores1 the geological formation of the mountain may be determined quite exactly4 ,where it is difficult or impracticable to make diamond drill borings on account of the depth of the mountain above the tunnel1 or because of its inaccessibility1 the engineer must resort to other methods of observation4 ,the present forms of mountains or hills are due to weathering1 or the action of the destructive atmospheric influences upon the original material4 ,from the manner in which the mountain or hill has resisted weathering1 therefore1 may be deduced in a general way both the nature and consistency of the materials of which it is composed4 ,thus we shall generally find mountains or hills of rounded outlines to consist of soft rocks or loose soils1 while under very steep and crested mountains hard rock usually exists4 ,to the general knowledge of the nature of its interior thus afforded by the exterior form of the mountain1 the engineer must add such information as the surface outcroppings and other local evidences permit4 ,for the purposes of the tunnel builder we may first classify all materials as either1 7#a7 hard rock1 7#b7 soft rock1 or 7#c7 soft soil4 ,hard rocks are those having sufficient cohesion to stand vertically when cut to any depth4 ,many of the primary rocks1 like granite1 gneiss1 feldspar1 and basalt1 belong to this class1 but others of the same group are affected by the atmosphere1 moisture1 and frost1 which gradually disintegrate them4 ,they are also often found interspersed with pyrites1 whose well-known tendency to disintegrate upon exposure to air introduces another destructive agency4 ,for these reasons we may divide hard rocks into two sub-classes2 viz41 hard rocks unaffected by the atmosphere1 and those affected by it4 ,this distinction is chiefly important in tunneling as determining whether or not a lining will be required4 ,soft rocks1 as the term implies1 are those in which the force of cohesion is less than in hard rocks1 and which in consequence offer less resistance to attacks tending to break down their original structure4 ,they are always affected by the atmosphere4 ,sandstones1 laminated clay shales1 mica-schists1 and all schistose stones1 chalk and some volcanic rocks1 can be classified in this group4 ,soft rocks require to be supported by timbering during excavation1 and need to be protected by a strong lining to exclude the air1 and to support the vertical pressures1 and prevent the fall of fragments4 ,soft soils are composed of detrital materials1 having so little cohesion that they may be excavated without the use of explosives4 ,tunnels excavated through these soils must be strongly timbered during excavation to support the vertical pressure and prevent caving2 and they also always require a strong lining4 ,gravel1 sand1 shale1 clay1 quicksand1 and peat are the soft soils generally encountered in the excavation of tunnels4 ,gravels and dry sand are the strongest and firmest2 shales are very firm1 but they possess the great defect of being liable to swell in the presence of water or merely by exposure to the air1 to such an extent that they have been known to crush the timbering built to support them4 ,quicksand and peat are proverbially treacherous materials4 ,clays are sometimes firm and tenacious1 but when laminated and in the presence of water are among the most treacherous soils4 ,laminated clays may be described as ordinary clays altered by chemical and mechanical agencies1 and several modifications of the same structure are often found in the same locality4 ,they are composed of lamin of lenticular form separated by smooth surfaces and easily detached from each other4 ,laminated clays generally have a dark color1 red1 ocher or greenish blue1 and are very often found alternating with strata of stiatites or calcareous material4 ,for purposes of construction they have been divided into three varieties4 ,laminated clays of the first variety are those which alternate with calcareous strata and are not so greatly altered as to lose their original stratification4 ,laminated clays of the second variety are those in which the calcareous strata are broken and reduced to small pieces1 but in which the former structure is not completely destroyed2 the clay is not reduced to a humid state4 ,laminated clays of the third variety are those in which the clay by the force of continued disturbance1 and in the presence of water1 has become plastic4 ,laminated clays are very treacherous soils2 quicksand and peat may be classed1 as regards their treacherous nature1 among the laminated clays of the third variety4 ,inclination of ,strata4--,knowing the inclination of the strata1 or the angle which they make with the horizon1 it is easy to determine where they intersect the vertical plane of the tunnel passing through the center line1 thus giving to a certain extent a knowledge of the different strata which will be met in the excavation4 ,on the inclination of the strata depend3 7#a7 ,the cost of the excavation2 the blasting1 for instance1 will be more efficient if the rocks are attacked perpendicular to the stratification2 7#b7 ,the character of the timbering or strutting2 the tendency of the rock to fall is greater if the strata are horizontal than if they are vertical2 7#c7 ,the character and thickness of the lining2 horizontal strata are in the weakest position to resist the vertical pressure from the load above when deprived of the supporting rock below1 while vertical strata1 when penetrated1 act as a sort of arch to support the pressure of the load above4 ,the foregoing remarks apply only to hard or soft rock materials4 ,in detrital formations the inclination of the strata is an important consideration1 because of the unsymmetrical pressures developed4 ,in excavating a tunnel through soft soil whose strata are inclined at #cj to the horizon1 for instance1 the tunnel will cut these strata at an angle of #cj4 ,by the excavation the natural equilibrium of the soil is disturbed1 and while the earth tends to fall and settle on both sides at an angle depending upon the friction and cohesion of the material1 this angle will be much greater on one side than on the other because of the inclination of the strata2 and hence the prism of falling earth on one side is greater than on the other1 and consequently the pressures are different1 or in other words1 they are unsymmetrical4 ,these unsymmetrical pressures are usually easily taken care of as far as the lining is concerned1 but they may cause serious cave-ins and badly distort the strutting4 ,caving-in during excavation may be prevented by cutting the materials according to their natural slope2 but the distortion of the strutting is a more serious problem to handle1 and one which oftentimes requires the utmost vigilance and care to prevent serious trouble4 ,presence of ,water4--,an idea of the likelihood of finding water in the tunnel may be obtained by studying the hydrographic basin of the locality4 ,from it the source and direction of the springs1 creeks1 ravines1 etc41 can be traced1 and from the geological map it can be seen where the strata bearing these waters meet the center line4 ,not only ought the surface water to be attentively studied1 but underground springs1 which are frequently encountered in the excavation of tunnels1 require careful attention4 ,both the surface and underground waters follow the pervious strata1 and are diverted by impervious strata4 ,rocks generally may be classed as impervious2 but they contain crevices and faults1 which often allow water to pass through them2 and it is1 therefore1 not uncommon to encounter large quantities of water in excavating tunnels through rock4 ,as a rule1 water will be found under high mountains1 which comes from the melted ice and snow percolating through the rock crevices4 ,some detrital soils1 like gravel and sand1 are pervious1 and others1 like clay and shale1 are impervious4 ,detrital soils lying above clay are almost certain to carry water just above the clay stratum4 ,in tunnel work1 therefore1 when the excavation keeps well within the clay stratum1 little trouble is likely to be had from water2 should1 however1 the excavation cut the clay surface and enter the pervious material above1 water is quite certain to be encountered4 ,the quantity of water encountered in any case depends upon the presence of high mountains near by1 and upon other circumstances which will attract the attention of the engineer4 ,a knowledge of the pressure of the water is desirable4 ,this may be obtained by observing closely its source and the character of the strata through which it passes4 ,water coming to the excavation through rock crevices will lose little of its pressure by friction1 while that which has passed some distance through sand will have lost a great deal of its pressure by friction4 ,water bearing sand1 and1 in fact1 any water bearing detrital material1 has its fluidity increased by water pressure2 and when this reaches the point where flow results1 trouble ensues4 ,the streams of water met in the construction of the ,st4 ,gothard tunnel had sufficient pressure to carry away timber and materials4 ,,chapter ,,ii4 ,,methods ,,of ,,determining ,,the ,,center ,,line ,,and ,,forms ,,and ,,dimensions ,,of ,,cross-,,section4 ,,determining ,,the ,,center ,,line4 ,tunnels may be either curvilinear or rectilinear1 but the latter form is the more common4 ,in either case the first task of the engineer1 after the ends of the tunnel have been definitely fixed1 is to locate the center line exactly4 ,this is done on the surface of the ground2 and its purpose is to find the exact length of the tunnel1 and to furnish a reference line by which the excavation is directed4 ,rectilinear ,tunnels4--,in short tunnels the center line may be accurately enough located for all practical purposes by means of a common theodolite4 ,the work is performed on a calm1 clear day1 so as to have the instrument and observations subjected to as little atmospheric disturbance as possible4 ,wooden stakes are employed to mark the various located points of the center line temporarily4 ,the observations are usually repeated once at least to check the errors1 and the stakes are altered as the corrections dictate2 and after the line is finally decided to be correctly fixed1 they are replaced by permanent monuments of stone accurately marked4 ,the method of checking the observations is described by ,mr4 ,w4 ,d4 ,haskoll#b as follows3 8,let the theodolite be carefully set up over one of the stakes1 with the nail driven into it1 selecting one that will command the best position so as to range backwards and forwards over the whole length of line1 and also obtain a view of the two distant points that range with the center line2 this being done1 let the centers of every stake 444 be carefully verified4 ,if this be carefully done1 and the centers be found correct1 and thoroughly in one visual line as seen through the telescope1 there will be no fear but that a perfectly straight line has been obtained40 #b 8,practical ,tunneling10 by ,f4 ,w4 ,simms4 ,illustration3 ,,fig4 #a4--;,diagram ,showing ,manner of ,lining in ,rectilinear ,tunnels4 ,the center line which has thus been located on the ground surface has to be transposed to the inside of the tunnel to direct the excavation4 ,to do this let ,a and ,b be the entrances and a and b be the two distinct fixed points which have been ranged in with the center line located on the ground surface over the hill ,a f ,b1 ,fig4 #a4 ,the instrument is set up at ,v1 any point on the line ,a a produced1 and a bearing secured by observation on the center line marked on the surface4 ,this bearing is then carried into the tunnel by plunging the telescope1 and setting pegs in the roof of the heading4 ,lamps hung from these pegs furnish the necessary sighting points4 ,this same operation is repeated on the opposite side of the hill to direct the excavation from that end of the tunnel4 ,these operations serve to locate only the first few points inside the tunnel4 ,as the excavation penetrates farther into the hill1 it becomes impossible to continue to locate the line from the outside point1 and the line has to be run from the points marked on the roof of the heading4 ,great accuracy is required in all these observations1 since a very small error at the beginning becomes greater and greater as the excavation advances4 ,to facilitate the accurate location of points on the roof of the tunnel1 a simple device was designed by ,mr4 ,beverley ,r4 ,value1 shown in ,fig4 #b4 ,two iron spikes1 each having a small hole in the flat end1 are driven into the rock about #i ins4 apart4 ,a brass bar1 #a in4 high1 in4 thick and #aj ins4 long1 having a hole near one end and a #a in4 slot at the other1 is screwed tightly into the head of the spikes4 ,the middle part of the bar is divided into inches and tenths of an inch4 ,a separate brass hanger is fitted to the bar1 having a vernier with its zero at the middle of the hanger and corresponding to a plumb line attached below4 ,the hanger is moved back and forth until it coincides with the line of sight of the transit1 and then the readings of the vernier are recorded4 ,any time that the hanger is placed on the bar and the vernier marks the same reading1 the plumb line will indicate the center line of the tunnel4 ,when1 instead of one bar1 two are inserted at a distance of #bj or #cj ft4 apart1 the plumb lines suspended from the hangers will represent the vertical plane passing through the axis of the tunnel in coincidence with the one staked out on the surface ground4 ,illustration3 ,,fig4 #b4--;,b4 ,r4 ,value's ,device for ,locating the ,center ,line ,inside of a ,tunnel4 ,the location of the center line of a long tunnel1 which is to be excavated under high mountains1 is a very difficult operation1 and the engineers usually leave this part of the work to astronomers1 who fix the stations from which the engineers direct the work of construction4 ,the center lines of all the great ,alpine tunnels were located by astronomers who used instruments of large size4 ,thus1 in ranging the center line of the ,st4 ,gothard tunnel1 the theodolite used had an object glass eight inches in diameter4#c ,instead of the ordinary mounting a masonry pedestal with a perfectly level top is employed to support the instrument during the observations4 ,the location is made by means of triangulation4 ,the various operations must be performed with the greatest accuracy1 and repeated several times in such a way as to reduce the errors to a minimum1 since the final meeting of the headings depends upon their elimination4 #c ,see also the ,simplon ,tunnel1 ,chapter ,x4 ,illustration3 ,,fig4 #c4--,triangulation ,system for ,establishing the ,center ,line of the ,st4 ,gothard ,tunnel4 ,the ,st4 ,gothard tunnel furnishes perhaps the best illustration of careful work in locating the center line of long rectilinear tunnels of any tunnel ever built4 ,the length of this tunnel is #i4be miles1 and the height of the mountain above it is very great4 ,the center line was located by triangulation by two different astronomers using different sets of triangles1 and working at different times4 ,the set or system of triangles used by ,dr4 ,koppe1 one of the observers1 is shown by ,fig4 #c2 it consists of very large and quite small triangles combined1 the latter being required because the entrances both at ,airolo and ,goeschenen were so low as to permit only of a short sight being taken4 ,the apices of the triangles were located by means of the contour maps of the ,swiss ,alpine ,club4 ,each angle was read ten times1 the instrument was collimated four times for each reading1 and was afterwards turned off #e or #aj to avoid errors of graduation4 ,the average of the errors in reading was about one second of arc4 ,the triangulation was compensated according to the method of least squares4 ,the probable error in the fixed direction was calculated to be #j4h of arc at ,goeschenen and #j4g of arc at ,airolo4 ,from this it was assumed that the probable deviation from the true center would be about two inches at the middle of the tunnel1 but when the headings finally met this deviation was found to reach eleven inches4 ,comparatively few tunnels are driven by working from the entrances alone1 the excavation being usually prosecuted at several points at once by means of shafts4 ,in these cases1 in order to direct the excavation correctly1 it is necessary to fix the center line on the bottom of the shaft4 ,this is accomplished in two ways1--one being employed when the shaft is located directly over the center line1 and the other when the shaft is located to one side of the center line4 ,when the shaft is located on the center line two small pillars are placed on opposite edges of the shaft and collimating with the center line as shown by ,fig4 #d4 ,on these two pillars the points corresponding to the center line are correctly marked1 and connected by a wire stretched between them4 ,to this wire two plumb bobs are fastened as far apart as possible4 ,these plumb bobs mark two points on the center line at the bottom of the shaft1 and from them the line is extended into the headings as the work advances4 ,in these operations1 heavy plumb bobs are used4 ,in the ,new ,york subway plumb bobs of steel1 weighing #be lbs4 each1 were used1 and to prevent rotation they were made with cross-sections1 in the shape of a ,greek cross1 and were sunk in buckets filled with water4 ,owing to the difference between the temperature at the top and that at the bottom of the shaft1 strong currents of air are produced1 which keep in constant oscillation the wires to which the bobs are suspended4 ,illustration3 ,,fig4 #d4--,method of ,transferring the ,center ,line down ,center ,shafts4 ,to determine the center line at the bottom of the shaft1 the headings are first driven from both sides of the shaft1 after which a transit is set up on the same alignment with the two wires1 and this will indicate the vertical plane passing through the axis of construction4 ,two points are then fixed on the roof of the tunnel in continuation of this vertical plane4 ,when the plumb bobs are removed from the shaft and two small plumb bobs are suspended to the two points mentioned1 they will always give the same vertical plane passing through the axis of construction transferred from the surface4 ,because of the continuous moving of the wires1 the fixing of the points on the roof of the tunnel is very troublesome1 and the operation should be repeated by different men at different times before the points are permanently fixed4 ,illustration3 ,,fig4 #e4--,method of ,transferring the ,center ,line down ,side ,shafts4 ,when the shaft is placed at one side of the tunnel the pillars or bench marks are placed normal to the center line on the edges of the shaft as shown by ,fig4 #e4 ,between the points ,a and ,b a wire is stretched1 and from it two plumb bobs are suspended1 as described in the preceding case2 these plumb bobs establish a vertical plane normal to the axis of the tunnel4 ,the excavation of the side tunnel is carried along the line ,,bw until it intersects the line of the main tunnel1 whose center line is determined by measuring off underground a distance equal to the distance ,,bo on the surface4 ,by setting the instrument over the underground point ,o1 and turning off a right angle from the line ,,bo1 the center line of the tunnel is extended into the headings4 ,curvilinear ,tunnels4--,there are various methods of locating the center lines of curvilinear tunnels1 but the method of tangent offsets is the one most commonly employed4 ,at the beginning the excavation is conducted as closely as may be to the line of the curve1 and as soon as it has progressed far enough the tangent ,,at1 ,fig4 #f1 is ranged out4 ,at ,b a point is located over which to set the instrument1 and the distance ,,ab is measured for the purpose of finding the ordinate of the right angle triangle ,,oab4 ,now ,,oa r1 ,,ab d1 and angle ,,abo4 ,then3 r ,tang4 ---4 d ,illustration3 ,,fig4 #f4--,method of ,laying ,out the ,center ,line of ,curvilinear ,tunnels4 ,doubling the value of and making the angle ,,abc #b 1 the line ,,bc will be fixed and the point ,c located by taking ,,ab ,,bc4 ,on ,,bc the ordinates are laid off to locate the curve4 ,prolong ,,cb so that ,,cd ,,cb4 ,then the portion of the curve ,,cf is symmetrical with ,,ce1 and the ordinates used to locate ,,ec may be employed to locate ,,cf1 by laying them off in the reverse order4 ,in curvilinear tunnels several cases may be considered4 7#a7 ,when the tunnel for almost its entire length is driven on a tangent with a curve at each end4 7#b7 ,when the tunnel begins with a curve and ends with a straight line4 7#c7 ,when the whole tunnel is in curve from portal to portal4 7#d7 ,the helicoidal or corkscrew tunnel4 99 99 99 99 99 7#a7 ,the axis of every one of the great ,alpine tunnels is a straight line1 with a curve at each end4 ,to range out the center line of one of these long tunnels from a curve1 no matter how accurately laid out1 will certainly cause an error1 which1 magnified with the distance1 may produce serious results4 ,to avoid these inconveniences1 the determination of the axis of the tunnel should be made from a straight line4 ,this means that the tunnel is at first excavated on a straight line for its entire length and after the headings driven from both portals have met1 the two portions of the tunnel or curve are excavated and constructed4 ,the portions of the tunnel excavated on straight lines for conveniences of construction may then be abandoned or used in cases of accidents or repairs4 ,when the axis of a short tunnel has a curve at each end and a straight line in the middle1 it is driven directly from the entrances2 first1 however1 excavating the curvilinear portions of the tunnel4 ,in such a case it would be advisable to proceed in the following manner4 ,drive the headings on the curvilinear portions of the tunnel1 staking out the center line by means of the offsets from the tangents4 ,at the ends of the curves lay out from both fronts the rectilineal portion of the tunnel4 ,only very narrow headings should be excavated at first while the whole section could be enlarged near the entrances4 ,the excavation of the headings at the front should advance very rapidly1 in order that the headings may meet in the shortest possible time4 ,when communication is established1 it is comparatively easy to correct an error resulting from driving the tunnel from the curves4 7#b7 ,when a tunnel begins with a curve and ends with a straight line1 the work of excavation should proceed from both ends4 ,from the straight end of the tunnel only the heading should be driven1 while from the curvilinear end the whole section could be opened at once4 ,by this arrangement the excavation progresses slowly from the curvilinear end and rapidly from the straight end of the tunnel4 ,once communication has been established and any error corrected1 the work of enlarging the profile of the tunnel may be pushed with the same activity from both ends4 7#c7 ,when the center line of the entire tunnel is a curve1 there is more probability of slight deviations from the true axis of the proposed work4 ,in such a case it would be advisable to first excavate a narrow heading and to concentrate all the efforts in driving the headings as rapidly as possible in order that they may meet in the shortest time4 ,the center line of these headings is staked out by the usual method of the offsets from the tangent4 ,the enlarging of the section of the tunnel could be commenced at both portals and be driven slowly until the headings have met and any errors corrected1 when the work could be pushed with the greatest activity all along the line4 7#d7 ,in corkscrew or helicoidal tunnels the entire center line is on a curve4 ,in these tunnels1 as a rule1 there is a great difference of level between the two portals1 one being much higher than the other1 so careful attention should be paid to the tunnel grade4 ,working in the limited spaces afforded by narrow headings it is very probable that errors may be made in fixing both the alignment and the grade of the tunnel4 ,to prevent these almost unavoidable errors1 it would be well to excavate at first only the headings1 to stake the center line in the roof of these headings and then to lay the grade of the tunnel as accurately as possible4 ,the work on the headings should be pushed as rapidly as possible in order that they may meet quickly1 so that the center line1 as temporarily laid out1 may be corrected and permanently fixed for the direction of successive operations4 ,in these tunnels the headings should be excavated near the center of the tunnel cross-section so that the sides and roof of the heading would be at some distance from the sides and roof of the proposed tunnel4 ,this arrangement will easily permit corrections to be made in case any slight difference from the true line was erroneously made during the excavation of the headings4 ,,form ,,and ,,dimensions ,,of ,,cross-,,section4 ,in deciding upon the sectional profile of a tunnel two factors have to be taken into consideration3 7#a7 ,the form of section best suited to the conditions1 and 7#b7 the interior dimensions of this section4 ,form of ,section4--,the form of the sectional profile of a tunnel should be such that the lining is of the best form to resist the pressures exerted by the unsupported walls of the tunnel excavation1 and these vary with the character of the material penetrated4 ,these pressures are both vertical and lateral in direction2 the roof1 deprived of support by the excavation1 tends to fall1 and the opposite sides for the same reason tend to slide inward along a plane more or less inclined1 depending upon the friction and cohesion of the material4 ,in some rocks the cohesion is so great that they will stand vertically1 while it may be very small in loose earth which slides along a plane whose inclination is directly proportional to the cohesion4 ,from the theory of resistance of profiles we know that the resistance of a line to exterior normal forces is directly proportional to its degree of curvature1 and consequently inversely proportional to the radius of the curve4 ,hence the sectional profile of a tunnel excavated through hard rock1 where there are no lateral pressures owing to the great cohesion of the material1 and having to resist only the vertical pressure1 should be designed to offer the greatest resistance at its highest point1 and the curve must1 therefore1 be sharper there1 and may decrease toward the base4 ,in quicksand1 mud1 or other material practically without cohesion1 the pressures will all be normal to the line of the profile1 and a circular section is the one best suited to resist them4 ,these theoretical considerations have been proved correct by actual experience1 and they may be employed to determine in a general way the form of section to be adopted4 ,applying them to very hard rock1 they give us a section with an arched roof and vertical side walls4 ,in softer materials they give us an elliptical section with its major axis vertical1 and in very soft quicksands and mud they give us the circular section4 ,these three forms of cross-section and their modifications are the ones commonly employed for tunnels4 ,an important exception to this general practice1 however1 is met with in some of the city underground rapid-transit railways built of late years1 where a rectangular or box section is employed4 ,these tunnels are usually of small depth1 so that the vertical pressures are comparatively light1 and the bending strains1 which they exert upon the flat roof1 are provided for by employing steel girders to form the roof lining4 ,illustration3 ,,fig4 #g4--;,diagram of ,polycentric ,sectional ,profile4 ,from what has been said it will be seen that it is impossible to establish a standard sectional profile to suit all conditions4 ,the best one for the majority of conditions1 and the one most commonly employed1 is a polycentric figure in which the number of centers and the length of the radii are fixed by the engineer to meet the particular conditions which exist4 ,in a general way this form of center may be considered as composed of two parts symmetrical in respect to the vertical axis4 ,fig4 #g shows such a profile1 in which ,,dh is the vertical axis4 ,the section is unsymmetrical in respect to the horizontal axis ,,ge4 ,the upper part forming the roof arch is usually a semi-circle or semi-oval1 while the lower part1 comprising the side walls and invert of floor1 varies greatly in outline4 ,sometimes the side walls are vertical and the invert is omitted1 as shown by ,fig4 #h2 and sometimes the side walls are inclined1 with their bottoms braced apart by the invert1 as shown by ,fig4 #i4 ,in more treacherous soils the side walls are curved1 and are connected by small curved sections to the invert1 as shown by ,fig4 #aj4 ,in the last example the side walls are commonly called skewbacks1 and the lower part of the section is a polycentric figure like the upper part1 but dissimilar in form4 ,in a tunnel section whose profile is composed entirely of arcs the following conditions are essential3 ,the centers of the springer arcs ,ga and ,ea1 ,fig4 #g1 must be located on the line ,,ge2 the center of the roof arc b,db must be located on the axis ,,hd2 the total number of centers must be an odd number2 the radii of the succeeding arcs from ,g toward ,d and ,e toward ,d must decrease in length1 and finally the sum of the angles subtended by the several arcs must equal #ahj4 ,illustration3 ,fig4 #h ,fig4 #i ,fig4 #aj ,,figs4 #h to #aj4--,typical ,sectional ,profiles for ,tunnel4 ,dimensions of ,section4--,the dimensions to be given to the cross-section of a tunnel depend upon the purpose for which it is to be used4 ,whatever the purpose of the tunnel1 the following three points have to be considered in determining the size of its cross-section3 7#a7 ,the size of clear opening required2 7#b7 the thickness of lining masonry necessary2 and 7#c7 the decrease in the clear opening from the deformation of the lining4 ,railway tunnels may be built either to accommodate one or two1 three and four tracks4 ,in single-track tunnels a clear space of at least #b ft4 on each side should be allowed for between the tunnel wall and the side of the largest standard locomotive or car1 and a clear space of at least #c ft4 should be allowed for between the roof and the top of the same locomotive or car4 ,since the roof of the tunnel is arch-shaped1 to secure a clearance of #c ft4 at every point will necessitate making the clearance at the center greater than this amount4 ,in double-track tunnels the same amounts of side and roof clearances have to be provided for1 and1 in addition1 there has to be a clearance of at least #b ft4 between trains4 ,on the three- and four-track tunnels only the width varies while the height remains almost equal to the two track4 ,referring to ,fig4 #g1 and assuming the line ,,ab to represent the level of the tracks1 then the ordinary dimensions in feet required for both single- and double-track tunnels are as follows3-- ---------------------------------------- ----------------- ,,height1 ,,width1 ,,height1 ,,height1 ,d4 ,f4 ,g4 ,e4 ,c4 ,f4 ,c4 ,h4 ,,feet4 ,,feet4 ,,feet4 ,,feet4 ---------------------------------------- ----------------- ,single track#ag4f to #ahaf4e to #ahf to #g4d to ,,ab ,double track#bf4f to #bhbf4f to #bhf4c to #f4i to ,,ab ---------------------------------------- ----------------- ,the dimensions of tunnels built for aqueduct purposes are determined so as to have an area of cross-section equal to the required waterway4 ,in the ,croton ,aqueduct two different types of cross-sections were used1 the circular one for tunnels through rock and the horseshoe section for tunnels through loose materials4 ,in the ,catskill aqueduct three different cross-sections have been selected1 the circular one for tunnels under pressure and the horseshoe for tunnels at the hydraulic gradient4 ,these1 however1 through rock have a cross-section formed of a semi-circular arch and vertical side walls1 while through earth the semi-circular arch is supported by skewback walls4 ,in tunnels built for railroad aqueduct sewer and any other purpose the thickness of the masonry lining to be allowed for varies with the material penetrated1 as will be explained in a succeeding chapter where the dimensions for various ordinary conditions are given in tabular form4 ,the lining masonry is subject to deformation in three ways3 by the sinking of the whole masonry structure1 by the squeezing together of the side walls by the lateral pressures1 and by the settling of the roof-arch4 ,the whole masonry structure never sinks more than three or four inches1 and merits little attention4 ,the movement of the side walls towards each other1 which may amount to three or four inches for each wall without endangering their stability1 has1 however1 to be allowed for2 and similar allowance must be made for the settling of the roof-arch1 which may amount to from nine inches to two feet1 when the arch is built first as in the ,belgian system and rests for some time upon the loose soil4 ,,chapter ,,iii4 ,,excavating ,,machines ,,and ,,rock ,,drills3 ,,explosives ,,and ,,blasting4 ,earth-,excavating ,machines4--,comparatively few of the labor-saving machines employed for breaking up and removing loose soil in ordinary surface excavation are used in tunnel excavation through the same material4 ,several forms of tunnel excavating machines have been tried at various times1 but only a few of them have attained any measure of success1 and these have seldom been employed in more than a single work4 ,in the ,central ,london underground railway work through clay a continuous bucket excavator 7,fig4 #aa7 was employed with considerable saving in time and labor over hand work4 ,in some recent tunnel work in ,america the contractors made quite successful use of a modified form of steam shovel4 ,these are the most recent attempts to use excavating machines in soft ground1 and they1 like all previous attempts1 must be classed as experiments rather than as examples of common practice4 ,the ,thomson machine1#d however1 can be employed in any tunnel driven through loose soil4 ,it occupies a comparatively small space and may easily work when the timbering is used to support the roof of the tunnel4 ,steam shovel instead may give efficient result only in the case that the whole section of the tunnel is open at once and there are no timbers to prevent the free swinging of the dipper handle and boom4 ,but in tunnels through loose soils it is almost impossible to open the whole section at once without the necessity of supporting the roof4 ,consequently the use of steam shovel in loose tunnels is very limited4 ,the shovel1 the spade1 and the pick1 wielded by hand1 are the standard tools now1 as in the past1 for excavating soft-ground tunnels4 #d ,the machine was designed by ,mr4 ,thomas ,thomson1 ,engineer for ,messrs4 ,walter ,scott ,co4 ,illustration3 ,,fig4 #aa4--,soft ,ground ,bucket ,excavating ,machine3 ,central ,london ,underground ,railway4 ,rock-,excavating ,machines4--,at one period during the work of constructing the ,hoosac tunnel considerable attention was devoted to the development of a rock excavating1 boring1 or tunneling machine4 ,this device was designed to cut a groove around the circumference of the tunnel thirteen inches wide and twenty-four feet in diameter by means of revolving cutters4 ,it proved a failure1 as did one of smaller size1 eight feet in diameter1 tried subsequently4 ,during and before the ,hoosac tunnel work a number of boring-machines of similar character were experimented with at the ,mont ,cenis tunnel and elsewhere in ,europe2 but1 like the ,american devices1 they were finally abandoned as impracticable4 ,hand ,drills4--,briefly described1 a drill is a bar of steel having a chisel-shaped end or cutting-edge4 ,the simplest form of hand drill is worked by one man1 who holds the drill in one hand1 and drives it with a hammer wielded by his other hand4 ,a more efficient method of hand-drill work is1 however1 where one man holds the drill1 and another swings the hammer or sledge4 ,another form of hand drill1 called a churn drill1 consists of a long1 heavy bar of steel1 which is alternately raised and dropped by the workman1 thus cutting a hole by repeated impacts4 ,in drilling by hand the workman holding the drill gives it a partial turn on its axis at every stroke in order to prevent wedging and to offer a fresh surface to the cutting-edge4 ,for the same reason the chips and dust which accumulate in the drill-hole are frequently removed4 ,the instruments used for this purpose are called scrapers or dippers1 and are usually very simple in construction4 ,a common form is a strong wire having its end bent at right angles1 and flattened so as to make a sort of scoop by which the drillings may be scraped or hoisted out of the hole4 ,it is generally advantageous to pour water into the drill-hole while drilling to keep the drill from heating4 ,power ,drills4--,when the conditions are such that use can be made of them1 it is nearly always preferable to use power drills1 on account of their greater speed of penetration and greater economy of work4 ,power drills are worked by direct steam pressure1 or by compressed air generated by steam or water power1 and stored in receivers from which it is led to the drills through iron pipes4 ,a great variety of forms of power drills are available for tunnel work in rock1 but they can nearly all be grouped in one of two classes3 7#a7 ,percussion drills1 and 7#b7 ,rotary drills4 ,percussion ,drills4--,the first ,american percussion drill was patented by ,mr4 ,j4 ,j4 ,couch of ,philadelphia1 ,penn41 in ,march1 #ahdi4 ,in ,may of the same year1 ,mr4 ,joseph ,w4 ,fowle1 who had assisted ,mr4 ,couch in developing his drill1 patented a percussion drill of his own invention4 ,the ,fowle drill was taken up and improved by ,mr4 ,charles ,burleigh1 and was first used on the ,hoosac tunnel4 ,in ,europe ,mr4 ,cav patented a percussion drill in ,france in ,october1 #ahea4 ,this invention was soon followed by several others2 but it was not until ,sommeiller's drill1 patented in #aheg and perfected in #ahfa1 was used on the ,mont ,cenis tunnel1 that the problem of the percussion drill was practically solved abroad4 ,since this time numerous percussion drill patents have been taken out in both ,america and ,europe4 ,a percussion drill consists of a cylinder1 in which works a piston carrying a long piston rod1 and which is supported in such a manner that the drill clamped to the end of the piston rod alternately strikes and is withdrawn from the rock as the piston reciprocates back and forth in the cylinder4 ,means are devised by which the piston rod and drill turn slightly on their axis after each stroke1 and also by which the drill is fed forward or advanced as the depth of the drill-hole increases4 ,the drills of this type which are in most common use in ,america are the ,ingersoll-,sergeant and the ,rand4 ,there are various other makes in common use1 however1 which differ from the two named and from each other chiefly in the methods by which the valve is operated4 ,all of these drills work either with direct steam pressure or with compressed air4 ,workable percussion drills operated by electricity are built1 but so far they do not seem to have been able to compete commercially with the older forms4 ,no attempt will be made here to make a selection between the various forms of percussion drills for tunnel work1 and for the differences in construction and the merits claimed for each the reader is referred to the makers of these machines4 ,all of the leading makes will give efficient service4 ,it goes almost without saying that a good percussion drill should operate with little waste of pressure1 and should be composed of but few parts1 which can be easily removed and changed4 ,drill ,mountings4--,for tunnel work the general ,european practice is to mount power drills upon a carriage moving on tracks in order that they be easily withdrawn during the firing of blasts4 ,connection is made with the steam or compressed air pipes by means of flexible hose which can easily be attached or detached as the drill advances or when it is moved for repairs or during blasts4 ,two1 four1 and sometimes more drills are mounted and work simultaneously on a single carriage4 ,in ,america it has been found that column mountings have been more successful for tunnel work than any other form4 ,the column mounting made by the ,ingersoll-,sergeant ,drill ,co4 is shown in ,fig4 #ab4 ,in using this form of mounting no tracks or other special apparatus is required2 it is not necessary1 as is the case with the carriage mounting1 to remove the dbris before resuming operations1 but as soon as the blasting has been finished and the smoke has sufficiently disappeared the column can be set up and drilling resumed4 ,illustration3 ,,fig4 #ab4--;,column ,mounting for ,percussion ,drill3 ,ingersoll-,sergeant ,drill ,co4 ,rotary ,drills4--,rotary drilling machines1 or more simply rotary drills1 were first used in #aheg in the ,mont ,cenis tunnel4 ,the advantages claimed for rotary drills in comparison with percussion drills are3 7#a7 ,that less power is required to drive the drill1 and the power is better utilized2 7#b7 once the machines work easily they do not require continual repairs1 and 7#c7 in driving holes of large size the interior nucleus is taken away intact1 thus reducing work and increasing the speed of drilling4 ,rotary drills are extensively used for geological1 mining1 well-driving1 and prospecting purposes2 but they are very seldom employed in tunnels in ,america1 although successfully used for this purpose in ,europe4 ,the reason they have not gained more favor among ,american tunnel builders is due to some extent perhaps to prejudice1 but chiefly to the great cost of the machine as compared with percussion drills1 and to the expense of diamonds for repairs4 ,those who advocate these machines for tunnel work point out1 however1 that under ordinary usage the diamonds have a very long life1--borings of #gjj lin4 ft4 being recorded without repairs to the diamonds4 ,illustration3 ,,fig4 #ac4--,sketch of ,diamond ,drill ,bit4 ,the form of rotary drill used chiefly for prospecting purposes is the diamond drill4 ,this machine consists of a hollow cylindrical bit having a cutting-edge of diamonds1 which is revolved at the rate of from two hundred to four hundred revolutions per minute by suitable machinery operated by steam or compressed air4 ,the diamonds are set in the cutting-edge of the bit so as to project outward from its annular face and also slightly inside and outside of its cylindrical sides 7,fig4 #ac74 ,when the drill rod with the bit attached is rotated and fed forward the bit cuts an annular hole into the rock2 the drillings being removed from the hole by a constant stream of water which is forced down through the hollow drill rod and emerges1 carrying the dbris with it1 up through the narrow space between the outside of the bit and the walls of the hole4 ,there are various makes of diamond drills1 but they all operate in essentially the same manner4 ,the rotary drill principally employed in ,europe in tunneling is the ,brandt4 ,the cutting-edge of the ,brandt drill consists of hardened steel teeth4 ,the bit is pressed against the rock by hydraulic pressure1 and usually makes from seven to eight revolutions per minute4 ,some of the water when freed goes through the hollow bit1 keeping it cool1 and cleaning the hole of dbris4 ,a water pressure of from #cjj to #dej lbs4 per square inch is required to operate these drills4 ,rotary rock-drills may be mounted either on carriages or on columns for tunnel work4 ,several machines have recently been constructed for the purpose of breaking the rock in tunnels without blasting1 but they did not meet the approval of tunnel engineers4 ,one of these machines is provided with numerous electric torches1 which are applied to the rock at the front4 ,by suddenly chilling the rock with a stream of cold water the stone will crumble away4 ,another machine was tested1 with little success1 in the excavation for the ,new ,grand ,central ,depot in ,new ,york4 ,on the face of this machine there is a multitude of chipping drills revolving on four arms and driven by air pressure4 ,they attack the rock and chip it into fragments1 which are carried away by an endless band4 ,,explosives ,,and ,,blasting4 ,when the holes are once drilled1 either by hand or power drills1 they are charged with explosives4 ,the principal explosives employed in tunneling are gunpowder1 nitroglycerine1 and dynamite4 ,gunpowder4--,gunpowder is composed of charcoal1 sulphur1 and saltpeter in proportions varying according to the quality of the powder4 ,for mining purposes the composition employed is #fe saltpeter1 #ae sulphur1 and #bj charcoal4 ,it is a black granulated powder having a specific gravity of #a4e2 the black color is given by the charcoal2 and the grains have an angular form1 and vary in size from in4 to in4 ,good blasting powder should contain no fine grains1 which may be detected by pouring some of the powder upon a sheet of white paper4 ,the force developed by the explosion of gunpowder is not accurately known2 it depends upon the space in which it is confined4 ,different authorities estimate the pressure at from #ae1jjj lbs4 per sq4 in4 in loose blasts to #bjj1jjj lbs4 per sq4 in4 in gunnery4 ,authorities also differ in opinion as to the character of the gases developed by the explosion of gunpowder1 a matter of vital concern to the tunnel engineer1 since they are likely to affect the health and comfort of his workmen4 ,it may be assumed in a general way1 however1 that the oxygen of the saltpeter converts nearly all of the carbon of the charcoal into carbon dioxide1 a portion of which combines with the potash of the saltpeter to form carbonate of potash1 the remainder continuing in the form of gas4 ,the sulphur is converted into sulphuric acid1 and forms a sulphate of potash1 which by reaction is decomposed into hyposulphite and sulphide4 ,the nitrogen of the saltpeter is almost entirely evolved in a free state2 and the carbon not having been wholly burnt into carbonic acid1 there is a proportion of carbonic oxide4 ,nitroglycerine4--,nitroglycerine is one of the modern explosives used as a substitute for gunpowder4 ,it is a fluid produced by mixing glycerine with nitric and sulphuric acids2 it freezes at #da ,f41 and burns very quietly1 developing carbonic acid1 nitrogen1 oxygen1 and water4 ,by percussion or by the explosion of some substances1 such as capsules of gunpowder or fulminate of mercury1 nitroglycerine produces a sudden explosion in which about #abej volumes of gases are produced4 ,the pressure of these gases has been calculated at #bf1jjj atmospheres1 or #cbd1jjj lbs4 per sq4 in4 ,nitroglycerine explodes very easily by percussion in its normal state1 but with great difficulty when frozen2 hence1 in ,america1 at the beginning of its use1 it was transported only in a frozen state4 ,when dirty1 nitroglycerine undergoes a spontaneous decomposition accompanied by the development of gases and the evolution of heat1 which1 reaching #chh ,f41 causes it to explode4 ,notwithstanding the enormous pressures which nitroglycerine develops1 it is very seldom used in its liquid state1 but is mixed with a granular absorbent earth composed of the shells of diatoms4 ,the fluid undergoes no chemical change by being absorbed1 and explodes1 freezes1 and burns under the same conditions as in the fluid state4 ,dynamite4--,the credit of rendering nitroglycerine available for the purposes of the engineer by mixing it with a granular absorbent is due to ,albert ,nobel of ,stockholm1 ,sweden1 who named the new material dynamite4 ,the nitroglycerine in dynamite loses very little of its original explosive power1 but is very much less easily exploded by percussion1 and can be employed in horizontal as well as vertical holes1 which was1 of course1 not possible in its liquid state4 ,dynamite must contain at least #ej of nitroglycerine4 ,some manufacturers1 instead of using diatomaceous earth1 use other absorbents which develop gases upon explosion and increase the force of the explosion4 ,these mixtures are classed under the general name of false dynamites4 ,a great many varieties of dynamite are manufactured1 and each manufacturer usually makes a number of grades to which he gives special names4 ,dynamite for railway work1 tunneling1 and mining contains about #ej of nitroglycerine2 for quarrying about #ce1 and for blasting soft rocks about #cj4 ,it is sold in cylindrical cartridges covered with paper4 ,storage of ,explosives4--,in driving tunnels through rock large quantities of explosives must be used1 and it is necessary to have some safe place for storing them4 ,in many ,states there are special laws governing the transportation and storage of explosives2 where there is no regulation by law the engineer should take suitable precautions of his own devising4 ,it is best to build a special house or hut in one of the most concealed portions of the work and away from the tunnel1 and protect it with a lightning-rod and from fire4 ,strict orders should be given to the watchman in charge not to allow persons inside with lamps or fire in any form1 and smoking should be prohibited4 ,the use of hammers for opening the boxes should be prohibited2 and dynamite1 gunpowder1 and fulminate of mercury should not be stored together in the same room4 ,a quantity of dynamite for two or three days' consumption may be stored near the entrance of the tunnel in a locked box1 the keys of which are kept by the foreman of the work4 ,when dynamite has been frozen the engineer should provide some arrangement by which it may be heated to a temperature not exceeding #abj ,f41 and absolutely forbid it being thawed out on a stove or by an open fire4 ,fuses4--,when gunpowder is used in tunneling it is ignited by the ,blickford match4 ,this match1 or fuse as it is more commonly called1 consists of a small rope of yarn or cotton having as a core a small continuous thread of fine gunpowder4 ,to protect the outside of the fuse from moisture it is coated with tar or some other impervious substance4 ,these fuses are so well made that they burn very uniformly at the rate of about #a ft4 in #bj seconds1 hence the moment of explosion can be pretty accurately fixed beforehand4 ,blickford matches have the objection for tunnel work of burning with a bad odor1 especially when they are coated with tar1 and to remedy this many others have been invented4 ,those of ,rzika and ,franzl are the best known of these4 ,the former has many advantages1 but it burns too quickly1 about #c ft4 per second1 and is expensive2 the latter consists of a small hollow rope filled with dynamite4 ,blickford matches cannot be used to explode dynamite1 the use of a cartridge being required4 ,these cartridges are small copper cylinders containing fulminate of mercury4 ,they may be attached to the end of the ,blickford match1 which being ignited the spark travels along its length until it reaches the copper cylinder1 where it explodes the fulminate of mercury1 which in turn explodes the dynamite4 ,blasts may also be fired by electricity1 which1 in fact1 is the most common and the preferable method1 because several blasts can be fired simultaneously1 and because the current is turned on at a great distance1 thus affording greater safety to the workmen4 ,the method of electric firing generally employed in ,america is known as the connecting series method1 and consists in firing several mines simultaneously4 ,the ends of the wires are scraped bare1 and the wire of the first hole of the series is twisted together with the wire of the second hole1 and so on2 finally the two odd wires of the first and last holes are connected to two wires of a single cable or to two separate cables extending to some safe place to which the men can retreat4 ,here the two cable wires are connected by binding screws to the poles of a battery1 or sometimes to a frictional electric machine4 ,the current passes through the wires1 making a spark at each break1 and so fires the fulminate of mercury1 which explodes the dynamite4 ,simultaneous firing by electricity by utilizing the united strength of the blasts at the same instant secures about #aj greater efficiency from the explosives4 ,another advantage of electric firing is that in case of a missfire of any one of the holes there is slight possibility of explosion afterwards1 and the place can be approached at once to discover the cause4 ,tamping4--,tamping is the material placed in the hole above the explosive to prevent the gases of explosion from escaping into the air4 ,tamping generally consists of clay4 ,when gunpowder is used the clay must be well rammed with a wooden tool1 and paper1 cotton1 or some other dry material must be placed between the moist clay and the powder4 ,when dynamite is used it is not necessary to ram the tamping1 since the suddenness of the explosion shatters the rock before the clay can be driven from the hole4 ,a few experienced men should be appointed to fire the blasts4 ,these men should give ample warning previous to the blast in order that all machinery and tools which might be injured by flying fragments may be removed out of danger1 and so that the workmen may seek safety4 ,when all is ready they should fire the blasts1 keeping accurate count of the explosions to ensure that no holes have missed fire1 and should call the workmen back when all danger is over4 ,in case any hole has missed fire it should be marked by a red lamp or flag4 ,nature of ,explosions4--,when the explosives are ignited a sudden development of gases results1 producing a sudden and violent increase of pressure1 usually accompanied by a loud report4 ,the energy of the explosion is exerted in all directions in the form of a sphere having its center at the point of explosion1 and the waves of energy lose their force as the distance from this central point increases4 ,the energy of the explosion at any point in the sphere of energy is1 therefore1 inversely proportional to the distance of this point from the center of explosion4 ,in the vicinity of the center of explosion the gases have sufficient power to destroy the force of cohesion and shatter the rock2 further on1 as they lose strength1 they only destroy the elasticity of the material and produce cracks2 and still further away they only produce a shock1 and do not affect the material4 ,within the sphere of energy there are1 therefore1 three other concentric spheres3 the first one being where cohesion is destroyed1 the second where elasticity is overcome1 and the third where the shock is transmitted by elasticity4 ,when the latter sphere comes below the surface1 the gases remain inside the rock2 but when the surface intersects either of the other two spheres1 the gases blow up the rock1 forming a cone or crater1 whose apex is at the point of explosion1 and which is called the blasting-cone4 ,the larger the blasting-cone is1 the greater is the amount of rock broken up2 and the object of the engineer should1 therefore1 always be so to regulate the depth of the hole and the quantity of explosive as to secure the largest possible blasting cone in each case4 ,experiments are required to determine the most efficient depth of hole1 and quantity of explosive to be employed1 since these differ in different kinds of rock1 with the position of the rock strata1 etc42 but in ordinary practice1 the depths of the holes are made from #b to #c ft4 in the heading and upper portion of the tunnel1 when drilled by hand2 and from #f to #h ft4 when drilled by power drills4 ,in the lower portion of the profile1 the holes are made deeper1 from #c ft4 to #d ft4 when drilled by hand1 and exceeding #f ft4 when drilled by power4 ,the distance of the holes apart should be about equal to the diameter of the blasting-cone2 as a general rule it is assumed that the base of the blasting-cone has a diameter equal to twice the depth of the hole4 ,the following table gives the average number of holes required in each part of the excavation for the ,st4 ,gothard tunnel in which the heading was excavated by machine drills while the other parts were excavated by hand drills3 ,,no4 ,,of ,,part4#e ,,name ,,of ,,part4 ,,no4 ,,of ,,holes4 #a4 ,heading #f to #i #b4 ,right wing of heading #c to #e #c4 ,left wing of heading #c to #e #d4 ,shallow trench with core #b #e4 ,deepening of trench to floor #f to #i #f4 ,narrow mass of core to left #c #g4 ,greater mass of core to left #f to #i #h4 ,culvert #a -------- ,total section #cj to #dc #e ,the location of the parts numbered is shown by ,fig4 #ad1 p4 #cf4 ,the quantity of explosives required for blasting depends upon the quality of the rock1 since the force of the explosives must overcome the cohesion of the rock1 which varies with its nature1 and often differs greatly in rocks of the same kind and composition4 ,the quantity of explosives required to secure the greatest efficiency in blasting any particular rock may be determined experimentally1 but in practice it is usually deduced by the following rules3 7#a7 ,the blasting force is directly proportional to the weight of the explosives used1 and 7#b7 the bulk of the blasted rock is proportional to the cube of the depth of the holes4 ,it is usually assumed1 also1 that the explosive should fill at least one-fourth the depth of the hole4 ,the following table gives the depth of holes and amount of dynamite used at each advance in the ,fort ,george ,tunnel illustrated on page #ace4 ---------------------------------------- ---------------- ,,order ,,of ,,firing4 ,,kinds ,,of ,,depth4 ,,charge4 ,,kind ,,of ,,holes4 ,,dynamite4 ---------------------------------------- ---------------- ,bench #ast round#d grading #c to #eej lbs4#dj climax ,holes #e bench #i #f #de #dj #bnd round#f trimming #c to #idb #dj ,heading #c;d round #h center cut#i #ef #fj ,holes #dth round#h side #h #dh #dj #eth round#f dry #h #cf #dj ---------------------------------------- ---------------- ,,chapter ,,iv4 ,,general ,,methods ,,of ,,excavation3 ,,shafts3 ,,classification ,,of ,,tunnels4 ,a number of different modes of procedure are followed in excavating tunnels1 and each of the more important of these will be considered in a separate chapter4 ,there are1 however1 certain characteristics common to all of these methods1 and these will be noted briefly here4 ,illustration3 ,,fig4 #ad4--;,diagram ,showing ,sequence of ,excavation for ,st4 ,gothard ,tunnel4 ,illustration3 ,,fig4 #ae4--;,diagram ,showing ,manner of ,determining ,correspondence of ,excavation to ,sectional ,profile4 ,division of ,section4--,it may be asserted at the outset that the whole area of the tunnel section is not ordinarily excavated at one time1 but that it is removed in sections1 and as each section is excavated it is thoroughly timbered or strutted4 ,the order in which these different sections are excavated varies with the method of excavation1 and it is clearly shown for each method in succeeding chapters4 ,as a single example to illustrate the proposition just made1 the division of the section and the sequence of excavation adopted at the ,st4 ,gothard tunnel is selected 7,fig4 #ad74 ,the different parts of the section were excavated in the order numbered2 the names given to each part1 and the number of holes employed in breaking it down1 are given by the table on page #ce4 ,whatever method is employed1 the work always begins by driving a heading1 which is the most difficult and expensive part of the excavation4 ,all the other operations required in breaking down the remainder of the tunnel section are usually designated by the general term of enlargement of the profile4 ,the various operations of excavation may1 therefore1 be classified either as excavation of the heading or enlargement of the profile4 ,excavation of the ,heading4--,there is considerable confusion among the different authorities regarding the exact definition of the term 8heading0 as it is used in tunnel work4 ,some authorities call a small passage driven at the top of the profile a heading1 and a similar passage driven at the bottom of the profile a drift2 others call any passage driven parallel to the tunnel axis1 whether at the top or at the bottom of the profile1 a drift2 and still others give the name 8heading0 to all such passages4 ,for the sake of distinctness of terminology it seems preferable to call the passage a heading when it is located at the top of the profile1 and a drift when it is located near the bottom4 ,headings and drifts are driven in advance of the general excavation for the following purposes3 7#a7 ,to fix correctly the axis of the tunnel2 7#b7 to allow the work to go on at different points without the gangs of laborers interfering with each other2 7#c7 to detect the nature of material to be dealt with and to be ready in any contingency to overcome any trouble caused by a change in the soil2 and 7#d7 to collect the water4 ,the dimensions of headings in actual practice vary according to the nature of the soil through which they are driven4 ,as a general rule they should not be less than #g ft4 in height1 so as to allow the men to work standing1 and have room left for the roof strutting4 ,the width should not be less than #f ft41 to allow two men to work at the front1 and to give room for the material cars without interfering with the wall strutting4 ,usually headings are made #h ft4 wide4 ,the length of headings in practice varies according to circumstances4 ,in very long tunnels through hard rock the headings are sometimes excavated from #ajjj ft4 to #bjjj ft4 in advance1 in order that they may meet as soon as possible and the ranging of the center line be verified1 and so that as great an area of rock as possible may be attacked at the same time in the work of enlarging the profile4 ,in short tunnels1 where the ranging of the center line is less liable to error1 shorter headings are employed1 and in soft soils they are made shorter and shorter as the cohesion of the soil decreases4 ,when the material has too little cohesion to stand alone1 the tops and sides of the heading require to be supported by strutting4 ,to prevent caving at the front of the heading1 the face of the excavation is made inclined1 the inclination following as near as may be the natural slope of the material4 ,enlargement of the ,profile4--,the enlargement of the profile is accomplished by excavating in succession several small prisms parallel to the heading1 and its full length1 which are so located that as each one is taken out the cross-section of the original heading is enlarged4 ,the number1 location1 and sequence of these prisms vary in different methods of excavation1 and are explained in succeeding chapters where these methods are described4 ,to direct the excavation so as to keep it always within the boundaries of the adopted profile1 the engineer first marks the center line on the roof of the heading by wooden or metal pegs1 or by some other suitable means by which a plumb line may be suspended4 ,he next draws to a large scale a profile of the proposed section2 and beginning at the top of the vertical axis he draws horizontal lines at regular intervals1 as shown by ,fig4 #ae1 until they intersect the boundary lines of the profile1 and designates on each of these lines the distance between the vertical axis and the point where it intersects the profile4 ,it is evident that if the foreman of excavation divides his plumb line in a manner corresponding to the engineer's drawing1 and then measures horizontally and at right angles to the vertical center plane of the tunnel the distance designated on the horizontal lines of the drawing1 he will have located points on the profile of the section1 or in other words have established the limits of excavation4 ,illustration3 ,,fig4 #af4--,polar ,protractor for ,determining ,profile of ,excavated ,cross-,section4 ,in the excavation of the ,croton ,aqueduct for the water supply of ,new ,york city1 an instrument called a polar protractor was used for determining the location of the sectional profile4 ,it was invented by ,mr4 ,alfred ,craven1 division engineer of the work4 ,this instrument consists of a circular disk graduated to degrees1 and mounted on a tripod in such a manner that it may be leveled up1 and also have a vertical motion and a motion about the vertical axis4 ,the construction is shown clearly by ,fig4 #af4 ,in use the device is mounted with its center at the axis of the tunnel4 ,a light wooden measuring-rod tapering to a point1 shod with brass and graduated to feet and hundredths of a foot1 lies upon the wooden arm or rest1 which revolves upon the face of the disk1 and slides out to a contact with the surface of the excavation at such points as are to be determined4 ,if the only information desired is whether or not the excavation is sufficient or beyond the established lines1 the rod is set to the proper radius1 and if it swings clear the fact is determined4 ,if a true copy of the actual cross-section is desired1 the rod is brought into contact with the significant points in the cross-section1 and the angles and distances are recorded4 ,the general method of directing the excavation in enlarging the profile by referring all points of the profile to the vertical axis is the one usually employed in tunneling1 and gives good results4 ,it is considered better in actual practice to have the excavation exceed the profile somewhat than to have it fall short of it1 since the voids can be more easily filled in with riprap than the encroaching rock can be excavated during the building of the masonry4 ,in tunnels where strutting is necessary the excavation must be made enough larger than the finished section to provide the space for it4 ,in soft-ground tunnels it is also usual to enlarge the excavation to allow for the probable slight sinking of the masonry4 ,the proper allowance for strutting is usually left to the judgment of the foreman of excavation1 but the allowance for settlement must be fixed by the engineer4 ,,shafts4 ,shafts are vertical walls or passages sunk along the line of the tunnel at one or more points between the entrances1 to permit the tunnel excavation to be attacked at several different points at once1 thus greatly reducing the time required for excavation4 ,shafts may be located directly over the center of the tunnel or to one side of it1 and1 while usually vertical1 are sometimes inclined4 ,during the construction of the tunnel the shafts serve the same purpose as the entrances2 hence they must afford a passageway for the excavated materials1 which have to be hoisted out1 and also for the construction tools and materials which have to be lowered down them4 ,they must also afford a passageway for workmen1 draft animals1 and for pipes for ventilation1 water1 compressed air1 etc4 ,the character of this traffic indicates the dimensions required1 but these depend also upon the method of hoisting employed4 ,thus1 when a windlass or horse gin is used1 and the materials are hoisted in buckets of small dimensions1 the dimensions of the shaft may also be small2 but when steam elevators are employed1 and the material is carried on cars run on to the platform of the elevator1 large dimensions must be given to the shaft4 ,generally the parts of the shaft used for different purposes are separated by partitions4 ,the elevator for workmen and the various pipes are placed in one compartment1 while the elevator for hoisting the excavated material and lowering construction material is placed in another4 ,shafts may be either temporary or permanent4 ,they are temporary when they are filled in after the tunnel is completed1 and permanent when they are left open to supply ventilation to the tunnel4 ,permanent shafts are usually made circular1 and lined with brick1 unless excavated in very hard and durable rock4 ,when sunk for temporary use only1 shafts are usually made rectangular with the greater dimension transverse to the tunnel4 ,they are strutted with timber4 ,a pump is generally located at the bottom of the shaft to collect the water which seeps in from the sides of the shaft and from the tunnel excavation4 ,the dimensions of this pump will of course vary with the amount of water encountered1 as will also the capacity of the pump for forcing it up and out of the shaft1 which has always to be kept dry4 ,the majority of engineers prefer to sink shafts directly over the center line of the tunnel4 ,side shafts are employed chiefly by ,french engineers4 ,the chief advantage of the former method is the great facility which it affords for hoisting out the materials1 while in favor of the latter method is the non-interference of the shaft with the operations inside the tunnel4 ,were it not that the side shaft requires the introduction of a transverse gallery connecting it with the tunnel1 it would be on the whole superior to the center shaft2 but the side gallery necessitates turning the cars at right angles1 and consequently the use of a very sharp curve or a turntable to reach the shaft bottom1 which is a disadvantage that may outweigh its advantages in some other respects4 ,it is impossible to state absolutely which of these methods of locating shafts is the best2 both present advantages and disadvantages1 and the use of one or the other is usually determined more by the local conditions than by any general superiority of either4 ,when side shafts are employed they are sometimes made inclined instead of vertical4 ,this form is used when the depth of the shaft is small4 ,by it the hauling is greatly simplified1 since the cars loaded at the front with excavated material can be hauled directly out of the shaft and to the dumping-place1 surmounting the inclined shaft by means of continuous cables4 ,the short galleries connecting the side shafts with the tunnel proper usually have a smaller section than the tunnel1 but are excavated in exactly the same manner4 ,another form of side shaft sometimes used is one reaching to the surface when the tunnel runs close to the side of cliff1 as is the case with some of the ,alpine railway tunnels4 ,,classification ,,of ,,tunnels4 ,tunnels are classified in various ways1 but the most logical method would appear to be a grouping according to the quality of the material through which they are driven2 and this method will be adopted here4 ,by this method we have first the following general classification3 7#a7 ,tunnels in hard rock2 7#b7 tunnels in ordinary loose soil2 7#c7 tunnels in quicksand2 7#d7 open-cut tunnels2 and 7#e7 submarine tunnels4 ,it is hardly necessary to say that this classification1 like all others1 is simply an arbitrary arrangement adopted for the sake of order and convenience in treating the subject4 ,tunnels in ,hard ,rock4--,with the numerous labor-saving methods and machines now available1 hard rock is perhaps the safest and easiest of all materials through which to drive a tunnel4 ,tunnels through hard rock may be excavated1 either by a drift or by a heading4 ,the difference depends upon whether the advance gallery is located close to the floor or near the soffit of the section4 ,tunnels in ,loose ,soils4--,in driving tunnels through loose soils many different methods have been devised1 which may be grouped as follows3 7#a7 ,tunnels excavated at the soffit--,belgian method2 7#b7 tunnels excavated along the perimeter--,german method2 7#c7 tunnels excavated in the whole section--,english1 ,austrian and ,american methods2 7#d7 tunnels excavated in two halves independent of each other--,italian method4 7#a7 ,excavating the tunnel by beginning at the soffit of the section1 or by the ,belgian method1 is the method of tunneling in loose soils most commonly employed in ,europe at the present time4 ,it consists in excavating the soffit of the section first2 then building the arch1 which is supported upon the unexcavated ground2 and finally in excavating the lower portion of the section1 and building the side walls and invert4 7#b7 ,in excavating tunnels along the perimeter an annular excavation is made1 following closely the outline of the sectional profile in which the lining masonry is built1 after which the center core is excavated4 ,in the ,german method two drifts are opened at each side of the tunnel near the bottom4 ,other drifts are excavated1 one above the other1 on each side to extend or heighten the first two until all the perimeter is open except across the bottom4 ,the masonry lining is then built from the bottom upwards on each side to the crown of the arch1 and then the center core is removed and the invert is built4 7#c7 ,this method1 as its name implies1 consists in taking out short lengths of the whole sectional profile before beginning the building of the masonry4 ,in the ,english method the invert is built first1 then the side walls1 and finally the arch4 ,the excavators and masons work alternately4 ,the ,austrian method differs in two particulars from the ,english3 the length of section opened is made great enough to allow the excavators to continue work ahead of the masons1 and the side walls and roof are built before the invert4 ,in the ,american method the whole section of the tunnel is open at once3 excavators and masons work simultaneously1 but a very large quantity of timbering is required4 7#d7 ,the ,italian method is very seldom employed on account of its expensiveness1 but it can often be used where the other methods fail4 ,it consists in excavating the lower half of the section1 and building the invert and side walls1 and then filling the space between the walls in again except for a narrow passageway for the cars2 next the upper part of the section is excavated1 as in the ,belgian method1 and the arch is built2 and finally the soil in the lower part is permanently removed4 ,tunnels in ,quicksand4--,tunnels through quicksand are driven by one of the ordinary soft-ground methods after draining away the water1 or else as submarine tunnels4 ,open-,cut ,tunnels4--,open-cut tunnels are those driven at such a small depth under the surface that it is more convenient to excavate an open cut1 build the tunnel masonry inside it1 and then refill the open spaces1 than it is to carry on the work entirely underground4 ,in firm soils the usual mode of operation is to excavate first two parallel trenches for the side walls1 then remove the core1 and build the arch and the invert4 ,in unstable soils1 since the invert must be built first1 it is usual to open up a single wide trench4 ,in infrequent cases where a tunnel is desired in a place which is to be filled in1 the masonry is built as a surface structure1 which in due time is covered4 ,submarine ,tunnels4--,the mode of procedure followed in excavating submarine tunnels depends upon whether the material penetrated is pervious or impervious to water4 ,in impervious material any of the ordinary methods of tunneling found suitable may be employed4 ,in pervious material the excavation may be accomplished either by means of compressed air to keep the water out of the excavation1 or by means of a shield closing the front of the excavation1 or by a combination of these two methods4 ,tunnels on the river bed are built by means of coffer dams which inclose alternate portions of the work1 by sinking a continuous series of pneumatic caissons and opening communication between them1 and by sinking the tunnel in sections constructed on land4 ,in hard rock4 ,by drifts4 ,by a heading4 ,by upper half3 the arch is built ,belgian method4 before the side walls4 ,by the perimeter3 excavated and lined before the central ,german method4 nucleus is removed4 ,in loose soil4,by whole section3 ,english method4 the lining begins after,austrian method4 the whole section is ,american method4 excavated4 ,by halves3 the lower half is excavated and lined1 ,italian method4 followed by the work of the upper half4 ,,methods ,,of ,,excavating,in quicksand4 ,,tunnels4 ,in resistant soils4 ,by two lateral narrow trenches4 ,open-cut tunnels4 ,in loose soils4 ,by one very large trench4 ,built up4 ,by slices4 ,at great depths under ,by any method4 the river bed4 ,by shield4 ,at small depths ,by compressed under the river air4 ,submarine bed4 ,by shield and tunnels4 compressed air4 ,by coffer dams4 ,by pneumatic ,on the river bed4 caissons4 ,by built-up sections4 ,the above diagram gives in compact form the classification of tunnels according to materials penetrated and methods of excavation adopted1 which have been described more fully in the succeeding paragraphs4 ,it may be noted here again that this is a purely arbitrary classification1 and serves mostly as a convenience in discussing the different classes of tunnels without confusion4 ,,chapter ,v4 ,,methods ,,of ,,timbering ,,or ,,strutting ,,tunnels4 ,the purpose of timbering or strutting in tunnel work is to prevent the caving-in of the roof and side walls of the excavation previous to the construction of the lining4 ,as the strutting has to resist all the pressures developed in the roof and side walls1 which may be exceedingly troublesome and of great intensity in loose soils1 its design and erection call for particular care4 ,the method of strutting adopted depends upon the method of excavation employed2 but in every case the problem is not only to build it strong enough to withstand the pressures developed1 but to do this as economically as possible1 and with as little hindrance as may be to the work which is going on simultaneously and which will come later4 ,only the latter general problems of strutting peculiar to all methods of tunnel work will be considered here4 ,for this consideration strutting may be classified according to the material of which it is built1 under the heads of timber structures and iron structures4 ,illustration3 ,,fig4 #ag4--;,joining ,tunnel ,struts by ,halving4 ,illustration3 ,,fig4 #ah4--,round ,timber ,post and ,cap ,bearing4 ,,timber ,,strutting4 ,timber is nearly always employed for strutting in tunnel work4 ,so long as it has the requisite strength1 any kind of timber is suitable for strutting1 since1 it being only temporarily employed1 its durability is a matter of slight importance4 ,timber with good elastic properties1 like pine or spruce1 is preferably chosen1 since it yields gradually under stress1 thus warning the engineer of the approach of danger2 while oak and other strong timbers resist until the last moment1 and then yield suddenly under the breaking load4 ,soft woods1 moreover1 are usually lighter in weight than hard woods1 which is a considerable advantage where so much handling is required in a restricted space4 ,round timbers are generally employed1 since they are less expensive1 and quite as satisfactory in other respects as sawed timbers4 ,in the ,english and ,austrian methods of strutting1 which are described further on1 a few of the principal struts are of sawed timbers4 ,the various timbers of the strutting are seldom attached by framed joints1 but wedges are used to give them the necessary bearing against each other4 ,where framed joints are employed they are made of the simplest form usually by halving the joining timbers1 as shown by ,fig4 #ag4 ,fig4 #ah shows a form of joint used where round posts carry beams of similar shape4 ,the reason why it is possible to do away with jointed connections to such a great extent1 is that the strains which the timbers have to resist are either compressive or bending strains1 and because the timbers are so short that they do not require to be spliced4 ,strutting of ,headings4--,the method of strutting the heading that is employed depends upon the material through which the heading is driven4 ,in solid rock strutting may not be required at all1 or only for the purpose of preventing the fall of loose blocks from the roof1 then vertical props are erected where required1 or horizontal beams are inserted into the side walls1 as shown by ,fig4 #ai4 ,these horizontal beams may be used singly at dangerous places1 or they may be placed from #b ft4 to #c ft4 apart all along the heading4 ,in the latter case they usually carry a lagging of planks1 which may be placed at intervals or close together1 and filled above with stone in case the roof of the excavation is very unstable4 ,planks used in this manner are usually called poling-boards4 ,where the side walls as well as the roof require support1 vertical side posts are employed to carry the roof beams1 as shown by ,fig4 #bj2 and1 when necessary1 poling-boards are inserted between these posts and the walls of the excavation4 ,illustration3 ,,fig4 #ai4--;,ceiling ,strutting for ,tunnel ,roofs4 ,illustration3 ,,fig4 #bj4--;,ceiling ,strutting with ,side ,post ,supports4 ,illustration3 ,,fig4 #ba4--,sill1 ,side ,post and ,cap ,cross ,frame ,strutting4 ,illustration3 ,,fig4 #bb4--,reinforced ,cross ,frame ,strutting for ,treacherous ,materials4 ,frame ,strutting4--,in very loose soils not only the roof and side walls1 but also the floor of the heading require strutting4 ,in these cases frame strutting is employed1 as shown by ,fig4 #ba4 ,it consists simply of a rectangular frame2 at the top there is a crown bar supported by two vertical side posts setting on a sill laid across the bottom of the heading4 ,these frames are spaced at close intervals1 and carry longitudinal planks or poling-boards4 ,the sill of the frame is sometimes omitted when the soil is stable enough to permit it1 and in its place wooden footing blocks are substituted to carry the side posts4 ,in soils where the pressures are great enough to bend the crown bar1 a secondary frame is employed1 as shown by ,fig4 #bb1 the two inclined roof members1 or rafters1 of which support the crown bar at the center4 ,illustration3 ,,fig4 #bc4--,longitudinal ,poling-,board ,system of ,roof ,strutting4 ,illustration3 ,,fig4 #bd4--,transverse ,poling-,board ,system of ,roof ,strutting4 ,it is the more common practice in driving headings through soft soils to use inclined poling-boards to support the roof4 ,fig4 #bc shows one method of doing this4 ,the method of operation is as follows3 ,assuming the poling-boards a and b to be in place1 and supported by the frames ,a1 ,b1 ,c1 as shown1 the first step in continuation of the work is to insert the poling-board c over the crown bar of frame ,c1 and under the block m4 ,excavation is then begun at the top1 and as fast as the soil is removed ahead of it the poling-board c is driven ahead until its rear end only slightly overhangs the crown bar of frame ,c4 ,the remainder of the face of the heading is then excavated nearly to the front end of the poling-board c1 and another frame is set up4 ,by a succession of these operations the heading is advanced4 ,the poling-boards at the sides of the heading are placed in a similar manner to the roof poling-boards4 ,a second method of using inclined poling-boards is shown by ,fig4 #bd4 ,here the poling-boards run transversely1 and are supported by the arrangement of timbering shown4 ,the chief advantage of using these inclined poling-boards1 particularly in the manner shown by ,fig4 #bc1 is that the excavators work under cover at all times1 and are thus safe from falling fragments or sudden cavings4 ,box ,strutting4--,in very treacherous soils1 such as quicksand1 peat1 and laminated clay1 box strutting is commonly employed4 ,the method of building this strutting is to set up at the face of the work a rectangular frame1 and use it as a guide in driving a lagging or boxing of horizontal planks into the soft soil ahead4 ,these planks have sharp edges1 and are driven to a distance of #b ft4 or #c ft4 into the face of the heading1 so as to inclose a rectangular body of earth4 ,this earth is excavated nearly to the ends of the planks1 and then another frame is inserted close up against the new face of the excavation1 which supports the planks so that the remainder of the earth included by them may be removed4 ,these two frames1 with their plank lagging1 constitute a 8box20 and a series of these boxes1 one succeeding another1 form the strutting of the heading4 ,strutting the ,face4--,in some cases it is found necessary to strut the face of the heading in order to prevent it from caving in4 ,this is generally done by setting plank vertically1 and bracing them up by means of inclined props whose feet abut against the sill of the nearest cross frame4 ,this strutting is erected while the workmen are placing the side and roof strutting1 and is removed to permit excavation4 ,full ,section ,timber ,strutting4--,for strutting the full section two forms of timbering are employed1 known as the polygonal system and the longitudinal system4 ,longitudinal strutting consists of a timber structure so arranged as to have all the principal members supporting the poling-boards parallel to the axis of the tunnel4 ,this system of strutting is peculiar to the ,english method of tunneling4 ,the longitudinal timbers rest on this finished masonry at one end1 and are carried on a cross frame or by props at the other end4 ,at intermediate points the longitudinals are braced apart by struts in planes transverse to the tunnel axis4 ,this construction makes a very strong strutting framework1 since the transverse struts act as arch ribs to stiffen the longitudinals2 but the use of transverse poling-boards requires the excavation of a larger cross-section than is necessary when longitudinal poling-boards are employed1 and this increases the cost both for the amount of earth excavated and the greater quantity of filling required4 ,in polygonal strutting the main members are in a plane normal to the axis of the tunnel4 ,they form a polygon whose sides follow closely the sectional profile of the excavation4 ,these polygonal frames are placed at more or less short intervals apart1 and are braced together by short longitudinal struts lying close to the sides of the excavation1 and running from one frame to the next1 and also by longer longitudinal members which extend over several frames4 ,the polygonal system of strutting is peculiar to the ,austrian method of tunneling1 and is fully described in a succeeding chapter4 ,one of its distinctive characteristics is that the poling-boards are inserted parallel to the tunnel axis4 ,polygonal strutting is generally held to be stronger than longitudinal strutting under uniform loads1 but it is more liable to distortion when the loads are unsymmetrical4 ,illustration3 ,,fig4 #be4--,shaft with ,single ,transverse ,strutting4 ,illustration3 ,,fig4 #bf4--,rectangular ,frame ,strutting for ,shafts4 ,illustration3 ,,fig4 #bg4--,reinforced ,rectangular ,frame ,strutting for ,shafts in ,treacherous ,materials4 ,strutting of ,shafts4--,tunnel shafts are strutted both to prevent the caving-in of the sides and to divide them into compartments4 ,when the material penetrated is very compact1 and caving is not likely1 a single series of transverse struts1 one above the other1 running from the top to the bottom of the shaft1 as shown by ,fig4 #be1 is used to divide it into two compartments4 ,in softer material1 where the sides of the shaft require support1 ,fig4 #bf shows a form of strutting commonly employed4 ,it consists of vertical corner posts braced apart at intervals by four horizontal struts placed close to the walls of the shaft4 ,the longer side struts are also braced apart at the center by a middle strut which divides the shaft into two compartments4 ,a lagging of vertical plank is placed between the walls of the shaft and the horizontal side struts4 ,in very loose soils the form of strutting shown by ,fig4 #bg is employed4 ,this is practically the same construction as is shown by ,fig4 #bf1 with the addition of an interior polygonal horizontal bracing in each half of the shaft4 ,referring to ,fig4 #bg1 the timbers a1 a1 etc41 are vertical and continuous from the top to the bottom of the shaft2 and the horizontal timbers1 b1 b1 etc41 are spaced at more or less close intervals vertically4 ,the lagging planks may be laid with spaces between them1 or close together1 or1 in case of very loose material1 with their edges overlapping4 ,the manner of constructing the strutting is also governed by the stability of the soil4 ,in firm soils it is possible to sink the shaft quite a depth without timbering1 and the timbering can be erected in sections of considerable length1 which is always an advantage1 but in loose soils the timbering has to follow closely the excavation4 ,the solid wall shaft struttings which have been described are discontinued at the point where the shaft intersects the tunnel excavation2 and from this point to the floor of the tunnel an open timbering is employed1 whose only duty is to support the weight of the solid strutting above4 ,this timbering is made in various forms1 but the most common is a timber truss or arch construction which spans the tunnel section4 ,quantity of ,timber4--,the quantity of timber employed in strutting a tunnel varies with the character of the material through which the tunnel is excavated3 it is small for solid-rock tunnels1 and large for soft-ground tunnels4 ,in the ,belgian method of excavation a smaller quantity of timber is used than in any of the other ordinary methods4 ,for single-track tunnels excavated by this method there will be needed on an average about #c to #c cu4 yds4 of timber per lineal foot of tunnel4 ,practical experience shows that about four-fifths of the timber once used can be employed for the second time4 ,in any of the methods in which the whole tunnel section is excavated at once1 the average amount of timber required per lineal foot is about #h4g cu4 yds4 ,of this amount about two-thirds can be used a second time4 ,in the ,italian method1 in which the upper half and the lower half are excavated separately1 about #e cu4 yds4 of timber are required per lineal foot of tunnel1 about one-half of which can be employed a second time4 ,for quicksand tunnels the amount of timbering required per lineal foot varies from #c to #e cubic yds4 ,shaft strutting requires from #a to #a cu4 yds4 of timber per lineal foot4 ,dimensions of ,timber4--,the dimensions of the principal members composing the strutting of headings1 full section1 and shafts1 are given in ,table ,i4 ,the planks used for lagging or the poling-boards are usually from #d ins4 to #f ins4 wide1 with a length depending upon the method of strutting employed4 ,,table ,i4 ,showing ,sizes of ,various ,timbers ,used in ,strutting ,tunnels ,driven ,through ,different ,materials4 ---------------------------------------- -------------------------- ,,rock4 ,,soft ,,soils4 ------------------------------ ,hard4,soft4,compact4,loose4 ,very loose4 ------------------------------ ins4 ins4 ins4 ins4 ins4 ,headings3 ,cap-pieces and vertical struts #f #h #aj #ab #ad ,sills #h #aj #ab ,struts #e #e #f #g #h ,distance apart of the frames in feet #f #d4e #c #b4f #b4f ,strutting of the tunnel1 longitudinal strutting3 ,crown bars #ab #ad #ad ,props vertical or inclined supporting the crown bars #aj #ab #ad ,sills #h #h #aj ,cap-pieces or saddles #aj #ab #ad ,struts to stiffen the structure #f #h #aj ,distance apart of the frames 7in feet7 #d4e #d #c ,polygonal strutting3 ,cap-pieces and contour pieces #h #aj #ab #ad #af ,vertical struts on top #aj #ab #ad #af #ah ,vertical struts below #ab #ad #af #bj #bd ,intermediate sills #ab #ad #af #bj #bd ,lower sills #ab #af #ah ,raking props #aj #aj #aj #ab #ab ,distance apart of the frames 7in feet7 #f #d4e #d #c #c ,shafts3 ,horizontal beams forming the frame #h #h #aj #ab #ad ,transverse beams #h #h #h #aj #ab ,vertical struts between the frames #h #h #aj #ab #ab ,struts to renforce the frame #f #h #h #h ,distance apart of the strutting 7in feet7 #f #d4e #d #c #b4f ---------------------------------------- ----------------------- ,,iron ,,strutting4 ,in #ahfb ,mr4 ,rziha employed old iron railway rails for strutting the ,naensen tunnel1 and his example was successfully followed in several tunnels built later where timber was scarce and expensive4 ,the advantages which iron strutting is claimed to possess over the more common wooden structure are3 its greater strength2 the smaller amount of space which it takes up2 and the fact that it does not wear out1 and may1 therefore1 be used over and over again4 ,illustration3 ,,fig4 #bh4--,strutting of ,timber ,posts and ,railway ,rail ,caps4 ,illustration3 ,,fig4 #bi4--,strutting made entirely of ,railway ,rails4 ,iron ,strutting in ,headings4--,in strutting the headings the cross frames have a crown bar consisting of a section of old railway rail carried either by wood or iron side posts4 ,when wooden side posts are used their upper ends have a dovetail mortise1 and are bound with an iron band1 as shown by ,fig4 #bh4 ,the base of the rail crown bar is set into the dovetail mortise and fastened by wedges4 ,when iron side posts are employed they usually consist of sections of railway rails1 and the crown bar is attached to them by fish-plate connections1 as shown by ,fig4 #bi4 ,the iron cross frames are set up as the heading advances1 and carry the plank lagging or poling-boards1 exactly in the same manner as the timber cross frames previously described4 ,illustration3 ,,fig4 #cj4--,rziha's ,combined ,strutting and ,centering of ,cast ,iron4 ,illustration3 ,,fig4 #ca4--;,cast-,iron ,segment of ,rziha's ,strutting and ,centering4 ,full ,section ,iron ,strutting4--,the iron strutting devised by ,mr4 ,rziha for full section work is shown by ,fig4 #cj4 ,briefly described1 it consists of voussoir-shaped cast-iron segments1 which are built up in arch form4 ,fig4 #ca shows the construction of one of the segments1 all of which are alike1 with the exception of the crown segment1 which has a mortise and tenon joint which is kept open by filling the mortise with sand4 ,the segments are bolted together by means of suitable bolt-holes in the vertical flanges1 and when fully connected form an arch rib of cast iron4 ,this arch rib1 ,a1 ,fig4 #cj1 carries a series of angle or ,t-iron frames bent into approximately voussoir shape1 as shown at ,b1 ,fig4 #cj4 ,above these frames are inserted the poling-boards1 running longitudinally1 and spanning the distance between consecutive arch ribs4 ,by removing the bent iron frames the cast-iron rib forms a center upon which to construct the masonry4 ,finally1 to remove the cast-iron rib itself1 the sand is drawn out of the mortise and tenon joint in the crown segment1 which allows the joint to close1 and loosen the segments so that they are easily unbutted4 ,the illustration1 ,fig4 #cj1 shows longitudinal poling-boards2 more often longitudinal crown bars of railway rails span the space between connective arch ribs1 and support transverse poling-boards4 ,in building the masonry1 work is begun at the bottom on each side1 the bent iron frames being removed one after another to give room for the masonry4 ,as each frame is removed1 it is replaced with a sort of screw-jack to support the poling-boards until the masonry is sufficiently completed to allow their removal4 ,the interior bracing of the arch rib shown at a a and b b consists of railway rails carried by brackets cast on to the segments4 ,a similar bracing of rails connects the successive arch ribs4 ,these lines of bracing serve to carry the scaffolding upon which the masons work in building the lining4 ,illustration3 ,,fig4 #cb4--;,cast-,iron ,segmental ,strutting for ,shafts4 ,iron ,shaft ,strutting4--,in soft-ground shaft work1 the use of an iron strutting1 consisting of consecutive cast-iron rings1 has sometimes been employed to advantage4 ,fig4 #cb shows the construction of one of these rings1 which1 it will be seen1 is composed of four segments connected to each other by means of bolted flanges4 ,the holes shown in the circumferential web of the ring are to allow for the seepage from the earth side walls4 ,the method of placing this cylindrical strutting is to start with a ring having a cutting-edge4 ,by means of excavation inside the ring1 and by ramming1 the ring is sunk into the ground a distance equal to its height4 ,another ring is then fastened by special hooks on top of the first one1 and the sinking continued until the second ring is down flush with the surface4 ,a third ring is then added1 and so on until the entire shaft is excavated and strutted4 ,as in timber shaft strutting1 the solid iron ring strutting is carried down only to the top of the tunnel section1 and below this point there is an open timber or iron supporting framework4 ,,chapter ,,vi4 ,,methods ,,of ,,hauling ,,in ,,tunnels4 ,the transportation from one point to another within the tunnel and its shafts of any material1 whether it is excavated spoil or construction material1 is defined as hauling4 ,in all engineering construction1 the transportation of excavated materials1 and materials for construction1 constitutes a very important part of the expense of the work2 but hauling in tunnels where the room is very limited1 and where work is constantly in progress over and at the sides of the track1 is a particularly expensive process4 ,hauling in tunnels may be done either by way of the entrances1 or by way of the shafts1 or by way of both the entrances and shafts4 ,illustration3 ,,fig4 #cc4--,platform ,car for ,tunnel ,work4 ,hauling by ,way of ,entrances4--,when the hauling is done by the way of the entrances1 the materials to be hauled are taken directly from the point of construction to the entrances1 or in the opposite direction1 by means of special cars of different patterns4 ,for general purposes1 these different patterns of cars may be grouped into three classes1--platform-cars1 dump-cars1 and box-cars4 ,representative examples of these several classes of cars are shown in ,figs4 #cc to #cff inclusive1 but it will be readily understood that there are many other forms4 #f ,reproduced from catalogue of ,arthur ,koppel1 ,new ,york4 ,briefly described1 platform-cars 7,fig4 #cc7 consist of a wooden platform mounted on tracks1 and they are usually employed for the transportation of timber1 ties1 etc4 ,dump-cars are used in greater numbers in tunnel work than any other form4 ,fig4 #cd shows a dump-car of metal construction1 and ,fig4 #ce one constructed with a metal under-frame and wooden box4 ,these cars are made to run on narrow-gauge tracks1 and usually have a capacity of about one to one and one-half cubic yards4 ,box-cars are more extensively employed in ,europe for tunnel work than in ,america4 ,fig4 #cf shows a typical ,european box-car for tunnel work4 ,it is made either to run on narrow-gauge or standard-gauge tracks4 ,illustration3 ,,fig4 #cd4--;,iron ,dump-,car for ,tunnel ,work4 ,illustration3 ,,fig4 #ce4--,wooden ,dump-,car for ,tunnel ,work4 ,illustration3 ,,fig4 #cf4--;,box-,car for ,tunnel ,work4 ,it is usually desirable in tunnel work to employ cars of different forms for different parts of the work4 ,in rock tunnels it is a common practice to use narrow-gauge cars of small size in the headings1 and larger1 broad-gauge cars for the enlargement of the profile4 ,where narrow-gauge cars are employed for all purposes1 it will also be found more convenient to use platform-cars for handling the construction material1 and dump-cars for removing the spoil4 ,the extent to which it is desirable to use cars of different forms will depend upon the character and conditions of the work1 and particularly upon how far it is possible to install the permanent track4 ,as a general ride1 it is considered preferable to lay the permanent tracks at once1 and do all the hauling upon them1 so that as soon as the tunnel is completed1 trains may pass through without delay4 ,to what extent this may be done1 or whether it can be done at all or not1 depends upon the method of excavation and other local conditions4 ,in soft-ground tunnels excavated by the ,english or ,austrian methods1 it is quite possible to lay the permanent tracks at first1 since the whole section is excavated at once1 and the excavation is kept but a little ahead of the completed tunnel4 ,in rock tunnels1 where the heading is driven far ahead of the completed section1 it is1 of course1 impossible to keep the permanent track close to the advance work1 and narrow-gauge tracks must be laid in the heading4 ,the same thing is true in soft-ground tunnels driven by successive headings and drifts4 ,in these cases1 therefore1 where narrow-gauge tracks have to be used for some portions of the work anyway1 the question comes up whether it is preferable to use temporary narrow-gauge tracks throughout1 or to lay the permanent track as far ahead as possible1 and then extend narrow-gauge tracks to the advance excavation4 ,in the latter case it will1 of course1 be necessary to trans-ship each load from the narrow-gauge to the standard-gauge cars1 or vice versa1 which means extra cost and trouble4 ,to avoid this1 the method is sometimes adopted of laying a third rail between the standard-gauge rails1 so that either standard- or narrow-gauge cars may be transported over the line4 ,whatever form the local conditions may require the system of construction tracks to assume1 it may be set down as a general rule that the permanent tracks should be kept as far advanced as possible1 and temporary tracks employed only where the permanent tracks are impracticable4 ,the motive power employed for hauling in tunnels may be furnished by animals or by mechanical motors4 ,animal power is generally employed in short tunnels and in the advance headings and galleries4 ,in long tunnels1 or where the excavated material has to be transported some distance away from the tunnel1 mechanical power is preferable1 for obvious reasons4 ,the motors most used are small steam locomotives1 special compressed-air locomotives1 and electric motors4 ,compressed air and electric locomotives are built in various forms1 and are particularly well adapted for tunnel work because of their small dimensions1 and freedom from smoke and heat4 ,hauling by ,way of ,shafts4--,when the excavated material and materials of construction are handled through shafts1 the operation of hauling may be divided into three processes3 the transportation of the materials along the floor of the tunnel1 the hoisting of them through the shaft1 and the surface transportation from and to the mouth of the shaft4 ,these three operations should be arranged to work in harmony with each other1 so as to avoid waste of time and unnecessary handling of the materials4 ,an endeavor should be made to avoid1 if possible1 breaking or trans-shipping the load from the time it starts at the heading until it is dumped at the spoil bank4 ,this can be accomplished in two ways4 ,one way is to hoist the boxes of the cars from their trucks at the bottom of the shaft1 and place them on similar trucks running on the surface tracks4 ,the other way is to run the loaded cars on to the elevator platform at the bottom1 hoist them1 and then run them on to the surface tracks4 ,if the first method is employed1 the car box is usually made of metal1 and is provided at its top edges with hooks or ears to which to attach the hoisting cables4 ,when the second method is used1 the elevator platform has tracks laid on it which connect with the tracks on the tunnel floor1 and also with those on the surface4 ,hoisting ,machinery4--,the machines most commonly employed for hoisting purposes in tunnel shafts are steam hoisting engines1 horse gins1 and windlasses operated by hand4 ,windlasses and horse gins are rather crude machines for hoisting loads1 and are used only in special circumstances1 where the shaft is of small depth1 when the amount of material to be hoisted is small1 or where for any reason the use of hoisting engines is precluded4 ,the steam hoisting engine is the standard machine for the rapid lifting of heavy vertical loads4 ,recently oil engines and electric hoists have also come to be used to some extent1 and under certain conditions these machines possess notable advantages4 ,the construction of hand windlasses is familiar to every one4 ,in tunnel work this device is located directly over the shaft1 with its axis a little more than half a man's height1 so that the crank handle does not rise above the shoulder line4 ,to develop its greatest efficiency the hoisting rope is passed around the windlass drum so that the two ends hang down the shaft1 and as one end descends the other ascends4 ,a skip1 or bucket1 is attached to each of the rope ends2 and by loading the descending skip with construction materials and the ascending skip with spoil1 the two skip loads tend to balance each other1 thus increasing the capacity of the windlass1 and decreasing the manual labor required to operate it4 ,skips varying from #j4c cu4 yd4 to #j4e cu4 yd4 are used4 ,the horse gin consists of a vertical cylinder or drum provided with radial arms to which the horses are hitched1 which revolve the cylinder by walking around it in a circle4 ,the hoisting rope is rove around the drum so that the two ends extend down the shaft with skips attached1 as described in speaking of the hand windlass4 ,the power of the horse gin is1 of course1 much greater than that of a windlass operated by hand1 skips of #a cu4 yd4 capacity being commonly used4 ,horse gins are no longer economical hoisting machines1 according to one prominent authority1 when ,v7,h #bj7 #ejjj1 where ,v equals the volume of material to be hoisted1 and ,h equals the height of the hoist1 the weight of the excavated material being #bajj lbs4 per cu4 yd4 ,as a general rule1 however1 it is assumed that it is not economical to employ horse gins with a depth of shaft exceeding #aej ft4 ,as already stated1 the most efficient and most commonly used device for hoisting at tunnel shafts is the steam hoisting engine4 ,there are numerous builders of hoisting engines1 each of which manufactures several patterns and sizes of engines4 ,in each case1 however1 the apparatus consists of a boiler supplying steam to a horizontal engine which operates one or more rope drums4 ,the engines are always reversible4 ,they may be employed to hoist the skips directly1 or to operate elevators upon which the skips or cars are loaded4 ,in either case the hoisting ropes pass from the engine drum to and around vertical sheaves situated directly over the shaft so as to secure the necessary vertical travel of the ropes down the shaft4 ,where the shaft is divided into two compartments1 each having an elevator or hoist1 double-drum engines are employed1 one drum being used for the operations in one compartment1 and the other for the operations in the other compartment4 ,where the work is to be of considerable duration1 or when it is done in cold weather1 more or less elaborate shelters or engine houses are built to cover and protect the machinery4 ,choice between the method of hoisting the skips directly1 and the method of using elevators1 depends upon the extent and character of the work4 ,where large quantities of material are to be hoisted rapidly1 it is generally considered preferable to employ elevators instead of hoisting the skips directly4 ,in direct hoisting at high speed1 oscillations are likely to be produced which may dash the skips against the sides of the shaft and cause accidents4 ,the loads which can be carried in single skips are also smaller than those possible where elevators are used2 and this1 combined with the slower hoisting speed required1 reduces the capacity of this method1 as compared with the use of elevators4 ,where elevators are employed1 however1 the plant required is much more extensive and costly2 it comprising not only the elevator cars with their safety devices1 etc41 but the construction of a guiding framework for these cars in the tunnel shaft4 ,for these various reasons the elevator becomes the preferable hoisting device where the quantity of material to be handled is large1 where the shafts are deep1 and where the work will extend over a long period of time2 but when the contrary conditions are the case1 direct hoisting of the skips is generally the cheaper4 ,the engineer has to integrate the various factors in each individual case1 and determine which method will best fulfill his purpose1 which is to handle the material at the least cost within the given time and conditions4 ,illustration3 ,,fig4 #cg4--;,elevator ,car for ,tunnel ,shafts4 ,the construction of elevators for tunnel work is simple4 ,the elevator car consists usually of an open framework box of timber and iron1 having a plank floor on which car tracks are laid1 and its roof arranged for connecting the hoisting cable 7,fig4 #cgg74 ,rigid construction is necessary to resist the hoisting strains4 ,the sides of the car are usually designed to slide against timber guides on the shaft walls4 ,some form of safety device1 of which there are several kinds1 should be employed to prevent the fall of the elevator1 in case the hoisting rope breaks1 or some mishap occurs to the hoisting machinery1 which endangers the fall of the car4 ,speaking tubes and electric-bell signals should also be provided to secure communication between the top and bottom of the shaft4 #g ,reproduced from the catalogue of the ,ledgerwood ,manufacturing ,company1 ,new ,york4 ,,chapter ,,vii4 ,,types ,,of ,,centers ,,and ,,molds ,,employed ,,in ,,constructing ,,tunnel ,,linings ,,of ,,masonry4 ,the masonry lining of a tunnel may be described as consisting of two or more segments of circular arches combined so as to form a continuous solid ring of masonry4 ,to direct the operations of the masons in constructing this masonry ring1 templates or patterns are provided which show the exact dimensions and form of the sectional profile which it is desired to secure4 ,these patterns or templates will vary in number and construction with the form of lining and the method of excavation adopted4 ,where the excavation is fully lined on all four sides1 the masonry work is usually divided into three parts1--the invert or floor masonry1 the side-wall masonry1 and the roof-arch masonry4 ,at least one separate pattern has to be employed in constructing each of these parts of the lining2 and they are known respectively as ground molds1 leading frames1 and arch centers1 or simply centers4 ,in the following paragraphs the form and construction usually employed for each of these three kinds of patterns is described4 ,ground ,molds4--,ground molds are employed in building the tunnel invert4 ,they are generally constructed of #c-;inch plank cut exactly to the form and dimensions of the invert masonry as shown in ,fig4 #ch4 ,to permit of convenience of handling in a restricted space1 they are generally made in two parts1 which are joined at the middle by means of iron fish-plates and bolts4 ,either one or two ground molds may be employed4 ,where two molds are used they are set up a short distance apart1 and cords are stretched from one to the other parallel to the axis of the tunnel1 by which the masons are guided in their work4 ,extreme care has to be taken in setting the molds to ensure that they are fixed at the proper grade1 and are in a plane normal to the axis of the tunnel4 ,where only one ground mold is employed1 the finished masonry is depended upon to supply the place of the second mold1 cords being stretched from it to the single mold placed the requisite distance ahead4 ,the leveling and centering of the molds is accomplished by means of transit and level4 ,illustration3 ,,fig4 #ch4--;,ground ,mold for ,constructing ,tunnel ,invert ,masonry4 ,illustration3 ,,fig4 #ci4--;,combined ,ground ,mold and ,leading ,frame for ,invert and ,side ,wall ,masonry4 ,two modifications of the form of ground mold shown by ,fig4 #ci are employed4 ,the first modification is peculiar to the ,english method of excavation1 and consists in combining the ground mold with the leading frame for the lower part of the side walls1 as shown by ,fig4 #ci4 ,the second modification is employed where the two halves or sides of the invert are built separately1 and it consists simply in using one-half of the mold shown by ,fig4 #ch4 ,when the last method of constructing the invert masonry is resorted to1 extreme care has to be observed in setting the half-mold in order to avoid error4 ,illustration3 ,,fig4 #dj4--,leading ,frame for ,constructing ,side ,wall ,masonry4 ,leading ,frames4--,as already stated1 leading frames are the patterns1 or molds1 used in building the side walls of the lining4 ,like the ground mold they are usually built of plank2 one side being cut to the curve of the profile1 and the other being made parallel to the vertical axis of the tunnel section4 ,the vertical side usually has some arrangement by which a plumb bob can be attached1 as shown by ,fig4 #dj1 to guide the workmen in erecting the frame4 ,the combined leading frame and ground mold shown in ,fig4 #ci has already been described4 ,the use of this frame is possible only where the masonry is begun at the invert and carried up on each side at the same time4 ,this mode of construction is peculiar to the ,english method of tunneling2 in all other methods the form of separate ground frame shown by ,fig4 #dj is employed4 ,the ground frames are lined in and leveled up by transit and level2 and1 as in setting the ground frames1 care must be taken to secure accuracy in both direction and elevation4 ,arch ,centers4--,the template or form upon which the roof arch is built is called a center4 ,unlike the ground molds and leading frames1 the arch centers have to support the weight of the masonry and the roof pressures during the construction of the lining1 and they1 therefore1 require to be made strong4 ,owing to the fact that the pressures are indeterminate1 it is impossible to design a rational center1 and resort is had to those constructions which past experience has shown to work satisfactorily under similar conditions4 ,in a general way it can always be assumed that the construction should be as simple as possible1 that the center should be so designed that it can be set up and removed with the least possible labor1 and that the different pieces of the framework and lagging should be as short as possible1 for convenience in handling4 ,tunnel centers are usually composed of two parts1--a mold or curved surface upon which the masonry rests1 and a framework which supports the mold4 ,the curved surface or mold consists of a lagging of narrow boards running parallel to the tunnel axis1 which rests upon the arched top members of two or more consecutive supporting frames4 ,the supporting frame is built in the form of a truss1 and must be made strong enough to withstand the heavy superimposed loads1 consisting of the arch masonry during construction1 and of the roof pressures which are transferred to the center when the strutting is removed to allow the masonry to be placed4 ,the framework of the center is supported either by posts resting upon the floor of the excavation1 or upon the invert masonry when this is built first1 as in the ,english and ,austrian methods1 or it may be supported directly upon the ground where the arch masonry is built first1 as in the ,belgian method of tunneling4 ,in describing the various methods of tunneling in succeeding chapters1 the center construction and method of supporting the center peculiar to each will be fully explained1 and only a few general remarks are necessary here4 ,centers may be classified according to their construction and composition into plank centers1 truss centers1 and iron centers4 ,illustration3 ,,fig4 #da4--,plank ,center for ,constructing the ,roof ,arch4 ,one of the most common forms of plank centers is shown by ,fig4 #da4 ,it consists of two half-polygons whose sides consist of #ae in4 #d ft4 planks having radial end-joints4 ,these two half-polygons are laid one upon the other so that they break joints1 as shown by the figure1 and the extrados of the frame is cut to the true curve of the roof arch4 ,the planks commonly used for making these centers are #d ins4 thick1 making the total thickness of the center #h ins4 ,plank centers of the construction described are suitable only for work where the pressures to be resisted are small1 as in tunnels through a fairly firm rock1 although there have been instances of their successful use in soft-ground tunnels4 ,where heavy loads have to be carried1 trussed centers are generally employed1 the trusses being composed of heavy square beams with scarfed and tenoned joints1 reinforced by iron plates4 ,different forms of trusses are employed in each of the different methods of tunneling1 and each of these is described in succeeding chapters2 but they are generally either of the king-post or queen-post type1 or some modification of them4 ,the king-post truss may be used alone1 with or without the tie-beam1 as shown by ,fig4 #db2 but generally a queen-post truss is made to form the base of support for a smaller king-post truss mounted on its top4 ,this arrangement gives a trapezoidal form to the center1 which approaches closely to the arch profile4 ,owing to the character of the pressures transmitted to the center1 the usual tension members can be made very light4 ,illustration3 ,,fig4 #db4--,trussed ,center for ,constructing the ,roof ,arch4 ,the combined center and strutting system devised by ,mr4 ,rziha has already been described in a previous chapter4 ,in recent ,european tunnel work quite extensive use has also been made of iron centers consisting of several segments of curved ,i-beams1 connected by fish-plate joints so as to form a semi-circular arch rib4 ,the ends or feet of these ,i-beam ribs have bearing-plates or shoes made by riveting angles to the ,i-beams4 ,centers constructed in a similar manner1 but made of sections of old railway rail1 were used in carrying out the tunnel work on the ,rhine ,river ,railroad in ,germany4 ,the advantages claimed for iron centers are that they take up less room1 and that they can be used over and over again4 ,setting ,up ,centers4--,according to the method of excavation followed in building the tunnel1 the centers for building the roof arch may have to be supported by posts resting on the tunnel floor2 or where the arch is built first1 as in the ,belgian and ,italian methods1 they may be carried on blocking resting on the unexcavated earth below4 ,whichever method is employed1 an unyielding support is essential1 and care must be taken that the centers are erected and maintained in a plane normal to the tunnel axis4 ,to prevent deflection and twisting1 the consecutive centers are usually braced together by longitudinal struts or by braces running to the adjacent strutting4 ,only skilled and experienced workmen should be employed in erecting the centers2 and they should work under the immediate direction of the engineer1 who must establish the axis and level of each center by transit and level4 ,lagging4--,by the lagging is meant the covering of narrow longitudinal boards resting upon the upper curved chords of the centers1 and spanning the opening between consecutive centers4 ,this lagging forms the curved surface or mold upon which the arch masonry is laid4 ,when the roof arch is of ashlar masonry the strips of lagging are seldom placed nearer together than the joints of the consecutive ring stones1 but in brick arches they are laid close together4 ,besides the weight of the arch masonry1 the lagging timbers support the short props which keep the poling-boards in place after the strutting is removed and until the arch masonry is completed4 ,striking the ,centers4--,the centers are usually brought to the proper elevation by means of wooden wedges inserted between the sill of the center and its support1 or between the bottom of the posts carrying the center and the tunnel floor4 ,these wedges are usually made of hard wood1 and are about #f ins4 wide by #d ins4 thick by #ah ins4 long4 ,to strike the center after the arch masonry is completed1 these wedges are withdrawn1 thus allowing the center to fall clear of the masonry4 ,usually the center is not removed immediately after striking1 so that if the arch masonry fails the ruins will remain upon the center4 ,the method of striking the iron center devised by ,mr4 ,rziha has been described in the previous chapter on strutting4 ,,chapter ,,viii4 ,,methods ,,of ,,lining ,,tunnels4 ,tunnels in soft soils and in loose rock1 and rock liable to disintegration1 are always provided with a lining to hold the walls and roof in place4 ,this lining may cover the entire sectional profile of the tunnel1 or only a part of it1 and it may be constructed of timber1 iron1 iron and masonry1 or1 more commonly1 of masonry alone4 ,timber ,lining4--,timber is seldom employed in lining tunnels except as a temporary expedient1 and is replaced by masonry as soon as circumstances will permit4 ,in the first construction of many ,american railways1 the necessity for extreme economy in construction1 and of getting the line open for traffic as soon as possible1 caused the engineers to line many tunnels with timber1 which was plentiful and cheap4 ,except for their small cost and the ease and rapidity with which they can be constructed1 however1 these timber linings possess few advantages4 ,it is only the matter of a few years when the decay of the timber makes it necessary to rebuild them1 and there is always the serious danger of fire4 ,in several instances timber-lined tunnels in ,america have been burned out1 causing serious delays in traffic1 and necessitating complete reconstruction4 ,usually this reconstruction has consisted in substituting masonry in place of the original timber lining4 ,in a succeeding chapter a description will be given of some of the methods employed in replacing timber tunnel linings with masonry4 ,various forms of timber lining are employed1 of which ,fig4 #dd and the illustrations in the chapter discussing the methods of relining timber-lined tunnels with masonry are typical examples4 ,illustration3 ,cross ,section4 ,longitudinal ,section4 ,,figs4 #dc and #dd4--;,a ,typical ,form of ,timber ,lining for ,tunnels4 ,iron ,lining4--,the use of iron lining for tunnels was introduced first on a large scale by ,mr4 ,peter ,william ,barlow in #ahfi1 for the second tunnel under the ,river ,thames at ,london1 ,england1 and it has greatly extended since that time4 ,the lining of the second ,thames tunnel consisted of cylindrical cast-iron rings #h ft4 in diameter1 the abutting edges of the successive rings being flanged and provided with holes for bolt fastenings4 ,each ring was made up of four segments1 three of which were longer than quadrants1 and one much smaller forming the 8key-stone0 or closing piece4 ,these segments were connected to each other by flanges and bolts4 ,to make the joints tight1 strips of pine or cement and hemp yarn were inserted between the flanges4 ,since the construction of the second ,thames tunnel1 iron lining has been employed for a great many submarine tunnels in ,england1 ,continental ,europe1 and ,america1 some of them having a section over #bh ft4 in diameter4 ,where circular iron lining is employed1 the bottom part of the section is leveled up with concrete or brick masonry to carry the tracks1 and the whole interior of the ring is covered with a cement plaster lining deep enough thoroughly to embed the interior joint flanges4 ,in the succeeding chapter describing the methods of driving tunnels by shields several forms of iron tunnel lining are fully described4 ,iron and ,masonry ,lining4--,during recent years a form of combined masonry and iron lining has been extensively employed in constructing city underground railways in both ,europe and ,america4 ,generally this form of lining is built with a rectangular section4 ,two types of construction are employed4 ,in the first1 masonry side walls carry a flat roof of girders and beams1 which carry a trough flooring filled with concrete1 or between which are sprung concrete or brick arches4 ,sometimes the roof framing consists of a series of parallel ,i-beams laid transversely across the tunnel1 and in other cases transverse plate girders carry longitudinal ,i-beams4 ,in the second type of construction the roof girders are supported by columns embedded in the side walls4 ,where the tunnel provides for two or four tracks1 intermediate column supports are in some cases introduced between the side columns4 ,in this construction the roofing consists of concrete filled troughs or of concrete or brick arches1 as in the construction first described4 ,examples of combined masonry and iron tunnel lining are illustrated in the succeeding chapter on tunneling under city streets4 ,masonry ,lining4--,the form of tunnel lining most commonly employed is brick or stone masonry4 ,concrete and reinforced concrete masonry lining has been employed in several tunnels built in recent years4 ,the masonry lining may inclose the whole section or only a part of it4 ,the floor or invert is the part most commonly omitted2 but sometimes also the side walls and invert are both omitted1 and the lining is confined simply to an arch supporting the roof4 ,the roof arch1 the side walls1 and the invert compose the tunnel lining2 and all three may consist of stone or brick alone1 or stone side walls may be employed with brick invert and roof arch4 ,rubble-stone masonry is usually employed1 except at the entrances1 where the masonry is exposed to view4 ,here ashlar masonry is usually used4 ,the stone selected for tunnel lining should be of a durable quality which weathers well4 ,where bricks are used they should be of good quality4 ,owing to the comparative ease with which brick arches can be built1 they are generally used to form the roof arch1 even where the side walls are of stone masonry4 ,masonry lining may be built in the form of a series of separate rings1 or in the form of a continuous structure extending from one end of the tunnel to the other4 ,the latter method of construction produces a stronger structure2 but in case of failure by crushing1 the damage done is likely to be more widespread than where separate rings are employed1 one or two of which may fail without injury to the others adjacent to them4 ,the construction is also somewhat simpler where separate rings are employed1 since no provision has to be made for bonding the whole lining into a continuous structure4 ,where a series of separate rings is employed1 the length of each ring runs from #e ft4 up to #bj ft41 it depending upon the character of the material penetrated1 and the method of construction employed4 ,for the purpose of detailed discussion the construction of masonry lining may be divided into four parts1--the side-wall foundations1 the side walls themselves1 the roof arch1 and the invert4 ,concrete and reinforced concrete linings are now extensively used on account of cheapness and facility of handling1 but they have the great disadvantage of resisting pressure after they become hard1 which is some time after being placed4 ,the strutting should1 therefore1 be left to support the roof so as to prevent direct pressure on the fresh material4 ,the roof1 as a rule1 is supported by longitudinal planks held in position by five or seven segments of arched frames placed across the tunnel4 ,a large quantity of timber and carpenter work is thus entirely wasted and these costly items1 in many cases1 make the concrete lining of a tunnel more expensive than the one built of brick and stone4 ,to avoid these inconveniences tunnels have been successfully lined with concrete on the side walls and concrete blocks in the arches4 ,these blocks have been built by hand and molded in the shape of the arch voussoirs4 ,foundations4--,in tunnels through rock of a hard and durable character the foundations for the side walls are usually laid directly on the rock4 ,in loose rock1 or rock liable to disintegration1 this method of construction is not generally a safe one1 and the foundation excavation should be sunk to a depth at which the atmospheric influences cannot affect the foundation bed4 ,in either case the foundation masonry is made thicker than that of the side walls proper1 so as to distribute the pressure over a greater area1 and to afford more room for adjusting the side-wall masonry to the proper profile4 ,in yielding soils a special foundation bed has to be prepared for the foundation masonry4 ,in some instances it is found sufficient to lay a course of planks upon which the masonry is constructed1 but a more solid construction is usually preferred4 ,this is obtained by placing a concrete footing from #a ft4 to #b ft4 deep all along the bottom of the foundation trench1 or in some cases by sinking wells at intervals along the trench and filling them with concrete1 so as to form a series of supporting pillars4 ,illustration3 ,,fig4 #de4--;,diagram ,showing ,forms ,adopted for ,side-,wall ,foundations4 ,the form given to the foundation courses and lower portions of the side walls varies4 ,where a large bearing area is required1 the back of the wall is carried up vertically as shown by the line ,,ab1 ,fig4 #de1 otherwise the rear face of the wall follows the line of excavation ,,ac4 ,for similar reasons the front face of the wall may be made vertical1 as at ,,fg1 or inclined1 as at ,,fh4 ,the line ,,fe indicates the shelf construction designed to support the feet of the posts used to carry the arch centers during the construction of the roof arch4 ,side ,walls4--,the construction of the side walls above the foundation courses is carried out as any similar piece of masonry elsewhere would be built4 ,to direct the work and insure that the inner faces of the walls follow accurately the curve of the chosen profile1 leading frames previously described are employed4 ,roof ,arch4--,for the construction of the roof arch1 the centers previously described are employed4 ,beginning at the edges of the center on each side1 the masonry is carried up a course at a time1 care being taken to have it progress at the same rate on both sides1 so that the load brought onto the centering is symmetrical4 ,as soon as the centers are erected1 the roof strutting is removed1 and replaced by short props which rest on the lagging of the centers and support the poling-boards4 ,these props are removed in succession as the arch masonry rises along the curve of the center1 and the space between the top of the arch masonry and the ceiling of the excavation is filled with small stones packed closely4 ,the keystone section of the arch is built last1 by inserting the stones or bricks from the front edge of the arch ring1 there being no room to set them in from the top1 as is the practice in ordinary open-arch construction4 ,the keying of the arch is an especially difficult operation1 and only experienced men skilled in the work should be employed to perform it4 ,the task becomes one of unusual difficulty when it becomes necessary to join the arches coming from opposite directions4 ,invert4--,in all but one or two methods of tunneling1 the invert is the last portion of the lining to be built4 ,in the ,english method of tunneling1 the invert is the first portion of the lining to be built1 and the same practice is sometimes necessary in soft soils where there is danger of the bottoms of the side walls being squeezed together by the lateral pressures unless the invert masonry is in place to hold them apart4 ,the ground molds previously described are employed to direct the construction of the invert masonry4 ,general ,observations4--,in describing the construction of the roof arch1 mention was made of the stone filling employed between the back of the masonry ring and the ceiling of the excavation4 ,the spaces behind the side walls are filled in a similar manner4 ,the object of this stone filling1 which should be closely packed1 is to distribute the vertical and lateral pressures in the walls of the excavation uniformly over the lining masonry4 ,as the masonry work progresses1 the strutting employed previously to support the walls of the excavation has to be removed4 ,this work requires care to prevent accident1 and should be placed in charge of experienced mechanics who are familiar with its construction1 and can remove it with the least damage to the timbers1 so that they may be used again1 and without causing the fall of the roof or the caving of the sides by removing too great a portion of the timbers at one time4 ,thickness of ,lining ,masonry4--,it is obvious1 of course1 that the masonry lining must be thick enough to support the pressure of the earth which it sustains2 but1 as it is impossible to estimate these pressures at all accurately1 it is difficult to say definitely just what thickness is required in any individual case4 ,rankine gives the following formulas for determining the depths of keystone required in different soils3 ,for firm soils 7 r7 d 7#j4ab----71 7 s 7 and for soft soils1 7 r7 d 7#j4dh----71 7 s 7 where d the depth of the crown in feet1 r the rise of the arch in feet1 and s the span of the arch in feet4 ,other writers1 among them ,professor ,curioni1 attempt to give rational methods for calculating the thickness of tunnel lining2 but they are all open to objection because of the amount of hypothesis required concerning pressures which are of necessity indeterminate4 ,therefore1 to avoid tedious and uncertain calculations1 the engineer adopts dimensions which experience has proven to be ample under similar conditions in the past4 ,thus we have all gradations in thickness1 from hard-rock tunnels requiring no lining1 and tunnels through rocks which simply require a thin shell to protect them from the atmosphere1 to soft-ground tunnels where a masonry lining #c ft4 or more in thickness is employed4 ,table ,,ii4 shows the thickness of masonry lining used in tunnels through soft soils of various kinds4 ,the thickness of the masonry lining is seldom uniform at all points1 as is indicated by ,table ,,ii4 ,figs4 #df and #dg show common methods of varying the thickness of lining at different points1 and are self-explanatory4 ,illustration3 ,,figs4 #df and #dg4--,transverse ,sections of ,tunnels ,showing ,methods of ,increasing the ,thickness of the ,lining at ,different ,points4 ,side ,tunnels4--,when tunnels are excavated by shafts located at one side of the center line1 short side tunnels or galleries are built to connect the bottoms of the shafts with the tunnel proper4 ,these side tunnels are usually from #cj ft4 to #dj ft4 long1 and are generally made from #ab ft4 to #ad ft4 high1 and about #aj ft4 wide4 ,the excavation1 strutting1 and lining of these side tunnels are carried on exactly as they are in the main tunnel1 with such exceptions as these short lengths make possible4 ,table ,,iii4 gives the thickness of lining used for side tunnels1 the figures being taken from ,european practice4 ,culverts4--,the purpose of culverts in tunnels is to collect the water which seeps into the tunnel from the walls and shafts4 ,the culvert is usually located along the center line of the tunnel at the bottom4 ,in soft-ground tunnels it is built of masonry1 and forms a part of the invert1 but in rock tunnels it is the common practice to cut a channel in the rock floor of the excavation4 ,both box and arch sections are employed for culverts4 ,the dimensions of the section vary1 of course1 with the amount of water which has to be carried away4 ,the following are the dimensions commonly employed3 ---------------------------------------- ------------- ,,kind ,,of ,,culvert4 ,,height ,,width ,,thickness ,,thickness ,,in ,,feet4,,in ,,feet4,,of ,,walls ,,of ,,covering ,,in ,,feet4 ,,in ,,feet4 ---------------------------------------- ------------- ,box culvert #a to #a4ea to #a4ej4h to #a4b #j4c ,arch culvert #a to #a4ea to #a4ej4h to #a4b #j4d ---------------------------------------- ------------- ,it should be understood that the dimensions given in the table are those for ordinary conditions of leakage2 where larger quantities of water are met with1 the size of the culverts has1 of course1 to be enlarged4 ,to permit the water to enter the culvert1 openings are provided at intervals along its side2 and these openings are usually provided with screens of loose stones which check the current1 and cause the suspended material to be deposited before it enters the culvert4 ,in cases where springs are encountered in excavating the tunnel1 it is necessary to make special provisions for confining their outflow and conducting it to the culvert4 ,in all cases the culverts should be provided with catch basins at intervals of from #aej ft4 to #cjj ft41 in which such suspended matter as enters the culverts is deposited1 and removed through covered openings over each basin4 ,at the ends of the tunnel the culvert is usually divided into two branches1 one running to the drain on each side of the track4 ,illustration3 ,,fig4 #dh4--,refuge ,niche in ,st4 ,gothard ,tunnel4 ,niches4--,in short tunnels niches are employed simply as places of refuge for trackmen and others during the passing of trains1 and are of small size4 ,in long tunnels they are made larger1 and are also employed as places for storing small tools and supplies employed in the maintenance of the tunnel4 ,niches are simply arched recesses built into the sides of the tunnel1 and lined with masonry2 ,fig4 #dh shows this construction quite clearly4 ,small refuge niches are usually built from #f ft4 to #i ft4 high1 from #c ft4 to #f ft4 wide1 and from #b ft4 to #c ft4 deep4 ,large niches designed for storing tools and supplies are made from #aj ft4 to #ab ft4 high1 from #h ft4 to #aj ft4 wide1 and from #ah ft4 to #bd ft4 deep1 and are provided with doors4 ,refuge niches are usually spaced from #fj ft4 to #ajj ft4 apart1 while the larger storage niches may be located as far as #cjjj ft4 apart4 ,the niche construction shown by ,fig4 #dh is that employed on the ,st4 ,gothard tunnel4 ,entrances4--,the entrances1 or portals1 of tunnels usually consist of more or less elaborate masonry structures1 depending upon the nature of the material penetrated4 ,in soft-ground tunnels extensive wing walls are often required to support the earth above and at the sides of the entrance2 while in tunnels through rock1 only a masonry portal is required1 to give a finish to the work4 ,often the engineer indulges himself in an elaborate architectural design for the portal masonry4 ,there is danger of carrying such designs too far for good taste unless care is employed2 and on this matter the writer can do no better than to quote the remarks of the late ,mr4 ,frederick ,w4 ,simms in his well-known 8,practical ,tunneling03 8,the designs for such constructions should be massive to be suitable as approaches to works presenting the appearance of gloom1 solidity1 and strength4 ,a light and highly decorated structure1 however elegant and well adapted for other purposes1 would be very unsuitable in such a situation2 it is plainness combined with boldness1 and massiveness without heaviness1 that in a tunnel entrance constitutes elegance1 and1 at the same time1 is the most economical40 ,illustration3 ,,fig4 #di4--;,east ,portal of ,hoosac ,tunnel4 ,fig4 #di is an engraving from a photograph of the east portal of the ,hoosac tunnel1 which is an especially good design4 ,the portals of the ,mount ,cenis tunnel were built of samples of stone encountered all along the line of excavation4 ,the stones were cut and dressed and utilized for walls and voussoirs4 ,the only ornament that is usually allowed on the portals is the date of the opening of the tunnel prominently cut in the stone above the arch4 ,,table ,,ii4 ,showing ,thickness of ,masonry ,lining for ,tunnels through ,soft ,ground4 ---------------------------------------- ------------------------- ,,character ,,of ,,material4 ,,keystone4 ,,springers4 ,,invert4 ---------------------------------------- ------------------------- ,ft4 ,ft4 ,ft4 ,laminated clay1 first variety #b4ae to #c #b4ge to #c4e #a4f to #b4e ,laminated clay1 second variety#c to #d4e #c4e to #e4e #b4e to #d ,laminated clay1 third variety #d4e to #f4e #e4e to #h4a #d to #d4e ,quicksand #b to #c4bhb to #d4a #a4cc to #b4e ---------------------------------------- ------------------------- ,,table ,,iii4 ,showing ,thickness of ,masonry ,lining for ,side ,tunnels through ,soft ,ground4 ---------------------------------------- --------------------- ,,character ,,of ,,material4 ,,keystone4,,springers4 ,,invert4 ---------------------------------------- --------------------- ,ft4 ,ft4 ,ft4 ,laminated clay1 first variety #a4f to #b4ca4h to #c #a4e to #b ,laminated clay1 second variety#b4c to #c #c to #d4ab to #b4f ,laminated clay1 third variety #c to #d #d4a to #e #b4f to #c4bi ,quicksand #a4f to #b4ea4c to #b #a4c to #b ---------------------------------------- --------------------- ,,chapter ,,ix4 ,,tunnels ,,through ,,hard ,,rock2 ,,general ,,discussion2 ,,representative ,,mechanical ,,installations ,,for ,,tunnel ,,work4 ,the present high development of labor-saving machinery for excavating rock makes this material one of the safest and easiest to tunnel of any with which the engineer ordinarily has to deal4 ,to operate this machinery requires1 however1 the development of a large amount of power1 its transmission to considerable distances1 and1 finally1 its economical application to the excavating tools4 ,the standard rock excavating machine is the power drill1 which requires either air or hydraulic pressure for its operation according to the special type employed4 ,under present conditions1 therefore1 the engineer is limited either to air or water under compression for the transmission of his power4 ,steam-power may be employed directly to operate percussion rock drills2 but owing to the heat and humidity which it generates in the confined space where the drills work1 and because of other reasons1 it is seldom employed directly4 ,electric transmission1 which offers so many advantages to the tunnel builder1 in most respects is largely excluded from use by the failure which has so far followed all attempts to apply it to the operation of rock drills4 ,as matters stand1 therefore1 the tunnel engineer is practically limited to steam and falling water for the generation of power1 and to compressed air and hydraulic pressure for its transmission4 ,whether the engineer should adopt water-power or steam to generate the power required for his excavating machinery depends upon their relative availability1 cost1 and suitability to the conditions of work in each particular case4 ,where fuel is plentiful and cheap1 and where water-power is not available at a comparatively reasonable cost1 steam-power will nearly always prove the more economical2 where1 however1 the reverse conditions exist1 which is usually the case in a mountainous country far from the coal regions1 and inadequately supplied with transportation facilities1 but rich in mountain torrents1 water-power will generally be the more economical4 ,in a succeeding chapter the power generating and transmission plants for a number of rock tunnels are described1 and here only a general consideration of the subject will be presented4 ,steam-,power ,plant4--,a steam-power plant for tunnel work should be much the same as a similar plant elsewhere1 except that in designing it the temporary character of its work must be taken into consideration4 ,this circumstance of its temporary employment prompts the omission of all construction except that necessary to the economical working of the plant during the period when its operation is required4 ,the power-house1 the foundations for the machinery1 and the general construction and arrangement1 should be the least expensive which will satisfy the requirements of economical and safe operation for the time required4 ,it will often be found more economical as a whole to operate the machinery with some loss of economy during the short time that it is in use than to go to much greater expense to secure better economy from the machinery by design and construction1 which will be of no further use after the tunnel is completed4 ,the longer the plant is to be required1 the nearer the construction may economically approach that of a permanent plant4 ,as regards the machinery itself1 whose further usefulness is not limited by the duration of any single piece of work1 true economy always dictates the purchase of the best quality4 ,speaking in a general way1 a steam-power plant for tunnel work comprises a boiler plant1 a plant of air compressors with their receivers1 and an electric light dynamo4 ,when hydraulic transmission of power is employed1 the air compressors are replaced by high-pressure pumps2 and when electric hauling is employed1 one or more dynamos may be required to generate electricity for power purposes1 as well as for lighting4 ,in addition to the power generating machines proper1 there must be the necessary piping and wiring for transmitting this power1 and1 of course1 the equipment of drills and other machines for doing the actual excavating1 hauling1 etc4 ,reservoirs4--,when water-power is employed1 a reservoir has to be formed by damming some near-by mountain stream at a point as high as practicable above the tunnel4 ,the provision of a reservoir1 instead of drawing the water directly from the stream1 serves two important purposes4 ,it insures a continuous supply and constant head of water in case of drought1 and also permits the water to deposit its sediment before it is delivered to the turbines4 ,the construction of these reservoirs may be of a temporary character1 or they may be made permanent structures1 and utilized after construction is completed to supply power for ventilation and other necessary purposes4 ,in the first case they are usually destroyed after construction is finished4 ,in either case1 it is almost unnecessary to say1 they should be built amply safe and strong according to good engineering practice in such works1 for the duration of time which they are expected to exist4 ,canals and ,pipe ,lines4--,for conveying the water from the reservoirs to the turbines1 canals or pipe lines are employed4 ,the latter form of conduit is generally preferable1 it being both less expensive and more easily constructed than the former4 ,it is advisable also to have duplicate lines of pipe to reduce the possibility of delay by accident or while necessary repairs are being made to one of the pipes4 ,the pipe lines terminate in a penstock leading into the turbine chamber1 and provided with the necessary valves for controlling the admission of water to the turbines4 ,turbines4--,there are numerous forms of turbines on the market1 but they may all be classed either as impulse turbines or as reaction turbines4 ,impulse turbines are those in which the whole available energy of the water is converted into kinetic energy before the water acts on the moving part of the turbine4 ,reaction turbines are those in which only a part of the available energy of the water is converted into kinetic energy before the water acts on the moving vanes4 ,impulse turbines give efficient results with any head and quantity of water1 but they give better results when the quantity of water varies and the head remains constant4 ,reaction turbines1 on the contrary1 give better results when the quantity of water remains constant and the head varies4 ,these observations indicate in a general way the form of turbine which will best meet the particular conditions in each case4 ,the number of turbines required1 and their dimensions1 will be determined in each case by the number of horse-power required and the quantity of water available4 ,the power of the turbines is transmitted to the air compressors or pumps by shafting and gearing4 ,air ,compressors4--,an air compressor is a machine--usually driven by steam1 although any other power may be used--by which air is compressed into a receiver from which it may be piped for use4 ,for a detailed description of the various forms of air compressors the reader should consult the catalogues of the several makers and the various text-books relating to air compression and compressed air4 ,air compressors1 like other machines1 suffer a loss of power by friction4 ,the greatest loss of power1 however1 results from the heat of compression4 ,when air is compressed1 it is heated1 and its relative volume is increased4 ,therefore1 a cubic foot of hot air in the compressor cylinder1 at say1 #fj lbs4 pressure1 does not make a cubic foot of air at #fj lbs4 pressure after cooling in the receiver4 ,in other words1 assuming pressure to be constant1 a loss of volume results due to the extraction of the heat of compression after the air leaves the compressor cylinder4 ,to reduce the amount of this loss1 air compressors are designed with means to extract the heat from the air before it leaves the compressor cylinder4 ,air compressors may first be divided into two classes1 according to the means employed for cooling the air1 as follows3 7#a7 ,wet compressors1 and 7#b7 dry compressors4 ,a wet compressor is one which introduces water directly into the cylinder during compression1 and a dry compressor is one which admits no water to the air during compression4 ,wet compressors may be subdivided into two classes3 7#a7 ,those which inject water in the form of spray into the cylinder during compression1 and 7#b7 those which use a water piston for forcing the air into confinement4 ,the following brief discussion of these various types of compressors is based on the concise practical discussion of ,mr4 ,w4 ,l4 ,saunders1 ,m4 ,am4 ,soc4 ,c4 ,e41 in 8,compressed ,air ,production40 ,the highest isothermal results are obtained by the injection of water into the cylinders1 since it is plain that the injection of cold water1 in the shape of a finely divided spray1 directly into the air during compression will lower the temperature to a greater degree than simply to surround the cylinder and parts by water jackets which is the means of cooling adopted with dry compressors4 ,a serious obstacle to water injection1 and that which condemns this type of compressor1 is the influence of the injected water upon the air cylinder and parts4 ,even when pure water is used1 the cylinders wear to such an extent as to produce leakage and to require reboring4 ,the limitation to the speed of a compressor is also an important objection4 ,the chief claim for the water piston compressor is that its piston is also its cooling device1 and that the heat of compression is absorbed by the water4 ,water is so poor a conductor of heat1 however1 that without the addition of sprays it is safe to say that this compressor has scarcely any cooling advantages at all so far as the cooling of the air during compression is concerned4 ,the water piston compressor operates at slow speed and is expensive4 ,its only advantage is that it has no dead spaces4 ,in the dry compressor a sacrifice is made in the efficiency of the cooling device to obtain low first cost1 economy in space1 light weight1 higher speed1 greater durability1 and greater general availability4 ,air compressors are also distinguished as double acting and simple acting4 ,they are simple acting when the cylinder is arranged to take in air at one stroke and force it out at the next1 and they are double acting when they take in and force out air at each stroke4 ,in form compressors may be simple or duplex4 ,they are simple when they have but one cylinder1 and duplex when they have two cylinders4 ,a straight line or direct acting compressor is one in which the steam and air cylinders are set tandem4 ,an indirect acting compressor is one in which the power is applied indirectly to the piston rod of the air cylinder through the medium of a crank4 ,mr4 ,w4 ,l4 ,saunders writes in regard to direct and indirect compression as follows3-- 8,the experience of ,american manufacturers1 which has been more extensive than that of others1 has proved the value of direct compression as distinguished from indirect4 ,by direct compression is meant the application of power to resistance through a single straight rod4 ,the steam and air cylinders are placed tandem4 ,such machines naturally show a low friction loss because of the direct application of power to resistance4 ,this friction loss has been recorded as low as #e1 while the best practice is about #aj with the type which conveys the power through the angle of a crank shaft to a cylinder connected to the shaft through an additional rod40 ,receivers4--,compressed air is stored in receivers which are simply iron tanks capable of withstanding a high internal pressure4 ,the purpose of these tanks is to provide a reservoir of compressed air1 and also to allow the air to deposit its moisture4 ,from the receivers the air is conveyed to the workings through iron pipes1 which decrease gradually in diameter from the receivers to the front4 ,rock ,drills4--,the various forms of rock drills used in tunneling have been described in ,chapter ,,iii41 and need not be considered in detail here except to say that ,american engineers usually employ percussion drills1 while ,european engineers also use rotary drills extensively4 ,a comparison between these two types of drills was made in excavating the ,aarlberg tunnel in ,austria1 where the ,brandt hydraulic rotary drill was used at one end1 and the ,ferroux percussion drill was used at the other end4 ,the rock was a mica-schist4 ,the average monthly progress was #dab ft41 with a maximum of #fdf ft41 with the rotary drills1 and an average of #ded ft4 with the percussion drill4 ,excavation4--,since considerable time is required to get the power plant established1 the excavation of rock tunnels is often begun by hand1 but hand work is usually continued for no longer a period than is necessary to get the power plant in operation4 ,generally speaking1 the greatest difficulty is encountered in excavating the advanced drift or heading4 ,based on the mode of blasting employed1 there are two methods of driving the advanced gallery1 known as the circular cut and the center cut methods4 ,in the first method a set of holes is first drilled near the center of the front in such a manner that they inclose a cone of rock2 the holes1 starting at the perimeter of the base of the cone1 converge toward a junction at its apex4 ,seldom more than four to six holes are comprised in this first set4 ,around these first holes are driven a ring of holes which inclose a cylinder of rock1 and if necessary succeeding rings of holes are driven outside of the first ring4 ,these holes are blasted in the order in which they are driven1 the first set taking out a cone of rock1 the second set enlarging this cone to a cylinder1 and the other sets enlarging this cylinder to the required dimensions of the heading4 ,the number of holes1 however1 varies with the quality of rock and they are seldom driven deeper than #d or #e ft4 ,this method of excavating the heading1 which is commonly followed by ,european engineers1 is illustrated in ,figs4 #ej to #eb4 ,in these figures are indicated the number of holes in each round and the sequence of rounds for the soft1 medium and hard rock1 as used in the ,turchino tunnel of the ,genova ,ovada ,asti line of the ,mediterranean ,railway of ,italy4 ,the heading was about #i ft4 square1 and five sets of holes were used in blasting1 the depths being #c4ia1 #d4bf and #d4f ft4 for soft1 medium and hard rock1 respectively1 and the amount of dynamite consumed was #b4ch1 #c4ia and #e4a pounds per cubic yard for the three classes of rock4 ,illustration3 in ,soft ,rock in ,medium ,rock in ,hard ,rock ,,figs4 #ej to #eb4--;,arrangement of ,drill ,holes in the ,heading of ,turchino ,tunnel4 ,illustration3 ,,figs4 #ec and #ed4--;,arrangement of ,drill ,holes in the ,heading of the ,fort ,george ,tunnel4 ,in the center-cut method1 which is the one commonly employed in ,america1 the holes are arranged in vertical rows1 and are driven from #h to #aj ft4 deep4 ,fig4 #ec shows the arrangement of the holes1 and the method of blasting them1 as used in the excavation of the heading for the ,fort ,george tunnel of the ,new ,york rapid transit4 ,the two center rows of holes converge toward each other so as to take out a wedge of rock2 others are bored straight1 or parallel1 with the vertical plane of the tunnel4 ,those bored around the perimeter are driven either outward or upward1 according as they are located1 close to the sides or roof of the tunnel4 ,in this case1 the holes of the center cut were driven #i ft4 deep1 while all the other holes were bored to a depth of #h ft4 ,the width of the advanced gallery or heading depends upon the quality of the rock4 ,in hard rock ,american engineers give it the full width of the tunnel section2 but this cannot be done in loose or fissured rock1 which has to be supported1 the headings here being usually made about #h #h ft4 ,the wider heading is always preferable1 where it is possible1 since more room is available for removing the rock1 and deeper holes can be bored and blasted4 ,the important rle played by the power plant and other mechanical installations in constructing tunnels through rock has already been mentioned4 ,in some methods of soft-ground tunneling1 and particularly in soft-ground subaqueous tunneling1 it is also often necessary to employ a mechanical installation but slightly inferior in size and cost to those used in tunneling rock4 ,it is proposed to describe very briefly here a few typical individual plants of this character1 which will in some respects give a better idea of this phase of tunnel work than the more general descriptions4 ,rock ,tunnels4--,the tunnels selected to illustrate the mechanical installations employed in tunneling through rock are3 ,the ,mont ,cenis1 ,hoosac ,tunnel1 the ,cascade ,tunnel1 the ,niagara ,falls ,power ,tunnel1 the ,palisades ,tunnel1 the ,croton ,aqueduct ,tunnel1 the ,strickler ,tunnel in ,america1 and the ,graveholz ,tunnel and the ,sonnstein ,tunnel in ,europe4 ,in addition there will be found in another chapter of this book a description of the mechanical installations at the ,st4 ,gothard1 ,pennsylvania and other tunnels4 ,mont ,cenis ,power ,plant4--,the mechanical installation consisted of the ,sommeilier air compressors built near the portals4 ,the ,sommeilier compressors1 ,mr4 ,w4 ,l4 ,saunders says1 were operated as a ram1 utilizing a natural head of water to force air at #hj lbs4 pressure into a receiver4 ,the column of water contained in the long pipe on the side of the hill was started and stopped automatically by valves controlled by engines4 ,the weight and momentum of the water forced a volume of air with such a shock against the discharge valve that it was opened1 and the air was discharged into the tank2 the valve was then closed1 the water checked2 a portion of it was allowed to discharge1 and the space was filled with air1 which was in turn forced into the tank4 ,only #gc of the power of the water was available1 #bg being lost by the friction of the water in the pipes1 valves1 bends1 etc4 ,of the #gc of net work1 #di4d was consumed in the perforators1 and #bc4f in a dummy engine for working the valves of the compressors and for special ventilation4 ,the compressed air was conveyed from each end through a cast-iron pipe #g in4 in diameter1 up to the front of the excavation4 ,the joints of the pipes were made with turned faces1 grooved to receive a ring of oakum which was tightly screwed and compressed into the joint4 ,to ascertain the amount of leakage of the pipes1 they and the tanks were filled with air compressed to #f atmospheres1 and the machines stopped2 after #ab hours the pressure was reduced to #e4g atmospheres1 or to #ie of the original pressure4 ,sommeilier's percussion drilling machines were used in the excavation of this tunnel4 ,they were provided with #h or #aj drills acting at the same time1 and mounted on carriages running on tracks4 ,these were withdrawn to a safe place during the blasting1 and advanced again after the broken rock was removed from the front and the new tracks laid4 ,machine shops were built at both ends of the tunnel for building and repairing the drilling machines1 bits1 tools1 etc4 ,a gas factory was built at each end for lighting purpose4 ,hoosac ,tunnel4--,the ,hoosac tunnel on the ,fitchburg ,r4,r4 in ,massachusetts is #be1jjj ft4 long1 and the longest tunnel in ,america4 ,the material through which the tunnel was driven was chiefly hard granitic gneiss1 conglomerate1 and mica-schist rock4 ,the excavation was conducted from the entrances and one shaft1 the wide heading and single-bench method being employed1 with the center-cut system of blasting which was here used for the first time4 ,the tunnel was begun in #ahed1 and continued by hand until #ahff1 when the mechanical plant was installed4 ,most of the particular machines employed have now become obsolete1 but as they were the first machines used for rock tunneling in ,america they deserve mention4 ,the drills used were ,burleigh percussion drills1 operated by compressed air4 ,six of these drills were mounted on a single carriage1 and two carriages were used at each front4 ,the air to operate these drills was supplied by air compressors operated by water-power at the portals and steam-power at the shaft4 ,the air compressors consisted of four horizontal single-acting air cylinders with poppet valves and water injection4 ,the compressors were designed by ,mr4 ,thomas ,deane1 the chief engineer of the tunnel4 ,palisades ,tunnel4--,the ,palisades tunnel was constructed to carry a double track railway line through the ridge of rocks bordering the west bank of the ,hudson ,river and known as the ,palisades4 ,it was located about opposite #aafth ,st4 in ,new ,york ,city4 ,the material penetrated was a hard trap rock very full of seams in places1 which caused large fragments to fall from the roof4 ,the excavation was made by a single wide heading and bench1 employing the center-cut method of blasting with eight center holes and #af side holes for the #g #ah ft4 heading4 ,ingersoll-,sergeant #b in4 drills were used1 four in each heading and six on each bench1 and #cj ft4 per #aj hours was considered good work for one drill4 ,the power-plant was situated at the west portal of the tunnel1 and the power was transmitted by electricity and compressed air to the middle shaft and east portal workings4 ,the plant consisted of eight #ajj ,h4 ,p4 boilers1 furnishing steam to four ,rand duplex #ah #bb in4 air compressors1 and an engine running a #cj arc light dynamo4 ,the compressed air was carried over the ridge by pipes1 varying from #aj ins4 to #e ins4 in diameter1 to the shaft and to the east portal1 and was used for operating the hoisting engines as well as the drills at these workings4 ,inside the tunnel1 specially designed derrick cars were employed to handle large stones1 they being also operated by compressed air4 ,this car ran on a center track1 while the mucking cars ran on side tracks1 and it was employed to lift the bodies of the cars from the trucks1 place them close to the front1 being worked where large stone could be rolled into them1 and return them to the trucks for removal4 ,in addition to handling the car bodies the derrick was used to lift heavy stones4 ,the hauling was done first by horse-power1 and later by dummy locomotives4 ,croton ,aqueduct ,tunnel4--,in the construction of the ,croton ,aqueduct for the water supply of ,new ,york ,city1 a tunnel #ca miles long was built1 running from the ,croton ,dam to the ,gate ,house at #aceth ,st4 in ,new ,york ,city4 ,the section of the tunnel varies in form1 but is generally either a circular or a horseshoe section4 ,in all cases the section was designed to have a capacity for the flow of water equal to a cylinder #ad ft4 in diameter4 ,to drive the tunnel1 #dj shafts were employed4 ,the material penetrated was of almost every character1 from quicksand to granitic rock1 but the bulk of the work was in rock of some character4 ,the excavation in rock was conducted by the wide heading and bench method1 employing the center-cut method of blasting4 ,four air drills1 mounted on two double-arm columns were employed in the heading4 ,the drills for the bench work were mounted on tripods4 ,steam-power was used exclusively for operating the compressors1 hoisting engines1 ventilating fans and pumps2 but the size and kind of boilers used1 as well as the kind and capacity of the machines which they operated1 varied greatly1 since a separate power-plant was employed for each shaft with a few exceptions4 ,a description of the plant at one of the shafts will give an indication of the size and character of those at the other shafts1 and for this purpose the plant at shaft #aj has been selected4 ,at shaft #aj steam was provided by two ,ingersoll boilers of #hj ,h4 ,p4 each1 and by a small upright boiler of #h ,h4 ,p4 ,there were two #ah #cj in4 ,ingersoll air compressors pumping into two #db in4 #aj ft4 and two #db in4 #ab ft4 ,ingersoll receivers4 ,in the excavation there were twelve #c in4 and six #c in4 ,ingersoll drills1 four drills mounted on two double arm columns being used on each heading1 and the remainder mounted on tripods being used on the bench4 ,two ,dickson cages operated by one #ab #ab in4 ,dickson reversible double hoisting engine provided transportation for material and supplies up and down the shaft4 ,a ,thomson-,houston ten-light dynamo operated by a ,lidgerwood engine provided light4 ,drainage was effected by means of two ,no4 #i and one ,no4 #f ,cameron pumps4 ,at this particular shaft the air exhausted from the drills gave ample ventilation1 especially when after each blast the smoke was cleared away by a jet of compressed air4 ,in other workings1 however1 where this means of ventilation was not sufficient1 ,baker blowers were generally employed4 ,strickler ,tunnel4--,the ,strickler tunnel for the water supply of ,colorado ,springs1 ,col41 is #fdda ft4 long with a section of #d ft4 #g ft4 ,it penetrates the ridge connecting ,pike's ,peak and the ,big ,horn ,mountains1 at an elevation of #aa1edj ft4 above sea level4 ,the material penetrated is a coarse porphyritic granite and morainal dbris1 the portion through the latter material being lined4 ,the mechanical installation consisted of a water-power electric plant operating air compressors4 ,the water from ,buxton ,creek having a fall of #bdjj ft4 was utilized to operate a #cf in4 #bbj ,h4 ,p4 ,pelton water-wheel1 which operated a #aej ,k4 ,w4 three-phase generator4 ,from this generator a #cejj volt current was transmitted to the east portal of the tunnel1 where a step-down transformer reduced it to a #bbj volt current to the motor4 ,the transmission line consisted of three ,no4 #e wires carried on cross-arm poles and provided with lightning arresters at intervals4 ,the plant at the east portal of the tunnel consisted of a #ge ,h4 ,p4 electric motor1 driving a #ge ,h4 ,p4 air compressor1 and of small motors to drive a ,sturtevant blower for ventilation1 to run the blacksmith shop1 and to light the tunnel1 shop1 and yards4 ,from the compressor air was piped into the tunnel at the east end1 and also over the mountain to the west portal workings4 ,two drills were used at each end1 and the air was also used for operating derricks and other machinery4 ,for removing the spoil a trolley carrier system was employed4 ,a longitudinal timber was fastened to the tunnel roof1 directly in the apex of the roof arch4 ,this timber carried by means of hangers a steel bar trolley rail on which the carriages ran4 ,outside of the portal this rail formed a loop1 so that the carriage could pass around the loop and be taken back to the working face4 ,each carriage carried a steel span of #a cu4 ft4 capacity1 so suspended that by means of a tripping device it was automatically dumped when the proper point on the loop was reached4 ,niagara ,falls ,power ,tunnel4--,the tail-race tunnel built to carry away the water discharged from the turbines of the ,niagara ,falls ,power ,co41 has a horse-shoe section #ai #ba ft4 and a length of #fgjj ft4 ,it was driven through rock from three shafts by the center-cut method of blasting4 ,in sinking shaft ,no4 #j very little water was encountered1 but at shafts ,nos4 #a and #b an inflow of #hjj gallons and #fjj gallons per minute1 respectively1 was encountered4 ,the principal plant was located at shaft ,no4 #b1 and consisted of eight #ajj ,h4,p4 boilers1 three #ah #cj in4 ,rand duplex air compressors1 a ,thomson-,houston electric-light plant1 and a sawmill with a capacity of #bj1jjj ft4 ,b4 ,m4 per day4 ,the shafts were fitted with ,otis automatic hoisting engines1 with double cages at shafts ,nos4 #a and #b1 and a single cage at shaft ,no4 #j4 ,the drills used were #be ,rand drills and three ,ingersoll-,sergeant drills4 ,the pumping plant at shaft ,no4 #b consisted of four ,no4 #g and one ,no4 #i ,cameron pumps1 and that at shaft ,no4 #b consisted of two ,no4 #g and two ,no4 #i ,cameron pumps and three ,snow pumps4 ,an auxiliary boiler plant consisting of two #fj ,h4 ,p4 boilers was located at shaft ,no4 #a1 and another1 consisting of one #ge ,h4 ,p4 boiler1 was located at shaft ,no4 #j4 ,cascade ,tunnel4--,the ,cascade tunnel was built in #ahhf-hh to carry the double tracks of the ,northern ,pacific ,ry4 through the ,cascade ,mountains in ,washington4 ,it is #ihej ft4 long with a cross-section #af ft4 wide and #bb ft4 high1 and is lined with masonry4 ,the material penetrated was a basaltic rock1 with a dip of the strata of about #e4 ,the rock was excavated by a wide heading and one bench1 using the center-cut system of blasting4 ,a strutting consisting of five-segment timber arches carried on side posts1 spaced from #b ft4 to #d ft4 apart1 and having a roof lagging of #d #f in4 timbers packed above with cord-wood4 ,the mechanical plant of the tunnel is of particular interest1 because of the fact that all the machinery and supplies had to be hauled from #hb to #hg miles by teams1 over a road cut through the forests covering the mountain slopes4 ,this work required from ,feb4 #bb to ,july #ae1 #ahhf1 to perform4 ,in many places the grades were so steep that the wagons had to be hauled by block and tackle4 ,the plant consisted of five engines1 two water-wheels1 five air compressors1 eight #gj ,h4 ,p4 steam-boilers1 four large exhaust fans1 two complete electric arc-lighting plants1 two fully equipped machine-shop outfits1 #cf air drills1 two locomotives1 #fj dump cars1 and two sawmill outfits1 with the necessary accessories for these various machines4 ,this plant was divided about equally between the two ends of the tunnel4 ,the cost of the plant and of the work of getting it into position was #abe1jjj4 ,graveholz ,tunnel4--,the ,graveholz tunnel on the ,bergen ,railway in ,norway is notable as being the longest tunnel in northern ,europe1 and also as being built for a single-track narrow-gauge railway4 ,this tunnel is #ag1djj feet long1 and is located at an elevation of #bijj feet above sea-level4 ,only about #c of the length of the tunnel is lined4 ,the mechanical installation consists of a turbine plant operating the various machines4 ,there are two turbines of #ajj ,h4 ,p4 and #abj ,h4 ,p4 taking water from a reservoir on the mountain slope1 and furnishing #bbj ,h4 ,p41 which is distributed about as follows3 ,boring-machines1 #fj ,h4 ,p42 ventilation1 #cj to #dj ,h4 ,p42 electric locomotives1 #ae ,h4 ,p42 machine shop1 #ae ,h4 ,p42 electric-lighting dynamo1 #be ,h4 ,p42 electric drills1 the surplus1 or some #dj ,h4 ,p4 ,the boring-machines and electric drills will be operated by the smaller #ajj ,h4 ,p4 turbine4 ,sonnstein ,tunnel4--,the ,sonnstein tunnel in ,germany is particularly interesting because of the exclusive use of ,brandt rotary drills4 ,the tunnel was driven through dolomite and hard limestone by means of a drift and two side galleries4 ,the dimensions of the drift were #g #g ft4 ,the power plant consisted of two steam pressure pumps1 one accumulator1 and four drills4 ,the steam-boiler plant1 in addition to operating the pumps1 also supplied power for operating a rotary pump for drainage and a blower for ventilation4 ,the hydraulic pressure required was #ge atmospheres in the dolomite1 and from #he to #ajj atmospheres in the limestone4 ,the drift was excavated with five #c in4 holes1 one being placed at the center and driven parallel to the axis of the tunnel1 and four being placed at the corners of a rectangle corresponding to the sides of the drift1 and driven at an angle diverging from the center hole4 ,the average depths of the holes were #d4c ft41 and the efficiency of the drills was #a in4 per minute4 ,one drill was employed at each front1 and was operated by a machinist and two helpers1 who worked eight-hour shifts1 with a blast between shifts at first1 and later twelve-hour shifts1 with a blast between shifts4 ,the #bd hours of the two shifts were divided as follows3 boring the holes1 #aj4g hours2 charging the holes1 #a4a hours2 removing the spoil1 #aa4g hours2 changing shifts1 #j4e hour4 ,the average progress per day for each machine was #f4g ft4 ,the total cost of the plant was #ag1dej4 ,st4 ,clair ,river ,tunnel4--,the submarine double-track railway tunnel under the ,st4 ,clair ,river for the ,grand ,trunk ,ry4 is #hejj ft4 long1 and was driven through clay by means of a shield1 as described in the succeeding chapter on the shield system of tunneling4 ,the mechanical plant installed for prosecuting the work was very complete4 ,to furnish steam to the air compressors1 pumps1 electric-light engines1 hoisting-engines1 etc41 a steam-plant was provided on each side of the river1 consisting of three #gj ,h4 ,p4 and four #hj ,h4 ,p4 ,scotch portable boilers4 ,the air-compressor plant at each end consisted of two #bj #bd in4 ,ingersoll air compressors4 ,to furnish light to the workings1 two #ajj candle-power ,edison dynamos were installed on the ,american side1 and two ,ball dynamos of the same size were installed on the ,canadian side4 ,the dynamos on both sides were driven by ,armington ,sims engines4 ,these dynamos furnished light to the tunnel workings and to the machine-shops and power-plant at each end4 ,root blowers of #aj1jjj cu4 ft4 per minute capacity provided ventilation4 ,the pumping plant consisted of one set of pumps installed for permanent drainage1 and another set installed for drainage during construction1 and also to remain in place as a part of the permanent plant4 ,the latter set consisted of two #ejj gallon ,worthington duplex pumps set first outside of each air lock1 closing the ends of the river portion of the tunnel4 ,for permanent drainage1 a drainage shaft was sunk on the ,canadian side of the river1 and connected with a pump at the bottom of the open-cut approach4 ,in this shaft were placed a vertical1 direct-acting1 compound-condensing pumping engine with two #ai in4 high-pressure and two #cc in4 low-pressure cylinders of #bd in4 stroke1 connected to double-acting pumps with a capacity of #cjjj gallons per minute1 and also two duplex pumps of #ejj gallons capacity per minute4 ,for permanent drainage on the ,american side1 four ,worthington pumps of #cjjj gallons' capacity were installed in a pump-house set back into the slope of the open-cut approach4 ,for the permanent drainage of the tunnel proper two #djj gallon pumps were placed at the lowest point of the tunnel grade4 ,spoil coming from the tunnel proper was hoisted to the top of the open cut by derricks operated by two #ej ,h4 ,p4 ,lidgerwood hoisting-engines4 ,the pressure pumping plant for supplying water to the hydraulic shield-jacks at each end of the tunnel consisted of duplex direct-acting engines with #ab in4 steam cylinders and #a in4 water cylinders1 supplying water at a pressure of #bjjj lbs4 per sq4 in4 ,,chapter ,x4 ,,tunnels ,,through ,,hard ,,rock 7,continued74 ,,excavation ,,by ,,drifts3 ,,the ,,simplon ,,and ,,murray ,,hill ,,tunnels4 ,illustration3 ,,fig4 #ee4--;,diagram ,showing ,sequence of ,excavations in ,drift ,method of ,tunneling ,rock4 ,general ,description4--,the method of tunneling through hard rock by drifts is preferred by ,european engineers4 ,all the great ,alpine tunnels1 from the ,mont ,cenis tunnel to the ,simplon1 are examples of tunneling by drifts4 ,in this method the sequence of excavation is shown diagrammatically by ,fig4 #ee4 ,the work begins by excavating a drift close to the floor of the proposed tunnel 7as shown in the center of the figure7 and far in advance of the excavation of any other part4 ,the section marked #b is next removed and still later the portions marked #c4 ,then with the removal of the parts marked #d the whole section of the tunnel will be open4 ,the drift is usually strutted by means of side posts carrying a cap-piece placed at intervals1 and having a ceiling of longitudinal planks resting on the successive caps4 ,in hard rock the roof of the section does not1 as a rule1 require regular strutting1 occasional supports being placed at intervals to prevent the fall of isolated fragments3 ,when the rock is disintegrated or full of seams1 a regular strutting may be necessary1 and this may be either longitudinal or polygonal in type4 ,when longitudinal strutting is employed1 a sill is laid across the roof of the drift1 and upon this are set up two struts converging toward the top and supporting a cap-piece close to the roof4 ,on this cap-piece are placed the first longitudinal crown bars carrying transverse poling-boards4 ,additional props standing on the sill and radiating outward are inserted as parts ,no4 #c are excavated4 ,these radial props carry longitudinal bars which in turn support transverse poling-boards4 ,when polygonal strutting is used1 it may take the form of three or five segment arches of heavy timbers4 ,in hard rock tunnels1 as a rule1 there is no danger of caving in because of heavy pressures1 and the whole section is left open for some time before it is lined4 ,the lining may be of concrete masonry1 but in many long tunnels1 excavated through hard rock1 the side walls are lined with rubble masonry and the arch with brick1 and1 in some instances1 even the arch has been lined with rubble masonry4 ,with skilful laborers at hand the rubble masonry lining has proved most efficient and economical1 because the rock is utilized as it is excavated without any further operation4 ,concrete1 however1 is more extensively employed for lining tunnels than any other material4 ,tunnels excavated by drifts enable simple means of hauling to be employed1 and this is one of the reasons why the method finds so much favor with ,european engineers4 ,the tracks are laid along the floor of the drift1 and carry all the spoil from parts ,nos4 #b1 #c1 and #d1 as well as from the front of the drift itself4 ,as fast as the full section is completed1 this single track in the drift is replaced by two tracks running close to the sides of the tunnel1 or by a broad-gauge track with a third rail4 ,,the ,,simplon ,,tunnel4#h ,before entering upon a description of the constructive details of this1 the longest railway tunnel in the world1 it may be well to give a general idea of the undertaking4 ,many schemes for the connection of ,italy and ,switzerland by a railway near the ,simplon ,road ,pass have been devised1 including one involving no great length of underground work1 the line mounting by steep gradients and sharp curves4 ,the present scheme1 put forward in #ahha by the ,jura-,simplon ,ry4 ,co41 consists broadly of piercing the ,alps between ,brigue1 the present railway terminus in the ,rhone ,valley1 and ,iselle1 in the gorge of the ,diveria1 on the ,italian side1 from which village the railway will descend to the existing southern terminus at ,domo d',ossola1 a distance of about #aa miles4 #h ,abstract from a paper read before the ,institution of ,civil ,engineers by ,charles ,b4 ,fox1 ,jan4 #bf1 #aijj4 ,in conjunction with this scheme a second tunnel is proposed1 to pierce the ,bernese ,alps under the ,ltschen ,pass from ,mittholz to a point near ,turtman in the ,rhone ,valley2 and thus1 instead of the long dtour by ,lausanne and the ,lake of ,geneva1 there will be an almost direct line from ,berne to ,milan via ,thun1 ,brigue1 and ,domo d',ossola4 ,starting from ,brigue1 the new line1 running gently up the valley for #a miles1 will1 on account of the proximity of the ,rhone1 which has already been slightly diverted1 enter the tunnels on a curve to the right of #ajej ft4 radius4 ,at a distance of #aec yards from the entrance1 the straight portion of the tunnel commences1 and extends for #ab miles4 ,the line then curves to the left with a radius of #acaa ft4 before emerging on the left bank of the ,diveria4 ,commencing at the northern entrance1 a gradient of #a in #ejj 7the minimum for efficient drainage7 rises for a length of #e miles to a level length of #eej yards in the center1 and then a gradient of #a in #adc descends to the ,italian side4 ,on the way to ,domo d',ossola one helical tunnel will be necessary1 as has been carried out on the ,st4 ,gothard4 ,there will be eventually two parallel tunnels having their centers #ef ft4 apart1 each carrying one line of way2 but at the present time only one heading1 that known as ,no4 #a1 is being excavated to full size1 ,no4 #b being left1 masonry lined where necessary1 for future developments4 ,by means of cross headings every #bbj yds4 the problems of transport and ventilation are greatly facilitated1 as will be seen later4 ,as both entrances are on curves1 a small 8gallery of direction0 is necessary1 to allow corrections of alinement to be made direct from the two observatories on the axis of the tunnel4 ,the outside installations are as nearly in duplicate as circumstances will allow1 and consist of the necessary offices1 workshops1 engine-sheds1 power-houses1 smithies1 and the numerous buildings entailed by an important engineering scheme4 ,great care is taken that the miners and men working in the tunnel shall not suffer from the sudden change from the warm headings to the cold ,alpine air outside2 and for this purpose a large building is in course of erection1 where they will be able to take off their damp working clothes1 have a hot and cold douche1 put on a warm dry suit1 and obtain refreshments at a moderate cost before returning to their homes4 ,instead of each man having a locker in which to stow his clothes1 a perfect forest of cords hangs down from the wooden ceiling1 #be ft4 above floor-level1 each cord passing over its own pulleys and down the wall to a numbered belaying-pin4 ,each cord supports three hooks and a soap-dish1 which1 when loaded with their owner's property1 are hauled up to the ceiling out of the way4 ,there are #bjjj of these cords1 spaced #a ft4 #f ins4 apart1 one to each man4 ,the engineers and foremen are more privileged1 being provided with dressing-rooms and baths1 partitioned off from the two main halls4 ,an extensive clothes washing and drying plant has been laid down1 and also a large restaurant and canteen4 ,at ,iselle1 a magazine holding #bbjj lbs4 of dynamite is surrounded and divided into two separate parts by earth-banks1 #af ft4 high4 ,the two wooden houses1 in which the explosive is stored1 are warmed by hot-water pipes to a temperature between #fa ,f4 and #gg ,f41 and are watched by a military patrol2 but at ,brigue a dynamite manufactory1 started by an enterprising company at the time of the commencement of the works1 supplies this commodity at frequent intervals1 thereby avoiding the necessity of storing in such large quantities4 ,this dynamite factory has been largely increased1 and supplies dynamite to nearly all the mining and tunneling enterprises in ,switzerland4 ,geological ,conditions4--,before the ,simplon tunnel was authorized1 expert evidence was taken as to the feasibility of the project4 ,the forecasts of the three engineers chosen1 in reference to the rock to be encountered and its probable temperature1 have1 as far as the galleries have gone 7an aggregate distance of nearly #b miles71 generally been found correct4 ,at the north end1 a dark argillaceous schist veined with quartz was met with1 and from time to time beds of gypsum and dolomite have been traversed1 the dip of the strata being on the whole favorable to progress1 though timbering is resorted to at dangerous places4 ,water was plentiful at the commencement2 in fact1 one inrush has not been stopped1 and is still flowing down the heading4 ,the total quantity of water flowing from the tunnel mouth is #af gallons per second1 of which #b gallons per second are accounted for by the drilling machines4 ,at ,iselle1 however1 a very hard antigorio gneiss obtains1 and is likely to extend for #d miles4 ,very dry and very compact1 it requires no timbering1 and represents no great difficulty to the powerful ,brandt rock-drills1 which work under a head of #cbhj ft4 of water4 ,the temperature of the rock depends not only on the depth from the surface1 but largely upon the general form of that surface combined with the conductivity of the rock4 ,taking these points into consideration with the experience gained from the construction of the ,st4 ,gothard tunnel1 #ie ,f4 was estimated as the probable maximum temperature1 owing to the height of ,monte ,leone 7#aa1ffj ft471 which lies almost directly over the tunnel axis4 ,survey4--,after having determined upon the general position of the tunnels1 taking into consideration the necessary gradients1 the temperature of the rock1 and a large bed of troublesome gypsum on the north side1 two fixed points on the proposed center line were taken1 one at each entrance of tunnel ,no4 #a1 and the bearings of these two points1 with reference to a triangulation survey made in #ahgf1 were calculated sufficiently accurately to determine1 for the time being1 the direction of the tunnel4 ,in #ahih1 a new triangulation survey was made1 taking in eleven summits1 ,monte ,leone holding the central position4 ,this survey was tied into that of the ,wasenhorn and ,faulhorn1 made by the ,swiss ,government1 and the accuracy was such that the probable error in the meeting of the two headings is only #f cms4 or #b ins4 ,on the top of each summit is placed a signal1 consisting of a small pillar of masonry founded on rock1 and capped with a sharp pointed cone of zinc1 #a ft4 #f ins4 high4 ,an observatory was built at each end of the tunnel in such a position that three of the summits could be seen1 a condition very difficult to fulfill on the south side owing to the depth of the gorge1 the mountains on either side being over #gjjj ft4 high4 ,having taken the angles to and from each visible signal1 and therefrom having calculated the direction of the tunnel1 it was necessary to fix1 with extreme accuracy1 sighting-points on the axis of the tunnel1 in order to avoid sighting on to the surrounding peaks for each subsequent correction of the alinement of the galleries4 ,to do this1 a theodolite #bd ins4 long and #b ins4 in diameter1 with a magnifying power of #dj times1 was set up in the observatory1 and about #ajj readings were taken of the angles between the surrounding signals and the required sighting-points4 ,in this manner the error likely to occur was diminished to less than #a4 ,thus at the north end two points were found about #eej yds4 before and behind the observatory1 while on the south side1 owing to the narrowness of the gorge1 the points could only be placed at #hb yds4 and #abf yds4 in front4 ,one of these sighting-points consists of a fine scratch ruled on a piece of glass fixed in an iron frame1 behind which is placed an acetylene lamp1--corrections of alinement are always done by night1--the whole being rigidly fixed into a niche cut in the rock and protected from climatic and other disturbing agencies by an iron plate4 ,method of ,checking ,alinement4--,the direction of heading ,no4 #a is checked by experts from the ,government ,survey ,department at ,lausanne about three times a year1 and for this purpose a transit instrument is set up in the observatory4 ,a number of three-legged iron tables are placed at intervals of #a mile or #b miles along the axis of tunnel ,no4 #a1 and upon each of these is placed a horizontal plane1 movable by means of an adjusting screw1 in a direction at right angles to the axis1 along a graduated scale4 ,on this plane are small sockets1 into which the legs of an acetylene lamp and screen1 or of the transit instrument1 can be quickly and accurately placed4 ,the screen has a vertical slit1 #c ins4 in height1 and variable between in4 and in4 in breadth1 according to the state of the atmosphere1 and at a distance shows a fine thread of light4 ,the instrument1 having first been sighted on to the illuminated scratch of the sighting-point1 is directed up the tunnel1 where a thread of light is shown from the first table4 ,with the aid of a telephone this light is adjusted so that its image is exactly coincident with the cross hairs1 and the reading on the graduated scale is noted4 ,this is done four or five times1 the average of these readings being taken as correct1 and the plane is clamped to that average4 ,the instrument is then taken to the first table and is placed quickly and accurately over the point just found 7by means of the sockets71 and the lamp is carried to the observatory4 ,after first sighting back1 a second point is given on the second table1 and so on4 ,these points are marked either temporarily in the roof of the heading by a short piece of cord hanging down1 or permanently by a brass point held by a small steel cylinder1 #h ins4 long and #c ins4 in diameter1 embedded in concrete in the rock floor1 and protected by a circular casting1 also sunk in cement concrete1 holding an iron cover resembling that of a small manhole4 ,from time to time the alinement is checked from these points by the engineers1 and after each blast the general direction is given by the hand from the temporary points4 ,to check the results of the triangulation survey1 astronomical observations have been taken simultaneously at each end4 ,with regard to the levels1 those given on the excellent ,government surveys have been taken as correct1 but they have also been checked over the pass4 ,details of ,tunnels4--,in cross-section1 tunnel ,no4 #a is #ac ft4 #g ins4 wide at formation level1 increasing to #af ft4 #e ins41 with a total height of #ah ft4 above rail-level1 and a cross-sectional area of about #bej sq4 ft4 ,this large section will allow of small repairs being executed in the roof without interruption of the traffic1 and will also allow of strengthening the walls by additional masonry on the inside4 ,the thickness of the lining1 never wholly absent1 and the material of which it is composed1 depend upon the pressure to be resisted1 and only in the worst case is an invert resorted to4 ,the side drain1 to which the rock floor is made to slope1 will be composed of half-pipes of #g to #a cement concrete4 ,the roof is constructed of radial stones4 ,tunnel ,no4 #b1 being left as a heading1 is driven on that side nearest to ,no4 #a1 to minimize the length of the cross-headings1 and measures #aj ft4 #b ins4 wide by #f ft4 #g ins4 high4 ,masonry is used only where necessary1 and in that case is so built as to form part of the lining of the tunnel when eventually completed4 ,concrete is put in to form a foundation for the side wall1 and a water channel4 ,the cross-headings1 connecting the two parallel headings1 occur every #bbj yds41 and are placed at an angle of #ef to the axis of the tunnel1 to avoid sharp curves in the contractors' railway lines4 ,they will eventually be used as much as possible for refuges1 chambers for storing the tools and equipment of the platelayers1 and signal-cabins4 ,the refuges1 #f ft4 #g ins4 wide by #f ft4 #g ins4 high and #c ft4 #c ins4 deep1 occur every #aaj yards1 every tenth being enlarged to #i ft4 #aj ins4 wide by #i ft4 #aj ins4 deep and #aj ft4 #b ins4 high1 still larger chambers being constructed at greater intervals4 ,method of ,excavation4--,the work at each end of the tunnel is carried on quite independently1 consequently1 though similar in principle1 the methods vary in detail1 apart from the fact that different geological strata require different treatment4 ,broadly speaking1 the two parallel headings1 each #ei sq4 ft4 in section1 are first driven by means of drilling-machines and the use of dynamite1 this work being carried on day and night1 seven days in the week2 ,no4 #a heading is then enlarged to full size by hand-drilling and dynamite4 ,on the ,italian side1 where the rock is hard and compact1 breakups are made at intervals of #ej yds41 and a top gallery is driven in both directions1 but1 for ventilation reasons1 is never allowed to get more than #d yds4 ahead of the break-up1 which is gradually lengthened and widened to the required section4 ,no timbering is required1 except to facilitate the excavation and the construction of the side walls4 ,steel centers are employed for the arch2 they entail fewer supports1 give more room1 and are capable of being used over again more frequently without damage4 ,they consist of two ,i-beams bent to a template and riveted together at the crown1 resting at either side on scaffolding at intervals of #f ft42 longitudinals #ab ft4 by #d ins4 by #d ins4 support the roof4 ,hand rock-drilling is carried out in the ordinary way1 one man holding the tool and a second striking2 measurements of excavation are taken every #b or #c yds41 a plumb-line is suspended from the center of the roof1 and at every half-meter 7#bj ins47 of height horizontal measurements are taken to each side4 ,at the ,brigue end a softer rock is encountered1 necessitating at times heavy timbering in the heading1 and especially in the final excavation to full size1 ,fig4 #ef4 ,the bottom heading1 #f ft4 #f in4 high1 is driven in the center1 and the heading is then widened to the full extent and timbered2 the concrete forming the water channel and the foundation for one side wall is put in2 the side walls are built to a height of #f ft4 #f ins41 and the tunnel is fully excavated to a further height of #f ft4 #f ins4 from the first staging4 ,the side walls are then continued up for the second #f ft4 #f ins41 and from the second floor a third height of #f ft4 #f ins4 is excavated and timbered4 ,finally the crown is cleared out1 heavy wooden centers are put in1 the arch is turned and all timbers are withdrawn except the top poling-boards1 supporting the loose rock4 ,illustration3 ,,fig4 #ef4--,sketches ,showing ,sequence of ,work in ,excavating and ,lining the ,simplon ,tunnel4 #a #b #c #d #e #f #g #h ,the masonry for the side walls is obtained either from the tunnel itself or from a neighboring quarry1 and varies in character according to the pressure2 but the face of the arch is always of cut or artificial stones1 the latter being #g to #a cement concrete4 ,where the alinement heading1 or the 8gallery of direction10 joins the curving portion of tunnel ,no4 #a1 the section is very much greater1 and necessitates special timbering4 ,transport 7,italian ,side74--,a small line of railway1 #b ft4 #g ins4 gauge1 with #dj-lb4 rails1 enters all three portals2 but since the construction of a wooden bridge over the ,diveria1 the route through the 8gallery of direction10 across heading ,no4 #b1 to tunnel ,no4 #a1 is used exclusively2 this railway leads to the face in both headings1 and1 where convenient1 from one heading to the other by the cross-galleries4 ,different types of wagons are in use2 but in general they are four-wheeled1 non-tipping box wagons1 supplied with brakes and holding #b cu4 yds4 of dbris4 ,a special type of locomotive is used1 designed to pass round curves of #ej ft4 radius1 and supplied with a specially large boiler to avoid firing in the tunnel4 ,illustration3 ,,fig4 #eg4--;,general ,details of the ,brandt ,rotary ,drills ,employed at the ,simplon ,tunnel4 ,method of ,working4--,the drilling-machines employed are of the ,brandt type1 ,fig4 #eg1 and are mounted in the following manner3 ,a small four-wheeled carriage supports at its center a beam1 the shorter arm of which carries the boring mechanism and the longer a counterpoise2 near its center is the distributor4 ,in the short arm is a clamp holding the rack-bar or butting column1 which is a wrought-iron cylinder with a plunger constituting a ram1 and is jammed by hydraulic pressure between the walls of the heading1 thus forming a rigid support for the boring-machine1 and an efficient abutment against the reaction of the drill4 ,this rack-bar can be rotated on its clamp in a plane parallel to the axis of the beam4 ,three or four separate boring-machines can be mounted on the rack-bar1 and can be adjusted in any reasonable position4 ,the boring-machine performs the double function of continually pressing the drill into the rock by means of a hollow ram 7,i7 and of imparting to the drill and ram a uniform rotary motion4 ,this rotary motion is given by a twin cylinder single-acting hydraulic motor 7,e71 the two pistons1 of #b ins4 stroke1 acting reciprocally as valves4 ,the cranks are fixed at an angle of #ij to each other on the shaft1 which carries a worm1 gearing with a worm-wheel 7,q7 mounted upon the shell 7,r7 of the hollow ram 7,i71 and this shell in turn engages the ram by a long feather1 leaving it free to slide axially to or from the face of the rock4 ,the average speed of the motor is #aej revolutions to #bjj revolutions per minute1 the maximum speed being #cjj revolutions per minute4 ,the loss of power between the worm and worm-wheel is only #ae at the most2 the worm being of hardened steel and the wheel of gun-metal1 the two surfaces in contact acquire a high degree of polish1 resulting in little wearing or heating4 ,taking into consideration all other sources of loss1 #gj of the total power is utilized4 ,the pressure on the drill is exerted by a cylinder and hollow ram 7,i71 which revolves about the differential piston 7,s71 which is fixed to the envelope holding the shell 7,r74 ,this envelope is rigidly connected to the bed-plate of the motor1 and1 by means of the vertical hinge and pin 7,t71 is held by the clamp 7,v7 embracing the rack-bar4 ,when water is admitted to the space in front of the differential piston the ram carrying the drilling-tool is thrust forward1 and when admitted to the annular space behind the piston1 the ram recedes1 withdrawing the tool from the blast-hole4 ,the drill proper is a hollow tube of tough steel #b ins4 in external diameter1 armed with three or four sharp and hardened teeth1 and makes from five to ten revolutions per minute1 according to the nature of the rock4 ,when the ram has reached the end of its stroke of #b ft4 #b ins41 the tool is quickly withdrawn from the hole and unscrewed from the ram2 an extension rod is then screwed into the tool and into the ram1 and the boring is continued1 additional lengths being added as the tool grinds forward2 each change of tool or rod takes about #ae secs4 to #be secs4 to perform4 ,the extension rods are forged steel tubes1 fitted with four-threaded screws1 and having the same external diameter as the drill4 ,they are made in standard lengths of #b ft4 #h ins41 #a ft4 #aj ins41 and #aa ins4 ,the total weight of the drilling-machine is #bfd lbs41 and that of the rack-bar when full of water is #cjh lbs4 ,the exhaust water from the two motor cylinders escapes through a tube in the center of the ram and along the bore of the extension rods and drill1 thereby scouring away the dbris and keeping the drill cool2 any superfluous water finds an exit through a hose below the motors and thence away down the heading4 ,the distributor1 already mentioned1 supplies each boring-machine and the rack-bar with hydraulic pressure from the mains1 with which connection is effected by means of flexible or articulated pipe connections1 allowing freedom in all directions4 ,the area of the piston for advancing the tool is #ae sq4 ins41 which1 under a pressure of #adgj lbs4 per sq4 in41 gives a pressure of over #aj tons on the tool1 while for withdrawing the tool #b tons is available4 ,in the rock found at ,iselle1 namely1 antigorio gneiss1 a hole #b ins4 in diameter and #c ft4 #c ins4 in length is drilled1 normally1 in #ab mins4 to #be mins42 a daily rate of advance of #ah ft4 to #ai ft4 #f ins4 is made in a heading having a minimum cross-section of #ei sq4 ft42 the time taken to drill ten to twelve holes1 #d ft4 #g ins4 deep1 is #b hrs4 ,when the dbris resulting from one operation has been sufficiently cleared away1 a steel flooring1 which is provided near the face to enable shoveling to be more easily done1 and to give an even floor for the wheels of the drilling-carriage1 is laid bare at the head of the line of rails1 and the drilling-machines are brought up on their carriage by eight or ten men4 ,when advanced sufficiently close to the face1 the rack-bar is slewed round across the gallery and is wedged up against the rock sides2 connection is made between the distributor and the hydraulic main1 by means of the flexible pipe1 and pressure is supplied by a small copper tube to the rack-bar ram1 thereby rigidly holding the machine4 ,next1 connections are made between the three drilling-machines and the distributor1 and in #bj mins4 from the time the machine was brought up all three drills are hard at work1 water pouring from the holes4 ,the noise of the motors and grinding-tools is sufficient to drown all but shouts2 and where the extension rods do not fit tightly1 small jets of water play in all directions1 necessitating the wearing of tarpaulins by the men directing the tools4 ,lighting is done wholly by small oil-lamps1 provided with a hook to facilitate fixing in any crack in the rock2 electricity will probably be used to light that portion of the tunnel which is completed4 ,two men are allotted to each drill1 one to drive the motor1 the other to direct and replenish the tool1 one foreman and two men in reserve completing the gang4 ,a small hammer is freely used to loosen the screw joints of the extension rods and drill4 ,a hole is usually commenced by a two-edged flat-pointed tool1 until a sufficient depth is reached to prevent the circular tool from wandering over the face of the rock1 but in many instances the hole is commenced with a circular tool4 ,the exhaust water during this period flows away by the hose underneath the motor4 ,in the antigorio gneiss1 ten to twelve holes are drilled for each attack1 three to four in the center to a depth of #c ft4 #c ins41 the remainder1 disposed round the outside of the face1 having a depth of #d ft4 #g ins4 ,the average time taken to complete the holes is #a hr4 to #b hrs4 ,instead of pulverizing the rock1 as do the diamond drills1 it is found that the rock is crushed1 and that headway is gained somewhat in the manner of a circular saw through wood4 ,the core of rock inside the tool breaks up into small pieces1 and can be taken out if necessary when the drill requires lengthening4 ,the lowest holes1 inclined downwards1 are full of water2 consequently two detonators and two fuses are inserted1 but apart from this1 water has little effect on the charge4 ,the fuses of the central holes are brought together and cut off shorter than those of the outer holes1 in order that they may explode first to increase the effect of the outer charges4 ,all portable objects1 such as drills1 pipe connections1 tools1 etc41 have meanwhile been carried back2 the steel flooring is covered over with a layer of dbris to prevent injury from falling rock1 and to the end of the hydraulic main is screwed a brass plug pierced by five holes2 and immediately the explosions occur a valve is opened in the tunnel1 and five jets of water play upon the rock1 laying the dust and clearing the air4 ,the necessity for this was shown on one occasion when this nozzle was broken by the explosion and the water had to be turned off immediately to avoid useless waste2 on reaching the face1 the atmosphere was found to be so highly charged with dust and smoke that it was impossible to distinguish the stones at the feet1 although a lamp had been placed on the ground2 and despite the fact that the air tube was in full blast1 the men experienced great difficulty in breathing4 ,a truck is now brought up1 and four men clear a passage in front1 through the heap of dbris1 two with picks and two with shovels1 while on either side and behind are as many men as space will permit4 ,the stone is thrown either to the sides of the heading or into the wagon1 shoveling being greatly aided by the steel flooring1 which1 before the explosion1 had been laid over the rails for nearly #aj yds4 down the tunnel to receive the falling rock4 ,these steel plates are taken up when cleared1 and the wagon is pushed forward until the drilling-machine can be brought up again1 leaving the remaining dbris at the sides to be handled at leisure during the next attack4 ,the roof and side walls are1 of course1 carefully examined with the pick1 to discover and detach any loose or hanging rock4 ,the times taken for each portion of the attack in this particular antigorio gneiss are as follows3 ,bringing up and adjustment of drills1 #bj mins42 drilling1 between #a hr4 and #b hrs42 charging and firing1 #ae mins42 clearing away dbris1 #b hrs42 or for one whole attack1 between #d hrs4 and #e hrs41 resulting in an advance of #c ft4 #i in41 or a daily advance of nearly #ah ft4 ,from this it appears that the time spent in clearing away the dbris equals that taken up in drilling1 and it is in this clearing that a saving of time is likely to be effected rather than in the process of drilling4 ,many schemes have been tried1 such as a mechanical plow for making a passage2 at ,brigue1 8marinage10 or clearing by means of powerful high-pressure water-jets1 directed down the tunnel1 was tried1 but the idea is not yet sufficiently developed4 ,another series of experiments has been tried at ,brigue with regard to the utilization of liquid air as an explosive agent instead of dynamite2 and for this purpose a plant has been laid down1 consisting of one ammonia-compressor1 two air-compressors1 and two refrigerators1 furnishing gallon of liquid air per hour at an expenditure of #ag ,h4 ,p4 ,the system used is that of ,professor ,linde1 who himself directs the experiments4 ,the great difficulty experienced is that of shortening the interval of time that must elapse between the manufacture of the cartridge and its explosion4 ,the liquid oxygen1 with which the cartridge1 containing kieselguhr 7silicious earth7 and paraffin1 is saturated1 evaporates very readily1 losing power every moment2 hence the effect of each cartridge cannot be guaranteed1 and though it is an exceedingly powerful explosive when used immediately after manufacture1 no practical result has yet been obtained4 ,power ,station4--,water is abundant at either end1 and therefore hydraulic power is the motive force employed4 ,on the ,italian side1 a dam #e ft4 high has been thrown across the ,diveria at a point near the ,swiss frontier1 about #c miles above the site of the installations4 ,a portion of the water thus held back enters1 through regulating doors and gratings1 a masonry channel leading to two parallel settling tanks1 each #aaa ft4 by #af ft41 whence1 after dropping all its sand and solid matter1 the now pure water passes into the water-house1 and1 after flowing over a dam1 through a grating and past the admission doors1 enters a metallic conduit of #c-;ft4 pipes4 ,each of the settling tanks and the approach canal are provided with doors at the lower end leading direct to the river1 through which all the sand and solid matter deposited can be scoured naturally by allowing the river-water to rush freely through4 ,for this purpose the floor of the basins is on an average gradient of #a in #cj4 ,for a similar reason the river-bed just outside the entrance to the approach canal is lined with wooden planks1 from which the stones collecting behind the dam can be scoured by allowing an iron flap1 hinged at the bottom1 to change its position from the vertical to the horizontal in a gap left purposely in the dam1 so causing a rushing torrent to sweep it clean4 ,the chief levels are3 ,level of water at dam #gid4jj meters above sea level4 in water-house #gic4gj at turbines #fah4ej giving a total fall of #age4bj ms4 or #egj ft41 and a pressure of #ag4eb atmospheres4 ,the quantity of water capable of being taken from the ,diveria in winter1 when the rivers which are dependent upon the mountain snows for their supply are at their lowest1 is calculated to be #ceb gallons per second4 ,thus1 taking the fall to be diminished by friction1 etc41 to #ddj ft41 and the useful effect at #gj1 there is obtained #bjjj ,h4 ,p4 on the turbine shaft4 ,the metallic conduit varies in material according to the pressure2 thus cast-iron pipes #c ft4 in diameter and in4 thick are used up to a pressure of #b atmospheres1 from which point they are of wrought-iron4 ,the cast-iron portion has of late caused a good deal of trouble1 owing to settlement of the piers causing occasional bursts1 consequently a masonry pier has been placed under each joint of this portion4 ,the following table gives the thicknesses and diameters1 varying with the pressure3 ---------------------------------------- - ,,water ,,thickness4 ,,diameter4 ,,weight ,,pressure4 ,,per ,,yard4 --------------------------------------- ,head ,milli-,inch4,feet4,inches4 ,lbs4 in ,feet4meters4 --------------------------------------- #bdf #f #c #j #cbf #caa #g 444 #c #j #chc #cfj #h 444 #c #j #dca #cic #i 444 #c #j #dhc #dbf #aj 444 #c #j #eef #dgf #ab 444 #c #j #fea #eij #af #c #c #igg --------------------------------------- ,this pipe is supported every #cj ft4 on small masonry piers1 on the top of which is placed a block of wood hollowed out to receive the pipe1 thus allowing any movement due to the contraction and expansion of the conduit4 ,however1 to prevent this movement becoming excessive1 the pipe is passed at intervals of #cjj yds4 to #ejj yds4 through a cubical block of masonry of #ac ft4 side1 strengthened by longitudinal tie-bars4 ,five bands of angle-bar riveted round the pipe1 with their flanges embedded in the masonry1 constitute a rigid fixed point4 ,straw mats are thrown over the pipe where it is exposed to the sun4 ,the temperature of the conduit is not1 however1 found to vary greatly1 since the pipe is kept full of water4 ,to supply the rock-drills with water at a maximum pressure of #ajj atmospheres1 or #adgj lbs4 per sq4 in41 a plant of four pairs of high-pressure pumps has been laid down1 and a still larger addition is in course of erection4 ,at present1 two ,pelton turbines of #bej ,h4,p4 each1 running at #agj revolutions per minute1 drive the pumps1 by means of toothed gearing1 at #fc revolutions per minute4 ,these pumps are of very simple but strong construction1 single suction and double delivery1 entailing one suction and one delivery-valve1 both heavy and both of small lift4 ,the larger portion of the plunger has exactly double the cross-sectional area of the smaller portion1 so that in the forward stroke half of the water taken in at the last admission is pumped into the high-pressure mains1 and at the same time a fresh supply of water is sucked in4 ,during the backward stroke half of this new supply is pumped into the mains1 and the remainder enters the second chamber1 to be pumped during the next forward stroke4 ,thus the work done in the two strokes is practically the same4 ,the pumps are in pairs1 and are set at an angle of #ij1 to insure uniform pressure and uniform delivery in the mains4 ,their size varies2 but at ,iselle there are three pairs1 with a stroke of #b ft4 #b ins41 and the plungers of #b in4 and #a ins4 7approximately7 in diameter1 supplying #a4cb gallons per second4 ,to avoid injury to the valves1 the water to be pumped is taken from a stream up the mountain side1 and is passed through filter screens4 ,the high-pressure water1 after passing an accumulator1 enters the tunnel in solid drawn wrought-iron tubes1 #c ins4 in internal diameter1 in4 thick1 and in lengths of #bf ft4 ,the diameter of these mains varies with their length1 so as to avoid loss of pressure4 ,with the #abej yds4 of tunnel now driven #aj atmospheres are lost4 ,at ,brigue the installations are1 as far as possible1 identical4 ,the ,rhone water1 however1 before reaching the water-house1 is carried from the filter basins1 a distance of #b miles1 in an armored canal built upon the ,hennebique system1#i the walls and supporting beams1 of cement concrete1 being strengthened by internal tie-bars of steel4 ,the concrete struts1 resembling balks of timber at a distance1 are occasionally #ce ft4 high and #a ft4 #g ins4 square4 ,the metallic conduit is #e ft4 in diameter1 with a minimum flow of #agf cu4 ft4 per second and a total fall of #ahe ft4 ,in case water-power should be unavailable1 three semi-portable steam engines1 two of #hj ,h4,p4 and one of #fj ,h4,p41 are always kept in readiness at each end of the tunnel1 and are geared by belts to the turbine shaft4 #i ,network of steel rods embedded in concrete4 ,ventilation4--,in tunneling1 one of the most important problems to be solved is that of ventilation1 and it is for this reason that the ,simplon tunnel consists of two parallel headings with cross cuts at intervals of #bbj yds4 ,at ,brigue1 a shaft #afd ft4 deep was sunk through the overlying rock until the 8gallery of direction0 was encountered4 ,up this chimney the foul air is drawn by wood fires1 the fresh air--a volume of #ai1jjj1jjj cu4 ft4 per day1 or #ac1bjj cu4 ft4 per minute--entering by heading ,no4 #b1 penetrating up to the last cross gallery1 and returning by tunnel ,no4 #a4 ,the entrances of ,no4 #a and the 8gallery of direction10 besides those of all the intermediate cross galleries1 are closed by doors4 ,by this arrangement1 however1 fresh air does not reach the working faces2 therefore a pipe1 #h ins4 in diameter1 is led from the fresh air in ,no4 #b to within #ae yds4 of the face of each heading1 and up this pipe a draft of air is induced by means of a jet of water1 the volume to each face being #hjj cu4 ft4 per minute4 ,one single jet of water from the high-pressure mains1 with a diameter of in41 is capable of supplying over #ajjj cu4 ft4 of air per minute at the end of #afj yds4 of pipe1 and during the attack the men at the drills are in a constant breeze with the thermometer standing at #gj ,f4 ,at ,iselle1 air is blown into the entrance of heading ,no4 #b at the rate of #ad1ajj cu4 ft4 per minute by two fans driven from the turbine shaft4 ,this air travels from the fans along a pipe #ah ins4 in diameter1 till a point #ae yds4 up the tunnel is reached1 where beyond a door the pipe narrows to form a nozzle #aj ins4 in diameter4 ,this door is kept open to allow the outside air to be induced up the tunnel1 as the headings are at present only #bejj yds4 long1 giving a resistance of not quite sufficient power to cause the air to return4 ,the fresh air then travels up ,no4 #b1 crossing over the top of the 8gallery of direction10 from which it is shut off by doors1 to the last cross gallery1 returning by ,no4 #a1 and finally leaving either by the 8gallery of direction0 or by ,no4 #a4 ,a system of cooling the air and driving it on by means of a large number of water-jets will be installed in ,no4 #b where that heading crosses over the 8gallery of direction10 but at present there is no need for it4 ,the average temperature at the face is #gc ,f4 during the drilling operation1 #gf ,f4 after firing the charges1 and a maximum of #hj ,f41 lately attaining to #hf ,f4 on the south side1 with #hj ,f4 and #he ,f4 before and after firing4 ,the temperature of the rock is taken at every #aaj yds4 in holes #e ft4 deep1 and shows a gradual increase according to the depth of over-laying rock1 to the conductivity of the rock1 and to the form of the mountain surface4 ,the maximum hitherto reached on the north side is #fh ,f41 while on the south side1 although a smaller distance has been traversed1 it attains to #gi ,f41 due to the more rapid increase in depth4 ,moreover1 the temperature of the rock is observed at the permanent stations1 #eej yds4 from the entrances1 in its relation to that of the tunnel and outside air1 and though on the north side that of the rock varies almost as quickly as that of the tunnel air1 on the south it is influenced very much less4 ,a few statistics may be of interest with regard to the progress of the last three months 7taken from the trimestrial report of ,january1 #aijj74 ,at ,brigue1 where there are three drilling-machines in ,no4 #a and two in the parallel heading1 the total length excavated was #iie yds4 or #fdji cu4 yds4 in #hi working days1 the average cross-sectional area being #eg sq4 ft4 ,this required #ejg attacks and #cjff holes1 which had a total depth of #bf1fjj ft4 and #ad1gjj re-sharpenings of the drilling-tool1 with #dd1jjj lbs4 of dynamite4 ,the average time occupied in drilling was #b hrs4 #de mins41 while charging1 firing1 and clearing away the dbris took #f hrs41 #ce mins4 ,at ,brigue #fdh men and #bi horses were employed at one time in the tunnel4 ,at ,iselle the numbers were #dif men and #af horses1 working in shifts of #h hrs4 ,outside the tunnel1 in the shops1 forges1 etc41 the men work #h hrs4 to #aa hrs4 per day1 the total being #eda men at ,brigue and #cdf men at ,iselle4 ,on the ,italian side1 where the rock is very much harder1 there were three drilling-machines in each heading2 the total length excavated1 with a cross-sectional area of #fb sq4 ft41 was #ifj yds4 or #fgjj cu4 yds4 in #ia working days4 ,this required #fa1bic re-sharpened tools1 #geh attacks1 #gidj holes with a total depth of #cc1jjj ft41 and #ef1jjj lbs4 of dynamite4 ,the average time spent in drilling was #b hrs4 #ee mins41 and in charging and clearing #b hrs4 #cf mins4 ,thus1 in the hard gneiss1 to excavate #a cu4 yd4 of rock required #h lbs4 of dynamite1 and each tool pierced #f ins4 of rock before it required re-sharpening4 ,,the ,,murray ,,hill ,,tunnel4 ,the drift method of excavating tunnels was followed in ,section ,,iv of the ,new ,york ,subway1 under ,park ,avenue between #ccrd and #dast ,streets4 ,at this point the four tracks of the subway pass under a rocky elevation1 known as ,murray ,hill1 in two double track parallel tunnels1 #dc ft4 apart1 center to center4 ,here already existed a double track tunnel which was built many years ago by the ,new ,york ,central and ,hudson ,river ,r4,r41 and is now used by the ,madison ,avenue surface cars4 ,the two subway tunnels were driven close below the existing tunnel and also very near the foundations of expensive residences along ,park ,avenue1 particularly on ,murray ,hill1 one of the best residential sections of the city4 ,material ,penetrated4--,the material penetrated by the excavation consisted chiefly of a surface outcrop of the mica-schist rock which underlies ,manhattan ,island4 ,the rock was for the most part in compact strata1 dipping at about #de from ,east to ,west1 but at intervals an unstable stratum was encountered which when free slid on the underlying stratum4 ,troubles from such slides were experienced during the construction of the tunnel4 ,cross-,section4--,the cross-section selected for the tunnels had vertical side walls and a three-centered roof arch with the flattest curve at the crown4 ,the interior dimensions were #be ft4 wide and #af ft4 high4 ,the selected cross-section was not the best suited for a tunnel to be driven through rock1 where the sharpest curve should be at the top1 but in this case the flattened curve was chosen because of local conditions2 chiefly1 the presence of the existing tunnel and the consequent necessity of leaving a certain thickness of rock between it and the new tunnel1 without depressing very much the grade of the subway4 ,illustration3 ,,fig4 #eh4--,sequence of ,excavation in the ,murray ,hill ,tunnel4 ,excavation4--,the two parallel tunnels were driven exclusively from the ends reached by shafts2 thus the tunnels were attacked at four parts4 ,it was in these tunnels that a comparative test was made of the different methods of driving tunnels through rock4 ,the contractor applied the heading and drift method at the southern ends of the tunnels1 the eastern tunnel being driven by means of a drift while in the western tunnel the usual heading method was followed4 ,this latter method is illustrated in the chapter following and the eastern tunnel at #ccrd ,street1 excavated by means of a drift1 is here considered4 ,fig4 #eh shows the sequence of cuts adopted for this tunnel4 ,it was begun by a bottom drift1 about #aj ft4 high1 #h ft4 wide and #g ft4 deep1 which was located at one side of the axis of the tunnel1 as indicated in the figure4 ,this drift was immediately widened by removing the portions marked #b4 ,about #ej ft4 in the rear the part marked #c was taken away1 thus clearing the entire lower portion of the tunnel4 ,section #d1 about #ej ft4 to the rear of section #c1 was then broken down and removed4 ,the methods of drilling and blasting were as follows3 ,in taking out the original drift1 a wedge-shaped center cut was made and then enlarged to the full size of the drift by drilling parallel holes4 ,the succeeding sections1 #b and #c1 were removed by driving parallel holes1 while the top section1 #d1 was taken away by a center cut and parallel holes4 ,the drills were mounted on columns1 two drills to a column1 and the holes were usually drilled about #g ft4 deep1 starting with a diameter of #b in4 and ending with a diameter of #a in4 ,they were blasted with #dj dynamite in light charges1 only a few holes being fired at a time1 usually not more than three or four4 ,illustration3 ,,fig4 #ei4--,traveling ,platform for the ,excavation of the ,upper ,side of the ,murray ,hill ,tunnel4 ,to remove section #d1 a traveling platform #aj ft4 long and #be ft4 wide was used4 ,this platform1 as shown in ,fig4 #ei1 consisted of two longitudinal beams mounted on four double flanged wheels which were running on tracks laid #bc ft4 apart4 ,resting on top of these beams were four #ab in4 #ab in4 uprights braced in every direction against the framework of the platform4 ,this frame was built of #ab in4 #ab in4 beams laid longitudinally1 the transverse beams being #ab in4 #ad ins4 ,the platform proper was made of #c in4 planks1 and was set #i ft4 above the tunnel floor4 ,the columns supporting the drills for the excavation of the upper section #d1 were set up above the platform which was then reinforced by other vertical props1 as indicated by the dotted lines in the figure4 ,these props1 however1 were placed so as to leave a clearance beneath the platform for the cars to carry away the dbris from the front4 ,during the blasting the platform was moved back so that the blasted rock fell to the floor of the tunnel1 whence it was loaded into boxes on the cars4 ,strutting4--,when the rock was seamy and full of fissures1 running in every direction1 it was necessary to support the roof of the excavation4 ,this was done in the following manner3 ,after part #d was removed the timbers supporting the roof of the excavation were set up4 ,in this case1 the polygonal strutting was used4 ,this consisted of heavy timber frames placed transversely to the axis of the tunnel and supporting the planks or poling-boards which ran longitudinally against the roof of the excavation4 ,the seven-segment arch frame was used in the ,murray ,hill tunnel4 ,at the bottom of part #d were placed longitudinally #ab #af in4 beams and upon them rested the inclined segments which1 with a horizontal one1 formed the arch frame as shown in ,fig4 #fj4 ,when the pressures were too heavy the crown segment was reinforced by a #f #ab in4 beam1 kept in place by two #ab #ab in4 inclined props which rested on the templates4 ,as the tunnel was lined with concrete1 the timbering was left in place and it was built outside the line of the extrados of the concrete lining4 ,timbering was only used for a short distance but it necessitated a larger amount of rock excavation when it was required4 ,illustration3 ,,fig4 #fj4--,timbering ,used in the ,murray ,hill ,tunnel4 ,hauling4--,great efficiency was shown in the method of hauling away the excavated materials4 ,three narrow-gauge parallel tracks were laid on the floor of the tunnel and extended to the faces of the advance drifts4 ,small flat cars were run on these tracks4 ,they carried steel boxes1 #e ft4 square and #ae ins4 deep1 fitted with three lifting rings and chains4 ,when filled1 the cars were run to the bottom of the shaft1 the boxes were hoisted by a stiff-legged derrick placed at the shaft head1 and the dbris was dumped into storage bins of #cjj cu4 yds4 capacity4 ,these bins were elevated #h ft4 above the street so that the wagons could be driven under it to take loads of spoil by means of chutes4 ,the broken rock was loaded into the boxes by hand4 ,concrete ,lining4--,the tunnel was lined with concrete which was manufactured by a quite elaborate plant4 ,a stone crushing plant1 consisting of bins for raw and crushed stone1 was erected at the shaft head and a mixing plant was suspended from the shaft4 ,on the platform of the shaft head were two bins side by side1 one for crushed stone1 the other for sand2 both of which communicated1 by means of trap doors1 with a hopper chute4 ,the materials from the hopper were delivered into a measuring box where cement was laid on top of the other ingredients by hand4 ,they were then conveyed through a canvas chute into a cubical mixer operated by an engine4 ,the mixer discharged its contents into skips set on cars at the bottom of the shaft and the concrete was hauled inside the tunnel ready for use4 ,the construction of the lining was accomplished by means of traveling platforms4 ,the footing courses were laid first4 ,because these projected inward about #ah ins4 from the faces of the finished sidewalks it was possible to lay a track rail on their top inner edges on each side of the tunnel4 ,these track rails carried the traveling platforms4 ,there were three of these platforms2 the forward one was used for building the side walls2 the center one1 for carrying a derrick2 the last one1 for building the roof arch4 ,the side wall platform was mounted on six wheels4 ,on each side there was mounted an adjustable lagging which was curved to conform to the inside profile of the side wall4 ,in operation this platform was run to the point where the side walls were to be constructed and the lagging was adjusted to position and fastened4 ,skips of concrete were then hoisted on its top1 their contents were shoveled into the space between the lagging and the wall of the excavation and were there rammed into place until the finished concrete had reached the top of the lagging4 ,when the concrete had set1 the wedges holding the lagging in place were loosened and the platform was moved ahead and adjusted for building a new section of wall4 ,the derrick platform was #bc ft4 wide and #ah ft4 long4 ,transversely1 it had three bays1 two of which were floored over and one was left without flooring to allow passage for the concrete skips to and from the cars1 on the tunnel floor beneath4 ,at the center of the floored area was mounted a derrick to handle the skips4 ,in operation1 the derrick platform came between the side wall platform ahead and the roof platform behind4 ,the construction of the roof platform was practically the same as the side wall platform with the addition of roof arch centers at each bent on which lagging could be placed4 ,the mode of procedure was to erect the form for a small space between the side walls already built and the haunches of the center1 to shovel concrete from the skips and to run it into place4 ,then the roof lagging1 a part at a time1 was placed upward from the haunches and the concrete was filled and rammed behind it4 ,the lining was built from the haunches upward until the two sides approached within a distance of about #e ft4 from each other at the crown4 ,this #e ft4 crown strip or key was built by working from the rear toward the front end of the platform4 ,plant4--,the plant used by the contractors for ,section ,,iv4 of the subway comprised a central power plant located about #djjj ft4 from the work4 ,this was on #dbnd ,street near the ,east ,river and furnished power for the work on both ,sections ,,iv4 and ,v4 ,the buildings consisted of an engine room #fc #cj ft4 and a boiler room1 #db #bh ft4 ,in the former room was located one ,rand-,corliss air compressor1 #bb #dj #dh ins41 having a capacity of #ejjj cu4 ft4 of free air per minute2 in the latter room there were two #bjj ,h4,p4 water tube boilers4 ,there were also the necessary equipment of feed water pump1 air condenser pump1 etc4 ,the compressors discharged into a #bj #e ft4 receiver of riveted steel through a #g in4 pipe4 ,the air from the receiver was carried by a #aj in4 pipe #c4bgg ft4 to the corner of ,park ,avenue and #dast ,street1 and was thence run south along ,park ,avenue in an #h in4 pipe1 from which #c in4 branches led to the four headings of the work4 ,ventilation4--,the ventilation of the tunnel caused very little trouble4 ,in cool weather the natural draft of the shafts and the air discharged from the drills served to keep the atmosphere wholesome4 ,in warm weather1 artificial means were necessary to clear the workings of foul air1 particularly after blasting4 ,they comprised at each end a #d ft4 ,american exhaust fan drawing air from a #ab in4 riveted galvanized iron pipe1 which extended to the working faces4 ,illumination4--,the tunnel was lighted by electric lamps which extended even to the working face4 ,during the blasting1 however1 all the lamps and wires within #ajj ft4 from the front were removed and gasoline torches were used2 they were also employed before the electric lamps and wires could be replaced1 to light the tunnel during the operation of clearing the dbris4 ,,chapter ,,xi4 ,,tunnels ,,through ,,hard ,,rock 7,continued74--,,excavation ,,by ,,headings4 ,,european ,,and ,,american ,,methods4 ,the more common method of tunneling through hard rock is to begin the work by a heading1 instead of by a drift4 ,this heading may be of small dimensions1 and the remainder of the section may also be removed in successive small parts1 or it may be the full width of the section1 and the enlargement of the section be made in one other cut4 ,illustration3 ,,fig4 #fa4--;,diagram ,showing ,sequence of ,excavation in ,heading ,method of ,tunneling ,rock4 ,general ,discussion4--,when the tunnel is excavated by means of several cuts1 which is the method usually employed in ,europe1 the sequence of work is as indicated by ,fig4 #fa4 ,work is begun by driving the center top heading ,no4 #a1 whose floor is at the level of the bottom of the roof arch1 and which is usually excavated by the circular cut method4 ,this heading is widened by removing parts ,nos4 #b and #c until the top part of the section is removed1 then the roof arch is built with its feet resting on the unexcavated rock below4 ,the lower portion of the section or bench is removed by first sinking the trench ,no4 #d1 after which part ,no4 #e is taken out1 and then parts ,nos4 #f and #g1 and the side walls built4 ,part ,no4 #h for the culvert is finally opened4 ,the heading is1 as a rule1 driven far in advance1 but the excavation of each of the other parts follows the preceding one at a distance behind of about #cjj ft4 ,the strutting1 when any is required1 is usually the typical radial strutting of the ,belgian method of tunneling4 ,the masonry lining is constructed practically the same as in tunnels excavated by a drift4 ,the hauling is done on a single track laid in the heading ,no4 #a1 which separates into double tracks where the full top section has been excavated by the removal of parts ,no4 #b4 ,these two tracks are again combined and form a single track along the top of part ,no4 #e1 which has been left wider than part ,no4 #d for this particular purpose4 ,when part ,no4 #c is excavated a standard-gauge track is laid on its floor2 and as the full section of the tunnel is completed by taking out parts ,nos4 #d and #e1 this single track is replaced by two standard-gauge tracks1 into which it switches4 ,spoil is transferred from the narrow-gauge tracks on the upper level1 to the standard-gauge tracks on the tunnel floor1 by means of chutes1 and building material is transferred in the opposite direction by means of hoisting apparatus4 ,when the excavation is made by a single wide heading1 and a single other cut for removing the bench1 which is the method preferred by ,american engineers1 it is called the ,heading and ,bench method4 ,the work begins by removing a top heading the full width of the section2 this heading is usually made #g ft4 or #h ft4 high1 and is excavated by the center cut method4 ,the method of strutting usually employed is to erect successive three- or five-segment timber arches1 whose feet rest on the top of the bench2 when the bench is removed1 posts are inserted under the feet of each arch4 ,these arches are covered with a lagging of plank4 ,in ,america it has often been the practice to let this strutting serve as a temporary lining1 and to replace it only after some time1 often after years1 with a permanent lining of masonry4 ,in a succeeding chapter1 some of the methods adopted in relining timber-lined arches with masonry are described4 ,the hauling is done by either narrow or broad gauge tracks laid on the floor of the completed section below4 ,a device called a bench carriage is often employed to enable the cars running on the heading tracks to dump their loads into the cars below1 without interfering with the work on the bench front4 ,this device consists of a wide platform carried on trucks1 running on rails at the sides of the tunnel floor1 so that it is level with the floor of the heading4 ,the front of this platform carries a hinged leaf which may be raised and lowered1 and which forms a sort of gang-plank reaching to the floor of the heading4 ,by running the heading cars out on to this traveling platform1 they can be dumped into the cars below entirely clear of the work in progress on the bench front4 ,for the purpose of illustrating the two methods of driving tunnels by a heading1 which have been briefly described1 the ,st4 ,gothard and the ,fort ,george tunnels have been selected4 ,the ,st4 ,gothard tunnel is selected1 as being one of the longest tunnels in the world1 and because it was excavated by a number of small parts2 and the ,fort ,george tunnel1 as being a double-track tunnel1 driven by a heading1 and bench1 and having a concrete lining4 ,,st4 ,,gothard ,,tunnel4 ,the ,st4 ,gothard tunnel penetrates the ,alps between ,italy and ,france1 and is #i miles long4 ,it was constructed in #ahgb-hb4 ,material ,penetrated4--,the ,st4 ,gothard tunnel was excavated through rock1 consisting chiefly of gneiss1 mica-schist1 serpentine1 and hornblende1 the strata having an inclination of from #de to #ij4 ,at many points the rock was fissured1 and disintegrated easily1 and water was encountered in large quantities1 causing much trouble4 ,excavation4--,the sequence of excavation is shown by ,fig4 #ad1 p4 #cf4 ,first the top center heading1 ,no4 #a1 whose dimensions varied from #h4be #h4f ft4 to #h4e #i ft41 according to the quality of the rock1 was driven never less than #ajjj ft4 and sometimes over #cjjj ft4 in advance of parts ,no4 #b4 ,the excavation of parts ,no4 #b opened up the full top section1 and parts ,nos4 #c1 #d1 #e1 #f1 and #g1 were removed in the order numbered4 ,strutting4--,where regular strutting was required1 the construction shown in ,fig4 #fb was adopted4 ,masonry4--,the ,st4 ,gothard tunnel is lined throughout with masonry4 ,after the upper portion of the section was fully excavated1 the roof arch was built with its feet resting upon short planks on the top of the bench4 ,plank centers were used in constructing the arch4 ,for the arch brick masonry was employed1 but the side walls were built of rubble masonry4 ,shelter niches1 about #c ft4 deep1 were built into the side walls at intervals1 and about every #c1jjj ft4 storage niches about #aj ft4 deep1 and closed with a door1 were constructed4 ,the culvert was of brick masonry4 ,mechanical ,installation4--,water-power was used exclusively in driving the ,st4 ,gothard tunnel4 ,at the north end1 the ,reuss1 and at the south end1 the ,tessin and the ,tremola1 rivers or torrents were dammed1 and their waters conducted to turbine plants at the opposite ends of the tunnel4 ,the power thus furnished by the ,reuss was about #a1ejj ,h4,p41 and the power furnished by the combined supply of the ,tessin and ,tremola was #a1bbj ,h4,p4 ,the turbine plant at both ends at first consisted of four horizontal impulse turbines1 but later1 two more turbines were added at the south end4 ,each of the two sets of four turbines first installed drove five groups of three compressors each1 and the two supplementary turbines drove two groups of four compressors each4 ,the compressors were of the ,colladon type with water injection1 and four groups of three compressors each were capable of furnishing #a1jjj cu4 yds4 of air compressed to between seven and eight atmospheres every hour1 or about #ajj ,h4,p4 per hour1 delivered to the drills at the front4 ,this air when exhausted provided about #h1jjj cu4 yds4 of fresh air per hour for ventilation4 ,the compressors at each entrance discharged into a group of four cylindrical receivers of wrought-iron each #e4c ft4 in diameter by #bi4e ft4 long1 and having a capacity of #eic cu4 ft4 ,the cylinders were placed horizontally1 the first one receiving the air at one end and discharging it at the other end into the next cylinder1 and so on4 ,by this arrangement the air was drained of its moisture1 and the discharge from the end receiver into the tunnel delivery pipes was not affected by the pulsations of the compressors4 ,the delivery pipe decreased from #h in4 in diameter at the receiver to #d ins4 in diameter1 and finally to #b ins4 in diameter1 at the front4 ,the drills employed were of various patterns4 ,the first one employed was the ,dubois ,franois 8perforator10 in which the drill-bit was fed forward by hand4 ,this was replaced by ,ferroux drills having an automatic feed4 ,jules ,mc,kean's 8perforator0 was employed at the north end of the tunnel4 ,all of these drills were of the percussion type1 and were mounted on carriages running on tracks4 ,their comparative efficiency was officially tested in drilling granitic gneiss with an operating air pressure of #e4e atmospheres with the following results3 ,,name ,,of ,,drill4 ,,penetration ,,ins4 ,,per ,,min4 ,ferroux #a4f ,mc,kean #a4d ,dubois ,franois #a4jd ,soummelier #j4he ,the heading was excavated by the circular cut method1 the holes being driven as follows3 ,near the center of the heading three holes were first drilled1 converging so as to inclose a pyramid with a triangular base4 ,around these center holes from #i to #ac others were driven parallel to the tunnel axis4 ,the center holes were blasted first1 and then the surrounding holes4 ,from #c to #e hours were required to drill the two sets of holes1 and from three to four hours were required to remove the blasted rock4 ,the number of holes drilled in removing each of the various parts was as follows3 ,part ,no4 #a #f to #i ,part ,no4 #b #f to #aj ,part ,no4 #c #b ,part ,no4 #d #f to #i ,part ,no4 #e #c ,part ,no4 #f #f to #i ,part ,no4 #g #a -------- ,total for full section #cf to #dj ,hauling4--,two different systems were employed for hauling the spoil and construction material in the ,st4 ,gothard tunnel4 ,to remove the spoil from parts ,nos4 #a and #b a narrow-gauge track was laid on the floor of the heading1 and the cars were hauled by horses1 the grade being descending from the fronts4 ,these narrow-gauge cars were dumped into larger broad-gauge cars running on the track laid on the floor of the completed section and hauled by compressed air locomotives 7,fig4 #fc74 ,to raise the incoming structural material from the broad-gauge cars to the narrow-gauge cars running on the level above1 hoisting devices were employed4 ,illustration3 ,,fig4 #fb4--,method of ,strutting ,roof1 ,st4 ,gothard ,tunnel4 ,illustration3 ,,fig4 #fc4--,sketch ,showing ,arrangement of ,car ,tracks1 ,st4 ,gothard ,tunnel4 ,,fort ,,george ,,tunnel4#aj ,from a point north of #aegth ,street and ,broadway almost to ,dyckman ,street1 that is1 a distance of nearly two miles1 the ,new ,york ,subway passes under an elevation known as ,fort ,washington ,heights1 which almost bounds ,manhattan ,island at its upper end near the ,harlem ,ship ,canal4 ,under this elevation the rapid transit railroad was constructed in tunnel4 ,the tunnel was driven from two intermediate shafts over #aaj ft4 deep1 located one at #afith ,street and the other at #ahast ,street and ,broadway4 ,both shafts were sunk at one side of the center line of the tunnel4 ,after these shafts had been utilized for working purposes during the construction of the tunnel1 they were equipped with electric elevators to carry passengers from the streets to the deep station4 #aj ,condensed from a paper by ,stephen ,w4 ,hopkins in ,harvard ,engineering ,journal1 ,april1 '#jh4 ,material4--,the material encountered in the excavation of the ,fort ,george tunnel was the usual mica schist met everywhere on ,manhattan ,island4 ,it was full of seams with strata running in every direction to such an extent that at many points the roof of the tunnel had to be supported by timbers2 at other parts along the line the rock was so disintegrated that it was considered a very loose and treacherous soil4 ,two serious accidents1 each accompanied by loss of life1 occurred during the construction of this tunnel4 ,both of them were caused by the sudden fall of a large ledge of rock which1 after the tunnel had been excavated to the full section1 remained hanging on the roof1 deprived of any support and held in place by the little cohesion of the material packing the seams4 ,excavation4--,the tunnel was excavated by the heading method in only two cuts1 viz41 the heading and bench as indicated in the ,fig4 #fe4 ,the heading1 almost as wide as the upper portion of the tunnel section1 was excavated in the manner explained on page #ia4 ,after the heading was removed1 the enlargement of the entire upper section of the tunnel was accomplished by driving three inclined holes at each side of the heading4 ,they were driven at different depths and inclinations1 as shown in the figure and were called trimming holes4 ,at the same time the bench was removed by means of five holes--three vertical and two inclined4 ,the line of subgrade was reached by means of five grading holes driven almost horizontal with a slight inclination downward4 ,the air drills for the heading were mounted on columns1 all the others on tripods4 ,the blasting was done in the following order3 the grading holes were blasted in the first round1 the bench and trimming in the second1 the center cut of the heading in the third1 the sides in the fourth and the dry holes in the last4 ,thus each advance of #g ft4 of the whole tunnel section was made by means of forty holes fired in five rounds which consumed #bgg lbs4 of dynamite with an average additional quantity of #gf lbs41 making a total of #cec lbs4 ,with the exception of the center cut1 where #fj dynamite was used1 all the other holes were discharged with #dj dynamite4 ,illustration3 ,cross ,section4 ,longitudinal ,section4 ,,fig4 #fd4--;,arrangement of ,drill ,holes in the ,fort ,george ,tunnel4 ,,fig4 #fe4--,longitudinal ,section of the ,heading and ,bench ,excavation at the ,fort ,george ,tunnel4 ,strutting4--,when the rock was of such a character as to be dangerous and required permanent timber support1 until the masonry lining was in place1 the method employed was as follows3 a top heading was first excavated about #aj ft4 deep and from #aj ft4 to #ab ft4 wide for some distance1 #ajj ft4 to #ejj ft41 the dangerous rock being supported by #aj #aj in4 yellow pine plumb or raking posts and sometimes by timber bents 78caps and legs074 ,the next process was to widen the heading to the full width of #cj ft4 for a length of about #bj ft41 placing timber supports under the dangerous rock as the widening-out progressed4 ,the excavation was deepened a little at the sides to #i4e ft4 below the roof grade 7ordered line of excavation7 or about #aa ft4 below the roof grade1 which was necessary when segmental timbering was to be used1 to allow for placing a #ab #ab in4 8wall plate0 7timber sill7 along each side4 ,these wall plates1 generally #bj ft4 long1 were set to the correct elevation and were leveled by blocking and wedging4 ,as soon as the wall plates were set1 the work of erecting the segmental timber sets1 one set at a time1 was begun by starting from the wall plates and supporting the timber on scaffolding until keyed in1 then it was blocked up to the rock at each joint and at other necessary points4 ,when two or more sets were erected1 lagging1 made of boards #b ins4 thick by #f to #aj ins4 wide1 was placed over the segmental timber 8sets0 and the space above the timber dry packed with small stone placed by hand4 ,sometimes there was enough room between the timber and the rock to do all the dry packing after the full number of sets1 generally six1 had been placed on the two wall plates4 ,the temporary timber posts and braces were taken out as the segmental timber sets were erected4 ,the seven timbers that made up a timber set were of yellow pine each #aj #aj ins41 #e ft4 #b ins4 long at the intrados and #e ft4 #f ins4 at the extrados4 ,the sets were spaced from #c ft4 to #e ft4 apart1 but generally #c4e ft4 and braced to each other at each joint of the segmental timbers by #f #h in4 spreaders which were wedged against the joint splices4 ,when the timbers were all erected on a set of wall plates 7#bj ft47 and the lagging and dry packing were completed the work of taking out the bench1 which had been partly drilled as the timber sets were erected1 was resumed4 ,the face of the bench1 which had been left about #d ft4 from the end of the previous set of wall plates1 was brought forward slowly by placing #aj #aj in4 plumb posts which extended below subgrade under the wall plates4 ,these posts were generally spaced the same as the timber sets above and directly under them4 ,when the face of the bench had been brought to within #c or #d ft4 of the forward end of the wall plate1 the process of widening out and timbering another #bj ft4 length of heading was begun4 ,in some places the rock1 though needing permanent support1 was such that the work of taking out the bench and widening the heading was carried on simultaneously without increasing the danger2 but the greater portion of the work1 when strutting was required1 was done as has been described4 ,illustration3 ,,fig4 #ff4--;,diagram ,showing the ,arrangement of ,drill ,holes in the ,heading and ,bench of the ,gallitsin ,tunnel4 ,hauling4--,the excavated material was loaded at the foot of the bench in dump cars which were run by mule power to the portal or the shaft according to location1 on #cf in4 gauge-service tracks4 ,inclines at #aeith ,street were graded from the portal at #aehth ,street to the street surface4 ,the cars were formed at this portal into a train and were taken up the incline to the dump at #afbnd ,street and the ,north ,river by construction locomotives4 ,at the #afhth ,street and #ahast ,street shafts1 the cars were hoisted to the surface in cages 7elevators74 ,in the former case1 they were taken to the dump at #afeth ,street and the ,north ,river by mules and gravity2 in the latter case1 to various dumps by teams4 ,at both shafts1 stone crushers were located1 therefore a great part of the material did not have to be hauled to the dumps or even taken to the surface as a great deal of stone was used in dry packing over the concrete arch4 ,the material from the portal at ,fort ,george was hauled by mules directly to the dump near by4 ,lining4--,the entire tunnel was lined with concrete1 consisting of a floor #d ins4 thick and vertical side walls #ah ins4 thick and #be ft4 apart1 which carried a semicircular arch #ah ins4 thick except in the timbered portions where the thickness was increased to #ba ins4 and to #bd and #bg ins4 in some places4 ,the springing line of the arch is #f ft4 #b ins4 above the concrete floor 7#e ft4 #f ins4 above the base of rail71 hence the maximum clearance above the base of rail is #ah ft4 ,the side walls and arch were built solid of rock to a height of #h ft4 above springing line and the space above that point between the concrete and the rock was packed by hand with small stones4 ,the concrete of the arch was laid on timber centers erected for that purpose4 ,the heading and bench method of excavating rock tunnels is not always followed in the manner just described but is employed with slight modifications4 ,there is a large variety of modifications but only the two most commonly used in practical works are given here4 ,the heading and bench method illustrated in ,fig4 #ff was used1 among others1 on the ,gallitsin tunnel along the ,pennsylvania ,r4,r4 at the summit of the ,alleghenies near ,altoona1 ,pa41 and more recently in the tunnels constructed by the same company under ,bergen ,hill1 ,n4 ,j41 for the entrance to ,new ,york ,city4 ,the shape of the cross-section of these tunnels was semicircular arch on vertical side walls4 ,the excavation was made in three consecutive cuts1 viz41 the heading marked #a in the figure1 the top bench #b1 and the lower bench #c4 ,a heading #g ft4 high and #aj ft4 wide was attached near the crown of the arch and the rock was removed by means of a center cut and parallel side holes1 the number of holes depending upon the consistency of the rock4 ,the part ,no4 #b was excavated by drilling holes at each side to different depths and at different inclinations in order to reach the line of the profile as well as the springing line of the proposed tunnel4 ,the central part of the top bench was excavated by means of holes driven vertically from the floor of the heading4 ,the bottom bench ,no4 #c1 included between the springing line of the arch and subgrade1 was removed by means of five vertical holes driven from the floor of the top bench4 ,the three different working parts were kept nearly #aj ft4 apart4 ,blasting was effected in reversed order to the figures marked in the diagram1 viz41 the bottom bench first and the heading last4 ,illustration3 ,,fig4 #fg4--;,diagram ,showing a ,modification of the ,heading and ,bench ,method4 ,still another modification of the heading and bench method1 commonly followed by ,american engineers1 is the one shown in ,fig4 #fg4 ,this consists in dividing the tunnel section in three parts by horizontal lines4 ,the resultant parts are first the heading excavated close to the roof1 and as wide as the whole section of the tunnel2 second1 the top bench in the middle1 and lastly the bottom bench excavated to the depth of the proposed tunnel floor4 ,the excavation proceeds in the numerical order1 beginning at the heading which was excavated1 as usual1 by means of a center cut and side holes to the full width of the proposed tunnel4 ,first the top bench1 then the bottom bench1 are removed by means of vertical holes driven from the floor of the heading and the floor of the top bench1 respectively4 ,,comparison ,,of ,,methods4 ,the differences between the drift and heading methods of excavating tunnels through rock1 consist chiefly in the excavations1 strutting1 and hauling4 ,when the drift method is employed an advanced gallery is opened along the floor of the tunnel before the upper part of the section is removed1 and when the heading method is employed the upper part of the section is completely excavated before any part of the section below is excavated4 ,when the drift method of driving is employed polygonal strutting is usually used1 and longitudinal strutting is employed with the heading method of driving4 ,in the drift method the hauling is done by one system of tracks at the same level1 while in the heading method two systems of tracks are employed at different levels4 ,it is1 perhaps1 impossible to state without qualification which method is the better4 ,european engineers who have been connected with both the ,mont ,cenis and ,st4 ,gothard tunnels1 driven by the drift and heading methods respectively1 had the opportunity to practically observe the advantages and disadvantages of these two methods4 ,their conclusion was that the drift method was more convenient for tunnels driven through hard and compact rock1 and that the heading method was better for tunnels of fissured and disintegrated rocks4 ,to prove this opinion1 experiments were made in one of the tunnels approaching the great ,st4 ,gothard tunnel4 ,on a short tunnel the excavation was made by the drift method from one portal1 while at the other1 the heading method was followed4 ,although the general rule was fully confirmed still the conditions at the portals were not identical4 ,more conclusive experiments were made by ,mr4 ,ira ,a4 ,shaler1 the contractor for ,section ,,iv41 of ,new ,york ,rapid ,transit ,railway4 ,he had the opportunity of driving two parallel tunnels under ,murray ,hill only #ag ft4 apart4 ,the eastern tunnel was driven by the drift method1 the western one by the heading method4 ,after the work had proceeded for a few months1 ,mr4 ,shaler stated that in his case the drift method was more convenient4 ,he could spare drilling several holes at each advance1 thus obtaining economy in time1 labor and material without considering the advantage of a simpler transportation of the dbris4 ,he promised to publish his results for the benefit of the profession1 but1 unfortunately1 lost his life in an accident in the tunnel before the completion of the work4 ,an advantage that the drift method affords in long tunnels is1 that the water1 which is usually found in large quantities under high mountains1 is easily collected in the drift and conveyed to the culvert1 while in the heading method the water from the advance gallery1 before being collected into the culvert built on the floor of the tunnel1 must pass through all the workings4 ,this may be a serious inconvenience when water is found in large quantities1 as1 for instance1 was the case in the ,st4 ,gothard tunnel1 where the stream amounted to #eg gallons per second4 ,,chapter ,,xii4 ,,excavating ,,tunnels ,,through ,,soft ,,ground2 ,,general ,,discussion2 ,,the ,,belgian ,,method4 ,,general ,,discussion4 ,it may be set down as a general truth that the excavation of tunnels through soft ground is the most difficult task which confronts the tunnel engineer4 ,under the general term of soft ground1 however1 a great variety of materials is included1 beginning with stratified soft rock and the most stable sands and clays1 and ending with laminated clay of the worst character4 ,from this it is evident that certain kinds of soft-ground tunneling may be less difficult than the tunneling of rock1 and that other kinds may present almost insurmountable difficulties4 ,classing both the easy and the difficult materials together1 however1 the accuracy of the statement first made holds good in a general way4 ,whatever the opinion may be in regard to this point1 however1 there is no chance for dispute in the statement that the difficulty of tunneling the softer and more treacherous clays1 peats1 and sands is greater than that of tunneling firm soils and rock2 and if we describe the methods which are used successfully in tunneling very unstable materials1 no difficulty need be experienced in modifying them to handle stable materials4 ,characteristics of ,soft-,ground ,tunneling4--,the principal characteristics which distinguish soft-ground tunneling are1 first1 that the material is excavated without the use of explosives1 and second1 that the excavation has to be strutted practically as fast as it is completed4 ,in treacherous soils the excavation also presents other characteristic phenomena3 ,the material forming the walls of the excavation tends to cave and slide4 ,this tendency may develop immediately upon excavation1 or it may be of slower growth1 due to weathering and other natural causes4 ,in either case the roof of the excavations tends to fall1 the sides tend to cave inward and squeeze together1 and the bottom tends to bulge or swell upward4 ,in materials of very unstable character these movements exert enormous pressures upon the timbering or strutting1 and in especially bad cases may destroy and crush the strutting completely4 ,outside the tunnel the surface of the ground above sinks for a considerable distance on each side of the line of the tunnel4 ,methods of ,soft-,ground ,tunneling4--,there are a variety of methods of tunneling through soft ground4 ,some of these1 like the quicksand method and the shield method1 differ in character entirely1 while in others1 like the ,belgian1 ,german1 ,english1 ,austrian1 and ,italian methods1 the difference consists simply in the different order in which the drifts and headings are driven1 in the difference in the number and size of these advance galleries1 and in the different forms of strutting framework employed4 ,in this book the shield method is considered individually2 but the description of the ,belgian1 ,german1 ,english1 ,austrian1 ,italian1 and quicksand methods are grouped together in this and the three succeeding chapters to permit of easy comparison4 ,,the ,,belgian ,,method ,,of ,,tunneling ,,through ,,soft ,,ground4 ,illustration3 ,,figs4 #fh and #fh;,a4--,diagrams ,showing ,sequence of ,excavations in the ,belgian ,method4 ,the ,belgian method of tunneling through soft ground was first employed in #ahbh in excavating the ,charleroy tunnel of the ,brussels-,charleroy ,canal in ,belgium1 and it takes its name from the country in which it originated4 ,the distinctive characteristic of the method is the construction of the roof arch before the side walls and invert are built4 ,the excavation1 therefore1 begins with the driving of a top center heading which is enlarged until the whole of the section above the springing lines of the arch is opened4 ,various modifications of the method have been developed1 and some of the more important of these will be described farther on1 but we shall begin its consideration here by describing first the original and usual mode of procedure4 ,excavation4--,fig4 #fh is the excavation diagram of the ,belgian method of tunneling4 ,the excavation is begun by opening the center top heading ,no4 #a1 which is carried ahead a greater or less distance1 depending upon the nature of the soil1 and is immediately strutted4 ,this heading is then deepened by excavating part ,no4 #b1 to a depth corresponding to the springing lines of the roof arch4 ,the next step is to remove the two side sections ,no4 #c1 by attacking them at the two fronts and at the sides with four gangs of excavators4 ,the regularity and efficiency of the mode of procedure described consist in adopting such dimensions for these several parts of the section that each will be excavated at the same rate of speed4 ,when the upper part of the section has been excavated as described1 the roof arch is built1 with its feet supported by the unexcavated earth below4 ,this portion of the section is excavated by taking out first the central trench ,no4 #d to the depth of the bottom of the tunnel1 and then by removing the two side parts ,no4 #e4 ,as these side parts ,no4 #e have to support the arch1 they have to be excavated in such a way as not to endanger it4 ,at intervals along the central trench ,no4 #d1 transverse or side trenches about #b ft4 wide are excavated on both sides1 and struts are inserted to support the masonry previously supported by the earth which has been removed4 ,the next step is to widen these side trenches1 and insert struts until all of the material in parts ,no4 #e is taken out4 ,when the material penetrated is firm enough to permit1 the plan of excavation illustrated by the diagram1 ,fig4 #fh;,a1 is substituted for the more typical one just described4 ,the only difference in the two methods consists in the plan of excavating the upper part of the profile1 which in the second method consists in driving first the center top heading ,no4 #a1 and then in taking out the remainder of the section above the springing lines of the arch in one operation1 while in the first method it is done in two operations4 ,the distance ahead of the masonry to which the various parts can be driven varies from #aj ft4 to1 in some cases1 #ajj ft41 being very short in treacherous ground1 and longer the more stable the material is4 ,strutting4--,the longitudinal method of strutting1 with the poling-boards running transversely of the tunnel1 is always employed in the ,belgian method of tunneling4 ,in driving the first center top heading1 pairs of vertical posts carrying a transverse cap-piece are erected at intervals4 ,on these cap-pieces are carried two longitudinal bars1 which in turn support the saddle planks4 ,as fast as part ,no4 #b1 ,fig4 #fh1 is excavated1 the vertical posts are replaced by the batter posts ,a and ,b1 ,fig4 #fi4 ,the excavation of parts ,no4 #c is begun at the top1 the poling-boards a and b being inserted as the work progresses4 ,to support the outer ends of these poling-boards1 the longitudinals ,x and ,y are inserted and supported by the batter posts ,c and ,d4 ,in exactly the same way the poling-boards c and d1 the longitudinals ,v and ,w1 and the struts ,e and ,f1 are placed in position2 and this procedure is repeated until the whole top part of the section is strutted1 as shown by ,fig4 #fi1 the cross struts x1 y1 z1 etc41 being inserted to hold the radial struts firmly in position4 ,the feet of the various radial props rest on the sill ,m ,n4 ,these fan-like timber structures are set up at intervals of from #c ft4 to #f ft41 depending upon the quality of the soil penetrated4 ,illustration3 ,,fig4 #fi4--,sketch ,showing ,radial ,roof ,strutting1 ,belgian ,method4 ,illustration3 ,,fig4 #gj4--,sketch ,showing ,roof ,arch ,center1 ,belgian ,method4 ,centers4--,either plank or trussed centers may be employed in laying the roof arch in the ,belgian method1 but the form of center commonly employed is a trussed center constructed as shown by ,fig4 #gj4 ,it may be said to consist of a king-post truss carried on top of a modified form of queen-post truss4 ,the collar-beam and the tie-beam of the queen-post truss are spaced about #g ft4 apart1 and the posts themselves are left far enough apart to allow the passage of workmen and cars between them4 ,the tie beam of the king-post truss is clamped to the collar-beam of the queen-post truss by iron bands4 ,on the rafters of the two trusses are fastened timbers1 with their outer edges cut to the curve of the roof arch4 ,these centers are set up midway between the fan-like strutting frames previously described4 ,they are usually built of square timbers4 ,the tie beams are usually #f #f in41 and the struts and posts #d #d in4 timbers4 ,the reason for giving the larger sectional dimensions to the tie beams1 contrary to the usual practice in constructing centers1 is that it has to serve as a sill for distributing the pressure to the foundation of unexcavated soil which supports the center4 ,sometimes a sub-sill is used to support the center upon the soil2 and in any case wedges are employed to carry it1 which can be removed for the purpose of striking the center4 ,after the arch is completed1 the centers may be removed immediately1 or may be left in position until the masonry has thoroughly set4 ,in either case the leading center over which the arch masonry terminates temporarily is left in position until the next section of the arch is built4 ,masonry4--,the masonry of the roof arch1 which is the first part built1 is of necessity begun at the springing lines1 and the first course rests on short lengths of heavy planks4 ,these planks1 besides giving an even surface upon which to begin the masonry1 are essential in furnishing a bearing to the struts inserted to support the arch while the earth below them1 part ,no4 #e1 ,fig4 #fh1 is being excavated4 ,as the arch masonry progresses from the springing lines upward1 the radial posts of the strutting are removed1 and replaced by short struts resting on the lagging of the centers1 which support the crown bars or longitudinals until the masonry is in place1 when they and the poling-boards are removed1 and the space between the arch masonry and walls of the excavation is filled with stone or well-rammed earth4 ,considering now the side wall masonry1 it will be remembered that in excavating the part ,no4 #e1 ,fig4 #fh1 of the section1 frequent side trenches were excavated1 and struts inserted to take the weight of the masonry4 ,these struts are inserted on a batter1 with their feet near the center of the tunnel floor1 so that the side wall masonry may be carried up behind them to a height as near as possible to the springing lines of the arch4 ,when this is done the struts are removed1 and the space remaining between the top of the partly finished side wall and the arch is filled in4 ,this leaves the arch supported by alternate lengths or pillars of unexcavated earth and completed side wall4 ,the next step is to remove the remaining sections of earth between the sections of side wall1 and fill in the space with masonry4 ,fig4 #ga is a cross-section1 showing the masonry completed for one-half and the inclined props in position for the other half2 and ,fig4 #gb is a longitudinal section showing the pillars of unexcavated earth between the consecutive sets of inclined struts and several other details of the lining1 strutting1 and excavating work4 ,illustration3 ,,fig4 #ga4--,sketch ,showing ,method of ,underpinning ,roof ,arch with the ,side ,wall ,masonry4 ,illustration3 ,,fig4 #gb4--,longitudinal ,section ,showing ,construction by the ,belgian ,method4 ,the invert masonry is built after the side walls are completed4 ,this is regarded as a defect of this method of tunneling1 since the lateral pressures may squeeze the side walls together and distort the arch before the invert is in place to brace them apart4 ,to prevent as much as possible the distortion of the arch after the centers are removed1 it is considered good practice to shore the masonry with horizontal beams having their ends abutting against plank1 as shown by ,fig4 #ga4 ,these horizontal beams should be placed at close intervals1 and be supported at intermediate points by vertical posts1 as shown by the illustration4 ,since the roof arch rests are for some time supported directly by the unexcavated earth below1 settlement is liable1 particularly in working through soft ground4 ,this fact may not be very important so long as the settlement is uniform1 and is not enough to encroach on the space necessary for the safe passage of travel4 ,to prevent the latter possibility the centers are placed from #i ins4 to #ae ins4 higher than their true positions1 depending upon the nature of the soil1 so that considerable settlement is possible without any danger of the necessary cross-section being infringed upon4 ,in conclusion it may be noted that the lining may be constructed in a series of consecutive rings1 or as a single cylindrical mass4 ,hauling4--,since in this method of tunneling the upper part of the section is excavated and lined before the excavation of the lower part is begun1 the upper portion is always more advanced than the lower4 ,to carry away the earth excavated at the front1 therefore1 an elevation has to be surmounted2 and this is usually done by constructing an inclined plane rising from the floor of the tunnel to the floor of the heading1 as shown by ,fig4 #gb4 ,this inclined plane has1 of course1 to be moved ahead as the work advances1 and to permit of this movement with as little interruption of the other work as possible1 two planes are employed4 ,one is erected at the right-hand side of the section1 and serves to carry the traffic while the left-hand side of the lower section is being removed some distance ahead and the other plane is being erected4 ,the inclination given to these planes depends upon the size of the loads to be hauled1 but they should always have as slight a grade as practicable4 ,narrow-gauge tracks are laid on these planes and along the floor of the upper part of the section passing through the center opening mentioned before as being left in the centers and strutting4 ,in excavating the top center heading there is1 of course1 another rise to its floor from the floor of the upper part of the section4 ,where1 as is usually the case in soft soils1 this top heading is not driven very far in advance1 the earth from the front is usually conveyed to the rear in wheelbarrows1 and dumped into the cars standing on the tracks below4 ,in firm soils1 where the heading is driven too far in advance to make this method of conveyance adequate1 tracks are also laid on the floor of the heading1 and an inclined plane is built connecting it with the tracks on the next level below4 ,in place of these inclined planes1 and also in place of those between the floor of the tunnel and the level above1 some form of hoisting device is sometimes employed to lift the cars from one level to the other4 ,there are some advantages to this method in point of economy1 but the hoisting-machines are not easily worked in the darkness1 and accidents are likely to occur4 ,illustration3 ,,fig4 #gc4--;,diagram ,showing ,sequence of ,excavation in ,modified ,belgian ,method4 ,in the advanced top heading and in the upper part of the section narrow-gauge tracks are necessarily employed1 and these may be continued along the floor of the finished section1 or the permanent broad-gauge railway tracks may be laid as fast as the full section is completed4 ,in the former case the permanent tracks are not laid until the entire tunnel is practically completed2 and in the latter case1 unless a third rail is laid1 the loads have to be transshipped from the broad- to the narrow-gauge tracks or vice versa4 ,it is the more general practice to use a third rail rather than to transship every load4 ,modifications4--,considering the extent to which the ,belgian method of tunneling has been employed1 it is not surprising that many modifications of the standard mode of procedure have been developed4 ,the modification which differs most from the standard form is1 perhaps1 that adopted in excavating the ,roosebeck tunnel in ,germany4 ,this method preserves the principal characteristic of the ,belgian method1 which is the construction of the upper part of the section first2 but instead of building the side walls from the bottom upward1 they are built in small sections from the top downward4 ,the excavation begins by driving the center top heading ,no4 #a1 ,fig4 #gc1 whose floor is at the level of the springing lines of the roof arch1 and then the two side parts ,no4 #b are excavated1 opening up the entire upper portion of the section in which the roof arch is built1 as in the regular ,belgian method4 ,the next step is to excavate part ,no4 #c1 shoring up the arch at frequent intervals4 ,between these sets of shoring the side walls are built1 resting on planks on the floor of part ,no4 #c1 and then the sets of shores are removed and replaced by masonry4 ,next part ,no4 #d is excavated1 shored1 and filled with masonry as was part ,no4 #c4 ,in exactly the same way parts #e1 #f1 #g1 and #h are constructed in the order numbered4 ,to prevent the distortion of the arch during the side-wall construction it is braced by horizontal struts1 as indicated above in ,fig4 #ga4 ,advantages4--,the advantages of the ,belgian method of tunneling may be summarized as follows3 7#a7 ,the excavation progresses simultaneously at several points without the different gangs of excavators interfering with each other1 thus securing rapidity and efficiency of work2 7#b7 the excavation is done by driving a number of drifts or parts of small section1 which are immediately strutted1 thus causing the minimum disturbance of the surrounding material2 7#c7 the roof of the tunnel1 which is the part of the lining exposed to the greatest pressures1 is built first4 ,illustration3 ,,fig4 #gd4--,sketch ,showing ,failure of ,roof ,arch by ,opening at ,crown4 ,disadvantages4--,the disadvantages of the ,belgian method of tunneling may be summarized as follows3 7#a7 ,the roof arch which rests at first on compressible soil is liable to sink2 7#b7 before the invert is built there is danger of the arch and side walls being distorted or sliding under the lateral pressures2 7#c7 the masonry of the side walls has to be underpinned to the arch masonry4 ,accidents and ,repairs4--,one of the most frequent accidents in the ,belgian method of tunneling is the sinking of the roof arch owing to its unstable foundation on the unexcavated soil of the lower portion of the section4 ,the amount of settlement may vary from a few inches in firm soil to over #b ft4 in loose soils4 ,to counteract the effect of this settlement it is the general practice to build the arch some inches higher than its normal position4 ,when the settlement is great enough to infringe seriously upon the tunnel section1 repairs have to be made2 and the only way of accomplishing them is to demolish the arch and rebuild it from the side walls4 ,it is usually considered best not to demolish the arch until the invert has been placed1 so that no further disturbance is likely to occur once the lining is completed anew4 ,the rotation of the arch about its keystone1 or the opening of the arch at the crown1 by the squeezing inward of the haunches by the lateral pressures1 is another characteristic accident4 ,fig4 #gd shows the nature of the distortion produced2 the segments of the arch move toward each other by revolving on the intradosal edges of the keystone1 which are broken away and crushed together with the operation1 while the extradosal edges are opened4 ,it is to prevent this occurrence that the horizontal struts shown in ,fig4 #ga are employed4 ,the manner of repairing this accident differs1 depending upon the extent of the injury4 ,when the intradosal edges of the keystone are but slightly crushed1 the repairing is done as directed by ,fig4 #ge4 ,when the keystone is completely crushed1 however1 the indications are that the material of the keystone1 usually brick1 is not strong enough to resist the pressures coming upon it1 and it is advisable to substitute a stronger material in the repairs1 and a stone keystone is constructed as shown by ,fig4 #ge4 ,the middle stone of this keystone extends through the depth of the arch ring1 and the two side stones only half-way through1 their purpose being merely to resist the crushing forces which are greatest at the intrados4 ,sometimes1 when the pressures are unsymmetrical1 the arch ring breaks at the haunches as well as the crown1 as shown by ,fig4 #ge1 which also indicates the mode of repairing4 ,this consists in demolishing the original arch1 and rebuilding it with stone voussoirs inserted in place of the brick in which the rupture occurred4 ,illustration3 ,,fig4 #ge4--,sketches ,showing ,methods of ,repairing ,roof ,arch ,failures4 ,,chapter ,,xiii4 ,,the ,,german ,,method--,,excavating ,,tunnels ,,through ,,soft ,,ground 7,continued72 ,,baltimore ,,belt ,,line ,,tunnel4 ,the ,german method of tunneling was first used in #ahjc in constructing the ,st4 ,quentin ,canal4 ,in #ahcg the ,knigsdorf tunnel of the ,cologne and ,aix la ,chapelle ,r4,r4 was excavated by the same method4 ,the success of the method in these two difficult pieces of soft-ground tunneling led to its extensive adoption throughout ,germany1 and for this reason it gradually came to be designated as the ,german method4 ,briefly explained the method consists in excavating first an annular gallery in which the side walls and roof arch are built complete before taking out the center core and building the invert4 ,illustration3 ,,fig4 #gf4--;,diagrams ,showing ,sequence of ,excavation in ,german ,method of ,tunneling4 ,excavation4--,the excavation of tunnels by the ,german method is begun either by driving two bottom side drifts or by driving a center top heading4 ,fig4 #gf shows the mode of procedure when bottom side drifts are used to start the work4 ,the two side drifts ,no4 #a are made from #g ft4 to #h ft4 wide1 and about one-third the total height of the full section2 the width of each heading has to be sufficient for the construction of the masonry and strutting1 and for the passage of narrow spoil cars alongside them4 ,these drifts are increased in height to the springing line of the arch by taking out the two drifts ,no4 #b4 ,next the top center heading ,no4 #c is driven1 and finally the two haunch headings ,no4 #d are excavated4 ,the center core ,no4 #e is utilized to support the strutting until the side walls and roof arch are completed1 when it is broken down and removed4 ,in case of very loose material1 where the first side drifts cannot be carried as high as one-third the height of the section1 it is the common practice to make them about one-fourth the height1 and to take out the side portions of the annular gallery in three parts1 as shown by ,fig4 #gf4 ,illustration3 ,,fig4 #gg4--;,diagram ,showing ,sequence of ,excavations in ,water ,bearing ,material1 ,german ,method4 ,the top center heading plan of commencing the excavation is usually employed in firm materials or when a vein of water is encountered in the upper part of the section4 ,in the latter contingency a small bottom drift ,a1 ,fig4 #gg1 is first driven to serve as a drain2 but in any case the excavation proper of the tunnel consists in first driving the center top heading ,no4 #a1 and then by working both ways along the profile parts1 ,nos4 #b1 #c1 #d1 and #e are removed4 ,part ,no4 #f is left to support the strutting until the side walls and roof arch are built1 when it is also excavated4 ,strutting4--,when the excavation is begun by bottom side drifts these drifts are strutted by erecting vertical posts close against the sides of the drift and placing a cap-piece transversely across the roof of the drift4 ,the side posts are usually supported by sills placed across the bottom of the drift4 ,these frameworks of posts1 cap1 and sill are erected at short intervals1 and the roof1 and1 if necessary1 the sides of the drift between them1 are sustained by means of longitudinal poling-boards extending from one frame to the next4 ,the cap-pieces of the strutting for the bottom drifts serve as sills for the exactly similar strutting of the heading next above4 ,to support the additional weight1 and to allow the construction of the side walls1 the strutting of the bottom drifts is strengthened by inserting an intermediate post between the original side posts of each frame4 ,these intermediate posts are not inserted at the center of the frames or bents1 but close to the wall masonry line as shown by ,fig4 #gh4 ,this eccentric position of the post avoids any interference with the hauling1 and also allows the removal of the adjacent side post when the masonry is constructed4 ,illustration3 ,,fig4 #gh4--,sketch ,showing ,work of ,excavating and ,timbering ,drifts and ,headings4 ,illustration3 ,,fig4 #gi4--,sketch ,showing ,method of ,roof ,strutting4 ,two methods of strutting the soffit of the excavation are employed1 one being a modification of the longitudinal system employed in the ,english method of tunneling described in a succeeding chapter1 and the other a modification of the ,belgian system previously described4 ,fig4 #gi shows the method of employing the radial strutting of the ,belgian system4 ,at the beginning the center top heading is strutted with rectangular bents such as are employed for strutting the drifts4 ,as this heading is enlarged by taking out the haunch sections1 radial posts are inserted1 as shown by ,fig4 #gi1 which also indicates the method of strutting the side trenches when the excavation is carried downward from the center top heading instead of upward from bottom side drifts4 ,masonry4--,whatever plan of excavation or strutting is employed1 the construction of the masonry lining in the ,german method of tunneling begins at the foundations of the side walls and is carried upward to the roof arch4 ,the invert1 if one is required1 is built after the center core of earth is removed4 ,centering4--,tunnel centers are generally employed in the ,german method of tunneling1 a common construction being shown by ,fig4 #hj4 ,it is essentially a queen-post truss1 the tie beam of which rests on a transverse sill as shown by the illustration4 ,the transverse sill is supported along its central portion by the unexcavated center core of earth1 and at its ends either directly on the vertical posts or on longitudinal beams resting on these posts4 ,the diagonal members of the queen-post truss form the bottom chords of small king-post trusses which are employed to build out the exterior member of the center to a closer approximation to the curve of the arch4 ,illustration3 ,,fig4 #hj4--,sketch ,showing ,roof ,arch ,centers and ,arch ,construction4 ,hauling4--,when the bottom side drift plan of excavation is employed1 the spoil from the front of the drift is removed in narrow-gauge cars running on a track laid as close as practicable to the center core4 ,these same cars are also employed to take the spoil from the drifts above1 through holes left in the ceiling strutting of the bottom drifts4 ,the spoil from the soffit sections may be removed by the same car lines used in excavating the drifts1 or a narrow-gauge track may be laid on the top of the center core for this special purpose4 ,in the latter case the soffit tracks are usually connected by means of inclined planes with the tracks on the bottoms of the side drifts4 ,generally1 however1 the separate soffit car line is not used unless the material is of such a firm character that the headings and drifts can be carried a great distance ahead of the masonry work4 ,with the center top heading plan of beginning the excavation1 the car track has1 of course1 to be laid on the top of the center core4 ,the center core itself is removed by means of car tracks along the floor of the completed tunnel4 ,advantages and ,disadvantages4--,like the ,belgian method of tunneling1 the ,german method has its advantages and disadvantages4 ,since the excavation consists at first of a narrow annular gallery only1 the equilibrium of the earth is not greatly disturbed1 and the strutting does not need to be so heavy as in methods where the opening is much larger4 ,the undisturbed center core also furnishes an excellent support for the strutting1 and for the centers upon which the roof arches are built4 ,another important advantage of the method is that the construction of the masonry lining is begun logically at the bottom1 and progresses upward1 and a more homogeneous and stable construction is possible4 ,the great disadvantage of the method is the small space in which the hauling has to be done4 ,the spoil cars practically fill the narrow drifts in passing to and from the front1 and interfere greatly with the work of the carpenters and masons4 ,another objection to the method is that the invert is the very last portion of the lining to be built4 ,this may not be a serious objection in reasonably compact and stable materials1 but in very loose soils there is always the danger of the side walls being squeezed together before the invert masonry is in position to hold them apart4 ,altogether the difficulties are of a character which tend to increase the expense of the method1 and this is the reason why to-day it is seldom used even in the country where it was first developed1 and for some time extensively employed4 ,for repairing accidents1 such as the caving in of completed tunnels1 the ,german method of tunneling is frequently used1 because of the ease with which the timbering is accomplished4 ,in such cases the cost of the method used cuts a small figure1 so long as it is safe and expeditious4 ,,baltimore ,,belt ,,line ,,tunnel4 ,in the last few years a modification of the ,german method was used in this country for the construction of several railroad tunnels4 ,the modification consists in excavating the two-side drifts up to the springing line of the arch of the proposed tunnel4 ,then a central heading1 which is afterward enlarged to the whole section of the tunnel1 is excavated close to the crown4 ,at the same time the masonry is constructed from the foundation up in the side drifts4 ,from the floor of the upper section already excavated and strutted1 the top of the masonry of the drifts is reached by means of small side cuts2 thus the lining is made continuous up to the keystone4 ,the central nucleus or bench is removed after the tunnel has been lined4 ,the most important tunnel excavated by this method was the ,baltimore ,belt ,line tunnel described as follows3 ,the ,baltimore ,belt ,ry4 ,co4 was organized in #ahij by officials of the ,baltimore ,ohio1 and ,western ,maryland railways1 and ,baltimore ,capitalists1 to build #g miles of double track railway1 mostly within the city limits of ,baltimore4 ,this railway was partly open cut and embankment1 and partly tunnel1 and its object was to afford the companies named facilities for reaching the center of the city with their passengers and freight4 ,to carry out the work the ,maryland ,construction ,co4 was organized by the parties interested1 and in ,september1 #ahij1 this company let the contract for construction to ,ryan ,mc,donald of ,baltimore1 ,md4 ,the chief difficulties of the work centered in the construction of the ,howard-street tunnel1 #hcej ft4 long1 running underneath the principal business section of the city4 ,material ,penetrated4--,the soil penetrated by the tunnel was of almost all kinds and consistencies1 but was chiefly sand of varying degrees of fineness penetrated by seams of loam1 clay1 and gravel4 ,some of the clay was so hard and tough that it could not be removed except by blasting4 ,rock was also found in a few places4 ,for the most part1 however1 the work was through soft ground1 furnishing more or less water1 which necessitated unusual precautions to avoid the settling of the street1 and consequent damage to the buildings along the line4 ,a large quantity of water was encountered4 ,generally this water could be removed by drainage and pumps1 and the earth be prevented from washing in by packing the space between the timbering with hay or other materials4 ,at points where the inflow was greatest1 and the earth was washed in despite the hay packing1 the method was adopted of driving #f-;in4 perforated pipes into the sides of the excavation1 and forcing cement grout through them into the soil to solidify it4 ,these pipes penetrated the ground about #aj ft41 and the method proved very efficient in preventing the inflow of water4 ,excavation4--,the excavation was carried out according to the ,german method of tunneling4 ,bottom side drifts were first driven1 and then heightened to the springing line of the roof arch4 ,next a center top heading was driven1 and the haunch sections taken out4 ,the object of beginning the excavations by bottom side drifts1 was to drain the soil of the upper part of the section4 ,the center core was removed after the side walls and roof arch were completed1 its removal being kept from #ej ft4 to #ge ft4 to the rear of the advanced heading4 ,the dimensions of the side drifts proper were about #h #h ft41 but they were often carried down much below the floor level to secure a solid foundation bed for the side walls4 ,strutting4--,the side drifts were strutted by means of frames composed of two batter posts resting on boards1 and having a cap-piece extending transversely across the roof of the drift4 ,these frames were spaced about #d ft4 apart4 ,the excavation was advanced in the usual way by driving poling-boards at the top and sides1 with a slight outward and upward inclination1 so that the next frame could be easily inserted leaving space enough between it and the sheeting to permit the next set of poling-boards to be inserted4 ,these poling-boards were driven as close together as practicable so as to prevent as much as possible the inflow of water and earth4 ,illustration3 ,,fig4 #ha4--,sketch ,showing ,method of ,excavating and ,strutting ,baltimore ,belt ,line ,tunnel4 ,the center top heading was strutted in the same manner as were the side drifts4 ,the arrangement of the strutting employed in enlarging the center top heading is shown clearly by ,fig4 #ha1 which also shows the manner of strutting the side drifts and face of the excavation1 and of building the masonry4 ,centers4--,both wood and iron centers were employed in building the roof arch4 ,the timber centering was constructed of square timbers1 as shown by ,fig4 #hb4 ,this construction of the iron centers is shown by ,fig4 #hc4 ,each of the iron centers consisted of two #f #f in4 angles butted together1 and bent into the form of an arch rib4 ,six of these ribs were set up #d ft4 apart4 ,they were made of two half ribs butted together at the crown1 and were held erect and the proper distance apart by spacing rods4 ,the rearmost rib was held fast to the completed arch masonry1 and in turn supported the forward ribs while the lagging was being placed4 ,illustration3 ,,fig4 #hb4--,roof ,arch ,construction with ,timber ,centers1 ,baltimore ,belt ,line ,tunnel4 ,masonry4--,the side walls of the lining were built first in the bottom side drifts1 as shown by ,fig4 #ha4 ,they were generally placed on a foundation of concrete1 from #a ft4 to #b ft4 thick4 ,as a rule the side walls were not built more than #bj ft4 in advance of the arch1 but occasionally this distance was increased to as much as #ij ft4 ,the roof arch consisted ordinarily of five rings of brick1 but at some places in especially unstable soil eight rings of brick were employed4 ,the arch was built in concentric sections about #ah ft4 in length4 ,all the timber of the strutting above the arch and outside of the side walls was left in place1 and the voids were filled with rubble masonry laid in cement mortar4 ,it required about #abe mason hours to build an #ah-;ft4 arch section4 ,figs4 #hb and #hc show various details of the masonry arch work4 ,illustration3 ,,fig4 #hc4--,roof ,arch ,construction with ,iron ,centers1 ,baltimore ,belt ,line ,tunnel4 ,owing to the very unstable character of the soil1 considerable difficulty was experienced in building the masonry invert4 ,the process adopted was as follows3 ,two parallel #ab #ab in4 timbers were first placed transversely across the tunnel1 abutting against longitudinal timbers or wedges resting against the side walls4 ,short sheet piles were then driven into the tunnel bottom outside of these timbers1 forming an inclosure similar to a cofferdam1 from which the earth could be excavated without disturbing the surrounding ground4 ,the earth being excavated1 a layer of concrete #h ins4 thick was placed1 and the brick masonry invert constructed on it4 ,in less stable ground each of the above described cofferdams was subdivided by transverse timbers and sheet piling into three smaller cofferdams4 ,here the masonry of the middle section was first constructed1 and then the side sections built4 ,where the ground was worst1 still more care was necessary1 and the bottom had to be covered with a sheeting of #a-;in4 plank held down by struts abutting against the large transverse timbers4 ,the invert masonry was constructed on this sheeting4 ,refuge niches #i ft4 high1 #c ft4 wide1 and #ae ins4 deep were built in the side walls4 ,accidents4--,in this tunnel1 owing to the quick striking of the centers1 it was found that the masonry lining flattened at the crown and bulged at the sides4 ,this was attributed to the insufficient time allowed for the mortar to set in the rubble filling4 ,earth packing was tried1 but gave still worse results4 ,finally dry rubble filling was adopted1 with satisfactory results4 ,there was necessarily some sinking of the surface4 ,this resulted partly from the necessity of changing and removing of the timbers1 and from the compression and springing of the timbers under the great pressures4 ,the crown of the arch also settled from #b ins4 to #f ins41 due to the compression of the mortar in the joints4 ,the maximum sinking of the surface of the street over the tunnel was about #ah ins42 it usually ran from #a to #ab ins4 ,some damage was done to the water and gas mains4 ,this damage was not usually serious1 but it of course necessitated immediate repairs1 and in some instances it was found best to reconstruct the mains for some distance4 ,at one point along the tunnel where very treacherous material was found1 the surface settlement caused the collapse of an adjacent building1 and necessitated its reconstruction4 ,,chapter ,,xiv4 ,,the ,,full ,,section ,,method ,,of ,,tunneling3 ,,english ,,method2 ,,american ,,method2 ,,austrian ,,method4 ,,english ,,method4 ,the ,english method of tunneling through soft ground1 as its name implies1 originated in ,england1 where1 owing to the general prevalence of comparatively firm chalks1 clays1 shales1 and sandstones1 it has gained unusual popularity4 ,the distinctive characteristics of the method are the excavation of the full section of the tunnel at once1 the use of longitudinal strutting1 and the alternate execution of the masonry work and excavation4 ,in ,america the method is generally designated as the longitudinal bar method1 owing to the mode of strutting1 which has gained particular favor in ,america1 and is commonly employed here even when the mode of excavation is distinctively ,german or ,belgian in other respects4 ,illustration3 ,,fig4 #hd4--;,diagram ,showing ,sequence of ,excavation in ,english ,method of ,tunneling4 ,excavation4--,although1 as stated above1 the distinctive characteristic of the ,english method is the excavation of the full section at once1 the digging is usually started by driving a small heading or drift to locate and establish the axis of the tunnel1 and to facilitate drainage in wet ground4 ,these advance galleries may be driven either in the upper or in the lower part of the section1 as the local conditions and choice of the engineer dictate4 ,whether the advance gallery is located at the top or at the bottom of the section makes no difference in the mode of enlarging the profile4 ,this work always begins at the upper part of the section4 ,a center top heading is driven and strutted by erecting posts carrying longitudinal bars supporting transverse poling-boards4 ,this heading is immediately widened by digging away the earth at each side1 and by strutting the opening by temporary posts resting on blocking1 and carrying longitudinal bars supporting poling-boards4 ,this process of widening is continued in this manner until the full roof section1 ,no4 #a1 ,fig4 #hd1 is opened1 when a heavy transverse sill is laid1 and permanent struts are erected from it to the longitudinal bars1 the temporary posts and blocking being removed4 ,the excavation of part ,no4 #b then begins by opening a center trench and widening it on each side1 temporary posts being erected to support the sill above4 ,as soon as part ,no4 #b is fully excavated1 a second transverse sill is placed below the first1 and struts are placed between them4 ,the excavation of part ,no4 #c is carried out in exactly the same manner as was part ,no4 #b4 ,the lengths of the various sections1 ,nos4 #a1 #b1 and #c1 generally run from #ab ft4 to #bj ft41 depending upon the character of the soil4 ,strutting4--,the strutting in the ,english method of tunneling consists of a transverse framework set close to the face of the excavation1 which supports one end of the longitudinal crown bars1 the other ends of which rest on the completed lining4 ,the transverse framework is composed of three horizontal sills arranged and supported as shown by ,fig4 #he4 ,the bottom sill ,a is carried by vertical posts resting on blocking on the floor of the excavation4 ,from the bottom sill vertical struts rise to support the middle sill ,b4 ,the top sill1 or miners' sill ,c1 is carried by vertical posts or struts rising from the middle sill ,b4 ,the vertical struts are usually round timbers from #f ins4 to #h ins4 in diameter2 and the sills are square timbers of sufficient section to carry the vertical loads1 and generally made up of two posts scarf-jointed and butted to permit them to be more easily handled4 ,in firm soils the struts between the sills are all set vertically1 but those at the extreme sides of the roof section are inclined4 ,in loose soils1 however1 where the sides of the excavation must be shored1 the ,v-bracing shown by ,fig4 #he is employed between one or more pairs of sills as the conditions necessitate4 ,the manner of holding the transverse framework upright is explained quite clearly by ,fig4 #he2 inclined props extending from the completed masonry to the sills of the framework being employed4 ,two props are used to each sill4 ,sometimes1 in addition to the props shown1 another nearly horizontal prop extends from the crown of the arch masonry to the middle piece of the strutting4 ,illustration3 ,,fig4 #he4--,sketches ,showing ,construction of ,strutting1 ,english ,method4 ,referring to ,fig4 #he1 it will be observed that the longitudinal crown bars are above the extrados of the roof arch4 ,when1 therefore1 the lining masonry has been completed close up to the transverse framework1 the latter is removed1 leaving the crown bars resting on the arch masonry2 and excavation1 which has been stopped while the masonry was being laid1 is continued for another #ab ft4 to #bj ft41 and the transverse framework is erected at the face1 and braced or propped against the completed lining as shown by ,fig4 #he4 ,the next step is to place the crown bars1 and this is done by pulling them ahead from their original position over the masonry of the completed section of the roof arch4 ,it will be understood that the crown bars are not pulled ahead their full length at one operation1 but are advanced by successive short movements as the excavation progresses1 their outer ends being supported by temporary posts until the transverse framework is built at the face of the excavation4 ,centers4--,two standard forms of centers are employed in the ,english method of tunneling1 as shown by ,figs4 #hf and #hg4 ,both consist of an outer portion1 constructed much like a typical plank center1 which is strengthened against distortion by an interior truss framework4 ,the elemental members of this truss framework take the form of a queen-post truss1 as is shown more particularly by ,fig4 #hf4 ,in ,fig4 #hg the queen-post truss construction is less easily distinguished1 owing to the cutting of the bottom tie-beam and other modifications1 but it can still be observed4 ,the possibility of cutting the tie-beam as shown in ,fig4 #hg1 without danger1 is due to the fact that the lateral pressures on the haunches of the center counteract the tendency of the center to flatten under load1 which is usually counteracted by the tie-beam alone4 ,the object of cutting the tie-beam is to afford room for the props running from the completed masonry to the transverse framework of the strutting as shown by ,fig4 #he4 ,illustration3 ,,figs4 #hf and #hg4--,sketches of ,typical ,timber ,roof-,arch ,centers1 ,english ,method4 ,generally four or five centers are used for each length of arch built4 ,they are set up so that the tie-beams rest on double opposite wedges carried by a transverse beam below4 ,this transverse beam in turn rests on another transverse beam which is supported by posts carried on blocking on the invert masonry4 ,it is usually made with a butted joint at the middle to permit its removal1 since it is so long that the masonry has to be built around its extreme ends4 ,the lagging is of the usual form1 and rests on the exterior edges of the curved upper member of the centers4 ,masonry4--,in the ,english method of tunneling1 the masonry begins with the construction of the invert1 and proceeds to the crown of the arch4 ,the lining is built in lengths1 or successive rings1 corresponding to the length of excavation1 which1 as previously stated1 is from #ab ft4 to #bj ft4 ,each ring or length of lining terminates close to the transverse strutting frame erected at the face of the excavation4 ,work is first begun on the invert at the point where the preceding ring of masonry ends1 and is continued to the transverse strutting frame at the front of the excavation4 ,as fast as the invert is completed1 work is begun on the side walls4 ,in very loose soils the longitudinal bars supporting the sides of the excavation are removed after the side walls are built2 but in firmer soils they may be taken out one by one just ahead of the masonry1 or in very firm soils it may be possible to remove them entirely before beginning the side walls4 ,in all cases it is necessary to fill the space between the masonry and the walls of the excavation with riprap or earth4 ,to build the roof arch the centers are first erected as described above1 and the crown bars are removed as previously described by pulling them ahead after the arch ring is completed4 ,as with the side walls1 the vacant space between the arch ring and the roof of the excavation must be filled in4 ,usually earth or small stones are used for filling2 but in very loose soils it is sometimes the practice not to remove the poling-boards1 but to support them by short brick pillars resting on the arch ring and then to fill around these pillars4 ,hauling4--,to haul away the material and take in supplies1 tracks are laid on the invert masonry4 ,generally the permanent tracks are laid as fast as the lining is completed4 ,a short section of temporary track is used to extend this permanent track close to the work of the advanced drift4 ,advantages and ,disadvantages4--,the great advantage of the ,english method of tunneling is that the masonry lining is built in one piece from the foundations to the crown1 making possible a strong1 homogeneous construction4 ,it also possesses a decided advantage because of the simple methods of hauling which are possible3 there being no differences of level to surmount1 no hoisting of cars nor trans-shipments of loads are necessary4 ,the chief disadvantage of the method is that the excavators and masons work alternately1 thus making the progress of the work slower perhaps than in any other method of tunneling commonly employed under similar conditions4 ,this disadvantage is overcome to a considerable extent when the tunnel is excavated by shafts1 and the work at the different headings is so arranged that the masons or excavators when freed from duty at one heading may be transferred to another where excavation or lining is to be done as the case may be4 ,another disadvantage of the ,english method arises from the excavation of the full section at once1 which in unstable soils necessitates strong and careful strutting1 and increases the danger of caving4 ,the fact also that the arch ring has to carry the weight of the crown bars1 and their loading at one end while the masonry is green1 increases the chances of the arch being distorted4 ,conclusion4--,the ,english method of tunneling in its entirety is confined in actual practice pretty closely to the country from which it receives its name4 ,a possible extension of its use more generally is considered by many as likely to follow the development of a successful excavating machine for soft material4 ,the space afforded by the opening of the full section at once1 especially adapts the method to the use of excavators like1 for example1 the endless chain bucket excavator used on the ,central ,london ,ry41 and illustrated in ,fig4 #aa4 ,the method also furnishes an excellent opportunity for electric hauling and lighting during construction4 ,the ,english method of tunneling has been used in building the ,hoosac1 ,musconetcong1 ,allegheny1 ,baltimore and ,potomac1 and other tunnels in ,america4 ,the names of the ,european tunnels built by this method are too numerous to mention here4 ,,american ,,method4 ,in this country tunnels through loose soils are excavated according to the 8,crown ,bar0 or ,american ,method4 ,this consists in opening the whole section of the tunnel before the construction of the lining as in the ,english ,method4 ,it differs from the ,english method1 however1 in that many timber structures are erected for the support of the roof1 and that the excavation and construction of the lining are far apart1 so allowing the miners and the masons to work continuously and without interfering with each other4 ,illustration3 ,,fig4 #hh4--,sequence of ,excavation in the ,american ,method4 ,illustration3 ,section ,a-,b4 ,,fig4 #hi4--,strutting the ,heading in the ,american ,method4 ,illustration3 ,section ,c-,d4 ,,fig4 #ij4--,temporary ,timbering of the ,roof in the ,american ,method4 ,illustration3 ,section ,e-,f4 ,,fig4 #ia4--,showing ,crown ,bars ,supported by ,segmental ,arches4 ,excavation4--,the diagram in ,fig4 #hh shows the sequence of excavation4 ,the work begins by driving a central heading usually #g #h ft41 strutted by means of vertical or batter posts and cap-piece4 ,fig4 #hi1aa the props resting on foot blocks4 ,between the cap-pieces of the consecutive frames are placed planks driven upward at a slightly inclined angle4 ,after the heading has been excavated and strutted1 the floor is lowered by removing the part marked #b in the figure4 ,the two batter posts supporting the cap-piece are now substituted by two longer ones resting on the floor of part #b and abutting against longitudinal beams which are inserted underneath the cap-pieces4 ,these longitudinal beams are called crown bars4 ,the new batter posts are resting either on foot blocks or sills according to the quality of soil and they are strongly wedged to the crown bars4 ,on each side of these crown bars are inserted poling-boards or planks close to each other1 which are driven downward4 ,the part marked #c in the figure is removed by enlarging the cut #a #b on both sides4 ,the plank1 inserted above the crown bar1 is driven in either preceding or following the excavation and another crown bar is inserted at the end of this plank4 ,this second crown bar is supported by a prop whose other end abuts against the foot of the rafter strutting the heading4 ,between this crown bar and the roof of the excavation1 other planks are placed transversally to the axis of the tunnel and are driven in until they are supported by a new crown bar1 etc4 ,the various props supporting the crown bars are placed radially or in a fan-like manner1 similar to the characteristic arrangement of the timbering in the ,belgian method4 ,bracers to strengthen the timbering and the roof of the excavation are inserted longitudinally between the various posts and transversally between the crown bars1 ,fig4 #ij4 ,as a rule1 only three or four of these radial structures are temporarily erected4 ,a trench is excavated at the side of the part marked #c in the figure to receive the wall plate which is a heavy timber laid on the floor parallel to the longitudinal axis of the tunnel4 ,on the wall plates are erected the arched timber sets composed of five or seven segments of hewn timbers so as to form a polygonal frame which is wedged to the crown bars and which will support the arch of the roof4 ,after one of these segmental timber sets is erected the temporary radial structure is removed and the upper section of the tunnel is cleared of any obstruction as the pressures are transferred to the wall plates1 ,fig4 #ia4 ,the bench marked #d in the figure is taken away and the vertical props inserted under the wall plates1 ,fig4 #ib4 #aa ,figs4 #hi to #ia are taken from a paper by ,s4 ,w4 ,hopkins in ,harvard ,engineering ,journal1 ,april1 '#jc1 on the ,fort ,george tunnel4 ,illustration3 ,section ,g-,h4 ,longitudinal ,section4 ,,fig4 #ib4--,transversal and ,longitudinal ,section of a ,tunnel ,excavated and ,strutted ,according to the ,american ,method4 ,strutting4--,the longitudinal strutting is used in connection with the ,american method of tunneling4 ,in fact1 the strutting consists of a series of longitudinal bars supporting planks laid transversally to the axis of the tunnel and abutting against the roof of the excavation4 ,these crown bars during the excavations and immediately after are temporarily supported by radial timbers forming almost a fan-like structure1 but this is soon substituted by a permanent one composed of a polygonal timber frame of five or seven segments which are cut to dimensions4 ,the batter posts of the heading1 the radial posts of the temporary timber structure and the crown bars are all round timbers from #aj to #ab ins4 in diameter4 ,all the other timbers are square edged1 the usual dimensions being #aj #aj ins4 or #ab #ab ins4 with the exception of the wall plates which are #ad #ad ins4 ,the dimensions of the various members of the strutting and the distance apart of the different frames vary with the quality of the soil4 ,for instance1 in ordinary loose soils the frames are placed between #d to #f ft41 but in very soft soils they are erected only #c or #c ft4 apart4 ,chiefly in the southwest1 in tunnels excavated according to the ,american method1 the timbering has been left as regular lining and it was only after many years when this temporary structure had decayed or was burned down1 that the tunnels were lined with masonry4 ,but in many instances the whole timber structure was left in place even when the tunnel was lined with masonry immediately after the excavation had been made4 ,this was usually done when the tunnel was lined with concrete masonry4 ,in such a case the timbering was left to support the pressures of the roof while the concrete was plastic and before it hardened4 ,centers4--,in the ,american method the whole section of the tunnel is open before the construction of the lining1 thus the masonry can be built from the foundations up4 ,the centers are designed so as to support only the weight of the masonry during its construction and not the pressures of the tunnel as in the other methods and consequently they are of light construction4 ,the centers described in the ,murray ,hill tunnel1 page #abc1 may be advantageously used in building the concrete lining in tunnels through loose soils excavated by the ,american method4 ,hauling4--,the excavation of the heading and the upper section of the tunnel is usually far ahead of the bench1 consequently the hauling of both the dbris and the building materials is made at two different levels1 viz41 on the bench and on the floor of the tunnel4 ,when the face of the heading and the excavation of the bench are not more than #ej ft4 apart1 the hauling can be conveniently done on the tunnel floor1 while the materials and dbris on the upper section of the tunnel are hauled by wheelbarrows or light cars propelled by handpower4 ,for a greater distance1 however1 it is more convenient to use light cars running on narrow-gauge tracks all through the tunnel4 ,in this case the tracks on the tunnel floor and on top of the bench are connected by means of an inclined platform where the cars may ascend and descend without interfering with the excavation of the bench4 ,here1 as a rule1 tunnels have been excavated in soils considered good1 generally through rock1 while loose soils have been encountered only in small sections4 ,the same method of excavation for whatever material is encountered is certainly very convenient1 as it affords a great regularity in the work2 hence its extensive use4 ,a great disadvantage of this method is the double strutting1 viz41 the polygonal and the longitudinal strutting succeeding each other1 whereas one of them could be easily spared4 ,another defect is that it requires a larger amount of excavation1 in case the strutting is left in place4 ,,austrian ,,method4 ,the ,austrian full-section method of tunneling through soft ground was first used in constructing the ,oberau tunnel on the ,leipsic and ,dresden ,r4,r41 in ,austria in #ahcg4 ,it consists in excavating the full section and building up the lining masonry from the foundations as in the ,english1 but with the important exception that the invert is built last instead of first in all cases except where the presence of very loose soil requires its construction first4 ,a still more important difference in the two methods is that the excavation is carried out in smaller sections and is continuous in the ,austrian method instead of alternating with the mason work as it does in the ,english method4 ,excavation4--,the excavation in the ,austrian method begins by driving the bottom center drift ,no4 #a1 ,fig4 #ic1 rising from the floor of the tunnel section nearly to the height of the springing lines of the roof arch4 ,when this drift has been driven ahead a distance varying from #ab ft4 to #bj ft4 or sometimes more1 the excavation of the center top heading ,no4 #b is driven for the same distance4 ,the next operation is to remove part ,no4 #c1 thus forming a central passage the full depth of the tunnel section at the center4 ,this trench is enlarged by removing parts ,nos4 #d1 #e1 #f1 #g1 and #h in the order named until the full section is opened4 ,a modification of this plan of excavation is shown by ,fig4 #id which is used in firm soils4 ,illustration3 ,,figs4 #ic and #id4--;,diagrams ,showing ,sequence of ,excavation in ,austrian ,method of ,tunneling4 ,strutting4--,each part of the section is strutted as fast as it is excavated4 ,the center bottom drift first excavated is strutted by laying a transverse sill across the floor1 raising two side posts from it1 and capping them with a transverse timber having its ends projecting beyond the side posts and halved as shown by ,fig4 #ie4 ,the top center heading ,no4 #b1 which is next excavated1 is strutted by means of two side posts resting on blocking and carrying a transverse cap as also shown by ,fig4 #ie4 ,sometimes the side posts in the heading strutting-frames are also carried on a transverse sill as are those of the bottom drift4 ,this construction is usually adopted in loose soils4 ,when the sill is employed1 the middle part1 ,no4 #c1 is strutted by inserting side posts between the bottom of the top sill and the cap of the frame in the drift below4 ,when1 however1 the posts of the top heading frame are carried on blocking1 it is the practice to replace them with long posts rising from the cap of the bottom drift frame to the cap of the top heading frame4 ,further1 when the intermediate sill is employed at the bottom level of the top heading it projects beyond the side posts and has its ends halved4 ,illustration3 ,,figs4 #ie to #ig4--,sketches ,showing ,construction of ,strutting1 ,austrian ,method4 ,after the completion of the center trench strutting the next task is to strut parts ,nos4 #d and #e4 ,this is done by continuing the upper sill by means of a timber having one end halved to join with the projecting end of the sill in position4 ,this extension timber is shown at a1 ,fig4 #if4 ,the next operation is to place the timber b1 having one end resting on the cap-piece of the top heading frame and the other beveled and resting on the top of the sill a near the end4 ,the timber b is laid tangent to the curve of the roof arch1 and to support it against flexure the strut c is inserted as shown4 ,to support the thrust of this strut the additional post d is inserted and the original bottom heading frame is reinforced as shown4 ,the next step is to insert the strut e1 and when this and the previous construction are duplicated on the opposite side of the tunnel section we have the strutting of the parts ,nos4 #a to #e2 inclusive1 complete4 ,part ,no4 #f is then removed and strutted by extending the bottom drift cap-piece by a timber similar to timber a above1 and then by inserting a side strut between the outer ends of these two timbers1 as indicated by ,fig4 #ig4 ,as the final parts4 ,nos4 #g and #h1 are removed1 the inclined prop a1 ,fig4 #ig1 is inserted as shown4 ,when the soil is loose some of the members of the framework are doubled and additional bracing is introduced as shown by ,fig4 #ig4 ,the frames just described are placed at intervals of about #d ft4 along the excavation1 and are braced apart by horizontal struts4 ,some of the longitudinal bearing beams1 as at b1 ,fig4 #ig1 also extend through two or three frames1 and help to tie them together4 ,finally1 the longitudinal poling-boards extending from one frame to the next along the walls of the excavation serve to connect them together4 ,the short transverse beam c1 ,fig4 #ij1 located just above the floor of the invert1 serves to carry the planking upon which the train car tracks are laid4 ,besides the timber strutting peculiar to the ,austrian method1 the ,rziha iron strutting described in a previous chapter is frequently used in tunneling by the ,austrian process4 ,illustration3 ,,fig4 #ih4--,sketch ,showing ,manner of ,constructing the ,lining ,masonry1 ,austrian ,method4 ,centers4--,the two forms of centers used in the ,english method of tunneling are also used in the ,austrian method4 ,one of the methods of supporting these centers is shown by ,fig4 #ih4 ,the tie-beam of the center rests on longitudinal timbers carried by the strutting frames and intermediate props4 ,in single-track tunnels it is the frequent practice also to carry the ends of the tie-beams in recesses left in the side wall masonry1 with intermediate props inserted to prevent flexure at the center4 ,when the ,rziha iron strutting is employed1 it also serves for the centering upon which the arch masonry is built4 ,masonry4--,in the ,austrian system of tunneling1 the lining is built from the foundations of the side walls upward to the crown of the roof arch in lengths in consecutive rings equal to the lengths of the consecutive openings of the full section1 or from #ab ft4 to #bj ft4 long4 ,except in infrequent cases in very loose materials the invert is the last part of the masonry to be built1 since to build it first requires the removal of the strutting which cannot easily or safely be accomplished until the side walls and roof arch are completed4 ,as the side wall foundations are built1 however1 their interior faces are left inclined1 as shown by ,figs4 #ig and #ih1 ready for the insertion of the invert1 and are meanwhile kept from sliding inward by the insertion of blocking between them and the bottom of the strutting4 ,fig4 #ih shows the nature of this blocking1 and also the manner in which the side wall and roof arch masonry is carried upward4 ,finally when the roof arch is keyed and the centers are struck1 the strutting is taken down and the invert is built4 ,advantages and ,disadvantages4--,the principal advantages claimed for the ,austrian method of tunneling are3 7#a7 ,the excavation being conducted by driving a large number of consecutive small galleries1 which are immediately strutted1 there is little disturbance of the surrounding material2 7#b7 the polygonal type of strutting adopted is easily erected and of great strength against symmetrical pressures2 7#c7 the masonry1 being built from the foundations up1 is a single homogeneous structure1 and is thus better able to withstand dangerous pressures2 7#d7 the excavation is so conducted that the masons and excavators do not interfere1 and both can work at the same time4 ,the disadvantages which the method possesses are3 7#a7 ,the strutting while very strong under symmetrical pressures1 either vertical or lateral1 is distorted easily by unsymmetrical vertical or lateral pressures1 and by pressure in the direction of the axis of the tunnel2 7#b7 the construction of the invert last exposes the side walls to the danger of being squeezed together1 causing a rotation of the arch of the nature discussed in describing the ,belgian method of tunneling4 ,,chapter ,,xv4 ,,special ,,treacherous ,,ground ,,method2 ,,italian ,,method2 ,,quicksand ,,tunneling2 ,,pilot ,,method4 ,,italian ,,method4 ,the ,italian method of tunneling was first employed in constructing the ,cristina tunnel on the ,foggia ,benevento ,r4,r4 in ,italy4 ,this tunnel penetrated a laminated clay of the most treacherous character1 and after various other soft-ground methods of tunneling had been tried and had failed1 ,mr4 ,procke1 the engineer1 devised and used successfully the method which is now known as the ,italian or ,cristina method4 ,the ,italian method is essentially a treacherous soil method4 ,it consists in excavating the bottom half of the section by means of several successive drifts1 and building the invert and side walls2 the space is then refilled and the upper half of the section is excavated1 and the remainder of the side walls and the roof arch are built2 finally1 the earth filling in the lower half of the section is re-excavated and the tunnel completed4 ,the method is an expensive one1 but it has proved remarkably successful in treacherous soils such as those of the ,apennine ,mountains1 in which some of the most notable ,italian tunnels are located4 ,it is1 moreover1 a single-track tunnel method1 since any soil which is so treacherous as to warrant its use is too treacherous to permit an opening to be excavated of sufficient size for a double-track railway1 except by the use of shields4 ,excavation4--,the plan of excavation in the ,italian method is shown by the diagram ,fig4 #ii4 ,work is begun by driving the center bottom heading ,no4 #a1 and this is widened by taking out parts ,no4 #b4 ,finally part ,no4 #c is removed1 and the lower half of the section is open4 ,as soon as the invert and side wall masonry has been built in this excavation1 parts ,no4 #b are filled in again with earth4 ,the excavation of the center top heading ,no4 #d is then begun1 and is enlarged by removing the earth of part ,no4 #e4 ,the faces of this last part are inclined so as to reduce their tendency to slide1 and to permit of a greater number of radial struts to be placed4 ,next1 parts ,no4 #f are excavated1 and when this is done the entire section1 except for the thin strip ,no4 #g1 has been opened4 ,at the ends of part ,no4 #g narrow trenches are sunk to reach the tops of the side walls already constructed in the lower half of the section4 ,the masonry is then completed for the upper half of the section1 and part ,no4 #g and the filling in parts ,no4 #b are removed4 ,the various drifts and headings and the parts excavated to enlarge them are seldom excavated more than from #f ft4 to #aj ft4 ahead of the lining4 ,illustration3 ,,fig4 #ii4--;,diagram ,showing ,sequence of ,excavation in ,italian ,method of ,tunneling4 ,illustration3 ,,fig4 #ajj4--,sketch ,showing ,strutting for ,lower ,part of ,section4 ,strutting4--,the bottom center drift1 which is first driven1 is strutted by means of frames consisting of side posts resting on floor blocks and carrying a cap-piece4 ,poling-boards are placed around the walls1 stretching from one frame to the next4 ,as soon as the invert is sufficiently completed to permit it1 the side posts of the strutting frames are replaced by short struts resting on the invert masonry as shown by ,fig4 #ajj4 ,to permit the old side posts to be removed and the new shorter ones to be inserted1 the cap-piece of the frame is temporarily supported by inclined props arranged as shown by ,fig4 #ajc4 ,when parts ,no4 #b are excavated the roof is strutted by inserting the transverse caps a1 ,fig4 #ajj1 the outer ends of which are carried by the system of struts b1 c1 d1 and e4 ,the longitudinal poling-boards supporting the ceiling and walls are held in place by the cap a and the side timber e4 ,to stiffen the frames longitudinally of the tunnel1 horizontal longitudinal struts are inserted between them4 ,the excavation of the upper half of the tunnel section is strutted as in the ,belgian method1 with radial struts carrying longitudinal roof bars and transverse poling-boards4 ,on account of the enormous pressures developed by the treacherous soils in which only is the ,italian method employed1 the radial strutting frames and crown bars must be of great strength1 while the successive frames must be placed at frequent intervals1 usually not more than #c ft4 ,after the masonry side walls have been built in the lower part of the excavation1 longitudinal planks are laid against the side posts of the center bottom drift frames1 to form an enclosure for the filling-in of parts ,no4 #b4 ,the object of this filling is principally to prevent the squeezing-in of the side walls4 ,illustration3 ,,figs4 #aja and #aja;,a4--,sketches ,showing ,construction of ,centers1 ,italian ,method4 ,centers4--,owing to the great pressures to be resisted in the treacherous soils in which the ,italian method is used1 the construction of the centers has to be very strong and rigid4 ,figs4 #aja and #aja;,a show two common types of center construction used with this method4 ,the construction shown in ,fig4 #aja is a strong one where only pressures normal to the axis of the tunnel have to be withstood1 but it is likely to twist under pressures parallel to the axis of the tunnel4 ,in the construction shown by ,fig4 #aja;,a1 special provision is made to resist pressures normal to the plane of the center or twisting pressures1 by the strength of the transverse bracing extending horizontally across the center4 ,illustration3 ,,fig4 #ajb4--,sketch ,showing ,invert and ,foundation ,masonry1 ,italian ,method4 ,masonry4--,the construction of the masonry lining begins with the invert1 as indicated by ,fig4 #ajj1 and is carried up to the roof of parts ,no4 #b1 as already indicated1 and is then discontinued until the upper parts ,nos4 #d1 #e1 and #f are excavated4 ,the next step is to sink side trenches at the ends of part ,no4 #g1 which reach to the top of the completed side walls4 ,this operation leaves the way clear to finish the side walls and to construct the roof arch in the ordinary manner of such work in tunneling4 ,since this method of tunneling is used only in very soft ground which yields under load1 the usual practice is to construct the invert and side walls on a continuous foundation course of concrete as indicated by ,fig4 #ajb4 ,the lining is usually built in successive rings1 and the usual precautions are taken with respect to filling in the voids behind the lining4 ,the thickness of the lining is based upon the figures for laminated clay of the third variety given in ,table ,,ii4 ,hauling4--,the system of hauling adopted with this method of tunneling is very simple1 since the excavation of the various parts is driven only from #f ft4 to #aj ft4 ahead1 and the work progresses slowly to allow for the construction of the heavy strutting required4 ,to take away the material from the center bottom drift1 narrow-gauge tracks carried by cross-beams between the side posts above the floor line are employed4 ,this same narrow-gauge line is employed to take away a portion of parts ,no4 #b1 the remaining portion being left and used for the refilling after the bottom portion of the lining has been built1 as previously described4 ,the upper half of the section being excavated1 as in the ,belgian method1 the system of hauling with inclined planes to the tunnel floor below1 which is a characteristic of that method1 may be employed4 ,it is the more usual practice1 however1 since the excavation is carried so little a distance ahead and progresses so slowly1 to handle the spoil from the upper part of the section by wheelbarrows which dump it into the cars running on the tunnel floor below4 ,hand labor is also used to raise the construction materials used in building the upper section4 ,the tracks on the tunnel floor1 besides extending to the front of the advanced bottom center drift1 have right and left switches to be employed in removing the refilling in parts ,no4 #b1 the spoil from the upper part of the section1 and the material of part ,no4 #g4 ,fig4 #ajc is a longitudinal section showing the plan of excavation and strutting adopted with the ,italian method4 ,illustration3 ,,fig4 #ajc4--,sketch ,showing ,longitudinal ,section of a ,tunnel under ,construction1 ,italian ,method4 ,modifications4--,it often happens that the filling placed between the side walls and the planking1 which is practically the space comprised by parts ,no4 #b1 is not sufficient to resist the inward pressure of the walls1 and they tip inward4 ,in these cases a common expedient is to substitute for the earth filling a temporary masonry arch sprung between the side walls with its feet near the bottom of the walls1 and its crown just below the level of their tops1 as shown by ,fig4 #ajg4 ,this construction was employed in the ,stazza tunnel in ,italy4 ,in this tunnel the excavation was begun by driving the center drift1 ,no4 #a1 ,fig4 #ajd1 and immediately strutting it as shown by ,fig4 #aje4 ,the other parts1 ,nos4 #b and #c1 completing the lower portion of the section1 were then taken out and strutted4 ,while part ,no4 #b was being excavated at the bottom1 and the center part of the invert built1 the longitudinal crown bars carrying the roof of the excavation were carried temporarily by the inclined props shown by ,fig4 #ajf4 ,after completing the invert and the side walls to a height of #b or #c ft41 a thick masonry arch was sprung between the side walls1 as shown in transverse section by ,fig4 #ajg1 and in longitudinal section by ,fig4 #ajf4 ,this arch braced the side walls against tipping inward1 and carried short struts to support the crown bars4 ,the haunches of the arch were also filled in with rammed earth4 ,the upper half of the section was excavated1 strutted1 and lined as in the standard ,italian method previously described4 ,when the lining was completed1 the arch inserted between the side walls was broken down and removed4 ,illustration3 ,,fig4 #ajd4--,sketch ,showing ,sequence of ,excavation1 ,stazza ,tunnel4 ,illustration3 ,,fig4 #aje4--,sketch ,showing ,method of ,strutting ,first ,drift1 ,stazza ,tunnel4 ,illustration3 ,,figs4 #ajf and #ajg4--,sketches ,showing ,temporary ,strutting ,arch ,construction1 ,stazza ,tunnel4 ,advantages and ,disadvantages4--,the great advantage claimed for the ,italian method of tunneling is that it is built in two separate parts1 each of which is separately excavated1 strutted1 and lined1 and thus can be employed successfully in very treacherous soils4 ,its chief disadvantage is its excessive cost1 which limits its use to tunnels through treacherous soils where other methods of timbering cannot be used4 ,,quicksand ,,tunneling4 ,when an underground stream of water passes with force through a bed of sand it produces the phenomenon known as quicksand4 ,this phenomenon is due to the fineness of the particles of sand and to the force of the water1 and its activity is directly proportional to them4 ,when sand is confined it furnishes a good foundation bed1 since it is practically incompressible4 ,to work successfully in quicksand1 therefore1 it is necessary to drain it and to confine the particles of sand so that they cannot flow away with the water4 ,this observation suggests the mode of procedure adopted in excavating tunnels through quicksand1 which is to drain the tunnel section by opening a gallery at its bottom to collect and carry away the water1 and to prevent the movement or flowing of the sand by strutting the sides of the excavation with a tight planking4 ,the sand having to be drained and confined as described1 the ordinary methods of soft-ground tunneling must be employed1 with the following modifications3 7#a7 ,the first work to be performed is to open a bottom gallery to drain the tunnel4 ,this gallery should be lined with boards laid close and braced sufficiently by interior frames to prevent distortion of the lining4 ,the interstices or seams between the lining boards should be packed with straw so as to permit the percolation of water and yet prevent the movement of the sand4 7#b7 ,as fast as the excavation progresses its walls should be strutted by planks laid close1 and held in position by interior framework2 the seams between the plank should be packed with straw4 7#c7 ,the masonry lining should be built in successive rings1 and the work so arranged that the water seeping in at the sides and roof is collected and removed from the tunnel immediately4 ,excavation4--,the best and most commonly employed method of driving tunnels through quicksand is a modification of the ,belgian method4 ,at first sight it may appear a hazardous work to support the roof arch1 as is the characteristic of this method1 on the unexcavated soil below1 when this soil is quicksand1 but if the sand is well confined and drained the risk is really not very great4 ,next to the ,belgian method the ,german method is perhaps the best for tunneling quicksand4 ,in these comparisons the shield system of tunneling is for the time being left out of consideration4 ,this method will be described in succeeding chapters4 ,whenever any of the systems of tunneling previously described are employed1 the first task is always to open a drainage gallery at the bottom of the section4 ,assuming the ,belgian method is to be the one adopted1 the first work is to drive a center bottom drift1 the floor of which is at the level of the extrados of the invert4 ,this drift is immediately strutted by successive transverse frames made up of a sill1 side posts1 and a cap which support a close plank strutting or lining1 with its joints packed with straw4 ,between the side posts of each cross-frame1 at about the height of the intrados of the invert1 a cross-beam is placed2 and on these cross-beams a plank flooring is laid1 which divides the drift horizontally into two sections1 as shown by ,fig4 #ajh2 the lower section forming a covered drain for the seepage water1 and the upper providing a passageway for workmen and cars4 ,the bottom drift is driven as far ahead as practicable1 in order to drain the sand for as great a distance in advance of the work as possible4 ,after the construction of the bottom drainage drift the excavation proper is begun1 as it ordinarily is in the ,belgian method by driving a top center heading1 as shown by ,fig4 #ajh4 ,this heading is deepened and widened after the manner usual to the ,belgian method1 until the top of the section is open down to the springing lines of the roof arch4 ,to collect the seepage water from the center top heading it is provided with a center bottom drain constructed like the drain in the bottom drift1 as shown by ,fig4 #ajh4 ,when the top heading is deepened to the level of the springing lines of the roof arch1 its bottom drain is reconstructed at the new level1 and serves to drain the full top section opened for the construction of the roof arch4 ,this top drain is usually constructed to empty into the drain in the bottom drift4 ,illustration3 ,,fig4 #ajh4--,sketch ,showing ,preliminary ,drainage ,galleries1 ,quicksand ,method4 ,illustration3 ,,fig4 #aji4--,sketch ,showing ,construction of ,roof ,strutting1 ,quicksand ,method4 ,strutting4--,the method of strutting the bottom drift has already been described4 ,for the remainder of the excavation the regular ,belgian method of radial roof strutting-frames is employed1 as shown by ,fig4 #aji4 ,contrary to what might be expected1 the number of radial struts required is not usually greater than would be used in many other soils besides quicksand4 ,single-track railway tunnels have been constructed through quicksand in several instances where the number of radial props required on each side of the center did not exceed four or five4 ,it is necessary1 however1 to place the poling-boards very close together1 and to pack the joints between them to prevent the inflow of the fine sand4 ,in strutting the lower part of the section it is also necessary to support the sides with tight planking4 ,this is usually held in place by longitudinal bars braced by short struts against the inclined props employed to carry the roof arch when the material on which they originally rested is removed4 ,this side strutting is shown at the right hand of ,fig4 #aaj4 ,illustration3 ,,fig4 #aaj4--,sketch ,showing ,construction of ,masonry ,lining1 ,quicksand ,method4 ,masonry4--,as soon as the upper part of the section has been opened the roof arch is built with its feet resting on planks laid on the unexcavated material below4 ,this arch is built exactly as in the regular ,belgian method previously described1 using the same forms of centers and the same methods throughout1 except that the poling-boards of the strutting are usually left remaining above the arch masonry4 ,to prevent the possibility of water percolating through the arch masonry1 many engineers also advise the plastering of the extrados of the arch with a layer of cement mortar4 ,this plastering is designed to lead the water along the haunches of the arch and down behind the side walls4 ,in constructing the masonry below the roof arch the invert is built first1 contrary to the regular ,belgian method1 and the side walls are carried up on each side from the invert masonry4 ,seepage holes are left in the invert masonry1 and also in the side walls just above the intrados of the invert4 ,at the center of the invert a culvert or drain is constructed1 as shown by ,fig4 #aaj1 inside the invert masonry4 ,this culvert is commonly made with an elliptical section with its major axis horizontal1 and having openings at frequent intervals at its top4 ,the thickness of the lining masonry required in quicksand is shown by ,table ,,ii4 ,removing the ,seepage ,water4--,after the tunnel is completed the water which seeps in through the weep-holes left in the masonry passes out of the tunnel1 following the direction of the descending grades4 ,during construction1 however1 special means will have to be provided for removing the water from the excavation1 their character depending upon the method of excavation and upon the grades of the tunnel bottom4 ,when the excavation is carried on from the entrances only1 unless the tunnel has a descending grade from the center toward each end1 the tunnel floor in one heading will be below the level of the entrance1 or1 in other words1 the descending grade will be toward the point where work is going on1 while at the opposite entrance the grade will be descending from the work4 ,in the latter case the removal of the seepage water is easily accomplished by means of a drainage channel along the bottom of the excavation4 ,in the former case the water which drains toward the front is collected in a sump1 and if there is not too great a difference in level between this sump and the entrance1 a siphon may be used to remove it4 ,where the siphon cannot be used1 pumps are installed to remove the water4 ,when the tunnel is excavated by shafts the condition of one high and one low front1 as compared with the level at the shaft1 is had at each shaft4 ,generally1 therefore1 a sump is constructed at the bottom of the shaft2 the culvert from the high front drains directly to the shaft sump1 while the water from the low-front sump is either siphoned or pumped to the shaft sump4 ,from the shaft sump the water is forced up the shaft to the surface by pumps4 ,,the ,,pilot ,,method4 ,the pilot system of tunneling has been successfully employed in constructing soft-ground sewer tunnels in ,america by the firm of ,anderson ,barr1 which controls the patents4 ,the most important work on which the system has been employed is the main relief sewer tunnel built in ,brooklyn1 ,n4,y41 in #ahib4 ,this work comprised #hjj ft4 of circular tunnel #ae ft4 in diameter1 #ddjj ft4 #ad ft4 in diameter1 #cbjj ft4 #ab ft4 in diameter1 and #ajjj ft4 #aj ft4 in diameter1 or #idjj ft4 of tunnel altogether4 ,the method of construction by the pilot system is as follows3 ,shafts large enough for the proper conveyance of materials from and into the tunnel are sunk at such places on the line of work as are most convenient for the purpose4 ,from these shafts a small tunnel1 technically a pilot1 about #f ft4 in diameter1 composed of rolled boiler iron plates riveted to light angle irons on four sides1 perforated for bolts1 and bent to the required radius of the pilot1 is built into the central part of the excavation on the axis of the tunnel4 ,this pilot is generally kept about #cj ft4 in advance of the completed excavation1 as shown by ,fig4 #aaa4 ,the material around the exterior of the pilot is then excavated1 using the pilot as a support for braces which radiate from it and secure in position the plates of the outside shell which holds the sand1 gravel1 or other material in place until the concentric rings of brick masonry are built4 ,ribs of ,t-iron bent to the radius of the interior of the brick work1 and supported by the braces radiating from the pilot1 are used as centering supports for the masonry4 ,on these ribs narrow lagging-boards are laid as the construction of the arch proceeds1 the braces holding the shell plates and the superincumbent mass being removed as the masonry progresses4 ,the key bricks of the arches are placed in position on ingeniously contrived key-boards1 about #ab ins4 in width1 which are fitted into rabbeted lagging-boards one after another as the key bricks are laid in place4 ,after the masonry has been in place at least twenty-four hours1 allowing the cement mortar time to set1 the braces1 ribs1 and lagging which support it are removed4 ,in the meantime the excavation1 bracing1 pilot1 and exterior shell have been carried forward1 preparing the way for more masonry4 ,the top plates of the shell are first placed in position1 the material being excavated in advance and supported by light poling-boards2 then the side-plates are butted to the top and the adjoining side-plates4 ,in the pilot the plates are united continuously around the perimeter of the circle1 while in the exterior shell the plates are used for about one-third of the perimeter on top1 unless treacherous material is encountered1 when the plates are continued down to the springing lines of the arch4 ,this iron lining is left in place4 ,the bottom is excavated so as to conform to the exterior lines of the masonry4 ,the excavation follows so closely to the outer lines of the normal section of the tunnel that very little loss occurs1 even in bad material2 and there is no loss where sufficient bond exists in the material to hold it in place until the poling-boards are in position4 ,illustration3 ,bracing4 ,arch ,construction4 ,longitudinal ,section4 ,,fig4 #aaa4--,sketch ,showing ,pilot ,method of ,tunneling4 ,in the ,brooklyn sewer tunnel work1 previously mentioned1 the pilot was built of steel plates in4 thick1 #ab ins4 wide1 and #cg ins4 long1 rolled to a radius of #c ft4 ,steel angles #d #d ins4 were riveted along all four sides of each plate1 and the plates were bolted together by -in4 machine-bolts4 ,the plates weighed #acf lbs4 each1 and six of them were required to make one complete ring #f ft4 in diameter4 ,in bolting them together1 iron shims were placed between the horizontal joints to form a footing for the wooden braces for the shell1 which radiate from the pilot4 ,the shell plates of the #ae-;ft4 section of the tunnel were of ,no4 #aj steel #ab ins4 wide and #cg ins4 long1 with steel angles #b #b ins41 riveted around the edges the same as for the pilot1 and put together with -in4 bolts4 ,these plates weighed #fa lbs4 each1 and eighteen of them were required to make one complete ring #ae ft4 in diameter4 ,the plates for the #ab-;ft4 section were ,no4 #ab steel #ab ins4 wide with #b #b -in4 angles4 ,seventeen plates were required to make a complete ring4 ,,chapter ,,xvi4 ,,open-,,cut ,,tunneling ,,methods2 ,,tunnels ,,under ,,city ,,streets2 ,,boston ,,subway ,,and ,,new ,,york ,,rapid ,,transit4 ,,open-,,cut ,,tunneling4 ,when a tunnel or rapid-transit subway has to be constructed at a small depth below the surface1 the excavation is generally performed more economically by making an open cut than by subterranean tunneling proper4 ,the necessary condition of small depth which makes open-cut tunneling desirable is most generally found in constructing rapid-transit subways or tunnels under city streets4 ,this fact introduces the chief difficulties encountered in such work1 since the surface traffic makes it necessary to obstruct the streets as little as possible1 and has led to the development of the several special methods commonly employed in performing it4 ,subways are usually constructed under and along important streets where electric cars are running4 ,the engineers have taken advantage of the presence of these lines to facilitate the construction of subways4 ,in ,new ,york1 for instance1 the tracks of the electric lines were supported by cast-iron yokes #d or #e ft4 apart and were surrounded by concrete1 leaving only a large hollow space in the middle for the wires and trolleys4 ,the rails from #dj to #fj ft4 long formed almost a solid concrete structure for their entire length4 ,the tracks and the street surface were supported by horizontal beams inserted underneath the tracks4 ,these were the caps of bents constructed underground whose rafters were finally resting on the subgrade of the proposed subway4 ,the various methods for constructing the subways may be classified as follows3 7#a7 ,the single wide trench method2 7#b7 the single narrow longitudinal trench method2 7#c7 the parallel longitudinal trench method2 7#d7 the slice method4 ,single ,longitudinal ,trench4--,the simplest manner by which to construct open-cut tunnels is to open a single cut or trench the full width of the tunnel masonry4 ,this trench is strutted by means of side sheetings of vertical planks1 held in place by transverse braces extending across the trench and abutting against longitudinal timbers laid against the sheeting plank4 ,the lining is built in this trench1 and is then filled around and above with well-rammed earth1 after which the surface of the ground is restored4 ,an especial merit of the single longitudinal trench method of open-cut tunneling is that it permits the construction of the lining in a single piece from the bottom up1 thus enabling better workmanship and stronger construction than when the separate parts are built at different times4 ,the great objection to the method when it is used for building subways under city streets is1 that it occupies so much room that the street usually has to be closed to regular traffic4 ,for this reason the single longitudinal trench method is seldom employed1 except in those portions of city subways which pass under public squares or parks where room is plenty4 ,this method was followed in the construction of the ,new ,york subway1 ,section #b1 along ,elm ,st41 a new street to be opened to traffic after the subway had been completed1 and at other points where local conditions allowed it4 ,illustration3 ,,fig4 #aab4--;,diagram ,showing ,sequence of ,construction in ,open-,cut ,tunnels4 ,a modification of this method was used in ,contract ,section #f1 on upper ,broadway4 ,the street at this point is very wide1 so by opening a trench as wide as the proposed four-track line of the subway there still remained room enough for ordinary traffic4 ,the electric car tracks were supported by means of trusses #fj or #gj ft4 long1 which were laid in couples parallel to the tracks and which rested on firm soil4 ,the soil under the car tracks was removed1 beginning with transversal cuts to receive the needles which were tied to the lower chord of the trusses by means of iron stirrups4 ,after the excavation had reached the subgrade1 posts were erected to support the needles thus forming bents upon which the tracks rested4 ,the trusses were removed and advanced to another section of the tunnel1 and1 in the clear space left1 the subway was built from foundation up4 ,the ,single ,narrow ,longitudinal ,trench4--,this method was used on ,contract ,section #e1 of the ,new ,york subway in order to comply with the peculiar conditions of the traffic along #dbnd ,st4 ,on this street1 on account of the ,new ,york ,central ,station1 there is a constant heavy traffic1 while pedestrians use the northern sidewalks almost exclusively4 ,a single longitudinal trench was then opened along the south side1 and from this trench all the work of excavation and construction was carried on4 ,at first the steel structure of the subway was erected in the trench and then a small heading was driven and strutted under and across the surface-car tracks4 ,afterward heavy ,i-beams were inserted1 which rested with one end on top of the steel bents and the other end blocked to the floor of the excavation4 ,these ,i-beams were located #e ft4 apart and they supported the surface of the street by means of longitudinal planks4 ,the soil was removed from the wide space underneath the ,i-beams and the subway was constructed from the foundation up4 ,when the structure had been completed1 the packing was placed between the roof of the structure and the surface of the street1 the ,i-beams withdrawn and the voids filled in4 ,parallel ,longitudinal ,trenches4--,the parallel longitudinal trench method of open-cut tunneling consists in excavating two narrow parallel trenches for the side walls1 leaving the center core to be removed after the side walls have been built4 ,the diagram1 ,fig4 #aab1 shows the sequence of operations in this method4 ,the two trenches ,no4 #a are first excavated a little wider than the side wall masonry1 and strutted as shown by ,fig4 #aac4 ,at the bottoms of these trenches a foundation course of concrete is laid1 as shown by ,fig4 #aad1 if the ground is soft2 or the masonry is started directly on the natural material1 if it is rock4 ,from the foundations the walls are carried up to the level of the springing lines of the roof arch1 if an arch is used2 or to the level of its ceiling1 if a flat roof is used4 ,after the completion of the side walls1 the portion of the excavation shown at ,no4 #b1 ,fig4 #aab1 is removed a sufficient depth to enable the roof arch to be built4 ,when the arch is completed1 it is filled above with well-rammed earth1 and the surface is restored4 ,the excavation of part ,no4 #c inclosed by the side walls and roof arch is carried on from the entrances and from shafts left at intervals along the line4 ,illustration3 ,,fig4 #aac4--,sketch ,showing ,method of ,timbering ,open-,cut ,tunnels1 ,double ,parallel ,trench ,method4 ,illustration3 ,,fig4 #aad4--,side-,wall ,foundation ,construction ,open-,cut ,tunnels4 ,a modification of the method just described was employed in constructing the ,paris underground railways4 ,it consists in excavating a single longitudinal trench along one side of the street1 and building the side wall in it as previously described4 ,when this side wall is completed to the roof1 the right half of part ,no4 #b1 ,fig4 #aab1 is excavated to the line ,,ab1 and the right-hand half of the roof arch is built4 ,the space above the arch is then refilled and the surface of the street restored1 after which the left-hand trench is dug and the side wall and roof-arch masonry is built just as in the opposite half4 ,generally the work is prosecuted by opening up lengths of trench at considerable intervals along the street and alternately on the left-and right-hand sides4 ,by this method one-half of the street width is everywhere open to traffic1 the travel simply passing from one side of the street to the other to avoid the excavation4 ,when the lining has been completed1 the center core of earth inclosed by it is removed from the entrances and shafts1 leaving the tunnel finished except for the invert and track construction1 etc4 ,another modification of the parallel longitudinal trenches method was used in the construction of the ,new ,york subway4 ,a narrow longitudinal trench was excavated on one side of the street near the sidewalk4 ,meanwhile the pavement of half of the street was removed and a wooden platform of heavy planks1 supported by longitudinal beams which were buried in the ground1 was substituted4 ,then small cuts underneath the car tracks were directed from the side trench and heavy beams or needles were placed in these cuts1 which also reached the longitudinal beams of the wooden platform4 ,the needles were wedged and blocked to the car track structure and the beams4 ,they were temporarily supported by cribs built from underneath as the excavation progressed4 ,when the subgrade was reached1 vertical and batter posts were inserted to support the needles1 thus forming regular timber bents underground4 ,in the space thus left open the subway was constructed to the middle of the street4 ,while the work was going on as described1 another longitudinal narrow trench was excavated at some distance on the other side of the street4 ,from this trench1 the work of constructing the other half of the subway was carried on in the manner just described4 ,after the work had been completed1 the timbers removed1 the voids filled in and the pavement of the street restored1 another equal section was attacked on both sides of the street4 ,transverse ,trenches4--,the transverse trench or 8slice0 method of open-cut tunneling has been employed in one work1 the ,boston ,subway4 ,this method is described in the specifications for the work prepared by the chief engineer1 ,mr4 ,h4 ,a4 ,carson1 ,m4 ,am4 ,soc4 ,c4 ,e41 as follows3-- 8,trenches about #ab ft4 wide shall be excavated across the street to as great a distance and depth as is necessary for the construction of the subway4 ,the top of this excavation shall be bridged during the night by strong beams and timbering1 whose upper surface is flush with the surface of the street4 ,these beams shall be used to support the railway tracks as well as the ordinary traffic4 ,in each trench a small portion or slice of the subway shall be constructed4 ,each slice of the subway thus built is to be properly joined in due time to the contiguous slices4 ,the contractor shall at all times have as many slice-trenches in process of excavation1 in process of being filled with masonry1 and in process of being back-filled with earth above the completed masonry1 as is necessary for the even and steady progress of the work towards completion at the time named in the contract40 ,in regard to the success of this method ,mr4 ,carson1 in his fourth annual report on the ,boston ,subway work1 says3 8,the method was such that the street railway tracks were not disturbed at all1 and the whole surface of the street1 if desired1 was left in daytime wholly free for the normal traffic40 ,tunnels on the ,surface4--,it occasionally happens when filling-in is to take place in the future1 or where landslides are liable to bury the tracks1 that a railway tunnel has to be built on the surface of the ground4 ,in such cases the construction of the tunnel consists simply in building the lining of the section on the ground surface with just enough excavation to secure the proper grade and foundation4 ,generally the lining is finished on the outside with a waterproof coating1 and is sometimes banked and partly covered with earth to protect the masonry from falling stones and similar shocks from other causes4 ,a recent example of tunnel construction of this character was described in 8,engineering ,news0 of ,sept4 #h1 #ahih4 ,in constructing the ,golden ,circle ,railroad1 in the ,cripple ,creek mining district of ,colorado1 the line had to be carried across a valley used as a dumping-ground for the refuse of the surrounding mines4 ,to protect the line from this refuse1 the engineer constructed a tunnel lining consisting of successive steel ribs1 filled between with masonry4 ,concluding ,remarks4--,from the fact that the open-cut method of tunneling consists first in excavating a cut1 and second in covering this cut to form an underground passageway1 it has been named the 8cut-and-cover0 method of tunneling4 ,the cut-and-cover method of tunneling is almost never employed elsewhere than in cities1 or where the surface of the ground has to be restored for the accommodation of traffic and business4 ,when it is not necessary to restore the original surface1 as is usually the case with tunnels built in the ordinary course of railway work1 it would obviously be absurd to do so except in extraordinary cases4 ,in a general way1 therefore1 it may be said that the cut-and-cover method of construction is confined to the building of tunnels under city streets2 and the discussion of this kind of tunnels follows logically the general description of the open-cut method of tunneling which has been given4 ,,tunnels ,,under ,,city ,,streets4 ,the three most common purposes of tunnels under city streets are3 to provide for the removal of railway tracks from the street surface1 and separate the street railway traffic from the vehicular and pedestrian traffic2 to provide for rapid transit railways from the business section to the outlying residence districts of the city2 and to provide conduits for sewage or subways for water and gas mains1 sewers1 wires1 etc4 ,within recent years the greatest works of tunneling under city streets have been designed and carried out to furnish improved transit facilities4 ,conditions of ,work4--,the construction of tunnels under city streets may be divided into two classes1 which may be briefly defined as shallow tunnels and deep tunnels4 ,shallow tunnels1 or those constructed at a small depth beneath the surface1 are usually built by one of the cut-and-cover methods2 deep tunnels1 or those built at a great depth1 beneath the surface are constructed by any of the various methods of tunneling described in this book1 the choice of the method depending upon the character of the material penetrated1 and the local conditions4 ,in building tunnels under city streets the first duty of the engineer is to disturb as little as possible the various existing structures and the activities for which these structures and the street are designed4 ,the character of the difficulties encountered in performing this duty will depend upon the depth at which the tunnel is driven4 ,in constructing shallow tunnels by the cut-and-cover method care has to be taken first of all not to disturb the street traffic any more than is absolutely necessary4 ,this condition precludes the single trench method of open cut tunneling in all places where the street traffic is at all dense1 and compels the engineer to use the methods employed in ,paris and ,new ,york1 as previously described1 or else the transverse trench or slice method employed in the ,boston ,subway4 ,these methods have to be modified when the work is done on streets having underground trolley and cable roads1 and in which are located gas and water pipes1 conduits for wires1 etc4 ,where underground trolley or cable railways are encountered1 a common mode of procedure is to excavate parallel side trenches for the side walls1 and turn the roof arch until it reaches the conduit carrying the cables or wires4 ,the earth is then removed from beneath the conduit structure in small sections1 and the arch completed as each section is opened4 ,as fast as the arch is completed the conduit structure is supported on it4 ,where pipes are encountered they may be supported by means of chains1 suspending them from heavy cross-beams1 or by means of strutting1 or they may be removed and rebuilt at a new level4 ,generally the conditions require a different solution of this problem at different points4 ,another serious difficulty of tunneling under city streets arises from the danger of disturbing the foundations of the adjacent buildings4 ,this danger exists only where the depth of the tunnel excavation extends below the depth of the building foundations1 and where the material penetrated is soft ground4 ,where the tunnel penetrates rock there is no danger of disturbing the building foundations4 ,to prevent trouble of this character requires simply that the excavation of the tunnel be so conducted that there is no inflow of the surrounding material1 which may1 by causing a settlement of the neighboring material1 allow the foundations resting on it to sink4 ,the ,baltimore ,belt tunnel1 described in a preceding chapter1 is an example of the method of work adopted in constructing a tunnel under city streets through very soft ground4 ,this may be classed as a deep tunnel4 ,another method of deep tunneling under city streets is the shield method1 examples of which are given in a succeeding chapter4 ,two notable examples of cut-and-cover methods of tunneling are the ,boston ,subway and the ,new ,york ,rapid ,transit ,ry41 a description of which follows4 ,boston ,subway4--,the ,boston ,subway may be defined as the underground terminal system of the surface street railway system of the city1 and as such it comprises various branches1 loops1 and stations4 ,the subway begins at the ,public ,garden on ,boylston ,st41 near ,charles ,st41 and passes with double tracks under ,boylston ,st4 to its intersection with ,tremont ,st41 where it meets the other double-track branch1 passing under ,tremont ,st4 and beginning at its intersection with ,shawmut ,ave4 ,from their intersection at ,tremont and ,boylston streets the two double-track branches proceed under ,tremont ,st4 with four tracks to ,scollay ,square4 ,at ,scollay ,square the subway divides again into two double-track branches1 one passing under ,hanover ,st41 and the other under ,washington ,st4 ,at the intersection of ,hanover and ,washington streets the two double-track branches combine again into a four-track line1 which runs under ,washington ,st4 to its terminus at ,haymarket ,square1 where it comes to the surface by means of an incline4 ,the subway1 therefore1 has three portals or entrances1 located respectively at ,boylston ,st41 ,shawmut ,ave41 and ,haymarket ,square4 ,it also has five stations and two loops1 the former being located at ,boylston ,st41 ,park ,st41 ,scollay ,square1 ,adams ,square1 and ,haymarket ,square1 and the latter at ,park ,st4 and ,adams ,square4 ,the total length of the subway is #aj1haj ft4 ,material ,penetrated4--,the material met with in constructing the subway was alluvial in character1 the lower strata being generally composed of blue clay and sand1 and the upper strata of more loose soil1 such as loam1 oyster shells1 gravel1 and peat4 ,at many points the material was so stable that the walls of the excavation would stand vertical for some time after excavation4 ,surface water was encountered1 but generally in small quantities1 except near the ,boylston ,st4 portal1 where it was so plentiful as to cause some trouble4 ,illustration3 ,,fig4 #aae4--,wide ,arch ,section1 ,boston ,subway4 ,cross-,section4--,the subway being built for two tracks in some places and for four tracks in other places1 it was necessary to vary the form and dimensions of the cross-section4 ,the cross-sections actually adopted are of three types4 ,fig4 #aae shows the section known as the wide-arch type1 in which the lining is solid masonry4 ,the second type was known as the double-barrel section1 and is shown by ,fig4 #aaf4 ,the third type of section is shown by ,fig4 #aag4 ,the lining consists of steel columns carrying transverse roof girders1 the roof girders being filled between with arches1 and the wall columns having concrete walls between them4 ,the wide-arch type and the double-barrel type of sections were employed in some portions of the ,tremont ,st4 line1 where the traffic was very dense1 since it was possible to construct them without opening the street4 ,much of the wide-arch line was constructed by the use of the roof shield1 which is described in the succeeding chapter on the shield system of tunneling4 ,illustration3 ,,fig4 #aaf4--;,double-,barrel ,section1 ,boston ,subway4 ,methods of ,construction4--,several different methods were employed in constructing the subway4 ,where ample space was available1 the single wide trench method of cut-and-cover construction was employed1 the earth being removed as fast as excavated4 ,in the streets1 except where regular tunneling was resorted to1 the parallel trench or transverse trench cut-and-cover methods were employed4 ,in the transverse trench method1 trenches about #ab ft4 wide were excavated across the street1 their length being equal to the extreme transverse width of the tunnel lining1 and their depth being equal to the depth of the tunnel floor4 ,these trenches were begun during the night1 and immediately roofed over with a timber platform flush with the street surface4 ,under these platforms the excavation was completed and the lining built4 ,as each trench or 8slice0 was completed1 the street above it was restored and the platform reconstructed over the succeeding trench or slice4 ,during the construction of each slice the street traffic1 including the street cars1 was carried by the timber platform4 ,illustration3 ,,fig4 #aag4--;,four-,track ,rectangular ,section1 ,boston ,subway4 ,illustration3 ,,fig4 #aah4--,section ,showing ,slice ,method of ,construction1 ,boston ,subway4 ,in the parallel trench method1 short parallel trenches were dug for the opposite side walls1 and also for the intermediate columns1 and completely roofed over during the night4 ,under this roofing the masonry of the side walls and column foundations and the columns themselves were erected4 ,when the side walls and columns had been erected1 the surface of the street between them was removed1 the roof beams laid1 and a platform covering erected1 as shown by ,fig4 #aah4 ,this roofing work was also done at night4 ,the subsequent work of building the roof arches1 removing the remainder of the earth1 and constructing the invert1 was carried on underneath the platform covering which carried the street traffic in the meantime4 ,the successive repetition of the processes described constructed the subway4 ,where the traffic was very dense on the street above1 tunneling was resorted to4 ,for small portions of this work the excavation was done in the ordinary way1 using timber strutting1 but much the greater portion of the tunnel work was performed by means of a roof shield4 ,in the latter case1 the side walls were first built in small bottom side drifts and were fitted with tracks on top to carry the roof shield4 ,the construction and operation of this shield are described fully in the succeeding chapter on the shield system of tunneling4 ,masonry4--,the masonry of the inclined approaches to the subway consists simply of two parallel stone masonry retaining walls4 ,in the wide-arch and double-barrel tunnel sections1 the side walls are of concrete and the roof arches are of brick masonry4 ,in the other parts of the subway the masonry consists of brick jack arches sprung between the roof beams and covered with concrete1 of concrete walls embedding the side columns1 and of the concrete invert and foundations for the columns4 ,figs4 #aae to #aah inclusive show the general details of the masonry work for each of the three sections4 ,the inside of the lining masonry is painted throughout with white paint4 ,stations4--,the design and construction of the stations for the ,boston ,subway were made the subjects of considerable thought4 ,all the stations consist of two island platforms of artificial stone having stairways leading to the street above4 ,the platforms are made #a ft4 higher than the rails4 ,the station structure itself is built of steel columns and roof beams with brick roof arches and concrete side walls4 ,its interior is lined with white enameled tiles4 ,the intermediate columns are cased with wood1 and have circular wooden seats at their bottoms4 ,each stairway is covered by a light housing1 consisting of a steel framework with a copper covering and an interior wood and tile finish4 ,ventilation4--,the subway is ventilated by means of exhaust fans located in seven fan chambers1 some of which contain two fans1 and others only one fan4 ,each of the fans has a capacity of from #cj1jjj to #cg1jjj cu4 ft4 of air per minute1 and is driven by electric motor1 taking current from the trolley wires4 ,this system of ventilation has worked satisfactorily4 ,disposal of ,rain ,water4--,the rain water which enters the subway from the inclined entrances1 together with that from leakage1 is lifted from #ab ft4 to #ah ft4 by automatic electric pumps to the city sewers4 ,the subway has pump-wells at the ,public ,garden1 at ,eliot ,st41 ,adams ,square1 and ,haymarket ,square4 ,in each of these wells are two vertical submerged centrifugal pumps made entirely of composition metal4 ,in each chamber above1 are two electric motors operating the pumps4 ,each motor is started and stopped according to the height of water by means of a float and an automatic release starting box4 ,the floats are so placed that only one pump is usually brought into use4 ,the other1 however1 comes into service in case the first pump is out of order or the water enters more rapidly than one pump can dispose of it4 ,in the latter case1 both motors continue to run until the same low level has been reached4 ,very little dampness except from atmospheric condensation is to be found on the interior walls or roof of the subway1 although numerous discolored patches1 caused by dampness and dust1 may be seen on some parts of the walls4 ,substantially all of the leakage comes through the small drains in the invert leading from hollows left in the side walls4 ,careful measurement was taken at the end of an unusually wet season to determine the actual amount of leakage1 and the total amount for the entire subway was found to be about #ha gallons per minute4 ,estimated ,quantities4--,the estimated quantities of material used in constructing the subway were as follows3 ,excavation #cfi1dej cu4 yds4 ,concrete #ge1ffj ,brick #aa1aje ,steel #h1aje tons ,granite #b1bhe cu4 yds4 ,piles #aag1ibe lin4 ft4 ,ribbed tiles #ab1ddj sq4 yds4 ,plaster #hh1aij ,waterproofing 7asphalt coating7 #aag1ihj ,artificial stone #f1gij ,enameled brick #b1baj ,enameled tiles #b1hee ,cost of the ,subway4--,the estimated cost of the subway made before the work was begun was approximately #d1jjj1jjj1 and the cost of construction did not exceed #c1gjj1jjj4 ,this includes ventilating and pump chambers1 changes of water and gas pipes1 sewers and other structures1 administration1 engineering1 interest on bonds1 and all cost whatsoever4 ,dividing this number by the total length we obtain a cost per linear foot of #cdb4cj4 ,new ,york ,rapid ,transit ,railway4--,the project of an underground rapid transit railway to run the entire length of ,manhattan ,island was originated some years previous to #ahij4 ,in #ahid1 however1 a ,rapid ,transit ,commission was appointed to prepare plans for such a road1 and after a large amount of trouble and delay this commission awarded the contract for construction to ,mr4 ,john ,b4 ,mc,donald of ,new ,york ,city1 on ,jan4 #ae1 #aijj4 ,route4--,the road starts from a loop which encircles the ,city ,hall ,park4 ,within this loop the tunnel construction is two-track2 but where the main line leaves the loop1 all four tracks come to the same level1 and continue side by side thereafter except at the points which will be noted as the description proceeds4 ,proceeding from the loop1 the four-track line passes under ,center and ,elm ,streets4 ,it continues under ,lafayette ,place1 across ,astor ,place and private property between ,astor ,place and ,ninth ,st4 to ,fourth ,ave4 ,the road then passes under ,fourth and ,park ,avenues until #db;d ,st4 is reached4 ,at this point the line turns west along #db;d ,st41 which it follows to ,broadway4 ,it turns northward again under ,broadway to the boulevard1 crossing the ,circle at #eith ,st4 ,the road then follows the boulevard until #igth ,st4 is reached1 where the four-track line is separated into two double-track lines4 ,at a suitable point north of #ifth ,st4 the outside tracks rise so as to permit the inside tracks1 on reaching a point near #ajc;d ,st41 to curve to the right1 passing under the north-bound track1 and to continue thence across and under private property to #ajdth ,st4 ,from there the two-track tunnel goes under #ajdth ,st4 and ,central ,park to #aajth ,st41 near ,lenox ,ave42 thence under ,lenox ,ave to a point near #adb;d ,st42 thence across and under private property and the intervening streets to the ,harlem ,river4 ,the road passes under the ,harlem ,river and across and under private property to #adith ,st41 which street it follows to ,third ,ave41 and then passes under ,westchester ,ave41 where1 at a convenient point1 the tracks emerge from the tunnel and are carried on a viaduct along and over ,westchester ,ave41 ,southern ,boulevard1 and ,boston ,road to ,bronx ,park4 ,this portion of the line1 from #ifth ,st4 to ,bronx ,park1 is known as the ,east ,side ,line4 ,from the northern side of #ifth ,st4 the outside tracks rise and after crossing over the inside tracks they are brought together on a location under the center line of the street and proceed along under the boulevard to a point between #abb;d and #abc;d ,streets4 ,at this point the tracks commence to emerge from the tunnel1 and are carried on a viaduct along and over the boulevard at a point between #acdth and #aceth ,streets1 where they again pass into the tunnel under and along the boulevard and ,eleventh ,ave4 to a point about #acej ft4 north of the center line of #aijth ,st4 ,there the tracks again emerge from the tunnel1 and are carried on a viaduct across and over private property to ,elwood ,st41 and over and along ,elwood ,st4 to ,kingsbridge ,st4 to ,kingsbridge ,ave41 private property1 the ,harlem ,ship ,canal and ,spuyten ,duyvil ,creek1 private property1 ,riverdale ,ave41 and ,broadway to a terminus near ,van ,cortland ,park4 ,that portion of the line from #ifth ,st4 to the above-mentioned terminus at ,van ,cortland ,park is known as the ,west ,side ,line4 ,the total length of the rapid transit road1 including the parts above and below the surface ground of the streets1 as well as both the ,east and ,west ,side ,lines1 is about #bb miles4 ,material ,penetrated4--,the soil through which the road was excavated was a varied one4 ,the lower portion of the road1 or the part including the loop up to nearly ,fourth ,st41 was excavated through loose soil1 but from ,fourth ,st4 to the ends it was excavated in rock4 ,the loose soil forming the southern part of ,manhattan ,island is chiefly composed of clay1 sand1 and old rubbish--a soil very easy to excavate4 ,water was met at some points1 but not in such quantities as to be a serious inconvenience4 ,from ,fourth ,st4 to the ends of both the east and west side lines1 the soil was chiefly composed of rock of gneissoid and mica-schistose character1 these rocks prevailing nearly throughout the whole of ,manhattan ,island4 ,the rock1 as a rule1 was not compact1 but full of seams and fissures1 and at many points it was found disintegrated and alternated with strata of loose soils1 and even pockets of quicksand were met with along the line of the road4 ,cross-,sections4--,the section of the underground road is of three different types1--the rectangular1 the barrel-vault1 and the circular4 ,the rectangular section4 ,fig4 #aai1 is used for the greater part of the road1 of which a portion is for four tracks and a portion for two tracks4 ,the dimensions adopted for the four tracks are #ej #ac ft41 and for the double tracks #be #ac ft4 ,the barrel-vault section1 composed of a polycentric arch1 having the flattest curve at the crown1 has been adopted for the tunnels under ,park ,avenue--while the semicircular arch is used for all the other portions of the road to be tunneled4 ,the circular section of #ae-;ft4 diameter is used under the ,harlem ,river1 and being for single track1 two parallel tunnels were built side by side4 ,illustration3 ,,fig4 #aai4--;,double-,track ,section1 ,new ,york ,rapid ,transit ,railway4 ,the main line from the ,city ,hall loop to about #ajb;d ,st4 consists of four tracks built side by side in one conduit1 except for that portion under the present ,fourth ,ave4 tunnel where two parallel double-track tunnels are employed4 ,the ,west ,side ,line will consist of double tracks laid in one conduit1 except across ,manhattan ,st4 and beyond #aijth ,st41 where it is carried on an elevated structure4 ,the ,east ,side ,line consists of a double-track tunnel driven from #ajb;d ,st41 and the boulevard under ,central ,park to #aajth ,st4 and ,lenox ,ave41 and two parallel circular tunnels excavated under the ,harlem ,river1--the other portions of the road being double-track1 subway and elevated structure4 ,methods of ,excavation4--,both the double-and four-track subway were built by using the different varieties of the cut-and-cover method4 ,the single wide-trench method was used for the construction of the double-track line and also for the construction of the four-track line where the local conditions allowed it4 ,the single narrow-trench method was used for the construction of the four-track subway at #db;d ,st41 to meet with the peculiar conditions of the traffic4 ,almost the total length of the four-track line of the subway was built by means of the two parallel side trenches4 ,the slice method1 so successfully employed in the ,boston ,subway1 was used only on #db;d ,st4 west of #fth ,avenue4 ,lining4--,the lining of the subway is of concrete1 carried by a framework of steel4 ,the floor consists of a foundation layer of concrete at least eight inches thick on good foundation1 but thicker1 according to conditions1 where the foundation is bad4 ,on top of this is placed another layer of concrete1 with a layer of waterproofing between the two4 ,in this top layer are set the stone pedestals for the steel columns1 and the members making up the tracks4 ,in the four-track subway1 the steel framework consists of transverse bents of columns1 and ,i-beams spaced about five feet apart along the tunnel4 ,the three interior columns of each bent are built-up bulb-angle and plate columns of ,h-section4 ,the wall columns are ,i-beams1 as are also the roof beams2 between the ,i-beams1 wall columns1 and roof beams there is a concrete filling1 so that the roof of the subway will be made up of concrete arches resting on the flanges of the ,i-beams of the roof4 ,the concrete used is of one part ,portland cement1 two parts sand1 and four parts broken stones4 ,the double-track subway is built in the same way1 except that only one column is placed between the tracks for the support of the roof4 ,all the concrete masonry of the roof1 foundations1 and side walls contains a layer of waterproofing1 so as to keep perfectly dry the underground road1 and prevent the percolation of water4 ,this waterproofing is made up as follows3 ,on the lowest stratum of concrete1 whose surface is made as smooth as possible1 a layer of hot asphalt is spread4 ,on this asphalt are immediately laid sheets or rolls of felt2 another layer of hot asphalt is then spread over the felt1 and then another layer of felt laid1 and so on1 until no less than two1 and no more than six1 layers of felt are laid1 with the felt between layers of asphalt4 ,on top of the upper surface of asphalt the remainder of the concrete is put in place so as to reach the required thickness of the concrete wall4 ,illustration3 ,,fig4 #abj4--,park ,avenue ,deep ,tunnel ,construction1 ,new ,york ,rapid ,transit ,railway4 ,tunnels4--,when the distance between the roof of the proposed structure and the street was #bj ft4 or over1 the ,standard ,subway construction was replaced by tunnels4 ,three important tunnels have been constructed along the line of the ,new ,york ,rapid ,transit and these are located between #cc;d and #db;d ,streets on ,park ,ave41 under ,central ,park northeast of #ajdth ,st4 and under ,broadway north of #aeb;d ,st4 ,the ,park ,ave4 construction 7,fig4 #abj7 consists of two parallel double-track tunnels1 located on each side of the street1 and about #aj ft4 below the present tunnel4 ,the soil being composed of good rock1 the tunnels were driven by a wide heading1 and one bench1 since no strutting was required1 and the masonry lining1 even of the roof1 was left far behind the front of the excavation4 ,the masonry lining consists of concrete walls and brick arches4 ,the tunnels under ,central ,park and under ,broadway being driven through a similar rock1 the same method of excavation and the same manner of lining was used4 ,the tunnel under the ,harlem ,river was driven through soft ground2 and it was constructed as a submarine tunnel1 according to the caisson process4 ,the tunnels were lined with iron made up of segments1 with radial and circumferential flanges4 ,concrete was placed inside and flush with the flanges4 ,illustration3 ,,fig4 #aba4--;,harlem ,river ,tunnel1 ,new ,york ,rapid ,transit ,railway4 ,the tracks1 both in the subway and tunnels1 are an intimate part of the concrete flooring4 ,the rail rests on a continuous bearing of wooden blocks1 laid with the grain running transversely with respect to the line of the rail1 and held in place by two channel iron guard rails4 ,the guard rails are bolted to metal cross-ties embedded in the concrete4 ,viaduct4--,a considerable portion of the double-track branch lines north of #ajc;d ,st4 is viaduct1 or elevated structure4 ,the viaduct construction on the ,west ,side ,line extends1 including approaches1 from #abb;d ,st4 to very near #aceth ,st4 ,of this distance1 #bjah ft4 #h ins4 are viaduct proper1 consisting of plate girder spans carried by trestle bents at the ends1 and by trestle towers for the central portion4 ,the columns of the bents and towers are built-up bulb-angle and plate columns of ,h-section of the same form as those used in the bents inside the subway4 ,the approaches proper are built of masonry4 ,the elevated line proper consists of plate girder spans1 supported on plate cross girders carried by columns4 ,stations4--,many stations are built along the line4 ,these are located on each side of the street4 ,the entrances at the stations consist of iron framework1 with glass roofs covering the descending stairways4 ,the passageways leading down are walled with white enameled bricks and wainscoted with slabs of marble4 ,the stations for the local trains are located on each side of the road close to the walls1 since the outside tracks are reserved for the local trains1 while the middle ones are reserved for the expresses4 ,the few stations for the express trains are located between the middle and outside tracks4 ,stations are provided with all the conveniences required1 having toilet rooms1 news stands1 benches1 etc41 and are lighted day and night by numerous arc lamps4 ,general4--,the contractor completed the work in four years4 ,no difficulty was encountered in doing this1 since the great extension of the road and the great width of the avenues under which it runs allowed work all along the line at the same time4 ,the work1 briefly summarized1 comprises the following items3-- ,length of all sections1 ft4 #aji1egj ,total excavation of earth1 cu4 yds4 #a1gjj1bbh ,earth to be filled back1 cu4 yds4 #ggc1jic ,rock excavated1 cu4 yds4 #iba1abh ,rock tunneled1 cu4 yds4 #cfh1fjf ,steel used in structure1 tons #fe1jdd ,cast iron used1 tons #g1ija ,concrete1 cu4 yds4 #dhi1abb ,brick1 cu4 yds4 #ah1eai ,waterproofing1 sq4 yds4 #gge1gie ,vault lights1 sq4 yds4 #f1fdj ,local stations1 number #dc ,express stations1 number #e ,station elevators1 number #aj ,track total1 lin4 ft4 #cje1chj underground1 lin4 ft4 #bde1ead elevated1 lin4 ft4 #ei1gff ,in addition to the construction of the railway itself1 it was necessary to construct or reconstruct certain sewers1 and to adjust1 readjust1 and maintain street railway lines1 water pipes1 subways1 and other surface and subsurface structures1 and to relay street pavements4 ,the total cost of the work1 according to the contract signed by ,mr4 ,mc,donald1 was #ce1jjj1jjj4 ,dividing this amount by the total length of the road1 which is #aji1egj lineal feet1 we have the unit cost a lineal foot #cae1 or a little less than unit of cost of the ,boston ,subway1 which was #cdb per lineal foot4 ,the road belongs to the city4 ,the contractor acts as an agent for the city in carrying out the work1 and he is the leaser of the road for fifty years4 ,the work was paid for as soon as the various parts of the road were completed1 and the money was obtained from an issue of city bonds4 ,during the fifty years' lease the contractor will pay the interest plus #a of the face value of the bonds4 ,this #a goes to the sinking-fund1 which within the fifty years at compound interest forms the total sum required for the redemption of bonds4 ,this first ,new ,york ,subway has been extended to ,brooklyn1 and more lines will be built so as to form a complete underground railway system to accommodate the ever-increasing traveling crowd of the ,american metropolis4 ,no new method of construction has been devised yet4 ,the only variation from the illustrated methods has been where the subway is built underneath the ,elevated ,road which had to be strongly supported during the construction of the subway4 ,this has been done in two different ways1 either by supporting the columns of the ,elevated ,road by means of two wooden ,a-frames abutting at the top and leaving a large space close to the foot of the column where a pit was excavated to the required depth of the subway1 or by attaching the columns to long iron girders placed longitudinally and resting with both ends in firm soil4 ,,chapter ,,xvii4 ,,submarine ,,tunneling3 ,,general ,,discussion4--,,the ,,severn ,,tunnel4 ,,general ,,discussion4 ,submarine tunnels1 or tunnels excavated under the beds of rivers1 lakes1 etc41 have been constructed in large numbers during the last quarter of a century1 and the projects for such tunnels1 which have not yet been carried to completion1 are still more numerous4 ,among the more notable completed works of this character may be noted the tunnel under the ,river ,severn and those under the ,river ,thames in ,england1 the one under the ,river ,seine in ,france1 those under the ,st4 ,clair1 ,detroit1 ,hudson1 ,harlem and ,east ,rivers1 and the one under the ,boston ,harbor for railways1 that under the ,east ,river for gas mains1 that under ,dorchester ,bay1 ,boston1 for sewage1 and those under ,lakes ,michigan and ,erie for the water supply of ,milwaukee1 ,chicago1 ,buffalo1 and ,cleveland in ,america4 ,for the details of the various projected submarine tunnels of note1 which include tunnels under the ,english and ,irish ,channels1 under the ,straits of ,gibraltar1 under the sound between ,copenhagen in ,denmark and ,malm in ,sweden1 under the ,messina ,straits between ,italy and ,sicily1 and under the ,straits of ,northumberland between ,new ,brunswick and ,prince ,edward ,island1 and those connecting the various islands of the ,straits of ,behring1 the reader is referred to the periodical literature of the last few years4 ,previous to attempting the driving of a submarine tunnel it is necessary to ascertain the character of the material it will penetrate4 ,this fact is generally determined by making diamond-drill borings along the line1 and the object of ascertaining it is to determine the method of excavation to be adopted4 ,if the material is permeable and the tunnel must pass at a small depth below the river bed1 a method will have to be adopted which provides for handling the difficulty of inflowing water4 ,if1 on the other hand1 the tunnel passes through impermeable material at a great depth1 there will be no unusual trouble from water1 and almost any of the ordinary methods of tunneling such materials may be employed4 ,shallow submarine tunnels through permeable material are usually driven by the shield method or by the compressed air method1 or by a method which is a combination of the first and second4 ,it is not an uncommon experience for a submarine tunnel to start out in firm soil and unexpectedly to find that this material becomes soft and treacherous as the work proceeds1 or that it is intersected by strata of soft material4 ,the method of dealing with this condition will vary with the circumstances1 but generally if any considerable amount of soft material has to be penetrated1 or if the inflow of water is very large1 the firm-ground system of work is changed to one of the methods employed for excavating soft-ground submarine tunnels4 ,the ,milwaukee water supply tunnel1 described elsewhere1 is a notable example of submarine tunnels1 began in firm material which unexpectedly developed a treacherous character after the work had proceeded some distance4 ,occasionally the task of building a submarine tunnel in the river bed arises4 ,in such cases the tunnel is usually built by means of cofferdams in shallow water1 and by means of caissons in deep water4 ,submarine tunnels under rivers are usually built with a descending grade from each end which terminates in a level middle position1 the longitudinal profile of the tunnel corresponding to the transverse profile of the river bottom4 ,where1 however1 such tunnels pass under the water with one end submerged1 and the other end rising to land like the water supply tunnels of ,chicago1 ,milwaukee1 and ,cleveland1 the longitudinal profile is commonly level1 or else descends from the shore to a level position reaching out under the water4 ,the drainage of submarine tunnels during construction is one of the most serious problems with which the engineer has to deal in such works4 ,this arises from the fact that1 since the entrances of the tunnel are higher than the other parts1 all of the seepage water remains in the tunnel unless pumped out1 and from the possibility of encountering faults or permeable strata1 which reach to the stream bed and give access to water in greater or less quantities4 ,generally1 therefore1 the excavation is conducted in such a manner that the inflowing water is led directly to sumps4 ,to drain these sumps pumping stations are necessary at the shore shafts1 and they should have ample capacity to handle the ordinary amount of seepage1 and enough surplus capacity to meet probable increases in the inflow4 ,for extraordinary emergencies this plant may have to be greatly enlarged1 but it is not usual to provide for these at the outset unless their likelihood is obvious from the start4 ,the character and size of the pumping plants used in constructing a number of well-known tunnels are described in ,chapter ,,xii4 ,in this book submarine tunnels will be classified as follows3 7#a7 ,tunnels in rock or very compact soils1 which are driven by any of the ordinary methods of tunneling similar materials on land2 7#b7 tunnels in loose soils1 which may be driven1 7a7 by compressed air1 7b7 by shields1 or 7c7 by shields and compressed air combined2 7#c7 tunnels on the river bed1 which are constructed1 7a7 by cofferdams1 or 7b7 by caissons4 ,to illustrate tunnels of the first class1 the ,river ,severn tunnel in ,england has been selected2 to illustrate those of the second class1 the several tunnels discussed in the chapter on the shield system of tunneling and the ,milwaukee tunnel is sufficient2 to illustrate those of the third class1 the ,van ,buren ,street tunnel in ,chicago1 the ,harlem1 the ,seine and the ,detroit ,river tunnels are selected4 ,,the ,,severn ,,tunnel4 ,the ,severn tunnel1 which carries the ,great ,western ,railway of ,england1 beneath the estuary of a large river1 is #d miles #fdb yards long4 ,it penetrates strata of conglomerate1 limestone1 carboniferous beds1 marl1 gravel1 and sand at a minimum depth of #dd ft4 below the deepest portion of the estuary bed4 ,the following description of the work is abstracted from a paper by ,mr4 ,l4 ,f4 ,vernon-,harcourt4#ab #ab ,proceedings ,inst4 ,c4 ,e41 vol4 cxxi4 ,the first work was the sinking of a shaft1 #ae ft4 in diameter1 lined with brickwork1 on the ,monmouthshire bank of the ,severn1 #bjj ft4 deep4 ,after the ,monmouthshire shaft had been sunk1 a heading #g ft4 square was driven under the river1 rising with a gradient of #a in #ejj from the shaft on the ,monmouthshire shore1 so as to drain the lowest part of the tunnel4 ,near to the first1 a second shaft was sunk and tubbed with iron1 in which the pumps were placed for removing the water from the tunnel works1 connection being made by a cross-heading with the heading from the first shaft4 ,there was also a shaft on the ,gloucestershire shore2 and two shafts inland from the first on the ,monmouthshire side1 to expedite the construction of the tunnel4 ,headings were then driven in both directions along the line of the tunnel1 from the four shafts2 and the drainage heading from the old shaft was continued1 in the line of the tunnel1 under the deep channel of the estuary1 and up the ascending gradient towards the ,gloucestershire shore1 till1 in ,october1 #ahgi1 it had reached to within about #acj yards of the end of the descending heading from the ,gloucestershire shaft4 ,during this period1 though the work had progressed slowly1 no large quantity of water had been met with in any of the headings1 in spite of their already extending under almost the whole width of the estuary4 ,on ,october #ah1 #ahhi1 however1 a great spring was tapped by the heading which was being driven landwards from the old shaft1 about #dj ft4 above the level of the drainage heading2 and the water poured out from this land spring in such quantity that1 flowing along the heading1 falling down the old shaft1 and thus finding its way into the drainage heading and the long heading of the tunnel under the estuary in connection with it1 it flooded the whole of the workings in communication with the old shaft1 which it also filled within twenty-four hours from the piercing of the spring4 ,to obtain increased security against any influx of water from the deep channel of the estuary into the tunnel1 the proposed level portion of the tunnel1 rather more than a furlong long under this part1 was lowered #ae ft4 by increasing the descending gradient on the ,monmouthshire side from #a in #ajj to #a in #ij1 and lowering the proposed rail level on the ,gloucestershire side #ae ft4 throughout the ascent1 so as not to increase the gradient of #a in #ajj against the load4 ,a new shaft1 #ah ft4 in diameter1 was sunk slightly nearer the estuary on the ,monmouthshire shore than the old one2 two shafts also were sunk on the land side of the great spring for pumping purposes2 and additional pumping machinery was erected4 ,the flow from the spring into the old shaft was arrested by a shield of oak fixed across the heading2 and at last1 after numerous failures and breakdowns of the pumps1 the headings were cleared of water1 after a diver1 supplied with a knapsack of compressed oxygen1 had closed a door in the long heading under the estuary2 and the works were resumed nearly fourteen months after the flooding occurred4 ,the great spring was then shut off from the workings by a wall across the heading leading to the old shaft2 and1 owing to the lowering of the level of the tunnel1 a new drainage heading had to be driven from the bottom of the new shaft at a lower level1 which was made #e ft4 in diameter1 and lined with brickwork1 whilst the old drainage heading was enlarged to #i ft4 in diameter1 and lined with brickwork1 so as to aid in the permanent ventilation of the tunnel4 ,the lowering of the level1 moreover1 converted the bottom tunnel headings into top headings1 so that along more than a mile of the tunnel the semicircular arch1 #bf ft4 in diameter1 was built first1 and then1 after lowering the headings1 the invert was laid and the side walls were built up4 ,bottom headings were driven along the remainder of the tunnel1 and the work was expedited by means of break-ups4 ,ventilation was effected in the works by a fan #ah inches in diameter and #g ft4 wide1 fixed at the top of the new deep shaft2 the rock was bored by drills worked by compressed air2 the blasting was eventually effected exclusively by tonite1 owing to its being freer from deleterious fumes than any other explosive2 and the workings were lighted by ,swan and ,brush electric lamps4 ,the tunnel is lined throughout with vitrified brickwork1 between #b ft4 to #c ft4 thick1 set in cement1 and has an invert #a ft4 to #c ft4 in thickness2 the lining was commenced towards the end of #ahhj1 the headings under the river were joined in ,september1 #ahha1 and the last length of the tunnel1 across the line of the great spring1 was completed in ,april1 #ahhe4 ,water came in from the river through a hole in a pool of the estuary1 close to the ,gloucestershire shore1 in ,april1 #ahha1 during the lining of a portion of the tunnel1 but fortunately before the headings were joined4 ,this influx was stopped by allowing the water to rise in the tunnel to tide-level1 to prevent the enlargement of the hole1 which was then filled up at low water with clay1 weighted on the top with clay in bags4 ,the great spring broke out again in ,october1 #ahhc1 and flooded the works a second time2 but within four weeks the water had been pumped out and the spring again imprisoned4 ,during this period an exceptionally high tide1 raised still higher by a southwesterly gale1 inundated the low-lying land on the ,monmouthshire side of the estuary1 and1 flowing down one of the inland shafts1 flooded a section of the tunnel1 but the pumps removed this water within a week4 ,in order to construct the portion of tunnel traversing the line of the great spring1 the water was diverted into a side heading below the level of the tunnel1 leading to the old shaft1 whence it was pumped1 and the fissure below the tunnel was filled with concrete1 over which the invert was built4 ,an attempt to imprison the spring1 on the completion of this length of tunnel1 having resulted in imposing an excessive pressure on the brickwork1 leading to fractures and leakage1 a shaft1 #bi ft4 in diameter1 was sunk at the side of the tunnel at this point in #ahhf1 and pumps were erected powerful enough to deal with the entire flow of the spring4 ,the tunnel was opened for traffic in ,december1 #ahhf1 and gives access to a double line of railway1 connecting the lines converging to ,bristol with the ,south ,wales railway and the western lines4 ,the pumping power provided at the shaft connected with the great spring1 and at four other shafts1 is capable of raising #ff1jjj1jjj gallons of water per day1 the maximum amount pumped from the tunnel being #cj1jjj1jjj gallons a day4 ,the ventilation of the tunnel is effected by fans placed in the two main shafts on each bank of the estuary1 and the fan in the ,monmouthshire shaft is #dj ft4 in diameter1 and #ab ft4 wide4 ,the tunnel gives passage to a large traffic1 numerous through-trains between the north and southwest of ,england making use of it4 ,,chapter ,,xviii4 ,,submarine ,,tunneling 7,continued72 ,,the ,,compressed ,,air ,,method4--,,the ,,milwaukee ,,water-,,works ,,tunnel4 ,tunnels excavated at shallow depth from the bed of the river are liable to cave in under the great weight of the water and material above the roof4 ,besides1 the progress of the work will be greatly interfered with by the water which may reach the tunnel passing through the loose soil in large quantities4 ,to contend with these two sources of trouble1 different methods of constructing subaqueous tunnels have been devised2 they are3 by compressed air1 by shield1 and finally by a combination of these two methods1 viz41 by shield and compressed air4 ,the compressed air method was suggested by ,mr4 ,haskin1 the promoter and the first builder of the ,hudson ,river tunnel4 ,in #ahgd1 when he began to sink the shaft for the construction of his tunnel1 several subaqueous tunnels had already been driven by means of shields4 ,mr4 ,haskin had ideas of his own1 and thought he could dispense with the shield and could trust to compressed air1 since he was firmly convinced that compressed air alone could expel the water and temporarily support the roof of the excavation prior to the building of the lining masonry4 ,in other words1 he expected to substitute a core of compressed air for the core of earth removed4 ,in the patent granted him for this method of tunneling1 he expresses himself as follows3 8,the distinguishing feature of my system is that1 instead of using temporary facings of timber or other rigid material1 ,i rely upon the air pressure to resist the caving in of the wall and infiltration of water until the masonry wall is completed4 ,the pressure is1 of course1 to be regulated by the exigencies of the occasion4 ,the effect of such a pressure has been found to drive water in from the surface of the excavation1 so that the sand becomes dry40 ,the compressed air method was soon found to be inefficient1 even in the construction of the ,hudson tunnel where the roof of the excavation was supported by timbering in the manner indicated in the pilot system4 ,thus large subaqueous railway tunnels cannot be driven exclusively by the compressed air method2 still it has been successfully employed in the construction of small tunnels driven for aqueduct purposes4 ,but the use of compressed air marked a great progress in the art of submarine tunneling4 ,,the ,,milwaukee ,,water-,,works ,,tunnel4 ,the following description of the ,milwaukee ,water-,works ,tunnel is an example of subaqueous tunnels driven through good soil in the usual manner employed in land tunnels2 but afterward when treacherous material was encountered1 the work was continued by means of compressed air4 ,the new water supply intake tunnel for the city of ,milwaukee1 ,wis41 is one of the most difficult examples of tunnel construction which ,american engineering practice has afforded4 ,the difficulties were in a large measure unexpected when the work was decided upon and put under way4 ,the tunnel began and ended in a hard1 impervious clay1 practically a rock1 and all the preliminary investigations led to the conclusion that the same favorable material would be encountered for its entire length4 ,with such material a brick-lined tunnel #g ft4 in diameter presented no unusual problems2 but after about #afdj ft4 had been excavated from the shore end the tunnel ran out of the hard clay1 and for the next #fjj ft4 or more a variety of water-bearing material was encountered1 which tried the skill and patience of the engineer to their utmost4 ,other difficulties were indeed met with1 but these were of minor importance in comparison with that of safely and successfully penetrating the water-bearing drift4 ,the work of sinking the shore shafts and excavating the first #afjj ft4 of tunnel did not prove especially difficult4 ,a hard1 compact1 and rock-like clay1 bearing very little moisture1 was encountered all along1 and was blasted and removed in the ordinary manner4 ,the only mishap which occurred with this portion of the work was the destruction of the contractor's boiler plant by fire on ,jan4 #ab1 #ahia1 which allowed the tunnel to fill with water1 and delayed work about a month4 ,by ,oct4 #ba1 #ahia1 #afdj ft4 had been driven1 averaging about #f ft4 per day1 all in the hard clay4 ,no timbering had been necessary1 and except for the first #ajj ft4 of the tunnel there was very little seepage4 ,on the afternoon of ,oct4 #ba water was observed coming out from one of the drill holes in the heading1 but no attention was paid to it4 ,shortly after a blast was fired1 and was immediately followed by a rush of water from the heading4 ,an unsuccessful attempt was made to check the flow1 and the pumps were started2 but they were unable to keep the water down1 and after seven hours' hard work the tunnel was abandoned4 ,by the next morning the tunnel and shaft were full of water4 ,several attempts were made to empty the tunnel2 but the limited pumping capacity was not equal to the task1 and it was finally decided to install larger pumps4 ,the pumping had1 however1 shown that about #ajjj gallons of water a minute was coming through the leak4 ,with the increased pumping plant the tunnel was finally laid dry ,feb4 #ac1 #ahib4 ,upon examination the head of the drift was found to be in the same undisturbed condition in which it was left when the water broke in three months before4 ,a brick bulkhead was built into the end of the brickwork of the tunnel1 and provided with a timber door for passage1 and two #aj-;in4 pipes for the outlet of the water4 ,with these openings closed1 the flow was checked sufficiently to allow the placing of pumps at the bottom of the shore shaft4 ,meanwhile the pressure of the water against the bulkhead caused dangerous leakage1 and so after the pumps were in position the #aj-;in4 pipes were opened1 relieving the pressure and allowing the water its normal rate of flow4 ,trouble with the pumps now arose1 and after various stoppages and breaks the discharge pipe finally fell1 disabling the whole plant4 ,it became necessary to close the #aj-;in4 pipes in the bulkhead and draw up the pumps4 ,this allowed the tunnel to again fill with water4 ,after thoroughly overhauling the pumping machinery1 the contractor again laid the tunnel dry on ,march #ai2 and after the pumps had been permanently placed so as to take care of the water1 an examination of the work was made4 ,it was found that the water was coming from the north1 and with the hope of avoiding the difficulties of the old heading1 it was decided to make a dtour of the south4 ,on ,april #af work was begun at a point about #ij ft4 back from the face1 and deflecting the line about #ch toward the south4 ,about #ch ft4 from the angle of junction a brick bulkhead with two #h-;in4 openings was built into the new bore4 ,the work progressed successfully for about #ge ft41 when water was again encountered2 and upon pushing forward the heading1 gravel and sand came in such quantities that it was found impracticable to continue the work further4 ,on ,june #a the bulkhead was permanently closed1 and the work in this direction was abandoned4 ,a further and closer examination was now made of the heading first abandoned4 ,upon breaking through the rock-like clay it was found that the water came from an underground stream flowing from the north through a well defined channel in red clay4 ,this channel was about #ac ft4 above the grade of the tunnel2 and above it in every direction visible was a bed of hard1 dry1 red clay1 while immediately in front of the face of the work was a bank of coarse gravel4 ,fig4 #abb is a sketch of the channel and stream where they entered the work4 ,in this last drawing the photograph has been followed exactly1 no particular being exaggerated in the slightest4 ,the water from this stream was clear and pure2 and a chemical analysis showed that it was not lake water1 but must come from some separate source4 ,illustration3 ,,fig4 #abb4--,sketch ,showing ,underground ,stream1 ,milwaukee ,water-,works ,tunnel4 ,while the engineer did not consider the difficulty of proceeding along the old line insurmountable1 it was decided to be less difficult on the whole to go back from #aej ft4 to #age ft4 and deflect the line to the north and upward1 so as to pass over the underground entrance4 ,instead of allowing the water to flow at its normal rate and take care of it by pumping1 the contractors desired to reduce the pumping1 and to this end they constructed a bulkhead just west of the deflection toward the south with a view of shutting off the water4 ,the water1 however1 accumulated with a pressure of some #ej lbs4 per sq4 in4 and penetrated the filling around the brick lining of the tunnel1 preventing the cutting through of the lining for the new line4 ,a second bulkhead was then built about #bj ft4 west of the first1 but with not much better results1 for upon closing it the water was found to leak through the brickwork for a long distance west4 ,finally on ,aug4 #b1 #ahib1 the contractors lifted their pumps and allowed the tunnel to fill again with water4 ,no further work was done on the tunnel by the contractors1 although they continued work on the lake shaft for some months4 ,difficulties had1 however1 arisen here1 which will be described further on2 and finally a disagreement arose between the contractors and the city over the delay in prosecuting the tunnel work and over one or two other questions1 which resulted in the ,city ,council suspending their contract and ordering the ,board of ,public ,works to go ahead with the work4 ,the first step to be taken by the engineer was to purchase adequate pumping machinery and empty the tunnel4 ,this was effected ,jan4 #ag1 #ahid2 and as soon as practicable thereafter the two bulkheads were removed and the tunnel cleaned1 tram-car tracks laid1 and everything prepared for work4 ,it was now determined to go ahead on the original line of the tunnel if possible1 and the bulkhead here was removed and work begun4 ,meanwhile1 a safety bulkhead had been built to replace the first one torn away4 ,this was provided with a door and drainage pipes4 ,work was begun on the original heading1 but had proceeded only a little way when the water broke in1 driving out the workmen4 ,this was removed three or four times1 when the flow suddenly increased to #cjjj gallons per minute4 ,an examination of the lake bottom above the break showed that it had settled down1 indicating that the new break connected with the lake bottom1 and making further work along the original line out of the question4 ,the question now arose what it was best to do4 ,it was impracticable to use a shield1 as the material ahead of the break required blasting1 and the pressure from above was enormous4 ,on account of its expense and difficulty of application the freezing process did not seem advisable1 and the plenum process was likewise out of the question on account of the great pressure which would be required at this depth4 ,the dtour to the south which had been made by the contractor had been unsuccessful1 and had left the ground in a treacherous condition4 ,to depress the tunnel was not advisable1 for it was not by any means certain that the bed of gravel could be avoided in that way2 and1 moreover1 it would be necessary to ascend again further on1 and thus leave a trap which would effectually cut off escape to those at work on the face if water again broke into the tunnel4 ,it was finally decided that the old plan of deflecting the line toward the north and upward so as to pass over the underground stream should be tried4 ,a hole was therefore cut through the tunnel lining #adcc ft4 from the shore1 and work was begun on a dtour of #bj toward the north and an upward grade of #aj4 ,fair progress was made on this new line1 gradually ascending into solid rock1 until ,may #aj1 when the test borings1 which were constantly made in every direction from the face1 showed that sand was being approached4 ,a brick bulkhead was therefore built into the masonry as a safeguard1 should it happen that water was encountered in large quantities4 ,as the borings seemed to indicate that the top surface of the rock underlying the sand was nearly level1 the lower half of the tunnel was first excavated1 leaving about #ah ins4 of the rock to serve as a roof 7,sketch a1 ,fig4 #abc71 and the brick invert was built for a distance of #eb ft4 ,the rock roof was then carefully broken through for short distances at a time1 and short sheeting driven ahead into the sand1 which proved to be a very fine quicksand flowing through the smallest openings4 ,extreme care had to be taken in this work1 but little by little the brickwork was pushed ahead until at a distance of #ij ft4 from the point where the sand was first met1 and #bjh ft4 from the old tunnel1 the sand stopped and the heading entered a hard clay4 ,all this work had been done on an ascending grade1 and the ascent was continued about #dj ft4 farther in the clay4 ,by this time a sufficient elevation was gained to pass over the underground stream1 and the tunnel line was changed to head toward the lake shaft1 and the grade reduced to a level4 ,the underground stream was passed without trouble and the tunnel continued for a distance of #ed ft4 without difficulty4 ,on ,july #aj the clay in the heading suddenly softened1 and before the miners could secure it by bracing1 the water rushed in1 followed by gravel1 filling up solidly some #cd ft4 of the tunnel before it was stopped by a timber bulkhead hastily built4 ,illustration3 ,longitudinal ,section ,showing ,method of ,construction in ,rock ,covered with ,quicksand4 ,sketch 8a04 ,section ,a-,b-,c-,d4 ,sketch 8c04 ,longitudinal ,section of ,tunnel4 ,sketch 8b04 ,cross ,section ,showing ,manner of ,constructing ,lining around ,boulder4 ,sketch 8d04 ,,fig4 #abc4--,sketch ,showing ,methods of ,lining1 ,milwaukee ,water-,works ,tunnel4 ,upon examining the lake bottom a cavity over #fj ft4 deep and #aj ft4 in diameter was found directly over the end of the tunnel1 which had been caused by the gravel breaking into the tunnel4 ,having now reached an elevation where it was possible to use compressed air1 it was determined to put in double air-locks and use the plenum process4 ,the locks were built1 and some #fgj cu4 yds4 of clay were dumped into the hole in the lake bottom4 ,on ,aug4 #d the air-locks were tried with #bf lbs4 air pressure2 but1 upon a temporary release of the pressure1 the water passed around the locks and back of the tunnel lining for some distance1 and even forced through the lining1 carrying considerable clay and fine sand with it4 ,upon sounding the lake bottom it was found that the cavity had again increased to a depth of #fe ft41 whereupon an additional #fjj cu4 yds4 of clay were dumped into it4 ,on account of the water leaking through the brickwork1 the only dry place to cut through the brickwork and build in an air-lock was just ahead of the brick bulkhead4 ,this lock was completed ,aug4 #bg1 and to avoid encountering the danger of the direct connection with the lake at the end of the drift1 it was decided to make another dtour to the north4 ,on ,aug4 #bh1 therefore1 the brick on the north side of the tunnel #ab ft4 back from the end of the brickwork was cut through under #be lbs4 air pressure1 and work proceeded in good1 hard clay4 ,the original air-lock was cut out and a new lock built into this clay about #cd ft4 from the last dtour1 to be used in case of further difficulties4 ,after building the tunnel for about #hj ft4 from the dtour1 the soundings again indicated the approach to gravel and water1 and on ,oct4 #ad the water broke through from the bottom in such volume and with such force that the men ran out1 closing every air-lock and the valves of every drain in their haste to escape1 until the brick bulkhead was reached4 ,it was with great difficulty that the portion of the tunnel up to the last air-lock was recovered and cleaned out4 ,it was now recognized that a pressure of from #ch to #dj lbs4 of air would be needed to hold this water1 and accordingly another compressor was added to the plant4 ,with a pressure of #cf lbs4 the water was driven out and the work again started4 ,at this time also an additional #cej cu4 yds4 of clay were dumped into the hole in the lake bottom4 ,altogether1 #afbj cu4 yds4 of clay had been put into this hole4 ,loose gravel and boulders1 some of immense size1 were now encountered1 and the work became exceedingly difficult on account of the great escape of air4 ,the interstices between the gravel and boulders were not filled with silt or sand1 but contained water4 ,moreover1 this material extended upward to the lake bottom1 as was shown by the escape of air at the surface of the lake4 ,for an area of several hundred square feet the surface of the water resembled a pot of boiling water4 ,at times the air would escape very rapidly2 and again only a few bubbles would show4 ,it need hardly be said that the work in this gravel was very slow4 ,it was impossible to blast or to tear out the large boulders whole1 as so much surface would be exposed that an inrush of water would take place despite the air pressure4 ,the method of procedure was to excavate a heading and build the brick roof arch first1 and then to take out the bench and build the invert4 ,fig4 #abc gives a number of sketches showing how the work was done4 ,a short piece of heading was taken out1 the top and face of the bench being meanwhile plastered with clay 7,sketches b and c1 ,fig4 #abc7 to reduce the escape of air1 and then the roof arch was built and supported on side sills resting on the bench4 ,bit by bit the roof arch was pushed forward until some little distance had been completed1 then the heading was plastered with clay and the bench taken out little by little and the invert built4 ,all the gravel except the small area upon which work was actually in progress was kept thoroughly plastered with clay2 and as the air escaped through the completed brickwork very rapidly1 water was allowed to cover a portion of the invert 7see ,sketch c1 ,fig4 #abc71 so as to reduce the area of escape4 ,when a large boulder was reached1 which lay partly within and partly without the tunnel section1 the lining was built out and around it1 as shown in ,sketch d1 ,fig4 #abc4 ,the boulder was then broken and taken out4 ,all through this gravel bed the cross-section of the lining is made irregular by the construction of these pockets in the lining to get around boulders4 ,sometimes they were on one side and sometimes on the other1 or on both1 or at the top or bottom4 ,in fact1 there was no regularity4 ,despite the hazard and danger of this work1 continual progress was made1 though sometimes it was only #d ft4 of completed tunnel per week1 working night and day2 and1 if some cases of caisson disease be excepted1 the only mishap occurring was a fire which got into the timber packing behind the lining and caused some trouble4 ,from the gravel the tunnel ran into clay and quicksand1 and then into hard1 dry clay similar to that encountered near the shore4 ,some difficulty was had with the quicksand1 but it was successfully overcome2 and when the hard clay was struck1 the trouble1 as far as the work from the shore shaft was concerned1 was virtually over4 ,meanwhile1 a different set of afflictions had come upon the engineer and contractors in sinking the lake shaft and driving the heading toward shore4 ,this shaft was intended to be built by sinking a cast-iron cylinder #aj ft4 in diameter1 made up of sections bolted together4 ,work was begun ,july #e1 #ahib1 and the sinking was accomplished first by weighting the cylinder1 and afterwards by pumping out the sand and water within it until the pressure from the outside broke through under the cutting edge and forced the sand into the cylinder1 allowing it to sink a little4 ,from #aj to #cj cu4 yds4 of sand were carried into the cylinder each time1 and finally it was feared that if the process continued1 the crib1 which had been previously erected1 would be undermined4 ,on ,sept4 #f1 therefore1 the contractors were ordered to discontinue this method of work4 ,no change was made1 however1 until ,oct4 #a1 when the cylinder had reached a depth of #fh ft41 and by this time there was quite a large cavity underneath the crib4 ,this was refilled1 and the cylinder pumped out1 and excavation begun inside of it4 ,on ,oct4 #aa a #b-;ft4 deep ring of brickwork was laid underneath the cutting edge2 but in trying to put in another ring beneath the first1 two days later1 the sand and water broke through the bottom1 driving the men out1 and filling the cylinder to a depth of #af ft4 with sand4 ,the pumps were started1 but the water could not be lowered to a greater depth than #fj ft4 ,at the request of the contractors1 the city engineer had a boring made at the center of the shaft to determine the character of the material to be further penetrated4 ,this boring showed that sand mixed with loam and gravel would be found for a depth of #bf ft41 then would come #ae ft4 of red clay1 and finally a layer of hard clay like that penetrated by the shore end of the tunnel4 ,about the middle of ,december the contractors made another attempt to pump the shaft1 but finding that the water came in at the rate of #be gallons a minute1 abandoned the attempt4 ,in the latter part of ,february preparations were made to put an air-lock in the shaft and use compressed air4 ,hardly had the work been begun by this system when1 on ,april #bj1 #ahic1 a terrific easterly storm swept the top of the crib bare of the buildings and machinery1 and drowned all but one of the #ae men at work there4 ,this disaster delayed the work for some time1 but in ,june the contractors erected a new building and new machinery1 and resumed work4 ,very little progress was made2 and the air escaped so rapidly that it loosened the sand surrounding the shaft and reduced the friction to such an extent that on ,july #bh the entire cylinder lifted bodily about #f ft41 and sand rushed in1 filling the lower part of the cylinder to within #de ft4 of the lake surface4 ,no further work was done by the contractors although they submitted a proposition to sink a steel cylinder inside the cast-iron cylinder and extending from #e ft4 above datum to #ajj ft4 below datum for #cjj per ft4 ,this proposition was refused by the city2 and since work on the tunnel proper had been abandoned by the contractors some time before1 as had already been described1 the city suspended their contract on ,oct4 #ai4 ,on ,oct4 #cj a contract was made with ,mr4 ,thos4 ,murphy of ,milwaukee1 ,wis41 to sink a steel cylinder inside the old iron cylinder4 ,the water was first pumped out of the old cylinder1 and a timber bulkhead built at the bottom4 ,on this the steel cylinder was built1 and then the bulkhead was removed4 ,air pressure was put on1 and the excavation proceeded successfully until the bottom layer of clay was met with1 when all chances for trouble ceased4 ,the cylinder1 as it was completed1 penetrated #i ft4 into the hard clay1 and was underpinned with brickwork for a depth of #bi ft4 or more1 to a point #d ft4 below the grade line of the tunnel4 ,at the lower end1 the section of the shaft was changed from a circle to a square4 ,later the steel cylinder was lined with brick4 ,on ,march #bh1 #ahid1 an agreement was made with ,mr4 ,thos4 ,murphy to construct the tunnel from the lake shaft toward the shore4 ,except that considerable water was encountered1 which1 owing to inadequate pumping machinery1 filled the tunnel and shaft at two different times1 and had to be removed1 no very great difficulty was had with this part of the work4 ,on ,july #bh1 #ahie1 the headings from the lake and shore shafts met4 ,meanwhile the cast-iron pipe intake1 the intake crib1 etc41 had been completed1 and practically all that remained to be done was to clean the tunnel and lift the pumping machinery at the shore shaft4 ,during the cleaning1 the air pressure had been kept up on account of the leakage through the brick lining1 and1 indeed1 the pressure was kept up until the last possible moment1 and everything made ready for removing the air-locks1 bulkheads1 pumps1 etc41 in the least possible time4 ,the pumps were the last to come out4 ,,chapter ,,xix4 ,,submarine ,,tunneling 7,continued74 ,,the ,,shield ,,system4 ,historical ,introduction4--,the invention of the shield system of tunneling through soft ground is generally accredited to ,sir ,isambard ,brunel1 a ,frenchman born in #agfi1 who emigrated to the ,united ,states in #agic1 where he remained six years1 and then went to ,england1 in which country his epoch-making invention in tunneling was developed and successfully employed in building the first ,thames tunnel1 and where he died in #ahdi1 a few years after the completion of this great work4 ,sir ,isambard is said to have obtained the idea of employing a shield to tunnel soft ground from observing the work of ship-worms4 ,he noticed that this little animal had a head provided with a boring apparatus with which it dug its way into the wood1 and that its body threw off a secretion which lined the hole behind it and rendered it impervious to water4 ,to duplicate this operation by mechanical means on a large enough scale to make it applicable to the construction of tunnels was the plan which occurred to the engineer2 and how closely he followed his animate model may be seen by examining the drawings of his first shield1 for which he secured a patent in #ahah4 ,briefly described1 this device consisted of an iron cylinder having at its front end an auger-like cutter1 whose revolution was intended to shove away the material ahead and thus advance the cylinder4 ,as the cylinder advanced the perimeter of the hole behind was to be lined with a spiral sheet-iron plating1 which was to be strengthened with an interior lining of masonry4 ,it will be seen that the mechanical resemblance of this device to the ship-worm1 on which it is alleged to have been modeled1 was remarkably close4 ,in the same patent in which ,sir ,isambard secured protection for his mechanical ship-worm he claimed equal rights of invention for another shield1 which is of far greater importance in being the prototype of the shield actually employed by him in constructing the first ,thames tunnel4 ,this alternative invention1 if it may be so termed1 consisted of a group of separate cells which could be advanced one or more at a time or all together4 ,the sides of these cells were to be provided with friction rollers to enable them to slide easily upon each other2 and it was also specified that the preferable motive power for advancing the cells was hydraulic jacks4 ,to summarize briefly1 therefore1 the two inventions of ,brunel comprehended the protecting cylinder or shield1 the closure of the face of the excavation1 the cellular division1 the hydraulic-jack propelling power1 and cylindrical iron lining1 which are the essential characteristics of the modern shield system of tunneling4 ,the next step required was the actual proof of the practicability of ,brunel's inventions1 and this soon came4 ,those who have read the history of the first ,thames tunnel will recall the early unsuccessful attempts at construction which had discouraged ,english engineers4 ,five years after ,brunel's patent was secured a company was formed to undertake the task again1 the plan being to use the shield system1 under the personal direction of its inventor as chief engineer4 ,for this work ,brunel selected the cellular shield mentioned as an alternative construction in his original patent4 ,he also chose to make this shield rectangular in form4 ,this choice is commonly accounted for by the fact that the strata to be penetrated by the tunnel were practically horizontal1 and that it was assumed by the engineer that a rectangular shield would for some reason best resist the pressures which would be developed4 ,whatever the reason may have been for the choice1 the fact remains that a rectangular shield was adopted4 ,the tunnel as designed consisted of two parallel horseshoe tunnels1 #ac ft4 #i ins4 wide and #af ft4 #d ins4 high and #abjj ft4 long1 separated from each other by a wall #d ft4 thick1 pierced by #fd arched openings of #d ft4 span1 the whole being surrounded with massive brickwork built to a rectangular section measuring over all #ch ft4 wide and #bb ft4 high4 ,the first shield designed by ,brunel for the work proved inadequate to resist the pressures1 and it was replaced by another somewhat larger shield of substantially the same design1 but of improved construction4 ,this last shield was #bb ft4 #c ins4 high and #cg ft4 #f ins4 wide4 ,it was divided vertically into twelve separate cast-iron frames placed close side by side1 and each frame was divided horizontally into three cells capable of separate movement1 but connected by a peculiar articulated construction1 which is indicated in a general way by ,fig4 #abd4 ,to close or cover the face of the excavation1 poling-boards held in place by numerous small screw-jacks were employed4 ,each cell or each frame could be advanced independently of the others1 the power for this operation being obtained by means of screw-jacks abutting against the completed masonry lining4 ,briefly described1 the mode of procedure was to remove the poling-boards in front of the top cell of one frame1 and excavate the material ahead for about #f ins4 ,this being done1 the top cell was advanced #f ins4 by means of the screw-jacks1 and the poling-boards were replaced4 ,the middle cell of the frame was then advanced #f ins4 by repeating the same process1 and finally the operation was duplicated for the bottom cell4 ,with the advance of the bottom cell one frame had been pushed ahead #f ins41 and by a succession of such operations the other eleven frames were advanced a distance of #f ins41 one after the other1 until the whole shield occupied a position #f ins4 in advance of that at which work was begun4 ,the next step was to fill the #f-;in4 space behind the shield with a ring of brickwork4 ,illustration3 ,,fig4 #abd4--,longitudinal ,section of ,brunel's ,shield1 ,first ,thames ,tunnel4 ,the illustration1 ,fig4 #abd1 is the section parallel to the vertical plane of the tunnel through the center of one of the frames1 and it shows quite clearly the complicated details of the shield construction4 ,two features which are to be particularly noted are the suspended staging and centering for constructing the roof arch1 and the top plate of the shield extending back and overlapping the roof masonry so as to close completely the roof of the excavation and prevent its falling4 ,notwithstanding its complicated construction and unwieldy weight of #abj tons1 this shield worked successfully1 and during several months the construction proceeded at the rate of #b ft4 every #bd hours4 ,there were two irruptions of water and mud from the river during the work1 but the apertures were effectually stopped by heaving bags of clay into the holes in the river bed1 and covering them over with tarpaulin1 with a layer of gravel over all4 ,the tunnel was completed in #ahdc1 at a cost of about #efjj per lineal yard1 and #bj years from the time work was first commenced1 including all delays4 ,illustration3 ,,fig4 #abe4--;,first ,shield ,invented by ,barlow4 ,the next tunnel to be built by the shield system was the tunnel under ,london ,tower constructed by ,barlow and ,greathead and begun in #ahfi4 ,in #ahfc ,mr4 ,peter ,w4 ,barlow secured a patent in ,england for a system of tunnel construction comprising the use of a circular shield and a cylindrical cast-iron lining4 ,the shield1 as shown by ,fig4 #abe1 was simply an iron or steel plate cylinder4 ,the cylinder plates were thinned down in front to form a cutting edge1 and they extended far enough back at the rear to enable the advance ring of the cast-iron lining to be set up within the cylinder4 ,in simplicity of form this shield was much superior to ,brunel's2 but it seems very doubtful1 since it had no diametrical bracing of any sort1 whether it would ever have withstood the combined pressure of the screw-jacks and of the surrounding earth in actual operation without serious distortion1 and1 probably1 total collapse4 ,it should also be noted that ,barlow's shield made no provision for protecting the face of the excavation1 although the inventor did state that if the soil made it necessary such a protection could be used4 ,the patent provided for the injection of liquid cement behind the cast-iron lining to fill the annular space left by the advancing tail-plates of the shield4 ,although ,barlow made vigorous efforts to get his shield used1 it was not until #ahfh that an opportunity presented itself4 ,in the meantime the inventor had been studying how to improve his original device1 and in #ahfh he secured additional patents covering these improvements4 ,briefly described1 they consisted in partly closing the shield with a diaphragm as shown by ,fig4 #abf4 ,the uninclosed portion of the shield is here shown at the center1 but the patent specified that it might also be located below the center in the bottom part of the shield4 ,the idea of the construction was that in case of an irruption of water the upper portion of the shield could be kept open by air pressure1 and work prosecuted in this open space until the shield had been driven ahead sufficiently to close the aperture1 when the normal condition of affairs would be resumed4 ,this was obviously an improvement of real merit4 ,the partial diaphragm also served to stiffen the shield somewhat against collapse1 but the thin plate cutting-edges and most of the other structural weaknesses were left unaltered4 ,to summarize briefly the improvements due to ,barlow's work1 we have3 the construction of the shield in a single piece2 the use of compressed air and a partial diaphragm for keeping the upper part of the shield open in case of irruptions of water2 and the injection of liquid cement to fill the voids behind the lining4 ,illustration3 ,longitudinal ,section4 ,cross ,section4 ,,fig4 #abf4--,second ,shield ,invented by ,barlow4 ,turning now to the ,london ,tower tunnel work1 it may first be noted that ,barlow found some difficulty in finding a contractor who was willing to undertake the job1 so little confidence had engineers generally in his shield system4 ,one man1 however1 ,mr4 ,j4 ,h4 ,greathead1 perceived that ,barlow's device presented merit1 although its design and construction were defective1 and he finally undertook the work and carried it to a brilliant success4 ,the tunnel was #acej ft4 long and #g ft4 in diameter1 and penetrated compact clay4 ,work was begun on the first shore shaft on ,feb4 #ab1 #ahfi1 and the tunnel was completed the following ,christmas1 or in something short of eleven months1 at a cost of #ad1ejj4 ,the shield used was ,barlow's idea put into practical shape by ,greathead4 ,it consisted of an iron cylinder1 or1 more properly1 a frustum of a cone whose circumferential sides were very slightly inclined to the axis1 the idea being that the friction would be less if the front end of the shield were slightly larger than the rear end4 ,the shell of the cone was made of -in4 plates4 ,the thinned plate cutting-edge of ,barlow's shield was replaced by ,greathead with a circular ring of cast iron4 ,greathead also altered the construction of the diaphragm by arranging the angle stiffeners so that they ran horizontally and vertically1 and by fastening the diaphragm plates to an interior cast-iron ring connected to the shell plates4 ,this was a decided structural improvement1 but it was accompanied with another modification which was quite as decided a retrogression from ,barlow's design4 ,greathead made the diaphragm opening rectangular and to extend very nearly from the top to the bottom of the shield1 thus abandoning the element of safety provided by ,barlow in case of an irruption of water4 ,fortunately the material penetrated by the shield for the ,tower tunnel was so compact that no trouble was had from water2 but the dangerous character of the construction was some years afterwards disastrously proven in driving the ,yarra ,river tunnel at ,melbourne1 ,australia4 ,to drive his shield ,greathead employed six #b-;in4 screw-jacks capable of developing a total force of #fj tons4 ,the tails of the jack bore against the completed lining1 which consisted of cast-iron rings #ah ins4 wide and in4 thick1 each ring being made up of a crown piece and three segments4 ,the different segments and rings were provided with double 7exterior and interior7 flanges1 by means of which they were bolted together4 ,the soil behind the lining was filled with liquid cement injected through small holes by means of a hand pump4 ,illustration3 ,,fig4 #abg4--,shield ,suggested by ,greathead for the ,proposed ,north and ,south ,woolwich ,subway4 ,illustration3 ,,fig4 #abh4--;,beach's ,shield ,used on ,broadway ,pneumatic ,railway ,tunnel4 ,the remarkable success of the ,london ,tower tunnel encouraged ,barlow to form in #ahga a company to tunnel the ,thames between ,southwark and the ,city1 and ,greathead1 in #ahgf1 to project a tunnel under the same waterway known as the ,north and ,south ,woolwich ,subway4 ,barlow's concession was abrogated by ,parliament in #ahgc1 without any work having been done4 ,greathead progressed far enough with his enterprise to construct a shield and a large amount of the iron lining when the contractors abandoned the work4 ,from the brief description of his shield given by ,greathead to the ,london ,society of ,civil ,engineers1 it contained several important differences from the shield built by him for the ,london ,tower tunnel1 as is shown by ,fig4 #abg4 ,the changes which deserve particular notice are the great extension of the shield behind the diaphragm1 the curved form of the diaphragm1 and the use of hydraulic jacks4 ,greathead had also designed for this work a special crane to be used in erecting the cast-iron segments of the lining4 ,illustration3 ,,fig4 #abi4--,shield for ,city and ,south ,london ,railway4 ,while these works had been progressing in ,england1 ,mr4 ,beach1 an ,american1 received a patent in the ,united ,states for a tunnel shield of the construction shown by ,fig4 #abh1 which was first tried practically in constructing a short length of tunnel under ,broadway for the nearly forgotten ,broadway ,pneumatic ,underground ,railway4 ,this shield1 as is indicated by the illustration1 consisted of a cylinder of wood with an iron-cutting-edge and an iron tail-ring4 ,extending transversely across the shield at the front end were a number of horizontal iron plates or shelves with cutting-edges1 as shown clearly by the drawing4 ,the shield was moved ahead by means of a number of hydraulic jacks supplied with power by a hand pump attached to the shield4 ,by means of suitable valves all or any lesser number of these jacks could be operated1 and by thus regulating the action of the motive power the direction of the shield could be altered at will4 ,work was abandoned on the ,broadway tunnel in #ahgj4 ,in #ahga-b ,beach's shield was used in building a short circular tunnel #h ft4 in diameter in ,cincinnati1 and a little later it was introduced into the ,cleveland water-works tunnel #h ft4 in diameter4 ,in this latter work1 which was through a very treacherous soil1 the shield gave a great deal of trouble1 and was finally so flattened by the pressures that it was abandoned4 ,the obviously defective features of this shield were its want of vertical bracing and the lack of any means of closing the front in soft soil4 ,illustration3 ,,fig4 #acj4--,shield for ,st4 ,clair ,river ,tunnel4 ,illustration3 ,longitudinal ,section4 ,cross ,section4 ,,fig4 #aca4--,shield for ,blackwall ,tunnel4 ,with the foregoing brief review of the early development of the shield system of tunneling1 we have arrived at a point where the methods of modern practice can be studied intelligently4 ,in the pages which follow we shall first illustrate fully the construction of a number of shields of typical and special construction1 and follow these illustrations with a general discussion of present practice in the various details of shield construction4 ,illustration3 ,transverse ,section4 ,longitudinal ,section4 ,,fig4 #acb4--;,elliptical ,shield for ,clichy ,sewer ,tunnel1 ,paris4 ,illustration3 ,longitudinal ,section4 ,cross ,section4 ,,fig4 #acc4--,semi-elliptical ,shield for ,clichy ,sewer ,tunnel4 ,mr4 ,raynald ,lgouez1 in his excellent book upon the shield system of tunneling1 considers that tunnel shields may be divided into three classes structurally1 according to the character of the material which they are designed to penetrate4 ,in the first class he places shields designed to work in a stiff and comparatively stable soil1 like the well-known ,london clay2 in the second class are placed those constructed to work in soft clays and silts2 and in the third class those intended for soils of an unstable granular nature4 ,this classification will1 in a general way1 be kept by the writer4 ,as a representative shield of the first class1 the one designed for the ,city and ,south ,london ,railway is illustrated in ,fig4 #abi4 ,the shields for the ,london ,tower tunnel1 the ,waterloo and ,city ,railway1 the ,glasgow ,district ,subway1 the ,siphons of ,clichy and ,concorde in ,paris1 and the ,glasgow ,port tunnel1 are of the same general design and construction4 ,to represent shields of the second class1 the ,st4 ,clair ,river and ,blackwall shields are shown in ,figs4 #acj and #aca4 ,the shields for the ,mersey ,river1 the ,hudson ,river1 and the ,east ,river tunnels also belong to this class4 ,to represent shields of the third class1 the elliptical and semi-elliptical shields of the ,clichy tunnel work in ,paris are shown by ,figs4 #acb and #acc4 ,the semi-circular shield of the ,boston ,subway is illustrated by ,fig4 #acd4 ,illustration3 ,half ,transverse ,section ,a-,b4 ,half ,rear-,end ,elevation4 ,details of ,casting ,supporting ,ends of ,jacks4 ,details of ,castings under ,ends of ,girders4 ,longitudinal ,section ,c-,d4 ,,fig4 #acd4--,roof ,shield for ,boston ,subway4 ,prelini's ,shield4--,in closing this short review mention will be made of a new shield designed and patented by the ,author and shown in ,fig4 #ace4 ,it is an articulated shield composed of two separated shields whose outer shells overlap each other4 ,the shields are connected together by means of hydraulic jacks attached all around the two diaphragms4 ,between these diaphragms is a large inclosed space called a safety chamber1 where the men can withdraw in case of accidents and where the air can be immediately raised to the required pressure4 ,this is an advantage in case of blow-outs1 because the flooding of the tunnel is prevented1 while the accident is limited to only a few feet from the front4 ,on account of the shield being advanced half at a time it is always under control and is thus better directed through grade and alignment4 ,besides1 this shield will not rotate around its axis and consequently it can be built of any shape1 thus permitting the construction of subaqueous tunnels of any cross-section and even with a wider foundation1 which is impossible to-day with the ordinary rotating shields of circular cross-section4 ,illustration3 ,,fig4 #ace4--,transversal and ,longitudinal ,section of ,prelini's ,shield4 ,,shield ,,construction4 ,general ,form4--,tunnel shields are usually cylindrical or semi-cylindrical in cross-section4 ,the cylinder may be circular1 elliptical1 or oval in section4 ,far the greater number of shields used in the past have been circular cylinders2 but in one part of the sewer tunnel of ,clichy1 in ,paris1 an elliptical shield with its major axis horizontal1 was used1 and the ,german engineer1 ,herr ,mackensen1 has designed an oval shield1 with its major axis vertical4 ,a semi-elliptical shield was employed on the ,clichy tunnel1 and semi-circular shields were used on the ,baltimore ,belt ,line tunnel and the ,boston ,subway in ,america4 ,generally1 also1 tunnel shields are right cylinders2 that is1 the front and rear edges are in vertical planes perpendicular to the axis of the cylinder4 ,occasionally1 however1 they are oblique cylinders2 that is1 the front or rear edges1 or both1 are in planes oblique to the axis of the cylinder4 ,one of these visor-shaped shields was employed on the ,clichy tunnel4 ,the ,shell4--,it is absolutely necessary that the exterior surface of the shell should be smooth1 and for this reason the exterior rivet heads must be countersunk4 ,it is generally admitted1 also1 that the shell should be perfectly cylindrical1 and not conical4 ,the conical form has some advantage in reducing the frictional resistance to the advance of the shield2 but this is generally considered to be more than counterbalanced by the danger of subsidence of the earth1 caused by the excessive void which it leaves behind the iron tunnel lining4 ,for the same reason the shell plate1 which overlaps the forward ring of the lining1 should be as thin as practicable1 but its thickness should not be reduced so that it will deflect under the earth pressure from above4 ,generally the shell is made of at least two thicknesses of plating1 the plates being arranged so as to break joints1 and1 thus1 to avoid the use of cover joints1 to interrupt the smooth surface which is so essential1 particularly on the exterior4 ,the thickness of the shell required will vary with the diameter of the shield1 and the character and strength of the diametrical bracing4 ,mr4 ,raynald ,lgouez suggests as a rule for determining the thickness of the shell1 that1 to a minimum thickness of #b mm41 should be added #a mm4 for every meter of diameter over #d meters4 ,referring to the illustrations1 ,figs4 #abh to #acb inclusive1 it will be noted that the ,st4 ,clair tunnel shield1 #ba ft4 in diameter1 had a shell of #a-;in4 steel plates with cover-plate joints and interior angle stiffeners2 the shell of the ,east ,river tunnel shield1 #aa ft4 in diameter1 was made up of one -in4 and one -in4 plate2 the ,blackwall tunnel shield1 #bg ft4 #i ins4 in diameter1 had a shell consisting of four thicknesses of -in4 plates2 and the ,clichy tunnel shield1 with a diameter of #b4jf meters1 had a shell #b millimeters thick4 ,front-,end ,construction4--,by the front end is meant that portion of the shield between the cutting-edge and the vertical diaphragm4 ,the length of this portion of the shield was formerly made quite small1 and where the material penetrated is very soft1 a short front-end construction yet has many advocates2 but the general tendency now is to extend the cutting-edge far enough ahead of the diaphragm to form a fair-sized working chamber4 ,excavation is far more easy and rapid when the face can be attacked directly from in front of the diaphragm than where the work has to be done from behind through the apertures in the diaphragm4 ,so long as the roof of the excavation is supported from falling1 experience has shown that it is easily possible to extend the excavation safely some distance ahead of the diaphragm4 ,in reasonably stable material1 like compact-clay1 the front face will usually stand alone for the short time necessary to excavate the section and advance the shield one stage4 ,in softer material the face can usually be sustained for the same short period by means of compressed air2 or the face of the excavation1 instead of being made vertical1 can be allowed to assume its natural slope4 ,in the latter case a visor-shaped front-end construction1 such as was used on some portions of the ,clichy tunnel1 is particularly advantageous4 ,the following figures show the lengths of the front ends of a number of representative tunnel shields4 ,city and ,south ,london #a ft4 ,st4 ,clair ,river #aa4be ,hudson ,river #e ,mersey ,river #c ,east ,river #c ,blackwall #f4e ,two general types of construction are employed for the cutting-edge4 ,the first type consists of a cast-iron or cast-steel ring1 beveled to form a chisel-like cutting-edge and bolted to the ends of the forward shell plates4 ,this construction was first employed in the shield for the ,london ,tower tunnel1 and has since been used on the ,city and ,south ,london1 ,waterloo and ,city1 and the ,clichy tunnels4 ,the second construction consists in bracing the forward shell plates by means of right triangular brackets1 whose perpendicular sides are riveted respectively to the shell plates and the diaphragm1 and whose inclined sides slant backward and downward from the front edge1 and carry a conical ring of plating4 ,the shields for the ,st4 ,clair ,river1 ,east ,river1 and ,blackwall tunnels show forms of this type of cutting-edge construction4 ,a modification of the second type of construction1 which consists in omitting the conical plating1 was employed on some of the shields for the ,clichy tunnel4 ,this modification is generally considered to be allowable only in materials which have little stability1 and which crumble down before the advance of the cutting-edge4 ,where the material is of a sticky or compact nature1 into which the shield in advancing must actually cut1 the beveled plating is necessary to insure a clean cutting action without wedging or jamming of the material4 ,cellular ,division4--,it is necessary in shields of large diameter to brace the shell horizontally and vertically against distortion4 ,this bracing also serves to form stagings for the workmen1 and to divide the shield into cells4 ,the following table shows the arrangement of the vertical and transverse bracing in several representative tunnel shields4 ---------------------------------------- --------- ,,name ,,of ,,tunnel4 ,,diameter4 ,,hori- ,,plates1 ,,vert4 ,,zontal4 ,,dist4 ,,braces4 ,,apart4 ---------------------------------------- -------- ,ft4 ,in4 ,no4 ,ft4 ,no4 ,hudson ,river #ai #aa #b #f4ed #b ,clichy #ai4d #j #b #f4ed ,none ,st4 ,clair ,river #ba #f #b #f4ih #c ,waterloo 7,station7#bd #aj #b #g4ab ,none ,blackwall #bg #h #b #f4j #c ,east ,river #aa ,none 444 #a ---------------------------------------- -------- ,referring first to the horizontal divisions1 it may be noted that they serve different purposes in different instances4 ,in the ,clichy tunnel shield the horizontal divisions formed simply working platforms2 in the ,waterloo tunnel shield they were designed to abut closely against the working face by means of special jacks1 and so to divide it into three separate divisions2 in the ,st4 ,clair tunnel they served as working platforms1 and also had cutting-edges for penetrating the material ahead2 and in the ,blackwall tunnel shield they served as working platforms1 and had cutting-edges as in the ,st4 ,clair tunnel shield1 and in addition the middle division was so devised that the two lower chambers of the shield could be kept under a higher pressure of air than the two upper chambers4 ,passing now to the vertical divisions1 they serve to brace the shell of the shield against vertical pressures1 and also to divide the horizontal chambers into cells2 but unlike the horizontal plates they are not provided with cutting-edges4 ,the ,st4 ,clair1 ,hudson ,river1 and ,blackwall tunnel shields illustrate the use of the vertical bracing for the double purpose of vertical bracing and of dividing the horizontal chambers into cells4 ,the ,waterloo tunnel shield is an example1 of vertical bracing employed solely as bracing4 ,the vertical division of the ,east ,river tunnel shield was employed in order to allow the shield to be dissembled in quadrants4 ,the ,diaphragm4--,the purpose of the shield diaphragm is to close the rear end of the shield and the tunnel behind from an inrush of water and earth from the face of the excavation4 ,it also serves the secondary purpose of stiffening the shell diametrically4 ,structurally the diaphragm separates the front-end construction previously described from the rear-end construction1 which will be described farther on2 and it is usually composed of iron or steel plating reinforced by beams or girders1 and pierced with one or several openings by which access is had to the working face4 ,in stable material1 where caving or an inrush of water and earth is not likely1 the diaphragm is omitted4 ,the shield of the ,waterloo tunnel is an example of this construction4 ,in more treacherous materials1 however1 not only is a diaphragm necessary1 but it is also necessary to diminish the size of the openings through it1 and to provide means for closing them entirely4 ,sometimes only one or two openings are left near the bottom of the diaphragm1 as in the ,st4 ,clair and ,mersey tunnel shields2 and sometimes a number of smaller openings are provided1 as in the ,east ,river and ,hudson ,river tunnel shields4 ,in highly treacherous materials subject to sudden and violent irruptions of earth from the excavation face1 it sometimes is the case that openings1 however small1 closed in the ordinary manner1 are impracticable1 and special construction has to be adopted to deal with the difficulty4 ,the shields for the ,mersey and for the ,blackwall tunnels are examples of such special devices4 ,in the ,mersey tunnel a second diaphragm was built behind the first1 extending from the bottom of the shield upward to about half its total height4 ,the aperture in the first diaphragm being near the bottom1 the space between the second and first diaphragms formed a trap to hold the inflowing material4 ,the ,blackwall tunnel shield1 as previously indicated1 had its front end divided into cells4 ,ordinarily the face of the excavation in front of each cell was left open1 but where material was encountered which irrupted into these cells a special means of closing the face was necessary4 ,this consisted of three poling-boards or shutters of iron held one above the other against the face of the excavation4 ,these shutters were supported by means of strong threaded rods passing through nuts fastened to the vertical frames1 which permitted each shutter to be advanced against or withdrawn from the face of the excavation independently of the others4 ,various other constructions have been devised to retain the face of the excavation in highly treacherous soils1 but few of them have been subjected to conclusive tests1 and they do not therefore justify consideration4 ,rear-end ,construction4--,by the rear end of the shield is meant that portion at the rear of the diaphragm4 ,it may be divided into two parts1 called respectively the body and the tail of the shield4 ,the chief purpose of the body of the shield is to furnish a place for the location of the jacks1 pumps1 motors1 etc41 employed in manipulating the shield4 ,it also serves a purpose in distributing the weight of the shield over a large area4 ,to facilitate the passage of the shield around curves1 or in changing from one grade to another1 it is desirable to make the body of the shield as short as possible4 ,in the ,mersey1 ,clichy1 and ,waterloo tunnel shields1 and1 in fact1 in most others which have been employed1 the shell plates of the body have been reinforced by a heavy cast-iron ring1 within and to which are attached the jacks and other apparatus4 ,the latest opinion1 however1 seems to point to the use of brackets and beams for strengthening the shell for the purpose named1 rather than to this heavy cast-iron construction4 ,in the ,hudson ,river1 ,st4 ,clair ,river1 and ,east ,river tunnel shields1 with their long and strongly braced front-end construction to carry the jacks1 the body of the shield1 so to speak1 is omitted and the rear-end construction consists simply of the tail plating4 ,in the ,blackwall shield1 the body of the shield shell provides the space necessary for the double diaphragms and the cells which they inclose4 ,in a general way1 it may be said that the present tendency of engineers is to favor as short and as light a body construction as can be secured4 ,the tail of the shield serves to support the earth while the lining is being erected2 and for this reason it overlaps the forward ring of the lining1 as shown clearly by most of the shields illustrated4 ,to fulfill this purpose1 the tail-plates should be perfectly smooth inside and outside1 so as to slide easily between the outside of the lining plates and the earth1 and should also be as thin as practicable1 in order not to leave a large void behind the lining to be filled in4 ,in soils which are fairly stable1 the tail construction is often visor-shaped2 that is1 the tail-plates overlap the lining only for1 say1 the roof from the springing lines up1 as in one of the shields for the ,clichy tunnel4 ,in unstable materials the tail-plating extends entirely around the shield and excavation4 ,the length of the tail-plating is usually sufficient to overlap two rings of the lining1 but in one of the ,clichy tunnel shields it will be noticed that it extended over three rings of lining4 ,this seemingly considerable space for thin steel plates is made possible by the fact that the extreme rear end of the tail always rests upon the last completed ring of lining4 ,in closing these remarks concerning the rear-end construction1 the accompanying table1 prepared by ,mr4 ,raynald ,lgouez1 will be of interest1 as a general summary of principal dimensions of most of the important tunnel shields which have been built4 ,the figures in this table have been converted from metric to ,english measure1 and some slight variation from the exact dimensions necessarily exists4 ,the different columns of the table show the diameter1 total length1 and the length of each of the three principal parts into which tunnel shields are ordinarily divided in construction as previously described3 ---------------------------------------- ---------------- ,,length ,,in ,,feet4 ,,name ,,of ,,shield4 ------------------------------- ,,diameter4,,tail4,,body4,,front4,,total 4 ---------------------------------------- ------------ ,concorde ,siphon #f4ge #b4ea #b4ee #a4af #f4fg ,clichy ,siphon #h4ci #b4ea #b4ee #a4af #f4af ,mersey #i4ig #e4fa #b4ih #b4ih #aa4eh ,east ,river #aj4ii #c4ea #j4cb #c4fg #g4ea ,city and ,south ,london #aj4ii #b4fe #b4hb #a4ja #f4di ,glasgow ,district #ab4jg #b4fe #b4hb #a4ja #f4di ,waterloo and ,city #ab4ii #b4ge #b4ih #a4bd #f4ih ,glasgow ,harbor #ag4be #b4ge #b4ih #a4jh #h4di ,hudson ,river #ai4ia #d4hb #b4ih #e4fg #aj4di ,st4 ,clair ,river #ba4eb #d4jj #b4ih #aa4be #ae4be ,clichy ,tunnel #bc4g-ai4h #d4jj #b4ih #f4hh #ag4bb ,clichy ,tunnel #bc4h-ai4d #g4ddaa4ij #d4df #bc4fe ,blackwall #bg4jj #f4ih #e4ij #f4ei #ai4dh ,waterloo ,station #bd4hf #c4cd #e4ea #a4ad #aj4jj ---------------------------------------- ------------ ,a shield of #fj or #ajj tons weight can hardly be directed along the line of the proposed tunnel and also through curves and grades1 especially when driven through loose or muddy soils4 ,the tunnels of the ,new ,york and ,hudson ,river ,railroad under the ,hudson1 and the tunnel of the ,new ,york ,rapid ,transit ,railway under the ,east ,river1 show marked evidence of how troublesome this work is4 ,to avoid these and other inconveniences encountered in every shield1 the ,author has designed a new shield which was briefly described at page #bea4 ,illustration3 ,,fig4 #acf4--;,elevation and ,section of ,hydraulic ,jack1 ,east ,river ,gas ,tunnel4 ,jacks4--,the motive power usually employed in driving modern tunnel shields is hydraulic jacks4 ,in some of the earlier shields screw-jacks were used1 but these soon gave way to the more powerful hydraulic device4 ,the manner of attaching the hydraulic jacks to the shield is always to fasten the cylinder castings at regular intervals around the inside of the shell1 with the piston rods extending backward to a bearing against the forward edge of the lining4 ,in the older forms of shield1 having an interior cast-iron reinforcing ring construction1 the jack cylinder castings were always attached to this cast-iron ring2 but in many of the later shields constructed without this cast-iron reinforcing ring1 the cylinder castings are attached to the shell by means of bracket and gusset connections4 ,the number and size of the jacks employed1 and the distance apart at which they are spaced1 depend upon the size of the shield and the character of the material in which it is designed to work4 ,in stiff and comparatively stable clays1 the skin friction of the shield is comparatively small1 and an aggregate jack-power of from #d to #e tons per square yard of the exterior friction surface of the shield has usually been found ample4 ,the cylinders are spaced about #e ft4 apart1 and have a working diameter of from #e to #f ins41 with a water pressure of about #ajjj lbs4 per sq4 in4 ,in soft1 sticky material1 giving a high skin friction1 the aggregate jack-power required per square yard of exterior shell surface rises to from #ah to #bd tons2 the jacks are spaced about #c ft4 apart2 and the working cylinder diameter and water pressure are1 respectively1 about #f or #g ins41 and from #djjj lbs4 to #fjjj lbs4 per sq4 in4 ,with these high pressures1 power pumps are necessary to give the required water pressure2 but where the pressure required does not exceed #ajjj lbs4 per sq4 in41 hand pumps may be1 and usually are1 employed4 ,fig4 #acf shows the hydraulic jacks used in the ,east ,river ,gas ,tunnel at ,new ,york4 ,the number of jacks required depends upon the diameter of the shield1 and1 of course1 upon the distance apart which they are placed4 ,in the ,city and ,south ,london tunnel shield six jacks were used1 and in the ,blackwall shield #bd were used4 ,the mechanical construction of the jacks for tunnel shields presents no features out of the usual lines of such devices used elsewhere4 ,the jacks used on the ,east ,river tunnel shield are shown by ,fig4 #acf4 ,two general methods are employed for transmitting the thrust of the piston rods against the tunnel lining4 ,the object sought in each is to distribute the thrust in such a manner that there is no danger of bending the thin front flange of the forward lining ring4 ,in ,english practice the plan usually adopted is to attach a shoe or bearing casting to the end of the piston rod1 which will distribute the pressure over a considerable area4 ,an example of this construction is the shield for the ,city and ,south ,london tunnel4 ,in the ,east ,river and ,st4 ,clair ,river tunnels built in ,america1 the tail of the piston rod is so constructed that the thrust is carried directly to the shell of the lining4 ,,lining4 ,either iron or masonry may be used for lining shield-driven tunnels but present practice is almost universally in favor of iron lining4 ,as usually built1 iron lining consists of a series of successive cast-iron rings1 the abutting edges of which are provided with flanges4 ,these flanges are connected by means of butts1 the joints being packed with thin strips of wood1 oakum1 cement1 or some other material to make them water-tight4 ,each lining ring is made up of four or more segments1 which are provided with flanges for bolted connections similar to those fastening the successive rings4 ,generally the crown segment is made considerably shorter than those forming the sides and bottom of the ring4 ,the erection of the iron segments forming the successive rings of the lining may be done by hand in tunnels of small diameter where the weights to be handled are comparatively light1 but in tunnels of large size special cranes attached to the shield or carried by the finished lining are employed4 ,the construction of the iron lining for the ,hudson ,river tunnel is illustrated in ,chapter ,,xx41 and that for the ,st4 ,clair ,river tunnel is shown by ,fig4 #acg4 ,illustration3 ,part ,transverse ,section4 ,longitudinal ,section4 ,,fig4 #acg4--;,cast-,iron ,lining1 ,st4 ,clair ,river ,tunnel4 ,,chapter ,,xx4 ,,submarine ,,tunneling 7,continued74 ,,the ,,shield ,,and ,,compressed ,,air ,,method4 ,,the ,,hudson ,,river ,,tunnel ,,of ,,the ,,pennsylvania ,,railroad4 ,the shield and compressed air method of excavating subaqueous tunnels is used when the distance is small between the roof of the tunnel and the bed of the river4 ,these tunnels are usually driven from the shafts sunk from each shore4 ,it is very seldom they can be driven also by an intermediate shaft4 ,this1 however1 was done in the case of the ,belmont tunnel under the ,east ,river4 ,here the tunnels passed under the man-of-war reef where a working shaft was sunk4 ,the plant is located at some convenient point near the head shaft4 ,it consists of a set of boilers to provide the power for the different machines4 ,they are low and high pressure compressors1 the former supply the air through the tunnel2 the latter1 the air for working the drills1 in case rock is encountered1 and power for hauling and hoisting purposes4 ,the various pumps force the water for the hydraulic rams that drive the shield and work the erector4 ,they also remove the water from the tunnel which always collects in variable quantities at the bottom of the excavation4 ,besides the machines for light and ventilation purposes1 the head shaft is provided with an overhead construction where are housed the hoisting machines1 the telephone and other means of communication with the work at the front4 ,usually a long trestle is built in connection with the head shaft1 leading to the dumping place and yard4 ,on this inclined elevated structure are located1 also1 the tracks upon which will run the small cars used inside the tunnel for hauling purposes4 ,the shafts are excavated on a square1 rectangular or circular plan and are usually lined with masonry4 ,it is only recently that shafts excavated through loose soils have been lined with the same cast-iron lining used in the tunnels1 the only difference being that the rings were laid flat on the ground and attached to those already sunk4 ,after the shaft has been sunk to the required level1 the tunnel is driven toward the river by any one of the methods used for land work4 ,at some convenient distance from the shaft1 the dimensions of the tunnel are enlarged for a length of #bj or #cj ft4 ,in this larger space1 called the shield chamber1 the shield is assembled1 mounted1 and1 when completed1 it is slowly pushed toward the river4 ,the tunnel is excavated from the shield chamber on1 with dimensions equal to the exterior shell of the shield4 ,the construction of the shield and the hydraulic jacks used for its advance are explained in a preceding chapter4 ,in very loose soils1 a solid bulkhead of masonry is built across the tunnel1 after the shield has advanced to a certain distance and some rings of the cast-iron lining have been erected4 ,the bulkhead is provided with three air locks--two near the floor of the tunnel1 for working purposes1 and one near the roof1 called the emergency lock1 which1 as the name suggests1 is used only in case of danger4 ,the air locks are steel cylinders from #aj to #ae ft4 long and #f ft4 in diameter1 made up of boiler plates4 ,they are provided with doors at each end1 besides the pipes for the admission and exit of compressed air4 ,the working locks also have narrow-gauge tracks for hauling purposes4 ,in rock or more consistent soil the bulkhead is constructed after the shield is far ahead1 since there is no immediate necessity1 under these conditions1 to use the compressed air4 ,in both the loose and good soils1 when the shield has been advanced over #ejj ft4 from the bulkhead1 a second bulkhead1 with air locks1 is erected in the tunnel4 ,the first is left in place but used only in case of emergency4 ,to direct the shield along the center line and through curves and grades1 accurate measurements are taken1 and the distance between the shield and the last ring inserted in the iron lining is regulated accordingly4 ,the alignment inside the tunnel is maintained in a very simple way4 ,for this purpose1 points corresponding to the center line are marked on the roof at distances of #ajj ft4 ,nearly #ajj ft4 from the shield1 a transit is set up on a strong scaffold spanning the tunnel1 and it is supported by the flanges of the iron lining4 ,a plumb-line is hung from one of the points of the roof already determined1 as indicating the center line2 and the transit man aligns his instrument with this plumb-line2 after this he 8plunges0 his telescope4 ,a rodman next places a horizontal rod of special construction between the flanges of the last ring of the lining4 ,this rod has in the center an open slot which carries a glass with a black vertical line4 ,the slot is graduated1 the zero of graduation remains in the center while the vertical line is moved right and left4 ,the rodman places a lamp behind the slot and the transit-man tells him how to move the dark line until it coincides with the axis of the tunnel4 ,if the ring1 just erected1 be a little out of alignment1 it is readjusted by pushing the shield a little more on the side that has swerved from the axis of the tunnel4 ,as the shield is pushed forward1 it is kept in place by four men with graduated rods1 one man on each side of the shield1 one on top and the other on the floor4 ,as the shield progresses1 they repeat aloud in succession1 the distance indicated on the rods1 which is the distance from the shield to the outer circumferential flange of the last ring of the lining4 ,when an advance of one foot has been made1 readings are taken at every inch2 and when very near the required distance1 they are taken at every quarter of an inch4 ,in this way it is not difficult to bring the shield back into line1 in case it may have shifted a little to the right or left4 ,when curves are met1 the rings are no longer cylindrical segments but tores1 so that the segments at one side are longer than those on the other4 ,in this case1 the shield is advanced more on one side by a quantity equal to the difference of the two sides of the ring to be erected4 ,at each advance the shield is moved #b ft4 or #b ft4 ahead1 the distance corresponding to the length of the cast-iron rings of the lining4 ,within the space now open between the shield and the lining another ring is inserted4 ,the ring is composed of different segments provided with flanges and holes bored so they can be bolted together4 ,the segments of the lining are very heavy and difficult to handle but they are easily set by means of the erector4 ,when the erector is not mounted on the shield1 it is located in the middle of a girder placed across the iron rings of the lining and just at the rear end of the shield4 ,the girder1 at both extremities1 has flanged wheels resting on rails which are placed on brackets4 ,these brackets are attached temporarily to the flanges of the iron lining4 ,the erector is provided with an arm capable to swing in a full circle4 ,its movements are regulated by two hydraulic jacks1 located horizontally on the spanning girder4 ,on the extreme end of the revolving arm are projections with holes for the bolts4 ,each segmental plate of the lining has a kind of plug in the center which is cast together with the plate and is provided with holes for the bolt4 ,in placing the segmental plates of the lining1 the arm of the erector is swung over the plate to be lifted1 then two bolts are passed through the holes in the projection of the erector1 and through those in the plug4 ,the arm of the erector is then moved upwards until the plate1 free from all obstacles1 is swung very near its intended position4 ,there it is adjusted and held until bolts are inserted to fix it to the plates of the preceding ring4 ,in connection with the method of excavating submarine tunnels by means of shield and compressed air1 the excavation varies with the quality of soil encountered4 ,in compact rock the usual heading and bench method1 so common in land tunnels1 is also employed in this case4 ,the shield is left behind in presence of good rock4 ,the men at the front attack the rock with air drilling machines and charges of dynamite4 ,the holes are driven at a smaller depth than in land work2 very light charges of dynamite are used and only a few holes fired at each round4 ,every precaution is taken in order not to disturb the shield and the bed of the river any more than is possible1 because at a shallow depth the blast would tend to widen the existing crevices in the rock and thus permit an inflow of water4 ,when the rock is fissured or disintegrated and the roof of the excavation at the front requires timbering1 the shield should be kept closer to the front4 ,in this way the quantity of timber for strutting is greatly reduced1 so lessening the probabilities of fires4 ,it is very difficult1 in compressed air1 to extinguish fires and in almost every instance the only way is to flood the tunnel4 ,this was done at the ,manhattan end of the tunnel under the ,east ,river for the extension to ,brooklyn of the ,new ,york ,subway4 ,the excavation is made by hand in loose but compact soils such as clay4 ,the men work on platforms located at the front of the shield and they are protected from the caving-in of the roof by a hood added for working through loose soils4 ,the men excavate the material which is shoveled inside the tunnel and is carried away in small cars4 ,the shield is very close to the front of the excavation in loose soil4 ,the ,east ,boston tunnel1 under ,boston ,harbor1 connecting with the ,boston ,subway1 was excavated through blue clay4 ,the minimum distance between the bottom of the water and the roof of the excavation was #ah ft4 ,the tunnel was excavated by means of compressed air and the shield which was only used for the roof4 ,it slid on top of concrete side walls built in two drifts which were excavated nearly #ajj ft4 ahead of the shield4 ,the tunnel was lined with concrete1 the arch being reinforced by longitudinal steel rods which received the thrust of jacks used for advancing the shield4 ,the material in the drifts under the shield and the bench was removed by hand and carried away in small cars4 ,subaqueous tunnels driven through very loose soils can be excavated by simply leaving the doors open while the shield is pushed ahead4 ,the material1 dislodged by the cutting edge of the shield1 is forced through the doors and falls on the floor whence it is removed in small cars4 ,in very loose soils the excavation has been made in a still more economic way2 the shield with closed doors is simply squeezed through the soil4 ,this method is financially convenient1 because all the excavating and hauling operations are eliminated and the tunnel progresses from #dj to #ej ft4 per day1 but clearly indicates a lack of stability4 ,in this manner1 the ,hudson ,river tunnel of the ,new ,york and ,new ,jersey ,railroad was constructed4 ,the pressure of the air in the tunnel depends upon the depth and as a rule it varies between #bj and #dj or even more pounds per square inch above atmospheric pressure4 ,working in compressed air causes a peculiar disease commonly known as 8bends0 or 8caisson disease0 often proving fatal4 ,to prevent and remedy the disease1 the engineers should order a set of rules to be strictly observed4 ,the preventative measures should be1 first1 to employ only sober1 strong and healthy men1 never one who has not successfully passed the examination of the attending physician2 second1 to order the lock tenders never to allow any man in or out of the tunnel unless he has spent at least ten minutes within the locks4 ,both compression and decompression should be thorough and it cannot be in less than this time4 ,a stop of only a few minutes in the locks is not sufficient and this incomplete compression or decompression is the real cause of the bends4 ,the men become careless after they have been in the compressed air for some time1 and they try to reduce this tiresome operation to a minimum1 hence the duty of the engineer to strictly enforce this rule4 ,the remedial measures should consist of constant medical attendance near the shafts and the erection of a compressed air hospital where the men affected by bends for lack of decompression may be attended and cured4 ,,the ,,hudson ,,river ,,tunnels ,,of ,,the ,,pennsylvania ,,railroad4#ac ,the tunnels constructed under the ,hudson ,river for the ,pennsylvania ,railroad1 consist of two parallel tubes driven side by side #ad ft4 apart4 ,the tubes are of circular cross-section1 #bc ft4 exterior diameter1 and are lined with cast-iron rings4 ,the tunnels were driven from two shafts1 one on the eastern shore of the ,hudson ,river near #cbnd ,st4 and #aath ,ave41 ,new ,york2 the other at ,weehawken1 ,new ,jersey1 near the piers of the ,erie ,railroad4 ,the horizontal distance between the shafts was #feej ft4 ,the permanent one at ,weehawken was built on a square plan1 #acj ft4 to a side4 ,it was lined with concrete masonry and the walls were battered in such a way as to become the shape of an inverted frustum of a pyramid4 ,it was provided with five openings at the bottom1 four of these are used by trains that run in the open1 the fifth one leads to a power house near by4 ,during the construction of the tunnels one-third of this shaft was used for the land portion of the tunnel under ,bergen ,hill1 while the remaining two-thirds were devoted to the construction of the tunnel under the river4 ,the working shaft on ,manhattan ,island was a side shaft of rectangular plan #cj ft4 by #bb ft41 the tunnel proper being connected by two drifts #aj ft4 by #aj ft4 each4 ,the shield rooms #bc ft4 long1 were situated on both sides of the river just in front of the shafts4 ,on the ,new ,york side1 the shields1 one for each tube1 were built inside the iron lining of the shield chamber1 and the hoisting tackle was slung from the iron lining4 ,the erection on the ,weehawken side was done in the bare rock excavation where timber falsework was used4 ,after the shields were finished and in position1 the first two rings of the lining were erected in the tail of the shield4 ,these rings were firmly braced to the rock and the chamber lining2 then the shields were shoved ahead by their own jacks1 another ring was built and so on4 #ac ,condensed from paper by ,james ,forgie1 8,eng4 ,news10 ,vol4 ,,lvi1 and by ,h4 ,b4 ,hewett and ,w4 ,l4 ,brown1 8,proc4 ,am4 ,soc4 ,c4 ,e401 ,vol4 ,,xxxvi4 ,illustration3 ,rear ,elevation of ,shield4 ,vertical ,section4 ,half ,section ,a-,b4 ,half ,section ,c-,d4 ,horizontal ,section4 ,,fig4 #ach4--;,general ,elevations and ,sections of ,shield4 ,shield4--,the shields used in these tunnels were designed by ,mr4 ,james ,forgie1 ,m4 ,inst4 ,c4 ,e4 and ,m4 ,am4 ,soc4 ,c4 ,e41 and were provided with three innovations3 the segmental doors1 the sliding platforms and the removable hood4 ,the shields1 ,fig4 #ach1 were circular1 #bc ft4 #f ins4 in external diameter1 and were #af ft4 long1 exclusive of the hood4 ,the tail of the shield overlapped the lining1 the maximum being #f ft4 #d ins4 during ordinary working2 the minimum1 #b ft4 during the operation of taking any ram out for repairing4 ,the shields had only one transverse bulkhead made up of two continuous horizontal platforms and three vertical partitions stiffening angular web plates fore and aft the ram chambers4 ,they were connected by angles and skin plates which formed a ring-shaped frame #be ins4 thick radially and nearly #e ft4 long4 ,between the vertical and horizontal partitions were left openings which either were partially or entirely closed by segmental doors pivoted on an axis parallel to the face of the shield bulkhead4 ,there were nine of such openings on each shield1 the clear width being #b ft4 #g ins41 the height varying from #b ft4 #b ins4 to #c ft4 #d ins41 according to the location4 ,the hood at the front of the shield was designed so as to be detached underground and was made of complete segments to permit easy erection or detachment4 ,the hood was extended as far as the upper platform1 thus protecting only the roof of the excavation4 ,it was attached to the shield by means of bolts1 and1 when removed1 it was replaced by the cast-steel cutting-edge1 built in #bd sections and placed all around the shield4 ,the eight sliding platforms1 another characteristic of this shield1 could be extended #b ft4 #i ins4 in front of the shield by means of hydraulic rams1 and1 when so extended1 were able to stand a pressure of #gijj lbs4 per sq4 ft4 ,these sliding platforms were used as hoods for the protection of the men working through loose soils1 while in rock they enabled the drilling and blasting to be carried on at three levels4 ,a water trap or bird fountain was constructed1 at the rear of the bulkhead of the shield1 by means of angle irons to which steel plates were bolted4 ,the opening to the face was so spacious that in an emergency the men could readily escape by getting over this trap into safety4 ,besides1 with the assistance of compressed air1 it was sufficient to perfectly trap the water-bearing ground1 in case the face collapsed4 ,including rams and erector1 the total weight of the shield was #aic tons4 ,hydraulic ,rams4--,the shield was operated by hydraulic pressure4 ,the machines were designed for a maximum pressure of #ejjj lbs41 to a minimum of #bjjj lbs41 while the average working pressure was #cejj lbs4 per sq4 in4 ,the forward movement of the shield was obtained by means of #bd single-acting rams #h in4 in diameter and with #ch in4 stroke4 ,each ram exerted a pressure of nearly #ajj tons1 so that the combined action of the #bd rams was equal to #bdjj tons4 ,each sliding platform was operated by two single-acting rams #c ins4 in diameter and with #b ft4 #i in4 stroke4 ,the rams were attached to the rear face of the shield and the front ends of the cylinders to the front ends of the sliding platforms1 and since the cylinders were movable and free-sliding so also were the platforms4 ,erector4--,the erector1 a box-shaped frame mounted on a central shaft1 revolved in bearings attached to the shield4 ,inside this frame there was a differential hydraulic plunger of #d in4 and #c in4 diameters and #dh in4 stroke4 ,to the plunger head were attached two channels which slide inside the box frame and to the projecting ends of which the grip was attached4 ,at the opposite end of the box frame was attached a counter-weight which balances about #gjj lbs4 of the tunnel segment at #aa ft4 radius4 ,the erector was revolved by two single-acting rams fixed horizontally to the back of the shield1 above the erector pivot1 through double chains and chain wheels which were keyed to the erector shaft4 ,air ,locks4--,two bulkhead walls1 forming the rear closure of the pneumatic sections1 were built in each end of each tunnel1 one just ahead of the shield chamber1 the other about #abjj ft4 ahead of the first4 ,the walls were built of ,portland concrete #aj ft4 thick1 and they were grouted with ,portland cement1 under a pressure of nearly #ajj lbs4 per sq4 in41 to make them thoroughly air-tight4 ,each wall had in it three locks2 for man1 material and emergency4 ,each was equipped with hand valves arranged to be operated from either outer end or from within4 ,the floors of the man and material locks were on a level with the working platform of the tunnel1 about #c ft4 #f ins4 above the invert2 the floor of the emergency lock was about #e ft4 above the horizontal axis of the tunnel4 ,the locks were made of steel plates and shapes1 with iron fittings riveted and bolted together4 ,the man lock was #aa ft4 long of elliptical cross-section1 #f ft4 vertical diameter and #e ft4 horizontal2 the material lock was #be ft4 long1 with circular cross-section1 #g ft4 diameter1 and the emergency lock was #bj ft4 long1 of elliptical cross-section1 #d ft4 vertical and #c ft4 horizontal diameters4 ,fig4 #aci shows the elevation of the air lock used in the ,pennsylvania tunnel4 ,illustration3 ,sectional ,elevation ,horizontal ,section ,,fig4 #aci4--,plan and ,elevation of ,first ,bulkhead ,wall in ,south ,tube ,manhattan4 ,excavation4--,in driving these tunnels almost any kind of material was encountered1 viz41 rock1 partly rock1 and partly loose soil1 sand and gravel1 and finally silt4 ,rock4--,much of the rock excavation was made before the shields were erected in order to avoid the handling of rock through the narrow openings of the shield doors4 ,throughout the cross-section the shield traveled on a cradle of concrete in which #b or #c steel rails were imbedded4 ,at the points where the excavation had been made for the full section of the tunnel1 it was only necessary to trim off the projecting corners of rock4 ,where only the bottom heading had been driven the excavation was completed just in front of the shield2 the drilling below the axis level being done from the heading itself1 and above that from the front sliding platforms of the shield4 ,the holes were placed near together and were drilled short2 very light charges of powder were used in order to lessen the chance of knocking the shield about too much4 ,mixed ,face4--,when the rock dipped to such an extent that the front of the tunnel was excavated partly in rock and partly in loose soil1 the compressed air was turned on1 starting with a pressure varying from #ab to #ah lbs4 ,when the surface of the rock was penetrated1 the soft face was held up at first by horizontal boards braced from the shield until the shield was shoved4 ,the braces were then taken out and1 after the shield had been shoved1 were replaced by others4 ,as the amount of soft ground in the surface increased1 the system of timbering was gradually changed to one of #b-;in4 poling-boards4 ,these rested on top of the shield and were supported by vertical breast-boards which in turn were held by #f-;in4 by #f-;in4 walings1 braced through the upper doors to the iron lining and from the sliding platforms of the shield4 ,sand and ,gravel4--,sand and gravel were only met at ,weehawken1 where two different methods were used4 ,the first method was employed when the roof of the excavation was through sand4 ,it consisted of excavating the ground #b ft4 #f ins4 ahead of the cutting-edge1 the roof being held in place by longitudinal poling-boards4 ,these boards rested on the outside of the skin at their back end1 and at the forward end on vertical breast-boards1 braced from the sliding platforms and through the shield doors to cross timbers in the tunnel4 ,the second method of timbering was used in the presence of gravel at the upper part of the excavation4 ,in such a case1 the excavation was only carried #a ft4 #c ins4 7half a shove7 ahead of the cutting-edge1 the roof being supported by transverse boards held by pipes which rested in holes left in the shield4 ,after a small section of the ground had been excavated a board supported by a pipe that was inserted underneath and wedged to it was placed against the ground4 ,these polings were kept below the level of the hood1 so that when the shield was shoved1 they would come inside of it2 in addition they were braced with vertical posts from the sliding platform4 ,the upper part of the face was held by longitudinal breast-boards braced from the sliding platform by vertical pieces4 ,the lower part of the face was supported by vertical sheeted poling1 braced to the tunnel through the lower doors4 ,straw and clay were used in front of the boards to prevent the escape of air which was very large1 when the tunnel was excavated through sand and gravel4 ,the average rate of progress in these materials was #e4a ft4 per day4 ,silt4--,when silt was encountered1 the shield was shoved into the ground without any excavation being done by hand ahead of the diaphragm4 ,as the shield advanced the silt was forced through the doors into the tunnel4 ,forcing the shield through the silt resulted in raising the bed of the river1 the amount that the bed was raised depending on the quantity of material brought into the shield4 ,when the whole volume of the excavation was brought in1 the surface of the bed was not affected2 when about #ej was taken in1 the surface was raised about #c ft42 if the shield was driven blind1 the bed was raised about #g ft4 ,when the shield was driven blind1 the tunnel began to rise for about #b ins41 and the iron lining was distorted1 the vertical diameter increasing and the horizontal one decreasing by about #a ins4 ,it was found1 however1 that the tunnel was not affected when part of the excavation was taken1 but if all of it was taken in or the shield was shoved with open doors1 the tunnel was lowered4 ,a powerful aid was thus found for the guidance of the shield2 for1 if high1 the shield could be brought down by increasing the quantity of muck taken in1 if low1 by decreasing it4 ,the junction of the shields under the river was made as follows3 ,when the two shields of one tunnel1 which had been driven from opposite sides of the river1 approached within #aj ft4 of each other1 they were stopped2 a #aj-;in4 pipe was driven between them1 and a final check of lines and levels was made through the pipe4 ,one shield was then started up with all doors closed1 while the doors of the stationary shield were opened for the muck driven ahead by the moving shield4 ,this was continued until the cutting-edges came together4 ,all doors in both shields were then opened and the shield mucked out4 ,the cutting-edges were taken off and the shields moved together again1 edge of skin to edge of skin4 ,as the sections of the cutting-edges were taken off1 the space between the skin edges was poled with #c-;in4 stuff4 ,when everything except the skin had been removed1 iron lining was built up inside the skins2 the gap at the junction was filled with concrete and long bolts were used from ring to ring on the circumferential joint4 ,lining4--,the tunnels were lined with cast-iron circular rings of the segmental bolted type4 ,in some special cases1 cast steel was used instead of cast iron4 ,the rings were made #cj ins4 long1 with an internal diameter of #ba ft4 #b ins4 and an external one of #bc ft4 ,the rings were composed of nine equal segments of #gg ins4 external circumferential length each1 except the two segments adjoining the key which were equal to the other segments with the difference1 that one end joint was not radial but formed so as to make an opening #ab4be ins4 wide at the outside and #ab4fj ins4 at the inside1 which was closed by the key segment4 ,each segment had six bolts in the circumferential joint1 the key had one1 so that there were #fg bolts in one circumferential joint4 ,each of the twelve longitudinal or radial joints had five bolts1 in all #abg bolts per ring4 ,the circumferential flanges of each plate were strengthened by two transverse webs or feathers on each flange4 ,each segment was provided with a #a in4 grout hole closed with a screw plug4 ,in order to pass around curves1 whether horizontal or vertical1 or to correct deviation from the line or grade1 tapering was used2 by this is meant the placing of rings in the tunnels which were wider than the standard rings1 either at one side 7horizontal tapers or liners71 or at the top 7depressors71 or at the bottom 7elevators74 ,tapers 1 or even #a in4 were used4 ,the taper rings were made by casting a ring with one circumferential flange much thicker than usual and then machining it off to the taper4 ,grouting4--,from the exterior of the tunnel already lined with cast-iron rings1 grout was forced through the holes closed by screw-plugs1 at a pressure of #ij lbs4 per sq4 in4 ,the grout was composed of #a ,portland cement and #a sand by volume and was forced in by a specially constructed machine1 so it formed a shell of cement nearly #c ins4 thick around the exterior of the iron lining4 ,the grouting began at the lower segment2 the cement was forced in until it reached the hole above1 then the hole was plugged1 and the grouting was carried on from the consecutive hole and so on until all the tunnel was finally encased in grout1 as it filled every crevice between the outside of the lining and the ground as excavated4 ,the cast-iron rings of the tunnel were covered with a concrete lining which was placed in the following order3 ,first1 on the invert2 second1 on the duct benches2 third1 on the arch2 fourth1 on the ducts2 fifth1 on the face of the bench4 ,before any concrete was placed1 the surface of the iron was cleaned by scrapers and wire brushes and by washing it with water4 ,the invert was built in sections #cj ft4 long and the duct benches were constructed soon after4 ,these duct benches were built with several steps for the ducts to be laid later4 ,they were built by means of a traveling stage on wheels which ran on tracks on the working platform of the tunnel4 ,the arch was constructed soon after4 ,first the portion from the duct benches to the haunches1 then the arch proper1 was built on traveling centers on tracks laid on the steps of the duct benches4 ,the concrete was received in -cu4-yd4 dumping buckets1 from the flat cars on which they were run2 the buckets were hoisted to the level of the lower platform of the arch by a small ,lidgerwood compressed air hoister4 ,at this level the concrete was dumped on a traveling car or stage and moved in that to the point on the form where it was to be placed4 ,for the lower part of the arch the concrete was thrown directly into the form from this traveling part of the stage4 ,fig4 #adj shows the cross-section of the tunnel with the iron lining and concrete4 ,illustration3 ,section in ,sand and ,gravel or ,rock ,section in ,hudson ,river ,silt1 with foundations ,,fig4 #adj4--,typical ,cross-,sections of ,one ,tube of ,pennsylvania ,railroad ,tunnel ,under the ,hudson ,river4 ,hauling4--,a working platform1 made up of #e-;ft4 sections1 was built inside the tunnel and kept close to the shield4 ,on this platform two lines of industrial railway tracks with switches and sidings at the locks1 and a heading1 were laid for hauling materials and spoils4 ,these lines converged into a single track in passing through the air locks4 ,at the shaft elevators1 they terminated in a steel plate floor to avoid switches4 ,between the locks of the bulkheads was installed an electrically driven cable system1 to haul the loaded muck up grade and to empty the flat cars4 ,from the first bulkhead to the shaft1 the cars were hauled up grade by a steam hauling engine4 ,at the ,manhattan end there was one #aj-;,h4,p4 engine for each tunnel1 while at ,weehawken one #be-;,h4,p4 engine served for both tunnels4 ,each shaft contained two elevators driven by a double-cable1 reversible single-drum steam-hoisting engine4 ,a grouty frame was built over the shafts1 and on the platforms over this frame were narrow-gauge tracks1 extending from the elevators to the muck-chutes and to points where the lining segments were loaded on the cars4 ,the elevators were arranged to stop at both the ground and the grouty platform levels4 ,the rolling-stock at each of the tunnels consisted of #ge flat cars for moving the tunnel segments1 and of about #ej muck cars1 each of #a cu4 yd4 capacity4 ,plant4--,the plants located at each end of the tunnel near the shafts were almost identical4 ,each consisted of three #ejj-;,h4,p4 ,stirtling boilers1 which supplied steam at #aej lbs4 pressure4 ,feed water was supplied by three #ac metropolitan injectors1 and two ,blake duplex pumps4 ,two ,worthington surface condensers1 each of #bbej sq4 ft4 condensing surface1 took care of the exhaust from the engines and compressors4 ,condensing water was pumped from the river through a #af-;in4 pipe4 ,the high-pressure air was supplied by a duplex ,ingersoll-,sergeant compressor1 with cross-compound steam end #ad #bf #cj ins4 and simple water-jacket air cylinders #ac #cf ins4 ,its capacity at #ajj r4p4m4 was #ajhe cu4 ft4 free air per minute4 ,the maximum pressure was #acj lbs4 per sq4 in4 ,the air for the pneumatic working was supplied by three #ad #bf #cj in4 duplex ,ingersoll-,sergeant compressors4 ,the maximum capacity of the three was #ab1jjj cu4 ft4 free air per minute at #abe r4p4m4 and a discharge pressure of #ej lbs4 per sq4 in4 ,the suction air was taken from the outside about #aj ft4 above the roof of the engine house4 ,three aftercoolers1 #cb ins4 #aa ft4 #d ins41 each having #hji sq4 ft4 cooling surface of tinned brass tubes1 cooled the low-pressure discharge to within #aj ,f4 of the temperature of the cooling-water4 ,from the aftercoolers1 the air passed into three steel receivers each #ed #ab ft41 placed outside the engine room and fitted with weighing safety valves4 ,the receivers were connected to two #aj-;in4 mains2 one serving the north1 the other the south tunnel4 ,a fourth receiver of the same size was built to receive the discharge of the high-pressure compressor1 through a #d-;in4 pipe4 ,the high-pressure water required for the shield was furnished by three ,blake direct-acting1 duplex pumps with outside packed plungers4 ,the steam end was #af #ah ins41 the water end #b #ah ins4 ,at #ee r4p4m4 pumping against #ejjj lbs4 per sq4 in41 the capacity of each pump was #eg gals4 per minute4 ,two of them1 one on each tunnel1 were sufficient to run the shields and the third was held in reserve4 ,the high-pressure water was conveyed to the front by means of a #b-;in4 double1 extra strong pipe which was buried between the engine room and the shaft1 in a trench1 to prevent freezing in cold weather4 ,the electric current for light and power was supplied by two #ajj-,k4,w4 #bej-volt ,g4,e4 direct-current generators directly connected to ,ball ,wood high-speed engines running at #bej r4p4m4 ,the switchboard had two machine panels1 two distributing panels and one panel carrying a circuit breaker for the traction circuit4 ,illumination4--,the tunnel was lighted by electricity1 there being two rows of lamps1 one in the crown and one in the south axial fine4 ,the lamps were #af-;c4p41 #bdj-volt1 two-wire system1 and were spaced #ce ft4 apart in the crown and #ab ft4 apart on the axial line4 ,in addition1 five nests of #e lamps each were used at the front4 ,candles were supplied for miscellaneous and emergency uses4 ,the sockets for electric globes were fitted to a wooden reflector1 coated with white enamel paint on the inside4 ,,chapter ,,xxi4 ,,submarine ,,tunneling 7,continued72 ,,tunnels ,,at ,,very ,,shallow ,,depth4 ,,the ,,cofferdam ,,method4 ,,the ,,pneumatic ,,caisson ,,method4 ,,the ,,joining ,,together ,,sections ,,of ,,tunnels ,,built ,,on ,,land4 ,the tunnels on the river bed or at such a shallow depth that only a few feet of material will remain between the bottom of the river and the roof of the tunnel can be built in three different ways1 viz41 7#a7 by a cofferdam2 7#b7 by pneumatic caissons2 7#c7 by sinking and joining together whole sections of tunnels that were built on land4 ,the ,cofferdam ,method4--,the ,van ,buren ,street ,tunnel1 ,chicago ,river4--,according to the cofferdam method1 the work is attacked at one of the shores1 and the tunnel built in sections of such length as not to interfere with the flow of water or the navigation of the river4 ,round the entire exterior line of the first section a double-walled cofferdam is built1 and strongly braced transversely1 so as to withstand the pressure of the water4 ,when the water is pumped out1 a single-walled cofferdam is built within the first1 leaving sufficient distance between the two to allow of the construction of the masonry4 ,the soil is then removed within the inner cofferdam1 and the tunnel constructed from the foundation4 ,when the end of the tunnel reaches the channel end of the cofferdam1 a crib-wall is erected over the end of the completed tunnel4 ,this crib1 in turn1 forms the end wall of another cofferdam1 built in continuation of the first1 so as to allow the second section to be proceeded with1 and at the same time to facilitate the removal of the cofferdams of the first section4 ,the work goes on continuously in this way until the distant shore is reached4 ,,van ,,buren ,,street ,,tunnel1 ,,chicago4 ,the ,van ,buren ,street tunnel1 built to carry a double-track street railway under the ,chicago ,river1 was completed in #ahid by the cofferdam method4 ,the special features of the tunnel#ad are3 7#a7 the unusually large dimensions of the cross-section of #cj ft4 #ae ft4 #i ins42 7#b7 its construction inside of cofferdams of great length and width2 7#c7 the construction under some very high buildings calling for great care and very strong temporary and permanent supports4 #ad 8,eng4 ,news10 ,april #ab1 #ahib4 ,the special feature of the work for our present purpose was the construction of the tunnel across the river4 ,to accomplish this a cofferdam was built out from the west shore of the river to its middle1 and the tunnel constructed within it like the building of any other structure within a cofferdam4 ,transverse and longitudinal sections of this cofferdam are shown by ,fig4 #ada4 ,as will be seen1 it was a simple double-wall cofferdam1 with a clear width between the walls of #eh ft41 and braced transversely as shown4 ,inside of this a single-wall cofferdam of piles was constructed1 with a clear width just sufficient to allow the construction of the masonry within it4 ,when the tunnel end reached the channel end of the cofferdam1 a crib-wall was built over the end of the completed tunnel1 as shown by the drawings4 ,this crib-wall was intended to form the end wall of another cofferdam1 which was built out from the east shore1 and within which the remaining half of the tunnel was built as the first half had been4 ,the drawings show the character of the tunnel masonry and of the centering upon which it was built4 ,illustration3 ,,transverse ,,section ,,of ,,cofferdam ,,and ,,tunnel ,,section ,,showing ,,method ,,of ,,constructing ,,crib ,,dam4 ,,fig4 #ada4--,sections of ,cofferdam1 ,van ,buren ,st4 ,tunnel1 ,chicago4 ,the ,van ,buren ,street tunnel was the last of the three tunnels under the ,chicago ,river1 constructed according to the cofferdam method4 ,at the time the tunnels were constructed the bed of the river was #ag ft4 deep4 ,in connection with the harbor and river improvements1 the ,federal ,government ordered the ,chicago ,river to be lowered so as to give a depth of #bf ft4 of water4 ,this necessitated the lowering of the tunnel roof and the excavation for a deeper floor which was a very difficult operation4 ,this work was described in 8,eng4 ,news10 ,sept41 #aijf4 ,,the ,,pneumatic ,,caisson ,,method4--,,the ,,tunnel ,,under ,,the ,,harlem ,,river4 ,in the early seventies ,prof4 ,winkler proposed to construct a tunnel under the ,river ,danube to connect the various portions of the ,vienna1 ,austria1 underground railway1 and to use caissons in the construction4 ,prof4 ,winkler proposed to build caissons from #cj ft4 to #de ft4 long1 with a width depending upon the lateral dimensions adopted for the tunnel masonry4 ,the caisson was to be made of metal plates and angle iron with riveted connections on all sides except those running vertically transverse to the tunnel axis1 whose connections were to be bolted4 ,in the middle of the roof an opening was to be left2 this was for the shaft having the air-locks to allow the passage of men1 materials1 and compressed air4 ,across the river two parallel rows of piles were to be driven into the river bed1 to fix the place where the caisson was to be sunk4 ,then the first caisson near the shore was to be lowered in the ordinary way1 and a second caisson was to be immediately sunk very close to the first one4 ,when both caissons had reached the plane of the tunnel floor1 the sides which were in contact were to be unbolted and removed1 and the small space between made water-tight4 ,the chambers of the two caissons were to be opened into a single large one communicating above by means of two shafts4 ,at the same time that the masonry was being built in the first two caissons1 from the inverted arch up1 a third caisson was to be sunk2 and when by excavation it had reached the plane of the projected tunnel floor1 the partitions were to be removed so that the three caissons were in communication1 forming a large single caisson4 ,then the outer partition of the first caisson was to be removed1 and the masonry of the submarine tunnel connected with the portion of the tunnel built on land4 ,in a similar manner all the caissons were to be sunk2 and when the last one was placed1 and the masonry lining constructed1 and connected with the portion of the tunnel built on the other shore of the river1 the partition walls were to be battered down1 and the submarine tunnel completely constructed and open to traffic4 ,the ,harlem ,river ,tunnel4--,the pneumatic caissons method was employed in the construction of the tunnel under the ,harlem ,river for the ,new ,york ,rapid ,transit ,railway4 ,the tunnel proper consisted of two parallel tubes riveted to each other and surrounded by a cradle of concrete as shown in ,fig4 #aba1 page #baf4 ,the tunnel was built in three sections3--,the first1 from the ,manhattan shore well towards the middle of the river2 the second1 from the shore of the ,bronx towards the middle of the river2 and the last1 the section uniting the other two and completing the tunnel4 ,each section was built within a specially constructed working-chamber1 consisting of timber side walls forming a wooden caisson1 so constructed that compressed air could be used4 ,this working-chamber of ,mr4 ,mc,bean presented some novel features1 inasmuch as the caisson was not built on land1 but under water4 ,in building the tunnel1 the ,harlem ,river was dredged to a certain depth1 so as to leave only #f ft4 or #h ft4 of excavation to be done before reaching the line of sub-grade of the proposed structure4 ,two service platforms were built on piles #aj ft4 apart longitudinally1 and cut off at a point above mean high-water mark1 braced in the usual manner1 and covered with heavy planks1 to serve as the floor of the platform4 ,on this platform were placed rails for the trains used in the transportation of materials4 ,these platforms were also used in maintaining the perfect alignment of the caissons4 ,within the platforms and along the dredged channel four longitudinal rows of piles were sunk4 ,these piles were accurately brought to line by beams bolted together1 and placed across and above the water-level4 ,a few beams were also added for the purpose of bracing the piles transversely1 after which they were cut off under water and capped4 ,illustration3 ,,fig4 #adb4--,showing ,working ,platforms and ,piles ,sunk in the ,dredged ,channel4 ,fig4 #adb shows the manner in which the working platforms were constructed1 and also the rows of piles sunk in the dredged channel4 ,between the piles a very strong frame was placed1 made up of waling pieces and two transverse beams #ad ins4 by #ad ins4 each1 placed one below the other at a distance of #e ft4 #h ins41 and strongly braced together4 ,guiding-beams were fixed on each side of the frame for the sheeting piles4 ,the frames were built in sections of different lengths1 and placed directly above the cap-pieces of the pile-bents sunk in the dredged channel4 ,the longitudinal sides of the caisson were constructed by sinking two rows of sheeting piles1 each row being close to a service platform4 ,the sheeting piles were made up of yellow-pine timbers #ab ins4 by #ab ins42 three piles bolted together formed a section #c ft4 wide4 ,each section was grooved and tongued1 so as to be firmly connected with the adjacent sections to be sunk4 ,the lower ends of the piles were cut wedge-shaped1 with a sharp edge to offer a small resistance while penetrating the soil4 ,the sheeting-piles were then cut off under water1 which operation was successfully carried out by means of a circular saw operated by a pile-driving machine4 ,the sheeting was also extended between two platforms to make a bulkhead1 and in this way the four sides of the caisson were built up4 ,particular attention was always given to the alignment of the sheeting piles1 which was obtained by guiding the piles with the timbers placed longitudinally1 one below the water-line in connection with the frames located between the pile-bents1 and the second along the inner edge of the service platform1 as shown in ,fig4 #adc4 ,illustration3 ,,fig4 #adc4--,showing ,sheeting-,piles for the ,sides of the ,caisson and ,trussed ,beam for the ,roof4 ,the caisson was completed by placing a roof covering the sides4 ,this roof was #dj ins4 thick1 made up of three layers of #ab-;in4 beams placed transversely to the axis of the caisson1 while between the beams planks #b ins4 thick were placed lengthwise and bolted together1 so as to make a firm1 solid structure4 ,the roof was built ashore1 in sections each varying from #ci ft4 to #acj ft4 long4 ,the edges of the roof fitted the sides of the caisson perfectly2 and when each section was towed to the proper spot1 it was sunk and made secure4 ,under the roof were placed six longitudinal beams1 #ab ins4 by #ad ins41 called 8rangers10 resting on the cap-pieces of the pile-bents that were laid across the space of the proposed tunnel2 while the extreme rangers were used for the purpose of fitting above the sheeting-piles of the caisson1 in order to make the latter water-tight4 ,the two extreme rangers were provided with ,t-irons1 the flat side being laid on the sheeting-piles1 while the web penetrated the ranger by reason of the weight of the load resting on the roof1 for the purpose of sinking it to the required point4 ,earth was next heaped on the roof1 and in this way a large working-chamber was prepared1 as shown in ,fig4 #add4 ,illustration3 ,,fig4 #add4--,showing the ,caisson with the ,working-,chamber4 ,the working-chamber built on the ,manhattan side of the ,harlem ,river was #baf ft4 long1 provided with two rectangular shafts #g ft4 by #ag ft41 rendered water-tight1 and rising above the high-water mark of the river4 ,within these shafts the air-locks of the tunnel tubes were placed1 so that the work could be carried on by means of compressed air4 ,the pressure of the air was used to expel the water1 being sufficiently intense to equilibrate a column of water equal to the depth of the lowest point of the roof of the caisson4 ,when the working-chamber was constructed1 the tunnel proper was begun by excavating the soil down to the required level2 the concrete was then laid on4 ,it was just at this point1 when a large part of the roof was constructed and supported only by the sheeting-piles of the sides of the caisson1 that the writer of this article feared that this novel method of tunneling would prove a failure4 ,the tendency of the timber to float1 aided as it was by the air pressure within the caisson1 was counteracted only by the weight of the earth heaped on the roof1 and by the friction of the soil against the feet of the sheeting-piles4 ,this friction was only a small quantity1 as the soil was loose1 so that it was considered rather risky and dangerous to place reliance on such a feeble quantity4 ,this fear was1 unfortunately1 justified on two occasions1 when on cutting off a portion of the pile-bents some of the sheeting-piles got loose and water flooded the whole chamber1 but1 happily1 without loss of life4 ,as the chamber was one of large dimensions1 the workmen had time enough to effect their escape4 ,it may be remarked that during these troubles only a few of the sheeting-piles were displaced1 while the caisson itself offered a stout and successful resistance1 due to its being strongly braced transversely4 ,the accidents were1 therefore1 limited to a few piles1 instead of affecting the entire caisson4 ,on the occasion of the first1 the repairs were effected by sinking the piles to a greater depth1 continuing down until rock was encountered4 ,after that1 the water was pumped out and the work resumed4 ,in repairing the second accident1 the sheeting-piles were driven down to bed-rock1 and the surrounding soil strengthened by cement forced through the loose soil around the piles4 ,this remedy proved effective1 and no further trouble occurred to delay the work on the ,manhattan side of the ,harlem ,river4 ,illustration3 ,,fig4 #ade4--,showing the ,tunnel ,constructed within the ,caisson4 ,on the concrete bed of the tunnel the segments of the metal lining were placed and surrounded by concrete1 as required by the plans and specifications 7,fig4 #ade74 ,the contractors had planned to unbolt the roof from its holdings1 to remove by means of dredgers the earth which had been heaped on it1 and thus set the roof afloat1 after which it was to be towed within the two working platforms already erected on the ,bronx shore4 ,but ,mr4 ,mc,bean devised a simpler and more economic1 but at the same time more dangerous1 way of constructing this second section of the tunnel4 ,he thought that the upper half of the tunnel proper could be used instead of the timber roof1 thereby reducing the capacity of the working chamber1 and limiting the use of compressed air4 ,in this way he dispensed with the removal of timber1 and also of the earth heaped on the roof4 ,in building this ,bronx section1 a channel was dredged along the line of the tunnel to a depth of #e ft4 from the foundation-bed of the proposed tunnel4 ,the working platforms were constructed on both sides of this channel1 quite similar to those erected on the other half of the tunnel2 and between them pile-bents were sunk1 capped with #ab-;in4 by #ab-;in4 beams4 ,over the cap-pieces rangers were placed longitudinally1 which also rested on the sides of the wooden working caisson1 ,fig4 #adf4 ,the sheeting-piles were cut off at level1 but much lower down than in the first half of the tunnel4 ,the roof was built on floats made of #ab-;in4 by #ab-;in4 timber laid transversely #d ft4 apart and supporting a floor of #c-;in4 by #ab-;in4 planks rendered water-tight4 ,the sides of the floats were made by verticals1 #d ins4 by #f ins41 and planks1 #c ins4 by #ab ins41 carefully caulked4 ,a temporary floor was built on the base of the float1 consisting of transverse beams1 #af ins4 by #af ins41 placed #h ft4 apart4 ,a center piece1 #aj ins4 by #af ins41 was laid so as to correspond with the axis of the tunnel2 and on each side of it1 other parallel beams1 #af ins4 by #af ins41 corresponding to each center of the circular metal lining of the tunnel2 the beams1 longitudinal and transversal1 were strongly bolted together4 ,the temporary floor was completed by boarding the spaces left between the various beams4 ,illustration3 ,,fig4 #adf4--,showing ,sides of the ,caisson and ,supports for the ,roof4 ,on this float1 the upper half of the tunnel was constructed by erecting the segments of the metal lining1 which were strongly supported1 so as to prevent any settling or distortion2 the concrete was then built up in a large flange with vertical suspension rods1 four to each bar4 ,the rings of the tunnel were #f ft4 each1 the weight of each lining being #da1jjj lbs41 the concrete covering #fah cubic feet4 ,the second part of the tunnel was #cjj ft4 long1 with roof constructed in three sections--two of #ij ft4 in length each and the third of #hd ft4 ,each of these sections alternated with a smaller section1 #ab ft4 long1 provided with air-locks4 ,the shortest of the three sections was the first one set up1 and was constructed close to the ,bronx side of the ,harlem ,river4 ,for this purpose the two extreme ends of the section were closed by means of steel plates forming diaphragms1 built #f ft4 inward1 thus leaving one ring projecting out at each end4 ,openings were left on the top of these projecting rings for access by divers4 ,the exterior of the upper half section of the permanent tunnel was filled with water until it was lowered into position4 ,it was directed by means of tackles attached to vertical eye-bars1 which were strongly fixed to the flanges of the springing line of the arch1 and bolted to the beams of the temporary floor4 ,in this way the roof was towed into place1 and lowered by means of stone ballast1 until it rested on the cap-pieces and frames of the pile abutments1 the sides of the roof remaining just on top of the sheeting-piles that formed the sides of the caisson1 as shown in ,fig4 #adg4 ,perfect alignment was obtained by wires strung at each end and along the side of the roof1 corresponding to points fixed on the working platforms and sighted with transits4 ,such accuracy was obtained that the circumferential flanges of the outer #f-;ft4 ring were brought into contact with those of the #ab-;ft4 section already constructed4 ,a diver then entered by the opening left in the projecting ring1 and bolted this section of the roof to the preceding one4 ,by removing the iron diaphragm1 the consecutive sections were united into one4 ,when the diver completed his work1 the opening was closed up1 and compressed air used to keep the water out of the box included between the roof and the temporary flooring4 ,illustration3 ,,fig4 #adg4--,showing the ,roof of the ,caisson ,formed by the ,upper ,half of the ,tunnel4 ,the remaining sections of the tunnel roof were built in the same way1 until the last abutted against the part of the work constructed within the caisson under the high wooden roof on the ,manhattan side of the river4 ,the following method was adopted for the purpose of connecting the few parts of the tunnel which had been differently constructed4 ,the diaphragm at the end of the last section of the tunnel roof was constructed so as to abut against the last circumferential flanges of the iron lining without leaving a projecting ring4 ,it was continued above the metal and concrete lining of the roof in a rectangular form1 and of the same height and width as the wooden bulkhead of the working-chamber on the ,manhattan side of the river4 ,the diaphragm was made of riveted plates and angles1 with an opening #bj ins4 by #cj ins41 bolted so as to be removable at will4 ,the diaphragm was of the same height as the roof and was connected with a roof-plate to the rangers supporting the thick wooden roof4 ,other steel plates1 placed vertically1 were riveted to the diaphragm and bolted to the caisson4 ,all this work was carried on by divers4 ,the wooden bulkhead was cut to the springing-line of the arch2 and between the two parts of the tunnel1 built by different methods1 a bulkhead was placed1 made of steel plates #ad ins4 long1 which prevented the entrance of water into the working-chamber4 ,illustration3 ,,fig4 #adh4--,showing the ,tunnel ,completed by ,building the ,lower ,half within the ,caisson4 ,when the different sections were joined together1 and all the openings closed and made water-tight1 cement-grout was poured on the roof1 and earth was heaped up to a height of #e ft4 ,the #cjj ft4 of the roof1 resting on sheeting-piles and provided with diaphragms at the extreme ends1 formed a water-tight working-chamber1 or caisson1 communicating with the exterior by means of the shafts and air-locks4 ,the lower portion of the tunnel was built under air-pressure4 ,the pile-bents were first cut off at the plane of the tunnel sub-grade1 after which the foundation-bed of concrete was laid4 ,the lower segments of the iron lining were then placed in position1 and the structure made continuous by building up the lateral walls1 consisting of concrete 7,fig4 #adh74 ,no accidents occurred while building the second part of the tunnel4 ,the ,harlem ,river tunnel was completed in contract time1 although the opening of the subway was delayed by difficulties encountered in tunneling through rock in the borough of the ,bronx4 ,the writer endeavored to obtain information regarding the expense per linear foot1 but all his efforts were rewarded with a general assurance that it proved to be the cheapest method4 ,,sinking ,,and ,,joining ,,together ,,sections ,,of ,,tunnels ,,built ,,on ,,land4 ,,the ,,seine4 ,,the ,,detroit ,,river ,,tunnels4 ,in the year #ahif1 ,mr4 ,erastus ,wyman secured a patent for building subaqueous tunnels close to the river1 by sinking and joining together small sections of tunnels previously built on land4 ,each section would have been provided with a long vertical tube for the air-lock when compressed air was to be admitted to expel the water and permit the construction of the lining within the sunken shell4 ,thus each section of the tunnel would have acted as a pneumatic caisson2 being1 however1 an improvement on ,professor ,winkler's suggestion inasmuch as the caisson was a portion of the tunnel itself1 instead of a simple inclosure for facilitating the construction of the shield4 ,mr4 ,wyman proposed to use this method in the construction of a tunnel between ,south ,brooklyn and ,stapleton1 ,staten ,island2 a charter was granted him but the tunnel was never built4 ,the ,tunnel under the ,seine ,river4--,the caisson method of building tunnels under water was used at ,paris1 ,france1 in the construction of the ,metropolitan ,railroad under the ,seine ,river4 ,the caissons designed by ,mr4 ,l4 ,chagnaud were for a double track line4 ,they were sunk1 ends to ends1 and formed a portion of the tunnel lining which was enveloped by a framework of metal embedded in concrete4 ,built-up frames carried a shell of steel plating on the sides1 from toes to springing lines1 and on the sides and roof of the working-chamber4 ,a temporary plate diaphragm closed the open ends4 ,this construction formed a vessel capable of floating with a very light draft4 ,the method of sinking the caissons was as follows3 ,the caisson was erected on the river bank and when completed it was launched and towed into position between pile stagings which served the double purpose of guiding the descent at the beginning of the sinking and of forming a working platform4 ,the caisson when launched and1 consequently1 before the cast-iron lining had been put in place within it1 weighed #bhj metric tons2 but1 beyond some difficulty in taking it under the bridges in the way1 the towing was accomplished without serious trouble4 ,illustration3 ,,fig4 #adi4--,transversal ,section of the ,caissons for the ,tunnel under the ,seine ,river4 ,previous to placing the caisson in position between the stagings1 the portion of the river bed it was to rest upon had been leveled by dredging4 ,once in position1 the first work was the erecting of the cast-iron lining segments within the framework4 ,work was then begun by filling the annular space between the lining and the shell with concrete2 this additional weight gradually sunk the caisson to the river bottom4 ,the working shafts1 made up of steel cylinders1 were placed as the sinking progressed to this point4 ,illustration3 ,section ,a-,b4 ,section ,c-,d4 ,plan at ,joint4 ,,fig4 #aej4--,showing the ,joining of the ,caissons at the ,pont ,mirabeau ,tunnel under the ,seine ,river4 ,after the caissons had been sunk to the required place and in continuation of one another1 a space of nearly #e ft4 was left between them4 ,the construction of the tunnel within the bank of earth separating the two caissons was as follows3 ,a cofferdam was built around this space4 ,it was formed by two diaphragms closing the ends of the tunnel1 and by two longitudinal walls sunk as temporary caissons1 one on each side of the tunnel and inclosing their ends4 ,this cofferdam was covered with a metal working-chamber whose lower edges rested on top of the four walls of the cofferdam4 ,the joints were made tight by means of rubber or packed clay4 ,the water in the cofferdam was then pumped out1 the earth excavated1 and the masonry built in continuation of the two ends of the tunnel sections4 ,the submerged sections of the tunnel which were allowed to remain full of water to render them more stable and to save effort in pumping them1 were now made dry2 the diaphragms were removed from the ends of the caisson tunnels and the work made continuous4 ,fig4 #adi shows the cross-section of the caissons4 ,at the ,pont ,mirabeau crossing of the ,seine1 a slightly different method was used1 described in 8,eng4 ,news10 ,may #ah1 #aiaa4 ,the caissons were sunk to the required line and grade with an intervening longitudinal space of #ae ins4 between two adjoining caissons4 ,at each end of this space1 which was filled with the river marl1 was sunk against the edges of the caissons a hollow cylinder #bj ins4 outside diameter4 ,the interior of these cylinders was excavated and filled with concrete1 thus forming a continuous wall on both sides of the two adjoining caissons4 ,the earth from the intervening space was then removed and concrete deposited from bottom opening tremies up to the level of the top of the caisson4 ,after nearly one month the tunnel was entered from the shaft and an opening the shape and size of the tunnel section cut through the diaphragms of the #ae-;in4 wall and the concrete tunnel lining made continuous between the two sections4 ,fig4 #aej shows the method of joining the caissons4 ,the ,detroit ,river ,tunnel4#ae--,with some modifications which permitted dispensing with compressed air1 the tunnel under the ,detroit ,river was built for the ,michigan ,central ,railroad1 connecting ,detroit with ,windsor1 ,canada4 ,the tunnel is #ffbe ft4 long2 of this1 however1 only #bfbe ft4 are under the river1 while the approach on the ,american side is #bjjj ft4 long and that on the ,canadian side1 #djjj ft4 ,the tunnel consists of two parallel circular tubes #bc ft4 in diameter1 built up of -in4 steel plate4 ,they are placed #bf ft4 apart1 center to center1 and are connected by diaphragms at #ab-;foot intervals4 #ae ,condensed from a paper by ,b4 ,h4 ,ryder4 ,each section of the subaqueous tunnel is approximately #bfb ft4 long4 ,there are ten of these sections and an eleventh a little over #fj ft4 long4 ,these tubes were built at the shipyards of the ,great ,lakes ,engineering ,works at ,st4 ,clair1 about #cj miles from ,detroit4 ,after the assembling was completed1 the ends of each tube were closed by temporary wooden bulkheads to make them float1 and the outside sheathed horizontally with heavy timbers bolted to the diaphragms4 ,this sheathing running lengthwise of the tube made a form or pocket1 into which the inclosing jacket of concrete was placed4 ,the sections were then launched and towed down to the tunnel site and sunk separately in a trench on the river bottom that had been previously dredged to receive them4 ,this trench was dug to a width of #ej ft4 and depth varying from #be to #ej ft4 by clamshell buckets1 swung from a scow1 working to a depth below the water level of #fj to #ij ft4 ,as a foundation for the sections1 a grillage was constructed on the surface and sunk in place in the trench by derricks swung from a scow4 ,the grillage was placed underneath each joint between the sections and built up of ,i-beams imbedded in concrete4 ,this grillage is the width of the trench and about #cj ft4 long1 with posts projecting downward from the four corners1 and these were seated into the river bottom1 by means of pile drivers1 to the desired grade4 ,then the eleven sections of the tunnel were lowered and connected1 one at a time4 ,by the aid of air tanks placed on each section the movement was controlled until the final sinking upon the grillage in the trench4 ,this operation called into play the greatest engineering skill and ingenuity4 ,when it is considered that the current velocity at the river bed is about #b ft4 per second and much higher along the surface1 some idea can be gained of the problems to be overcome4 ,the movement of the enormous sections must be absolutely under control4 ,thirty-five-ton blocks of concrete were sunk in the river bottom up and down stream to act as anchors1 and through them cables were rigged and connected back to the hoisting engines on the derrick scows4 ,these were prevented from moving by spuds at each corner1 securely driven into the river bottom at depths sometimes as great as #ij ft4 ,controlling cables were also run from the sections to the tremie scow to pull one structure close to the adjoining section previously sunk1 and the divers made the necessary connection4 ,fig4 #aea shows cross-sections and plans of the tunnel as given in 8,eng4 ,record10 ,march #b1 #aijg4 ,illustration3 ,,half ,,cross ,,section ,y-,y ,,half ,,cross ,,section ,z-,z ,,half ,,horizontal ,,section ,x-,x ,,half ,,top ,,view ,,fig4 #aea4--;,cross-,sections and ,plans of the ,detroit ,river ,tunnel4 ,steel masts had been previously attached to each end of the sections to enable the engineers on shore to determine the alignment and locate the exact position during the sinking4 ,concrete was then deposited in the pockets1 completely surrounding the tubes1 forming a solid monolithic structure from end to end4 ,this was done by means of the tremie process4 ,a #cb-;ft4 by #afj-;ft4 scow was equipped with a concrete mixing plant and the tremie pipes1 three in number1 through which the concrete was deposited4 ,each pipe is #ab ins4 in diameter1 of spiral riveted steel1 #hj ft4 long4 ,these pipes could be raised or lowered1 reaching from the receiving hoppers on the scow to the bottom of the trench4 ,when the pipes were filled with concrete and lowered into position1 a continuous flow was maintained4 ,as fast as the concrete escaped at the bottom end of the pipe it was replenished at the top2 this process continuing until the entire space surrounding the section was filled to the desired level1 and under the pressure produced not only by the depth of water under which it was submerged1 but also by the weight of the long column of concrete contained in the tubes4 ,it is interesting to note that this is the first time a large amount of concrete has been deposited at a depth of #gj ft4 by this method1 and upon the accomplishment of this task in a measure depended the successful building of the tunnel4 ,inside the tubes was placed a lining of reinforced concrete #bj ins4 thick4 ,side walls were built up from this ring to provide ducts1 which carry the electrical cables for the distribution of power1 lighting1 signal and telegraph wires4 ,they also serve to provide a footwalk along the side of the tunnel4 ,there are cross passages in the tunnel every #bjj ft41 and also various niches for the different equipment needed in connection with the signaling1 telephone and fire alarm system4 ,the tunnel is lighted with #hjj #af-;candle-power incandescent lights4 ,the track construction is new4 ,there is no ballast used1 the ties being laid in concrete4 ,a ditch in the center of each track carries the rainfall that will flow down from the summits to sumps which are drained by centrifugal pumps4 ,one remarkable feature of its construction is that compressed air was not used in the building of the subaqueous tunnel1 but it was necessary in building the approach tunnels4 ,this is contrary to the usual program where compressed air is required in subaqueous work1 and not ordinarily used in approach or land tunnel construction4 ,the trains are operated by very heavy electric locomotives1 operated by the third-rail system4 ,the tunnel was constructed under the supervision of ,w4 ,s4 ,kinnear1 ,chief ,engineer of the ,detroit ,river ,tunnel ,co42 ,butler ,bros4 of ,new ,york were the general contractors4 ,,chapter ,,xxii4 ,,accidents ,,and ,,repairs ,,in ,,tunnels ,,during ,,and ,,after ,,construction4 ,in the excavation of tunnels it often happens that the disturbance of the equilibrium of the surrounding material by the excavation develops forces of such intensity that the timbering or lining is crushed and the tunnel destroyed4 ,to provide against accidents of this kind in a theoretically perfect manner would require the engineer to have an accurate knowledge of the character1 direction and intensity of the forces developed1 and this is practically impossible1 since all of these factors differ with the nature and structure of the material penetrated4 ,the best that can be done1 therefore1 is to determine the general character and structure of the material penetrated1 as fully as practicable1 by means of borings and geological surveys1 and then to employ timbering and masonry of such dimensions and character as have withstood successfully the pressures developed in previous tunnels excavated through similar material4 ,if1 despite these precautions1 accidents occur1 the engineer is compelled to devise methods of checking and repairing them1 and it is the purpose of this chapter to point out briefly the most common kinds of accidents1 their causes1 and the usual methods of repairing them4 ,accidents ,during ,construction4--,accidents may happen both during or after construction1 but it is during construction1 when the equilibrium of the surrounding material is first disturbed1 and when the only support of the pressures developed is the timber strutting that they most commonly occur4 ,causes of ,collapse4--,collapse in tunnels may be caused3 7#a7 by the weight of the earth overhead1 which is left unsupported by the excavation2 7#b7 by defective or insufficient strutting2 and 7#c7 by defective or weak masonry4 7#a7 ,the danger of collapse of the roof of the excavation is influenced by several conditions4 ,one of these is the method of excavation adopted4 ,it is obvious that the larger the volume of the supporting earth is1 which is removed1 the greater will be the tendency of the roof to fall1 and the more intense will be the pressures which the strutting will be called upon to support4 ,thus the ,english and ,austrian methods of tunneling1 where the full section is excavated before any of the lining is placed1 and where1 as the consequence1 the strutting has to sustain all of the pressures1 present more likelihood of the roof caving in than any of the other common methods4 ,the character and structure of the material penetrated also influence the danger of a collapse4 ,a loose soil with little cohesion is of course more likely to cave than one which is more stable4 ,rock where strata are horizontal1 or which is seamy and fissured1 is more likely to break down under the roof pressures than one with vertical strata and of homogeneous structure4 ,soft sod containing boulders whose weight develops local stresses in the roof timbering is likely to be more dangerous than one which is more homogeneous4 ,a factor which greatly increases the danger of collapse1 especially in soft soils1 is the presence of water4 ,this element often changes a soil which is comparatively stable1 when dry1 into one which is highly unstable and treacherous4 ,the liability of the material to disintegration by atmospheric influences and various other conditions1 which will occur to the reader1 may influence its stability to a dangerous extent1 and result in collapse4 7#b7 ,collapse is often the result of using defective or insufficient strutting4 ,of course1 in one sense1 any strutting which fails under the pressures developed1 however enormous they may be1 can be said to be insufficient1 but as used here the term means a strutting with an insufficient factor of safety to meet probable increases or variations in pressure4 ,insufficient strutting may be due to the use of too light timbers1 to the spacing of the roof timbers too far apart1 to the yielding of the foundations1 to insufficient bearing surface at the joints1 etc4 ,collapse is often caused by the premature removal of the strutting during the construction of the masonry4 ,the masons1 to secure more free space in which to work1 are very likely1 unless watched1 to remove too many of the timbers and seriously weaken the strutting4 7#c7 ,the third cause of collapse is badly built masonry4 ,poor masonry may be due to the use of defective stone or brick1 to the thinness of the lining1 to poor mortar1 to weak centers which allow the arch to become distorted during construction1 to poor bonding of the stone or bricks1 to the premature removal of the centers1 to driving some of the roof timbers inside it1 etc4 ,prevention of ,collapse4--,tunnels very seldom collapse without giving some previous warning of the possible failure1 and also of the manner in which the failure is likely to occur4 ,from these indications the engineer is often able to foresee the nature of the danger and take steps to check it4 ,the danger may occur either during excavation or after the lining is built4 ,during excavation the danger of collapse is indicated beforehand by the partial crushing or deflection of the strutting timbers4 ,if the timbers are too light or the bearing surfaces are too small1 crushing takes place where the pressures are the greatest1 and the timbers bend1 burst1 or crack in places1 and the joints open in other places4 ,the remedy in such cases is to insert additional timbers to strengthen the weak points1 or it may be necessary to construct a double strutting throughout4 ,when the distance spanned by the roof timbers is too great1 failure is generally indicated by the excessive deflection of these timbers1 and this may often be remedied by inserting intermediate struts or props4 ,in some respects the best remedy under any of these conditions is to construct the masonry as soon as possible4 ,when collapse is likely to occur after the masonry is completed1 its probability is generally indicated by the cracking and distortion of the lining4 ,a study of the cause is quite likely to show that it is the percolation of water through the material surrounding the lining which causes cavities behind the lining in some places1 and an increase of the pressures in other places4 ,when it is certain that this water comes from the surface streams above1 these streams may often be diverted or have their beds lined with concrete to prevent further percolation4 ,when percolating water is not the cause of the trouble1 a usually efficient remedy is to sink a shaft over the weak point1 and refill it with material of more stable character4 ,these1 and the remedies previously suggested1 are designed to prevent failure without resorting to reconstruction4 ,when they or similar means prove insufficient1 reconstruction or repairs have to be resorted to4 ,repairing ,failures4--,tunnels may collapse in several ways3 7#a7 ,the front and sides of the excavation may cave in2 7#b7 the floor or bottom may bulge or sink2 7#c7 the roof may fall in2 7#d7 the material above the entrances may slide and fill them up4 7#a7 ,one of the most common accidents is the caving of the front and sides of the excavation4 ,this may often be prevented by taking care that the face of the excavation follows the natural slope of the material instead of being more or less nearly vertical4 ,when1 however1 caving does occur it may usually be repaired by removing the fallen material1 strongly shoring the cavity1 and filling in behind with stone1 timber1 or fascines4 7#b7 ,the bulging or rising of the bottom of the tunnel may usually be considered as a consequence of the squeezing together of the side walls4 ,it usually occurs in very loose soils1 and is chiefly important from the fact that the reconstruction of the side walls is made necessary4 ,the sinking of the tunnel bottom is a more serious occurrence4 ,it seldom happens unless there is a cavity beneath the floor1 due either to natural causes or to the fact that mining operations have gone on in the hill or mountain penetrated by the tunnel4 ,when the bottom of the tunnel sinks1 three cases may be considered3 7a7 when the sinking is limited to the middle of the tunnel floor2 7b7 when only a portion of the foundation masonry is affected2 and1 7c7 when the entire lining is disturbed4 ,in the first case repairs are easily made by filling in the cavity with new material4 ,in the second case the unimpaired portion of the masonry is temporarily supported by shoring while the injured portion is removed and rebuilt on a firm foundation4 ,the remaining cavity is then filled4 ,in the case of the complete failure of the lining1 the method of repairing employed when the roof falls1 and described below1 is usually adopted4 7#c7 ,the most dangerous of all failures is the falling of the tunnel roof4 ,in such casualties two cases may be considered3 7a7 ,when the falling mass completely fills the tunnel section1 and 7b7 when it fills only a portion of the section4 ,illustration3 ,,fig4 #aeb4--,tunneling through ,caved ,material by ,heading4 ,when the whole section is filled by the fallen material1 the problem may be considered as the excavation of a new tunnel of short length inside the old tunnel1 and under rather more difficult conditions4 ,the first task1 particularly if men have been imprisoned behind the fallen material1 is to open communication through it between the two uninjured portions of the tunnel4 ,it is advisable to do this even when there is no danger to life because of imprisoned workmen1 since it enables the work of repairing to be conducted from both directions4 ,the excavation of a passageway through the fallen material is rendered difficult1 both because the fallen material is of an unstable character1 and also because it is usually filled with the lining masonry1 timbering1 etc4 ,when1 therefore1 the accident has happened before the full section of the original material has been removed1 the first heading or drift is driven through this original material rather than through the fallen dbris4 ,any of the regular soft-ground methods of tunneling may be employed1 but it is usually better to select one which allows the masonry to be built with as little excavation as possible at first4 ,for this reason the ,german method of tunneling is particularly suited to repair work of this nature4 ,the ,belgian method may also be used to advantage1 particularly when the caving extends to the surface of the ground above1 and the upper portion of the dbris is1 therefore1 practically the same material as that through which the original tunnel was driven4 ,the greatest defect of the ,belgian method for making repairs is that the roof arch is supported by a rather unstable mass of mingled earth1 stone1 and timber1 which constitutes the bottom layer of the fallen material4 ,the method of strutting the work when the ,german or ,belgian method is used is shown by ,fig4 #aeb4 ,it sometimes happens that the fallen dbris is so unstable that it will not carry safely the arch masonry in the ,belgian method or the strutting in the ,german method1 and in these cases one of the full-section methods of excavation is usually adopted4 ,the nature of the strutting employed is shown by ,fig4 #aec4 ,when the section has been opened and the new masonry built1 great care should be taken to fill the cavity behind the masonry with timber or stone2 and should the disturbance reach to the ground surface it is often a good plan to sink a shaft through the disturbed material1 and fill it with more stable material4 ,illustration3 ,,fig4 #aec4--,tunneling through ,caved ,material by ,drifts4 ,when the fallen dbris fills only a part of the section1 the first thing to provide against is the occurrence of any further caving2 and this is usually done by building a protecting roof above the line of the future roof masonry4 ,figs4 #aed and #aee show two methods of constructing this temporary roof1 which it will be noticed is filled above with cordwood packing4 ,as soon as the temporary roof is completed1 the lining masonry is constructed4 ,illustration3 ,,figs4 #aed and #aee4--;,filling in ,roof ,cavity ,formed by ,falling ,material4 ,illustration3 ,,fig4 #aef4--,timbering to ,prevent ,landslides at ,portal4 7#d7 ,landslides which close the tunnel entrance are repaired in a variety of ways4 ,fig4 #aef shows a common method of preventing the extension of a landslide which has been started by the excavation for the entrance masonry4 ,fig4 #aeg shows a method often adopted when the slope is quite flat and the amount of sliding material is small4 ,it consists essentially of removing the fallen material and building a new portal farther back2 that is1 the open cut is extended and the tunnel is shortened4 ,when the amount of the sliding material is very large1 the contrary practice of lengthening the tunnel and shortening the open cut1 as shown by ,fig4 #aeh1 may be adopted4 ,illustration3 ,,fig4 #aeg4--,shortening ,tunnel ,crushed by ,landslide at ,portal4 ,accidents ,after ,construction4--,accidents after the completion of the tunnel may be divided into two classes3 first1 those which entirely obstruct the passage of trains1 of which the collapse of the roof is the most common2 and second1 those which allow traffic to be continued while the repairs are being made1 such as the bulging inward of a portion of the lining without total collapse4 ,in the first case the first duty of the engineer is to open communication through the fallen dbris1 so that passengers at least may be transferred from one part of the tunnel to the other and proceed on their way4 ,this is done by driving a heading1 and strongly timbering it to serve as a passageway4 ,if the tunnel is single tracked this heading is afterwards enlarged until the whole section is opened4 ,in double-track tunnels the method generally adopted is to open first one side of the section and timber it strongly1 so as to clear one track for traffic4 ,while the trains are running through this temporary passageway the other half of the section is opened and repaired2 the traffic is then shifted to the new permanent track1 and the temporary structure first employed is replaced with a permanent lining4 ,when the accident is such that the repairs can be made without obstructing traffic entirely1 various modes of procedure are followed4 ,in all cases great care has to be exercised to prevent accident to the trains and to the tunnel workmen4 ,the work should be done in small sections so as to disturb as little as possible the already troubled equilibrium of the soil2 the strutting should be placed so as to give ample clearing space to passing trains1 and the trains themselves should be run at slow speeds past the site of the repairs4 ,to illustrate the two kinds of accidents and the methods of repairing them1 which have been mentioned1 the accidents at the ,giovi tunnel in ,italy and at the ,chattanooga tunnel in ,america have been selected4 ,illustration3 ,,fig4 #aeh4--;,extending ,tunnel through ,landslide at ,portal4 ,giovi ,tunnel ,accident4--,in ,september1 #ahfi1 at a point about #bbj ft4 from the south portal of the ,giovi tunnel1 a disturbance of the masonry lining for a length of about #eb ft4 was observed4 ,accurate measurements showed that the lining was not symmetrical with respect to the vertical axis of the sectional profile4 ,it was concluded that owing to some disturbance of the surrounding soil unsymmetrical vertical and lateral pressures were acting on the masonry4 ,close watch was kept of the distorted masonry1 which for some time remained unchanged in position4 ,in #ahgb1 however1 new crevices were observed to have developed1 and shortly afterwards1 in ,january1 #ahgc1 the injured portion of the masonry caved in1 obstructing the whole tunnel section4 ,the fallen material consisted chiefly of clay in a nearly plastic state4 ,the surface of the ground above was observed to have settled4 ,investigation showed also that the cause of the caving was the percolation of water from a nearby creek4 ,the water had soaked the ground1 and decreased its stability to such an extent that the masonry lining was unable to withstand the increased vertical and lateral pressures4 ,the mode of procedure decided upon for repairing the damage was3 7#a7 ,to open at least one track for the temporary accommodation of traffic2 7#b7 ,to remove permanently the causes which had produced the collapse2 7#c7 ,to build a new and much stronger lining4 ,close to the western side wall1 which was still standing1 the dbris was removed1 and the opening strongly strutted in order to allow the laying of a single track to restablish communication4 ,at the same time a shaft was sunk from the surface above the caved portion of the tunnel1 for the double purpose of facilitating the removal of the fallen material and of affording ventilation4 ,the depth of the surface above the tunnel was #da4f ft41 which made the construction of the shaft a comparatively easy matter4 ,the shaft itself was #f ft4 wide and #ah ft4 long1 with its longer dimensions parallel to the tunnel1 and it was lined with a rectangular horizontal frame and vertical-poling board construction4 ,after temporary communication had been opened on the western track of the tunnel1 the remainder of the fallen earth was removed and the excavation strutted4 ,the new masonry lining was then built4 ,to remove permanently the cause of the cave-in1 which was the percolation of water from a close-by stream1 this stream was diverted to a new channel constructed with a concrete bed and side walls4 ,the failure of the original lining occurred by cracks developing at the crown1 haunches1 and springing lines4 ,the new lining was made considerably thicker than the original lining1 and at the points where failure had first occurred in the original arch cut-stone voussoirs were inserted in the brickwork of the new arch as described in ,chapter ,,xiii4 ,chattanooga ,tunnel4--,the ,western ,atlantic ,ry4 passes through the ,chattanooga mountains by means of a single-track tunnel #a1dgg ft4 long1 constructed in #ahdh-di4 ,the lining consisted of a brickwork roof arch and stone masonry side walls4 ,after the tunnel had been opened to traffic1 this lining bulged inward at places1 contracting the tunnel section to such an extent that it was decided to reconstruct the distorted portions4 ,after careful surveys and calculations had been made1 it was decided to take down and reconstruct about #agj ft4 of the lining4 ,owing to contracted space in the tunnel1 it was necessary to remove all men1 tools1 and material1 whenever trains were to pass through2 and in order to do this a work-train of three cars was fitted up with necessary scaffolds1 and supplied with gasoline torches for lighting purposes4 ,mortar was mixed on the cars1 and all material remained on them until used4 ,dbris torn out of the old wall was loaded on the cars1 and hauled to the waste dump4 ,a siding was built near the ,west end of the tunnel for the use of this train1 and a telephone system was installed between the entrances and the working-train4 ,on account of the contracted working-space and the greater ease with which brick could be handled1 it was decided to rebuild the walls out of brick instead of stone4 ,in tearing out the old wall a hole was first cut through the three bottom courses of the arch and gradually widened4 ,when the opening became four or five feet long1 a small jack was placed near the center of it and brought to a bearing against the arch to sustain it4 ,after cutting the opening to a length of from #g to #aj ft4 depending on the stability of the earth backing1 the jack was removed and a piece of #haf in4 timber placed under the arch and brought up to a bearing with jacks4 ,one end of the timber rested on the old wall1 the other on a seat built into the adjoining section of new wall4 ,wedges were then driven under the ends of timber and the jacks removed4 ,with this timber in place1 the old wall could be taken down with ease1 the only trouble being that small stones and earth fell in from above and behind the arch4 ,this was obviated by placing a #b in4 plank across the opening and just back of the #haf in4 timber4 ,at several points1 however1 the earth backing was saturated with water1 and it became necessary to put in lagging as the old wall was removed4 ,this timbering would be taken out as the new work was built up4 ,a suitable foundation for the new wall was secured at a depth from #b to #d ft41 and a concrete footing was used4 ,the section of the new wall was then built up as near as possible to the #haf in4 timber2 the timber was then removed and the new wall built up and keyed under the arch4 ,the new wall had a minimum width of #b ft4 at the top1 and #d ft4 at the base of rail1 and was provided with weep holes at intervals4 ,to facilitate matters1 work was carried on simultaneously at two or three different places1 the intention being to get one place torn out and ready for the bricklayers by the time they completed a section of the new wall at another place4 ,in rebuilding the arch1 sections extending from the springing line up as far as was necessary to obtain the desired clearance1 and from #b to #d ft4 in length1 were removed4 ,near the sides1 the earth above the arch was a stiff clay1 which was self-sustaining2 but near the center there occurred a stratum of gravel and clay saturated with water4 ,this gave considerable trouble1 falling through almost continuously until timbering could be placed4 ,one end of this timber rested on the old arch1 the other on the adjoining section of the new work4 ,as the new work was to be set #f to #ac ins4 back from the old1 it was necessary to block up this distance on top of the old arch1 to carry the end of the lagging timber1 in order that the timber should be clear of the new arch4 ,owing to the small clearance between the car roof and the arch1 a special form of centering was required1 one that would occupy as small space as possible4 ,bar iron #a in4 thick1 #d ins4 wide1 and #bj ft4 long was curved to a radius of #f ft41 and on the underside of this was riveted a #f-;in4 plate in4 thick4 ,this plate projected #a in4 on the sides of the centering1 and carried the ends of the #a in4 boards used for lagging4 ,the rivets were counter-sunk on the outside of the centering to present a smooth surface next the arch4 ,in keying up a section of the new work1 a space about #ah ins4 square had to be left open for the use of the workmen4 ,as soon as the next section had been torn out1 this space was built up4 ,in building up the last section1 this space had to be filled from below1 which proved to be a tedious undertaking4 ,the opening was gradually reduced to a size of #aj #ah in41 and the top ring then completed and keyed up1 the adhesion of mortar holding the bricks in place until the key could be driven home4 ,the next ring was treated in a similar manner1 and so on to the face ring4 ,altogether #dab lin4 ft4 of the walls and #agh lin4 ft4 of the arch were taken down and rebuilt1 amounting in all to #fjg cu4 yds4 of masonry at the total cost of #g1ddj1 or about #ab4be per cu4 yds4 ,the regular trains arrived so frequently at the tunnel that slightly over two hours was the longest working-time between any two trains1 and usually less than one hour at a time was all that it could be worked4 ,in addition to the regular trains1 a large number of extra trains1 moving troops1 had to be accommodated4 ,work was in progress eight months1 and during that time there was no delay to a passenger train4 ,the repairs were completed in ,august1 #ahii4 ,the work was under the direction of ,mr4 ,w4 ,h4 ,whorley1 engineer of the ,western ,atlantic ,r4 ,r41 and foreman of construction1 ,a4 ,h4 ,richards4 ,a recent examination failed to reveal any sign of settlement cracks at the junction points of the new and old work4 ,,chapter ,,xxiii4 ,,relining ,,timber-,,lined ,,tunnels ,,with ,,masonry4 ,the original construction of many ,american railway tunnels with a timber lining to reduce the cost and hasten the work has made it necessary to reline them1 as time has passed1 with some more permanent material4 ,in most cases the work of removing the old lining and replacing it with the new masonry has had to be done without interfering with the running of trains1 and a number of ingenious methods have been developed by engineers for accomplishing this task4 ,three of these methods which have been employed1 respectively1 in relining the ,boulder tunnel on the ,montana ,central ,ry41 in ,montana1 the ,mullan tunnel on the ,northern ,pacific ,ry41 in ,montana1 and the ,little ,tom tunnel on the ,norfolk ,western ,r4 ,r41 in ,virginia1 have been selected as fairly representative of this class of tunnel work4 ,boulder ,tunnel4--,this tunnel penetrates a spur of the main range of the ,rocky ,mountains1 at an elevation at the summit of grade of #e1ded ft41 and is #f1aab ft4 in length4 ,its alignment is a tangent1 with the exception of #aej ft4 of #cj curve at the north end4 ,the material penetrated is blue trap-rock with seams for #d1iej ft4 from the north end1 and syenitic boulders with the intervening spaces filled with disintegrated material for the remaining #a1afj ft4 ,the dimensions and character of the old timber lining and of the new masonry lining replacing it are shown in ,figs4 #aei and #afj4 ,the form of masonry adopted consisted of coarse rubble side walls of granite1 #ac ft4 #h ins4 high1 and generally #bj ins4 thick1 with a full center circular arch of four rings of brick laid in rowlock form4 ,when greater strength was needed the thickness of the side walls was increased to #cj ins4 and that of the arch to six rings of brick4 ,illustration3 ,cross ,section4 ,longitudinal ,section4 ,cross ,section4 ,cross ,section4 ,,figs4 #aei and #afj4--,relining ,timber-,lined ,tunnel4 ,the first plan adopted in putting in the masonry was to remove all the timbering2 but owing to the large number of falls and slides this was abandoned1 and the plan followed was to leave in the three roof segments of the timbering with the overlying cord-wood packing and dbris4 ,in carrying on the work the first step was to remove the side timbers4 ,this was done by supporting the roof timbers1 as shown in ,fig4 #aei2 that is1 the first and fourth arch rib of an #h-;ft4 section containing four arch ribs were supported by temporary posts4 ,the intermediate arch ribs were supported against the downward pressure by #f #f in4 timbers1 extending from the side ribs near the tops of the temporary posts to the opposite sides of the intermediate roof segments1 as shown in the longitudinal section1 ,fig4 #afj4 ,to resist the pressure from the sides1 #d #f in4 braces were placed across the tunnel from near the center of the intermediate segments to the upper ends of the hip segments1 as shown in the cross-section1 ,fig4 #aei4 ,the hip segments were then sawed off below the notch1 and the side timbering removed and the masonry built4 ,the stone was conveyed into the tunnel on flat cars1 and laid by means of small derricks located on the cars4 ,two derricks were used1 one for each side wall1 and the work on both walls was carried on simultaneously4 ,the arch was built upon a centering1 the ribs of which were #e ins4 less in diameter than the distance between the side walls1 so as to permit the use of #b ins4 lagging4 ,each center had three ribs1 made in #a-;in4 or #b-;in4 board segments1 #aj ins4 thick and #ad ins4 deep4 ,these ribs were mounted on frames1 which followed the opposite walls1 and were #d ft4 apart1 making the total length of the center out to out about #i ft4 ,the frames1 upon which the ribs were supported1 are shown in ,fig4 #afa4 ,as will be seen1 they were mounted on dollys to enable the center to be moved from one section to another4 ,jacks were used to raise and lower the center into its proper position4 ,illustration3 ,cross ,section4 ,longitudinal ,section4 ,,fig4 #afa4--,relining ,timber-,lined ,tunnel1 ,great ,northern ,ry4 ,the arch was built up from the springing lines on both sides at the same time1 four masons being employed4 ,the rings were built beginning with the intrados1 which was brought up1 say1 a distance of about #b ft4 from the springing line4 ,then the back of the ring was well plastered with from in4 to in4 of mortar1 and the second ring brought up to the same height and plastered on the back1 and so on until the last ring was laid4 ,after bringing the full width of the arch up some distance1 new laggings were placed on the ribs for an additional height of #b ft4 and the same process was repeated4 ,all the space between the extrados of the masonry arch and the old lining was compactly filled with dry rubble4 ,when high enough so that the hip segments had a foot or more bearing on the masonry the segments were securely wedged and blocked up against the brickwork1 and the longitudinal #d #f in4 timbers removed4 ,the remaining space was now clear for completion of the arch1 and both sides were brought up until there was not sufficient space for four masons to work1 when the keying was completed by two masons beginning at the completed and working back toward the toothed end4 ,the brickwork was built from the top of a staging-car4 ,illustration3 ,cross ,section4 ,longitudinal ,section4 ,,fig4 #afb4--,relining ,timber-,lined ,tunnel1 ,great ,northern ,ry4 ,in a few instances where slides occurred after the removal of the slide timbering1 the method of re timbering the tunnel shown in ,fig4 #afb was adopted4 ,two side drifts were first run #b ft4 wide by #d ft4 high1 and the plate timbers placed in position and blocked4 ,cross drifts were then run1 and the roof segments placed1 and the core down to the level of the bottoms of the side drifts taken out4 ,the lower wall plates were then placed and the hip segments inserted4 ,the bench was then taken down by degrees1 the side plates being held by jacks1 and the posts placed one at a time4 ,as the masonry at the points where slides occur consists of #cj-;in4 walls and six-ring arch1 the timbering was #bb ft4 wide in the clear1 with other dimensions as shown in ,fig4 #afb4 ,only a single crew of brick and stone masons was employed4 ,in order to prepare the sections for these masons it was necessary to have timber and trimming crews at work throughout the whole day of #bd hours1 so that an engine and two train crews were in constant attendance4 ,the single mason crews were able to complete #h ft4 of side wall and arch in #bd hours4 ,the number of men actually employed at the tunnel was #ce4 ,this included electric-light maintenance1 and all other labor pertaining to the work4 ,the tunnel was lighted by an ,edison dynamo of #bj arc light capacity1 one arc light being placed on each side of the tunnel at all working-places4 ,each lamp carried a coil of wire #bj or #cj ft4 long to allow it to be shifted from place to place without delay4 ,mullan ,tunnel4--,this tunnel is #c1hej ft4 long1 and crosses the main range of the ,rocky ,mountains1 about #bj miles west of ,helena1 ,mont4 ,the tunnel is on a tangent throughout1 and has a grade of #bj falling toward the east4 ,the summit of the grade1 west of the tunnel1 is #e1edh ft4 above sea level1 and the mountain above the line of the tunnel rises to an elevation of #e1hee ft4 ,owing to the treacherous nature of the material through which the tunnel passed1 it had been a constant menace to traffic ever since its construction in #ahhc1 and numerous delays to trains had been caused by the falls of rock and fires in the timber lining4 ,for these reasons it was finally decided to build a permanent masonry lining1 and work on this was begun in ,july1 #ahib4 ,illustration3 ,with ,wall ,plates4 ,without ,wall ,plates4 ,old ,timber ,sections4 ,minimum ,section4 ,average ,section4 ,permanent ,work4 ,,fig4 #afc4--,relining ,timber ,lined ,tunnel1 ,great ,northern ,ry4 ,the original timbering consisted of sets spaced #d ft4 apart c4 to c41 with #ab #ab in4 posts supporting wall plates1 and a five-segment arch of #ab #ab in4 timbers joined by #a-;in4 dowels4 ,the arch was covered with #d-;in4 lagging1 and the space between this and the roof was filled with cordwood4 ,except where the width had been reduced by timbering placed inside the original timbering to increase the strength1 the clear width was #af ft41 and the clear height #bj ft4 above the top of the rail4 ,fig4 #afc shows the timbering and also the form of masonry lining adopted4 ,the side walls are of concrete and the arch of brick4 ,this new masonry1 of course1 required the removal of all the original timbering4 ,the manner of doing this work is as follows3 ,a #g-;ft4 section1 ,a ,b1 ,fig4 #afd1 was first prepared by removing one post and supporting the arch by struts1 ,s ,s4 ,after clearing away any backing1 and excavating for the foundation of the side wall1 two temporary posts1 ,f ,f1 were set up1 and fastened by hook bolts4 ,fig4 #adf1 ,l1 and a lagging was built to form a mold for the concrete4 ,several of these #g-;ft4 sections were prepared at a time1 each two being separated by a #e-;ft4 section of timbering4 ,illustration3 ,section1 with ,concrete ,car4 ,with ,wall ,plate4 ,without ,wall ,plate4 ,longitudinal ,section4 ,,fig4 #afd4--;,construction of ,centering ,mullan ,tunnel4 ,the mortar car was then run along1 and enough mortar 7#a cement to #c sand7 was run by the chute into each section to make an #h-;in4 layer of concrete4 ,as the car passed along to each section1 broken stone was shoveled into the last preceding section until all the mortar was taken up4 ,the walls were thus built up in #h-;in4 layers1 and became hard enough to support the arches in about #aj to #ad days4 ,the arches were then allowed to rest on the wall1 and the posts of the remaining #e-;ft4 sections were removed1 and the concrete wall built up in the same way as before4 ,the average progress per working-day was #cj ft4 of side wall1 or about #de cu4 yds42 and the average cost1 including all work required in removing the timber work1 train service1 lights and tools1 engineering and superintendence1 and interest on plant1 was #h per cubic yard4 ,illustration3 ,,fig4 #afe4--;,centering ,mullan ,tunnel4 ,the centering used for putting in the brick arches is shown in ,fig4 #afe4 ,from #c ft4 to #i ft4 of arch was put in at a time1 the length depending upon the nature of the ground4 ,to remove the old timber arch1 one of the segments was partly sawed through2 and then a small charge of giant powder was exploded in it1 the resulting dbris1 cordwood1 rock1 etc41 being caught by a platform car extending underneath4 ,from this car the dbris was removed to another car1 which conveyed it out of the tunnel4 ,the center was then placed and the brickwork begun1 the cement car shown in ,fig4 #afd being used for mixing the mortar4 ,the size of the bricks used was #b #b #i ins41 four rings making a #bj-;in4 arch and giving #a4fb cu4 yds4 of masonry in the arch per lin4 ft4 of tunnel4 ,the bricks were laid in rowlock bond1 two gangs1 of three bricklayers and six helpers each1 laying about #ab lin4 ft4 per day4 ,the brickwork cost about #ag per cu4 yd4 ,the total cost of the new lining averaged about #ej per lin4 ft4 ,illustration3 ,cross ,section4 ,longitudinal ,section4 ,,fig4 #aff4--,relining ,timber-,lined ,tunnel1 ,norfolk and ,western ,ry4 ,little ,tom ,tunnel4--,the tunnel has a total length of #a1ijb ft41 but only #a1daj ft4 of it were originally lined with timber4 ,this old timber lining consists of bents spaced #c ft4 apart1 and located as shown by the dotted lines in the cross-section1 ,fig4 #aff4 ,instead of renewing this timber1 it was decided to replace it with a brick lining4 ,although the tunnel was constructed through rock1 this rock is of a seamy character1 and in some portions of the tunnel it disintegrates on exposure to the air4 ,in removing the timber to make place for the new lining some of the roof was found close to the lagging1 but often also considerable sections showed breakages in the roof extending to a height varying from #a ft4 to #ab ft4 above the upper side of the timbering4 ,this dangerous condition of the roof made it necessary that only a small section of the timber lining should be removed at one time4 ,it made it necessary1 also1 that the brick arch should be built quickly to close this opening1 and finally that all details of centers1 etc41 should be arranged so as to furnish ample clearance to trains4 ,the accompanying illustrations show the solution of the problem which was arrived at4 ,illustration3 ,,fig4 #afg4--,relining ,timber-,lined ,tunnel1 ,norfolk and ,western ,ry4 ,referring to the transverse and longitudinal sections shown by ,fig4 #aff1 it will be seen that two side trestles were built to carry an adjustable centering for the roof arch4 ,two sections of these trestles and centerings were used alternately1 one being carried ahead and set up to remove the timbering while the masons were at work on the other4 ,the manner of setting up and adjusting the trestles and centerings is shown by ,fig4 #aff and also by ,fig4 #afg1 which is an enlarged detail drawing of the set screw and rollers for the centering ribs4 ,the following is the bill of material required for one set of trestles and one center3 ,trestles3 ,caps and sills #h pieces #h #h ins4 #bj ft4 ,posts #ah #h #h #aa ,braces #af #f #d #g ,centerings3 ,ribs #bg #b #ah #g ,bracing #ab #b #h #g ,support to crown lagging #b #f #f #aj ,crown lagging #bj #c #f #b ,side lagging #cj #c #f #aj ,side strips #b #b #ab #i ,blocking for rollers #a #e #h #ab #f screw and roller castings complete with bolts and lever2 #aad bolts -ins4 in diameter2 #g ,u4 ,h4 hexagonal nut and #b cast washers each4 ,with this arrangement the progress made per day varied from #b lin4 ft4 to #c lin4 ft4 of lining complete4 ,by work complete is meant the entire lining1 including stone packing between the brickwork and the rock4 ,on ,feb4 #bc1 #aijj1 #cfc ft4 of lining had been completed1 at a cost of #cc4ej per lin4 ft4 ,this cost includes the cost of removing the old timber1 the loose rock above it1 and all other work whatsoever4 ,,chapter ,,xxiv4 ,,the ,,ventilation ,,and ,,lighting ,,of ,,tunnels ,,during ,,construction4 ,,ventilation4 ,in long tunnels1 especially when excavated in hard rock1 proper ventilation is of great importance1 because the air cannot be easily renewed1 and the amount of oxygen consumed by miners horses and lamps during construction is very large4 ,the gases produced by blasting also tend to fill the head of excavation with foul air4 ,pure atmospheric air contains about #ba of oxygen and only #j4jd of carbonic acid2 when the latter gas reaches #j4a the fact is indicated by the bad odor2 at #j4c the air is considered foul1 and when it reaches #j4e it is dangerous4 ,it is generally admitted that the standard of purity of the air is when it contains #j4jh of carbonic acid4 ,a large quantity of carbonic acid in the air is easily detected by observing the lamps1 which then give out a dim red light and smoke perceptibly2 the workmen also suffer from headache and pains in the eyes1 and breathe with difficulty4 ,naturally1 miners cannot easily work in foul air and1 therefore1 make very slow progress4 ,it is1 therefore1 to the interest of the engineer to afford good ventilation1 not only because of his duty to care for the safety and health of his men1 but also for reasons of economy1 so that the men may work with the greatest possible ease1 thus assuring the rapid progress of the work4 ,it would be impossible to change completely the atmosphere inside a tunnel1 as the gases developed from blasting will penetrate into all the cavities and gather there1 but the fresh air carried inside by ventilation has a very small percentage of carbonic acid1 mixes with that which contains a greater quantity1 and dilutes it until the air reaches the standard of purity4 ,we have not here considered the gases developed from the decomposition of carboniferous and sulphuric rocks1 which may be met with in some tunnels1 and which render ventilation still more necessary4 ,tunnels may be ventilated either by natural or artificial means4 ,natural ,ventilation4--,it is well known that if two rooms of different temperatures are put in communication with each other1 e4g41 by opening a door1 a draft from the colder room will enter the other from the bottom1 and a similar draft at the top1 but with a contrary direction1 will carry the hot air into the colder room1 thus producing perfect ventilation1 until the two rooms have the same temperature4 ,now1 during the construction of tunnels the temperature inside may be considered as constant1 or independent of the outside atmospheric variations2 hence during summer and winter1 there will always be a draft affording ventilation1 owing to the difference of temperature inside and outside the tunnel4 ,in winter time the cold air outside will enter at the bottom of the entrances and headings1 or along the sides of the shafts1 and the hot air will pass out near the top of the headings or entrances or the center of the shafts2 in summer the air currents will take the contrary direction4 ,natural ventilation in tunnels is improved when the excavation of the heading reaches a shaft1 because the interior air can then communicate with the exterior at two points1 at different levels4 ,in such cases a force equal to the difference in weight between a column of air in the shaft and a similar one of different density at the entrance of the tunnel1 will act upon the mass of air in the tunnel and keep it in movement1 thus producing ventilation4 ,consequently1 during winter1 when the outside air has greater weight than that inside1 the air will come in by the headings and go out by the shaft1 and in the summer it will enter at the shaft and pass out at the entrance4 ,sometimes to afford better ventilation shafts #h or #ab in4 in diameter are sunk exclusively for the purpose of changing the air4 ,when the inside temperature is equal to that outside1 as often happens during the spring and autumn1 there are no drafts1 and consequently the air in the excavation is not renewed and becomes foul2 then fires are lighted under the shaft and a draft is artificially produced4 ,the hot air going out through the shaft1 as through a chimney1 allows the fresh air to come in as in ordinary ventilation4 ,when the head of the excavation is very far from the entrances1 or when the mountain is too high to allow excavation by shafts1 it is quite impossible to secure good natural ventilation1 especially during the spring and autumn months1 and the engineer has to resort to some artificial means by which to supply fresh air to the workmen4 ,artificial ,ventilation4--,artificial ventilation in tunnels may be obtained in two different ways1 known as the vacuum and plenum methods4 ,their characteristic difference consists in this1 that in the vacuum method the air is drawn from the inside and the vacuum thus produced causes the fresh air from the outside to rush in1 while the plenum method consists in forcing in the fresh air which dilutes the carbonic air produced inside the tunnel by workingmen and explosives4 ,in the vacuum method the pressure of the atmosphere inside the tunnel is always less than the pressure outside1 while in the plenum method the pressure within is always greater than that outside4 ,ventilation is the result of this difference of pressure1 as the tendency of the air toward equilibrium produces continuous drafts4 ,both these methods have their advantages and disadvantages2 but in the presence of hard rock1 when explosives are continually required1 the vacuum method is considered the best1 because the gases attracted to the exhaust pipes are expelled without passing through the whole length of the tunnel1 thus avoiding the trouble that a draft of foul air will give to the workmen who are within the tunnel4 ,in both these methods it is necessary to separate the fresh air from the foul one2 and this is done by means of pipes which will exhaust and expel the foul air in the vacuum method1 or force to the front a current of fresh air when the plenum method is used4 ,artificial ventilation may also be obtained by compressed air which is set free after it has driven the machines1 especially in tunnels excavated through rock1 when rock drilling machines moved by compressed air are employed4 ,vacuum ,method ,contrivances4--,the most common of the vacuum appliances consists in the simple arrangement of a pipe leading from the head of the tunnel out through the fire of a furnace4 ,the air in the pipe is rarefied by the heat of the furnace and then set free from the other end of the pipe1 thus creating a partial vacuum in the pipe1 into which the foul air of the head rushes1 the fresh air from the entrance taking its place1 and thus ventilating the tunnel4 ,a similar arrangement may be used with shafts1 and the foul air may be driven out by a furnace which is placed either at the top or bottom of the shaft4 ,such furnaces act the same as those commonly used for heating purposes in the houses1 with this difference1 that1 instead of fresh air being forced in1 foul air is expelled4 ,another simple arrangement for producing a vacuum is by means of a steam jet which is thrown into the pipe1 and which helps the expulsion of the air by heating it1 thus producing a different density which originates a draft besides that mechanically originated by the force of the steam jet1 which tends to carry out the foul air of the pipes4 ,foul air may also be expelled by means of exhaust fans which are connected with pipes near the entrance of the tunnel4 ,the fan consists of a box containing a kind of a paddle wheel turned by steam or water power and arranged so as to revolve at a high speed4 ,the air inside the pipe is forced out by blades attached to the wheel1 and thus the foul air of the front is driven away and fresh air from the entrance rushes in to take its place1 and perfect ventilation is obtained4 ,the best manner of expelling foul air from tunnels1 according to the vacuum method1 is by means of bell exhausters4 ,this consists of two sets of bells connected by an oscillating beam and balancing each other4 ,each set consists of a movable bell1 which covers and surrounds a fixed bell with a water joint4 ,in the central part of the fixed bell there are valves which open upwards1 and on the bottom of each movable bell there are valves which open from the outside4 ,when one bell ascends1 the valves at the bottom are closed1 the air beneath is then rarefied1 and a vacuum is produced2 the valves in the central part of the fixed bell filled with water are opened1 and there is an aspiratory action from the pipe leading to the headings1 and the foul air is thus carried away4 ,the apparatus makes about ten oscillations per minute1 and the dimensions of the bells depend upon the quantity of air to be exhausted in a minute4 ,in the ,st4 ,gothard tunnel1 where these bell exhausters were used1 they exhausted #af1ejj cu4 ft4 of air per minute4 ,plenum ,method ,contrivances4--,fresh air may be driven into tunnels to dilute the carbonic acid by two different ways1 viz41 by water blast and by fans4 ,water when running at a great velocity produces a movement in the air which may be sometimes usefully and economically employed for ventilating tunnels4 ,water falling vertically is let run into a large horizontal zinc pipe having a funnel at the outer end2 into this the air attracted by the velocity of the water is forced4 ,by an opening at the bottom the water is afterward withdrawn from the pipe1 and there remains only the air which is pushed forward by the air which is being continually sucked in by the velocity of the water4 ,the best and most common means of ventilation by the plenum method is by fans4 ,there are numerous varieties of these fans in the market1 but they all consist of a kind of fan wheel which by rapid revolution forces the fresh air into the pipe leading to the headings of the tunnel or to the working places4 ,instead of a large single fan1 such as is used for mining purposes1 it is better to have a number of small fans acting independently of each other1 conveying the fresh air where it is needed through independent pipes4 ,saccardo's ,system4--,a new method of ventilating tunnels was devised by ,mr4 ,saccardo for the ventilation of the ,pracchia tunnel along the ,bologna and ,lucca ,railway in ,italy4 ,at the highest end of the tunnel the mouth was contracted inward in a funnel shaped form so as to just admit a train4 ,immediately at this contraction1 a lateral tunnel1 #ej feet long1 branched off from one side of the main tunnel4 ,at the mouth of this lateral tunnel was installed a fan which forced air into the tunnel and with #gj revolutions per minute delivered #c4ecb cu4 ft4 of air per second at a water pressure of #a in4 ,this air current was directed inward through a second contraction or funnel1 parallel to the one at the entrance and #bc ft4 beyond it4 ,in operation the action of the artificial air current was to suck in a considerable volume of outside air1 while the air pressure was sufficient to counterbalance the movement of air produced by a train moving at a velocity of #af4a ft4 per second4 ,mr4 ,saccardo's method was employed in ventilating a tunnel on the ,norfolk and ,western ,railway with satisfactory results4 ,compressed ,air4--,in the excavation of tunnels in hard rock a number of rock drilling machines are employed which are moved by compressed air at a pressure of not less than five atmospheres4 ,at each stroke about #ajj cu4 ins4 of compressed air are set free1 and at an average of #aj strokes per minute there would be #ejjj cu4 ins4 of air at five atmospheres or #be1jjj cu4 ins41 or a little more than #age cu4 ft4 of fresh air at normal pressure set free every minute by each of the machines employed4 ,but the air exhausted from the drilling machine is foul4 ,regarding ventilation by compressed air1 ,mr4 ,adolph ,sutro1 in a lecture delivered to the mining students of the ,university of ,california1 said3 8,i will note a curious fact which ,i have never seen explained1 and which is worthy of close investigation by means of experiments4 ,in the ,sutro tunnel we found that the compressed air used for driving the machine drills1 after having been compressed and expanded and discharged from the drills1 was not wholesome to breathe1 and the men and mules would all crowd around the end of the blower pipe to get fresh air4 ,whether the air in being compressed has parted with some of its oxygen or because vitiated from some other cause1 ,i do not know1 and ,i hope that this subject will at some future day be carefully examined into40 ,in the ,december1 #aija1 number of 8,compressed ,air10 a magazine especially devoted to the useful application of compressed air1 is read3 ,compressed air wasted from power drills is so contaminated with oil from the cylinders that it cannot be taken into consideration as ventilation4 ,it is as important to displace it with pure air as it is to drive out or draw off other vitiated air4 ,the ventilation should be an independent supply provided by fan or blower1 delivering by pipe at the point where miners are working4 ,quantity of ,air4--,the quantity of air to be introduced into tunnels must be in proportion to the oxygen consumed by the men1 the animals1 and the explosions4 ,it is allowed that the quantity of air required for breathing purpose and explosions is as follows3 #a workman with lamp needs #bdj cu4 yds4 of fresh air in #bd hours4 #a horse #hej #a lb4 gunpowder #ajj #a lb4 dynamite #aej ,in a long tunnel excavated through hard rock the number of workmen all together may be assumed at #djj at each end1 and each workman is supposed to be furnished with a lamp4 ,no less than ten horses are employed1 and the average quantity of dynamite consumed is #fjj lbs4 per day4 ,from the data given the consumption of air by workmen and lamps would be3 #bdj #djj #if1jjj cu4 yds42 the consumption of air by horses would be #hej #aj #hejj cu4 yds42 the consumption of air by dynamite would be #aej #fjj #ij1jjj cu4 yds42 making a total consumption of air per day of #aid1ejj cu4 yds41 or about #hjjj cu4 yds4 per hour4 ,to obtain good ventilation1 then1 it will be necessary to furnish every hour a quantity of fresh air amounting to not less than #hjjj cu4 yds4 ,since1 however1 a large quantity of pure air is expelled with the foul air1 it is necessary greatly to increase this quantity4 ,it may be observed1 in closing1 that the water having its particles divided1 as in a fog or mist1 rapidly precipitates the gases produced by explosions4 ,now1 when hydraulic machines are used1 there is a hollow ball pierced by holes that are almost imperceptible1 from which the compressed water spreads in very subtile particles1 and this causes the fall of the gases from explosions4 ,such a method of precipitating gases is very good1 but does not have the advantage of supplying new oxygen to replace that consumed by the men1 animals1 lamps1 and explosions2 besides1 it has the defect of increasing the quantity of water to be removed4 ,in tunnels the pipes used either for conveying the fresh air or for carrying away the foul air1 are of iron1 having a diameter of about #h in42 they are fixed along the side walls about #c ft4 above the inverted arch4 ,,lighting4 ,the object and necessity of a perfect lighting of the tunnel-workings during construction are so obvious that they need not be enlarged upon4 ,comparatively few tunnels require lighting after completion2 and these are generally tunnels for passenger traffic under city streets1 of which the ,boston ,subway is a representative ,american example4 ,considering the methods of lighting tunnels during construction1 we may1 for sake of convenience1 chiefly1 divide the means of supplying light into 7#a7 lamps and lanterns usually burning oil2 7#b7 coal-gas lighting2 7#c7 acetylene gas lighting2 and 7#d7 electric lighting4 ,lamps and ,lanterns4--,lamps and lanterns are commonly employed by engineers for making surveys inside the tunnel1 and to light the instrument4 ,for ranging in the center line1 a convenient form of lamp consists of an oil light inclosed in glass chimney covered with sheet metal1 except for a slit at the front and back through which the light shines1 and on which the observer sights his instrument4 ,to direct the operations of his rodmen the engineer usually employs a lantern1 either with white or colored glass1 much like the ordinary railway trainman's lantern1 which he swings according to some prearranged code of signals4 ,lamps and lanterns are used by the workmen both for signaling and for lighting the workings4 ,for signaling purposes red lanterns are usually placed to denote the presence of unexploded blasts or other points of possible danger2 and colored or white lights are usually placed on the front and rear of spoil and material trains4 ,for lighting purposes1 two forms of lamps are employed1 which may be somewhat crudely designated as lamps for individual use and lamps for general lighting4 ,individual lamps are usually of small size1 and burn oil2 they may be carried in front of the miner's helmet1 or be fixed to standards1 which can be set up close to the work being done by each man4 ,miners' safety lamps should be employed where there is danger from gas4 ,a great variety of lamps for mining and tunneling purposes are on the market1 for descriptions of which the reader is referred to the catalogues of their manufacturers4 ,lamps for general lighting are always of larger size than lamps for individual use4 ,a common form consists of a cylinder ten or twelve inches in diameter1 provided with a hook or bail for suspension1 and filled with benzine1 gasolene1 or other similar oil4 ,connected with this cylinder is a pipe of considerable length and small diameter through which the benzine or gasolene vapor runs1 and burns when lighted with a brilliant flame4 ,lamps of this type burning gasolene were extensively employed in building the ,croton ,aqueduct tunnel4 ,various patented forms of lamps for burning coal-oil products are on the market1 for descriptions of which the manufacturers' catalogues may be consulted4 ,coal-gas ,lighting4--,a common method of lighting tunnel workings is by piping coal-gas into the headings and drifts from some nearby permanent gas plant1 or from a special gas works constructed especially for the work4 ,gas lighting has the great advantage over lamps and lanterns of giving a light which is more brilliant and steady4 ,its great objection is the danger of explosion caused by leaks in the pipes1 by breaks caused by flying fragments of rock1 and by the carelessness of workmen who neglect to turn off completely the burners when they extinguish the lights4 ,in nearly every tunnel where gas has been used for lighting1 the records of the work show the occurrence of accidents which have sometimes been very serious1 particularly when fire has been communicated to the tunnel timbering4 ,acetylene ,gas ,lighting4--,the comparatively recent development of acetylene gas manufactured from carbide of calcium has given little opportunity for its use in tunnel lighting1 and the only instance of its use in the ,united ,states1 so far as the author knows1 is the water-works tunnel conduit for the city of ,washington1 ,d4 ,c4 ,col4 ,a4 ,m4 ,miller1 ,u4 ,s4 ,engineer ,corps1 who is in charge of this work1 describes the method adopted in his annual report for #ahii as follows3-- 8,it had been the practice to do all work underground by the light of miners' lamps and torches4 ,this means of illumination is very poor for mechanical work4 ,the fumes and smoke from blasting1 added to the smoke from torches and lamps1 render the atmosphere underground1 especially when the barometer conditions were unfavorable to ventilation1 very offensive and discomforting to the workmen4 ,an investigation of the subject of lighting the tunnel by other means1 more especially at the locality where the mechanics were at work1--brick and stone masons1 and the workmen on the iron lining1--resulted in the selection of acetylene gas as the most available and economical in this special emergency4 ,accordingly1 an acetylene gas plant for #cjj burners was erected at ,champlain-,avenue shaft1 and one for #fj lights at ,foundry ,branch4 ,the engine-houses at the shafts1 the head-houses1 and localities in the tunnel1 when required1 are lighted by these plants4 8,gas pipes were carried down the ,champlain-,avenue shaft and along the tunnel both in an easterly and westerly direction1 with cocks for burners at proper intervals every #cj feet2 and this system sufficed for illumination from ,hock ,creek to ,harvard ,university1 a distance of over two miles4 ,the plant erected at ,foundry ,branch was in like manner utilized for the illumination from that point in both directions4 8,by connecting with the stopcocks by means of a rubber hose1 a movable light1 chandelier1 or #8,christmas-tree' of any required number of burners is used1 thus concentrating the light in the immediate vicinity of the work1 and also enabling the illumination to be carried into the cavities or #8crow-nests1' so called1 behind the defective old lining4 8,this method of illuminating has proved very satisfactory and quite economical4 ,it is especially valuable as enabling good work to be done1 and facilitating a thorough inspection of the same40 ,electric ,lighting4--,by far the most perfect1 and at present the most commonly employed means for lighting tunnel workings1 is electricity4 ,the light furnished by electric lamps is steady and brilliant1 and does not consume oxygen or give off offensive gases4 ,the wires are easily removed and extended1 and the lamps are easily put in place and removed4 ,about the only objection to the method is the fragility of the lamps1 which are easily broken by the flying stones and the concussion produced by blasting4 ,,chapter ,,xxv4 ,,the ,,cost ,,of ,,tunnel ,,excavation ,,and ,,the ,,time ,,required ,,for ,,the ,,work4 ,cost4--,the cost of a tunnel will depend upon the cost of the two principal operations required in its construction1 viz41 the excavation of the cross section and the lining of the excavation with masonry1 metal1 or timber4 ,these two operations may in turn be subdivided1 in respect to expense1 into cost of labor and cost of materials4 ,it is a comparatively simple matter to calculate the cost of the building materials required to construct a tunnel2 but it is very difficult to estimate with accuracy what the cost of labor will be4 ,the reason for this is that it is impossible to foresee exactly what the conditions will be2 the character of the material may change greatly as the work proceeds1 increasing or decreasing the cost of excavation2 water may be encountered in quantities which will materially increase the difficulties of the work1 etc4 ,nevertheless1 while accurate preliminary estimates of cost are not practicable1 it is always desirable to attempt to obtain some idea of the probable expense of the work before beginning it1 and the more usual means of getting at this point will be discussed here4 ,two methods of estimating the cost of tunnel work are employed4 ,the first is to calculate the probable expense of the various items of work1 based upon the available data1 per unit of length1 and then add to this a margin of at least #aj to allow for contingencies2 the second is to apply to the new work the unit cost of some previous tunnel built under substantially the same conditions4 ,in the first method it is usual to consider the strutting and hauling as constituting a part of the work of excavation4 ,to estimate the cost of excavation involves the consideration of three general items1 viz41 the excavation proper1 the strutting of the walls of the excavation1 and the hauling of the excavated materials and the materials of construction4 ,the cost of excavating the preliminary headings or drifts is greater per unit of material removed than that of excavating the enlargement of the section4 ,the cost of bottom drifts is also always greater than that of top headings1 the material penetrated remaining the same4 ,mr4 ,rziha gives the comparative unit costs of excavating drifts1 headings1 and enlargement of the profile as follows3-- ,bottom drifts #i4bj per cu4 yd4 ,top headings #d4hj ,enlargement of profile #b4hd ,the cost of hauling increases with the length of the tunnel4 ,this fact and amount of this increase are indicated by the following actual prices for the ,arlberg tunnel3-- ,top heading #f4gf per cu4 yd41 increasing #cg cts4 per mile ,bottom drift #g4dj #bf ,enlargement of profile #b4gj #aj ,in all the prices given above1 the cost of strutting and hauling is included in the cost of excavation4 ,the cost of excavation is not always the same for the same character of materials in different tunnels4 ,the following figures show the prices paid for the excavation of calcareous rock in four different ,german tunnels3-- ,berliner ,nordhausen ,wetzler ,r4,r4 #a4bd per cu4 yd4 ,ofen #a4cj ,stafflach #b4gf ,gries #a4ib ,the method of tunneling has little influence upon the cost of the work1 as shown by the following figures from tunnels excavated through calcareous rock by different methods3-- ,ofen tunnel ,austrian method #ic4ai per lin4 ft4 ,dorremberg tunnel ,belgian method #hf4jh ,stafflach tunnel ,english method #ia4fi ,the ,martha and ,merten tunnels1 excavated through soft ground by the ,austrian and ,german methods respectively1 cost #hg4ie and #hg4ee per lin4 ft4 respectively4 ,in the excavation of the various sections of the tunnel for the new ,croton ,aqueduct in ,america1 the following prices were paid3-- ,excavation of heading #h to #aj4jj per cu4 yd4 ,tunnel in soft ground #h to #i4jj ,tunnel in rock #g to #h4ej ,brick masonry #aj4jj ,timber in place #dj per ,m4 ft4 ,b4 ,m4 ,it is the practice in ,america to include the work of hauling under excavation1 but not to include the strutting1 which is paid for separately4 ,in some cases only the market price of the timber is paid for separately1 the cost of setting up being included in the price of excavation4 ,the writer prefers the ,european practice of including the total cost of timbering under excavation1 since the two operations are so closely connected1 and since the contractor employs the same timber over and over again4 ,knowing the dimensions of the several members of the strutting1 it is a simple1 although somewhat tedious1 process to calculate the total quantity required4 ,an idea of the quantity of timber required for strutting in soft ground may be had from the data given on page #ee4 ,the quantity will decrease as the cohesion of the material penetrated increases1 until it becomes so small in hard rock-tunnels as to cut very little figure in the total cost4 ,the cost of hoisting excavated materials through shafts depends upon the depth from which it is hoisted1 and upon the character of hoisting apparatus employed4 ,the following table1 showing the cost of hoisting for different lifts and by different methods1 is given by ,rziha1 the cost being in francs per cubic meter3-- ---------------------------------------- ------------ ,,height ,,windlass4 ,,horse ,,gins4 ,,steam ,,hoists4 ,,in ---------------------------------------- ---- ,,metres4 ,,one ,,horse4,,two ,,horses4 ,francs ,francs ,francs ,francs per ,cu4 ,m4per ,cu4 ,m4 per ,cu4 ,m4 per ,cu4 ,m4 ---------------------------------------- ----------- #ae #j4agb #j4jgg #j4jfb #j4jce #cj #j4bab #j4jhg #j4jgj #j4jde #de #j4beg #j4ajj #j4jhj #j4jej #fj #j4cje #j4aab #j4jib #j4jhb #ij #j4daj #j4aeb #j4aaj #j4jhg #abj #j4ece #j4aie #j4ace #j4jib #aej #j4gbb #j4bdj #j4aeg #j4aab ---------------------------------------- ----------- ,mr4 ,sjourn1 a ,french engineer1 who has been connected with the construction of numerous tunnels by the ,belgian method where he was in position to secure comparative figures1 has given the following rules for calculating the cost of tunnels4 ,assuming ,a to represent the cost of excavating a cu4 yd4 in the open air1 the cost of excavating the same quantity underground in driving headings will be from #i ,a to #aa ,a1 and in enlarging the profile it will be about #e ,a4 ,the cost of constructing single-track tunnels varies with the thickness of the lining1 and may be calculated by the following formulas3 ,without lining1 ,c #e4e ,a4 ,with roof arch only1 ,c #f4d #f4d ,a4 ,with lining #ah in4 thick1 ,c #i4d #g ,a4 ,with lining #b ft4 thick1 ,c #aa #h ,a4 ,in these formulas ,c is the cost per cu4 yd4 of excavation1 including the masonry4 ,for double-track tunnels the amounts given by the above formulas may be used by reducing them about #g or #h4 ,the second method of estimating the cost of tunnel work consists in assuming as a unit the unit cost of tunnels previously excavated under similar conditions4 ,mr4 ,la ,dame gives the following unit prices for a number of tunnels driven through different materials3 ---------------------------------------- ------------------------ ,,nature ,,of ,,soil4 ,,tunnels1 ,,excav4 ,,per ,,cost ,,per ,,max4 ,,and ,,min4 ,,no4 ,,of ,,cu4 ,,yd4 ,,lin4 ,,ft4 ,,per ,,lin4 ,,ft4 ---------------------------------------- ------------------------ ,granite-gneiss #ef #c4jg #c4he #ajj4 #fa4df #aij4dj ,schist #ci #a4ch #a4ec #ge4db #dc4aa #gj4fh ,triassic #c 444 #ij4he #hd4ge #ic4cc ,jurassic #fi #a4bc #a4ch #gg4hf #ce4bd #aeg4b ,cretaceous #cd #j4fa #j4gg #ei4fj #bg4cg #ib4be ,tertiary and modern #ci #j4cc #j4fa #aje4hj #ea4eb #ahh4cf ---------------------------------------- ------------------------ ,in the following table is given a list of tunnels excavated through different soils1 from the most compact to very loose materials1 and driven according to the various methods which have been illustrated4 ,,double-,,track ,,tunnels4 ---------------------------------------- ------------ ,,name ,,of ,,quality ,,of ,,soil4 ,,cost ,,per ,,method ,,of ,,tunnels4 ,,lin4 ,,ft4 ,,tunneling4 ---------------------------------------- ------------ ,mt4 ,cenis ,granitic1 #bgc4gc ,drift4 ,st4 ,gothard 444 #aic4fc ,heading4 ,stammerich ,granitic1 #aeg4ij ,english4 ,stalle ,broken schist1 #bij4eh ,austrian4 ,bothenfels ,dolomite1 #aae4fd ,english4 ,dorremberg ,calcareous1 #hf4jh ,belgian4 ,stafflach ,calcareous1 #ia4fi ,english4 ,ofen ,calcareous1 #ic4ai ,austrian4 ,wartha ,grewack1 #hg4ie ,austrian4 ,mertin ,grewack1 #hg4ee ,german4 ,schloss ,matrei,clay schist1 #id4be ,english4 ,trietbitte ,clay and sand1 #bbi4j ,german4 ,canaan ,clay-slate1 #fi4ej ,wide heading4 ,church-,hill ,clay with shells1 #agh4j 444 ,bergen ,no4 #a ,trap rock1 #ahb4ca 444 ---------------------------------------- ------------ ,,single-,,track ,,tunnels4 ---------------------------------------- ----------------- ,,name ,,of ,,quality ,,of ,,soil4 ,,cost ,,per ,,method ,,of ,,tunnels4 ,,lin4 ,,ft4 ,,tunneling4 ---------------------------------------- ----------------- ,mt4 ,cenis ,gneiss1 #hb4bg ,heading4 ,stalletti ,granite and quartz1 #fb4ge ,austrian4 ,marein ,clay schist1 #fd4cf ,english4 ,welsberg ,gravel1 #afe4jg ,austrian4 ,sancina ,clay of #ast variety1#abi4dj ,belgian4 ,starre ,clay of #b;d variety1 #aia4fa ,belgian4 ,cristina ,clay of #c;d variety1 #cjg4db ,italian4 ,burk 444 #hc4ij ,wide heading4 ,brafford ,ridge444 #he4cc ,wide heading4 ,dunbeithe ,limestone1 #gj4dg ,wide heading4 ,fergusson ,sandstone1 #cg4dfaf,wide heading4 ,port ,henry ,limestone1 #hj4jjag,wide heading4 ,points ,granite1 #gb4jjaf,wide heading4 ---------------------------------------- ----------------- #af ,are unlined4 #ag ,lined with timber4 ,the ,habas tunnel through quicksand1 between ,dax and ,ramoux1 ,france1 cost #aah4ej per lin4 ft4 ,the cost of the ,boston subway was #cdb4dj per lin4 ft4 ,the ,severn and ,mersey tunnels1 constructed through rock under water1 cost respectively #bjh4ch and #bfc per lin4 ft4 ,the ,first ,thames ,tunnel1 driven by ,brunel's shield1 cost #affa4ff per lin4 ft4 ,the ,hudson ,river and ,st4 ,clair ,river tunnels1 excavated through soft ground by means of shields and compressed air1 cost respectively #cje and #cae per lin4 ft4 ,the ,blackwall double-track tunnel under the ,river ,thames1 which is the largest tunnel ever built by the shield system1 cost #fjj per lin4 ft4 ,in making estimates of the cost of projected tunnel work based on the cost of tunnels previously constructed through similar materials1 it is important to keep in mind the date and location of the work used as the basis for calculations4 ,for example1 a tunnel excavated in ,italy1 where labor is very cheap1 will cost less than one excavated in ,america1 where labor is dear1 all other conditions being the same4 ,other reasons for variation in cost due to difference of date and location of construction will suggest themselves1 and should be taken into full consideration in estimating the cost of the new work4 ,time4--,the time required to excavate a tunnel depends upon the character of the material penetrated and upon the method of work adopted4 ,tunnels driven through soft ground by hand require about the same time to construct as tunnels driven through hard rock by the aid of machinery4 ,tunnels can be driven through hard rock at about as great a speed as through soft or fissured rock1 chiefly because the work of blasting is more efficient in hard rock1 and because no time is required in timbering4 ,the following table shows the average rate of progress in different parts of the tunnel excavation through both hard and soft materials in feet per month3-- ---------------------------------------- -------------------------- ,,quality ,,heading4 ,,excavation ,,enlargement ,,of ,,soil4 ,,of ,,shafts4 ,,of ,,profile4 ---------------------------------------- --------- ,by hand4 ,by ,by hand4 ,by ,by hand4 machine4 machine4 ---------------------------------------- ------------------------ ,very loose soil#af4g- #bf4h #f4f-af4g #f4f- #af4g ,loose soil #cc4d-ajj #af4g-cc4d #af4g- #cc4d ,soft rock #ff4h #bcc4h-ccdcc4d-ff4hff4h-acb4f #cc4d- #ej ,hard rock #ej - #ff4hbcc4h-ccdcc4d-ej #ff4h-acb4f #ff4h-ajj ,very hard rock #cc4d #bcc4h-ccdaf4g-cc4dff4h-acb4f #ff4h-ajj ---------------------------------------- ------------------------ ,the following tables showing the average rate of progress have been compiled from the actual records made in the tunnels named3 ---------------------------------------- --------------------- ,,name ,,of ,,dimensions ,,monthly ,,character ,,of ,,observations4 ,,tunnel4 ,,in ,,feet4 ,,progress ,,material4 ,,in ,,feet4 ---------------------------------------- --------------------- ,excavation of headings by hand3 ,mount ,cenis #aj #aj #fe4h ,schist1 ,bottom drift4 ,sutro #f4g #e4g #gj4ad ,quartzose1 444 ,st4 ,gothard #h4d #h4g #gj4ad ,granite1 ,top heading4 ,excavation of headings by machine3 ,mount ,cenis #aj #aj #ahh4g ,calcareous schist1 ,bottom drift4 ,sutro #h4ae #aj #bbg4de ,quartzose1 444 ,st4 ,gothard #h4d #h4g #cci4de ,granite1 ,top heading4 ,trari #h #i4ce #afg ,gneiss1 ,top heading4 ,arlberg #h4ce #i4ce #dgd4b ,mica schist1 ,bottom drift4 ,palisades #af #g #afj ,trap rock1 ,top heading4 ,busk #ae #g #abf ,granite1 ,top heading4 ,cascade #af #h #ahj ,basaltic rock1,top heading4 ,franklin #ae #g #bdj 444 ,top heading4 ---------------------------------------- --------------------- ,the following table shows the monthly progress of completed tunnel in feet excavated through rock3 ---------------------------------------- ----- ,,name ,,of ,,tunnel4,,progress,,material4 ,,method4 ,,in ,,feet4 ---------------------------------------- ----- ,cascade #bjg ,basalt1 ,top heading4 ,palisades #ahf ,trap rock1,top heading4 ,busk #aij ,granite1 ,top heading4 ,tennessee ,pass #afi4e ,granite1 ,top heading4 ---------------------------------------- ----- ,the average monthly progress in feet of excavating tunnels through treacherous ground may be quite generally assumed to be for3 7#a7 clay of the first variety from #dc4d ft4 to #fj ft42 for clay of the second variety from #cc4d ft4 to #dc4d ft42 for clay of the third variety from #bc4c ft4 to #cc4d ft41 and for quicksand from #cj ft4 to #ej ft4 ,the monthly progress in feet made in sinking the shafts of the ,hoosac and ,musconetcong tunnels in ,america was as follows3-- ---------------------------------------- ---------------- ,,name ,,of ,,tunnel4 ,,dimensions ,,depth ,,progress,,character ,,of ,,in ,,feet4 ,,in ,,feet4 ,,in ,,feet4 ,,material4 ---------------------------------------- ---------------- ,hoosac3 ,east shaft #ae4d #bg4g #ajce #ba4g ,mica schist4 ,west shaft #h #af #bfg #af4g ,gneiss4 ,musconetcong3 ,vertical shaft #h4ce #af4g #aac4e #ajj ,loose rock4 ,inclined shaft #h4ce #bf #cjd4 #cb ,loose rock4 ---------------------------------------- ---------------- ,the average monthly progress of sinking shafts in treacherous soils may be assumed to be as follows3 clay of first variety1 #ej ft4 to #ge ft2 clay of second variety1 #cf4ge to #ej ft2 clay of third variety1 #bc4d ft4 to #cf4ge ft2 quicksand1 #af4g ft4 to #cc4d ft4 ,for the reason that the details change with the various conditions encountered in every work1 all the tunnel operations have been treated in a general way1 purposely avoiding to give any detail4 ,also the rate of progress and items of cost of tunnels have been given in a broad manner because they greatly vary in the different works4 ,this information1 however1 can be easily obtained by consulting the ,engineering ,magazines1 where are reported all the tunnel works of ,america and ,europe1 and where are given so many details which are very valuable to expert engineers in charge of similar works1 but not to students and people who are looking only for general knowledge4 ,,index ,accidents and ,repairs in the ,belgian ,method1 #aeb ,accidents in ,tunnels3 ,after ,construction1 #cjh ,baltimore ,belt ,line1 #afe ,chattanooga ,tunnel1 #caa ,during ,construction1 #cja ,general ,discussion1 #cja ,giovi ,tunnel1 #cji ,repairing of1 #cjd ,acetylene ,gas ,lighting1 #ccd ,air ,compressors1 ,description of1 #hg ,air ,locks1 #bfd-bgb ,air ,pressure1 #bfh ,american ,method3 ,general ,description1 #agb ,excavation1 #agb ,strutting1 #agd ,hauling1 #age ,arrangement of ,drill ,holes1 #ij ,artificial ,ventilation1 #cbg ,austrian ,method of ,tunneling3 ,advantages and ,disadvantages1 #ahj ,excavation1 #agf ,general ,description1 #agf ,lining1 #ahj ,strutting1 #agg ,average ,progress in ,tunnels1 #cdb ,baltimore ,belt ,line ,tunnel1 ,general ,description1 #afj ,barlow's ,shield1 #bdb ,beach's ,shield1 #bdf ,belgian ,method3 ,accidents and ,repairs1 #aeb ,advantages and ,disadvantages1 #aeb ,excavation1 #ade ,general ,description1 #add ,lining1 #adh ,hauling1 #aej ,strutting1 #adf ,bench1 #aca ,bends1 #bfh ,blackwall's ,tunnel ,shield1 #bdh ,blasting-cone1 #cc ,blickford ,match1 #ca ,boston ,subway3 ,general ,descriptions1 #bjc ,roof ,shield1 #bea ,boulder ,tunnel ,relined1 #cae ,box-cars1 #fa ,box ,strutting1 #ea ,brandt ,drilling ,machine1 #bh1 #aab ,brown1 ,w4 ,l41 #bfi ,brunel's ,shield1 #bdj ,caissons1 #bic ,canals and ,pipe ,lines1 #hf ,cascade ,tunnel1 #ih ,center-cut1 #ia ,center ,line3 ,curvilinear ,tunnels1 #ad ,determination of1 #i ,rectilinear ,tunnels1 #i ,simplon ,tunnel1 #ajf ,submarine ,tunnels1 #bfe ,triangulation1 #ab ,transferred through ,center ,shafts1 #ac ,transferred through ,side ,shafts1 #ad ,value's ,device1 #aj ,centers3 ,for ,arches1 #fh ,english ,method1 #afi ,ground ,molds1 #ff ,italian ,method1 #ahd ,lagging1 #ga ,leading ,frames1 #fg ,setting ,up1 #gj ,striking1 #ga ,chattanooga ,tunnel1 ,accident1 #caa ,city and ,south ,london ,railway ,shield1 #bej ,classification of ,tunnels1 #db ,coal-gas ,lighting1 #ccc ,cofferdam ,method of ,tunneling1 #bha ,van ,buren ,street ,tunnel1 ,chicago1 #bhb ,collapse of ,tunnels1 #cjb ,compressed ,air3 ,for ,power1 #hg ,for ,ventilation1 #ccj ,concrete ,lining1 #ge ,fort ,george ,tunnel1 #aci ,murray ,hill ,tunnel1 #abf ,cost of3 ,double-track ,tunnels1 #cdj ,hauling1 #cch ,headings1 #ccg ,hoisting1 #cch ,single-track ,tunnel1 #cdj ,submarine ,tunnels1 #cda ,subways1 #bji-bag ,tunnels1 #ccf ,craven1 ,alfred1 #ci ,craven's ,sunflower1 #ci ,cross-section3 ,dimensions of1 #bj ,form of1 #ah ,hudson ,river ,tunnel ,pennsylvania ,railroad1 #bgg ,crown-bar 7see ,american ,method74 ,subways1 #bjd-baa ,croton ,aqueduct ,tunnel1 #ie ,culverts1 #hj ,detroit ,river ,tunnel1 #bif ,diamond ,drilling ,machine1 #bg ,directing the ,shield1 #bfe ,drift1 #cg ,drift ,method3 ,general ,discussion1 #ajb ,murray ,hill ,tunnel1 #abc ,simplon ,tunnel1 #ajc ,drilling ,machines3 ,brandt1 #aab ,ingersoll1 #bf ,drills3 ,diamond1 #bg ,hand1 #bc ,mountings for1 #be ,percussion1 #bd ,power1 #bd ,rotary1 #bg ,dumping ,cars1 #fj ,electric ,firing1 #cb ,electric ,lighting1 #cce ,english ,method3 ,advantages and ,disadvantages1 #aga ,centers1 #afi ,excavation1 #aff ,general ,discussion1 #aff ,lining1 #agj ,strutting1 #afg ,enlargement of the ,profile1 #ch ,entrances1 #ha ,erector1 #bgb ,excavation3 ,american ,method1 #agb ,arrangement of ,drill ,holes1 #ij ,austrian ,method1 #agf ,belgian ,method1 #ade ,center-cut1 #ia ,enlargement of ,profile1 #ch ,english ,method1 #aff ,fort ,george ,tunnel1 #acf ,german ,method1 #aee ,headings1 #cg1 #ia ,hudson ,river ,tunnel of ,pennsylvania ,railroad1 #bgc ,italian ,method1 #ahb ,murray ,hill ,tunnel1 #abd ,quicksand ,method1 #ahi ,pilot ,method1 #aic ,shield and ,compressed ,air ,method1 #bfg ,simplon ,tunnel1 #aaj ,excavating ,machines3 ,for ,earth1 #bb ,for ,rock1 #bc ,explosions1 #cc ,dynamite1 #cj ,gunpowder1 #bh ,nitroglycerine1 #bi ,quantity of1 #cd ,storage of1 #cj ,failure of ,tunnel ,roof1 #cje ,forgie1 ,james1 #bfi ,fort ,george ,tunnel1 #ace ,foundations for ,lining1 #gf ,fox1 ,charles ,b41 #ajc ,frame ,strutting1 #di ,fuses1 #ca ,geological ,survey1 #c ,german ,method3 ,advantages and ,disadvantages1 #aei ,excavation1 #aee ,general ,description1 #aee ,hauling1 #aeh ,strutting1 #aef ,giovi ,tunnel ,accident1 #cji ,graveholz ,tunnel1 #ih ,greathead's ,shield1 #bde ,hand ,drills1 #bc ,harlem ,river ,tunnel1 #bhe ,hauling3 ,american ,method1 #age ,belgian ,method1 #aej ,italian ,method1 #ahe ,german ,method1 #aeh ,hudson ,river ,tunnel of ,pennsylvania ,railroad1 #bgh ,motive ,power1 #fa ,by ,way of ,entrances1 #ei ,simplon ,tunnel1 #aaa ,by ,way of ,shafts1 #fb ,heading and ,bench ,method3 ,fort ,george ,tunnel1 #ace ,general ,discussion1 #acj ,st4 ,gothard ,tunnel1 #a ,headings1 #cg1 #ia ,hewett1 ,h4 ,b41 #bfi ,history of ,tunnels1 xiii ,hoisting ,machines3 ,general ,discussion1 #fb ,elevators1 #fd ,horse ,gins1 #fc ,windlass1 #fc ,hoosac ,tunnel1 #ic ,hopkins1 ,stephen ,w41 #ace ,hudson ,river ,tunnel of ,pennsylvania ,railroad1 #bfi ,hydraulic ,jacks1 #bfj1 #bga ,hydraulic ,rams1 #bga ,illumination3 ,acetylene ,gas1 #ccd ,coal-gas1 #ccc ,electric1 #cce ,hudson ,river ,tunnel of ,pennsylvania ,railroad1 #bhj ,lamps and ,lanterns1 #ccj ,inclination of ,strata1 #f ,ingersoll ,drilling ,machine1 #bf ,inverted ,arch ,lining1 #gg ,iron and ,masonry ,lining1 #gd ,iron ,lining1 #gc1 #bfa1 #bgf ,iron ,strutting1 #ee ,full ,section1 #ef ,headings1 #ef ,shafts1 #eg ,italian ,method3 ,advantages and ,disadvantages1 #ahh ,excavation1 #ahb ,general ,description1 #ahb ,modifications1 #ahf ,strutting1 #ahc ,jacks1 #bfj1 #bga ,joining the ,caissons1 #bie ,lagging1 #ga ,lamps and ,lanterns1 #ccj ,lighting 7see ,illumination74 ,lining3 ,austrian ,method1 #ahj ,belgian ,method1 #adh ,concrete1 #abf1 #aci ,english ,method1 #agj ,foundations1 #gf ,general ,observations1 #gh ,german ,method1 #aeh ,hudson ,river ,tunnel ,pennsylvania ,railroad1 #bgf ,invert1 #gg ,iron1 #gc1 #bfa1 #bgf ,iron and ,masonry1 #gd ,italian ,method1 #ahe ,masonry1 #gd ,quicksand ,method1 #aia ,roof ,arch1 #gg ,side ,tunnels1 #gi1 #hc ,side ,walls1 #gg ,subways1 #bjg-bac ,timber1 #gb ,thickness of ,masonry1 #gh1 #hc ,little ,tom ,tunnel ,relined1 #cba ,loose ,soil 7see ,soft ,ground74 ,masonry 7see ,centers74 ,masonry ,culverts1 #hj ,masonry 7see ,lining74 ,masonry ,lining1 #gd ,masonry ,niches1 #ha ,mc,bean1 ,daniel1 #bhe ,mechanical ,installations for ,tunnel ,work1 #hd ,milwaukee ,tunnel1 #bbf ,mont ,cenis ,tunnel1 #ib ,monthly ,progress of ,tunnels1 #cdb ,mullan ,tunnel ,relined1 #cai ,murray ,hill ,tunnel1 #abc ,natural ,ventilation1 #cbf ,new ,york ,rapid ,transit ,subway1 #bji ,niagara ,falls ,power ,tunnel1 #ig ,niches1 #ha ,open ,cut or ,tunnel1 #a ,open-cut ,tunneling3 ,general ,discussion1 #aie ,parallel ,longitudinal ,trenches1 #aig ,single ,trench1 #aif ,single ,narrow ,trench1 #aig ,transverse ,trenches1 #bjj ,tunnels on the ,surface1 #bjj ,palisade ,tunnel1 #id ,pennsylvania ,railroad ,shield1 #bgj ,percussion ,drills1 #bd ,pilot ,method of ,tunneling1 #aib ,plank ,centers1 #fi ,platform ,cars1 #ei ,plenum ,method of ,ventilation1 #cbi ,pneumatic ,caissons1 #bhg ,polar ,protractor1 #ci ,portals1 #ha ,power ,drills1 #bd ,power ,plants3 ,air ,compressors1 #hg ,canals and ,pipe ,lines1 #hf ,cascade ,tunnel1 #ih ,croton ,aqueduct ,tunnel1 #ie ,general ,description1 #hd ,graveholz ,tunnel1 #ih ,hoosac ,tunnel1 #ic ,hudson ,river ,tunnel ,pennsylvania ,railroad1 #bgi ,mont ,cenis ,tunnel1 #ib ,murray ,hill ,tunnel1 #abh ,niagara ,falls ,power ,tunnel1 #ig ,palisades ,tunnel1 #id ,receivers1 #hi ,reservoirs1 #hf ,simplon ,tunnel1 #aag ,sonnstein ,tunnel1 #ii ,st4 ,clair ,river ,tunnel1 #ii ,st4 ,gothard ,tunnel1 #acc ,steam1 #he ,strickler ,tunnel1 #if ,turbines1 #hf ,prelini's ,shield1 #bea ,presence of ,water1 #g ,prevention of ,collapse1 #cjc ,progress in ,sinking ,shafts1 #cdc ,progress of ,excavation1 #cdb ,progress of the ,work1 #cdb ,progress in ,simplon ,tunnel1 #abb ,quantity of ,air for ,ventilation1 #cca ,quicksand ,tunneling3 ,general ,discussion1 #ahh ,removing the ,seepage ,water1 #aia ,quantity of ,timber in ,strutting1 #ed ,receivers1 #hi ,relining ,tunnels1 #cae ,boulder ,tunnel1 #cae ,little ,tom ,tunnel1 #cba ,mullan ,tunnel1 #cai ,repairing of ,accidents in ,tunnels1 #cjh ,reservoirs1 #hf ,roof ,arch ,lining1 #gg ,roof ,shield for ,boston ,subway1 #bea ,roof of ,caissons1 #bhg-bia ,rotary ,drills1 #bg ,ryder1 ,b4 ,h41 #bif ,saccardo ,system of ,ventilation1 #ccj ,saunders1 ,w4 ,l41 #hh ,seepage ,water1 #aia ,seine ,river ,tunnel1 #bic ,setting up ,centers1 #gj ,severn ,tunnel1 #bba ,shafts1 ,description of1 #dj ,shaler1 ,ira ,a41 #adb ,shield and ,compressed ,air ,method1 #bfc ,shield ,construction3 ,diaphragm1 #bef ,cellular ,division1 #bee ,dimensions of ,shields1 #bei ,front ,end1 #bed ,general ,form1 #beb ,rear ,end1 #beg ,shell1 #bec ,shield ,method3 ,barlow ,shield1 #bdb ,beach's ,shield1 #bde ,blackwall ,tunnel ,shield1 #bdh ,brunel ,shield1 #bdj ,city and ,south ,london ,railway ,shield1 #bej ,greathead's ,shield1 #bde ,history1 #bch ,prelini's ,shield1 #bea ,st4 ,clair ,river ,tunnel ,shield1 #bdg ,side ,shafts1 #da ,side ,tunnels ,lining1 #gi ,side ,walls ,lining1 #gg ,simplon ,tunnel1 #ajc ,soils ,encountered in ,tunnels1 #c ,sonnstein ,tunnel1 #ii ,stations of ,subways1 #bjg-baf ,st4 ,clair ,river ,tunnel ,shield1 #bdg ,st4 ,gothard ,tunnel1 #acb ,steam ,power ,plant1 #he ,stratification of the ,soils1 #f ,strickler ,tunnel1 #if ,striking the ,centers1 #ga ,strutting3 ,american ,method1 #agd ,austrian ,method1 #agg ,belgian ,method1 #adf ,dimensions of ,timber1 #ed ,english ,method1 #afg ,fort ,george ,tunnel1 #acg ,full ,section1 #ea ,german ,method1 #aef ,headings1 #dh ,italian ,method1 #ahc ,murray ,hill ,tunnel1 #abe ,pilot ,method1 #aic ,quantity of ,timber1 #ed ,shafts1 #eb ,iron3 ,full ,section1 #ef ,headings1 #ef ,shafts1 #eg ,submarine ,tunneling3 ,cofferdam ,method1 #bha ,compressed ,air ,method1 #bbe ,detroit ,river ,tunnel1 #bif ,general ,discussion1 #bah ,harlem ,river ,tunnel1 #bhe ,hudson ,river ,tunnel ,pennsylvania ,railroad1 #bfi ,lining1 #bfa ,milwaukee ,water-,works ,tunnel1 #bbf ,pneumatic ,caisson ,method1 #bhd ,seine ,river ,tunnel1 #bic ,severn ,tunnel1 #bba ,shield and ,compressed ,air ,method1 #bfc ,shield ,system1 #bch ,sinking and ,joining ,sections ,built on ,land1 #bic ,van ,buren ,street ,tunnel1 #bhb ,subways3 ,boston1 #bjc ,cost of1 #bji-bag ,cross-sections1 #bjd-baa ,general ,discussion1 #aie-bjb ,lining1 #bjg-bac ,new ,york ,rapid ,transit ,railway1 #bji ,stations1 #bjg-baf ,sutro1 ,adolph1 #ccj ,tamping1 #cb ,thickness of ,lining ,masonry1 #gh1 #hc ,thomson ,excavating ,machine1 #bb ,timber ,lining1 #gb ,timbering 7see ,strutting74 ,tremies1 #bii ,trussed ,centers1 #gj ,tunnel or ,open ,cut1 #a ,tunnels3 ,baltimore ,belt ,line1 #afj ,classification of1 #db ,fort ,george1 #ace ,murray ,hill1 #abc ,simplon1 #ajc ,st4 ,gothard1 #acb ,hard ,rock1 #hd ,drift ,method1 #ajb ,comparison of ,methods1 #ada ,heading and ,bench ,method1 #aeb ,heading ,method1 #acj ,soft ,ground3 ,american ,method1 #agb ,austrian ,method1 #agf ,belgian ,method1 #add ,english ,method1 #aff ,german ,method1 #aee ,italian ,method1 #ahb ,pilot ,method1 #aib ,quicksand ,method1 #ahh ,submarine3 ,detroit ,river ,tunnel1 #bif ,harlem ,river ,tunnel1 #bhe ,hudson ,river ,tunnel of ,pennsylvania ,railroad1 #bfi ,milwaukee ,tunnel1 #bbf ,seine ,river ,tunnel1 #bic ,severn ,tunnel1 #bba ,van ,buren ,street ,tunnel1 ,chicago1 #bhb ,under ,city ,streets3 ,general ,description1 #bja ,boston ,subway1 #bjc ,turbines1 #hf ,vacuum ,method of ,ventilation1 #cbh ,value1 ,beverley ,r41 #aj ,van ,buren ,street ,tunnel1 #bhb ,ventilation1 #cbe ,artificial1 #cbg ,compressed ,air1 #ccj ,natural1 #cbf ,plenum ,method1 #cbi ,quantity of ,air1 #cca ,saccardo's ,system1 #ccj ,simplon ,tunnel1 #abj ,vacuum ,method1 #cbh ,vernon-,harcourt1 ,l4 ,f41 #bba ,working ,platforms1 #bhf ,wyman1 ,erastus1 #bic ,transcriber's ,notes ,inconsistencies in spelling and hyphenation have been retained except as mentioned below2 non-,english words and phrases have not been corrected except as listed below4 ,the 7minor7 differences between the ,table of ,contents and the chapter headings have not been rectified4 ,page #cf_/acb3 ,figs4 #ad and #fa are identical4 ,page #ib_/ic1 ,sommeilier3 possibly an error for ,sommeiller4 ,page #acd1 ,soummelier3 possibly an error for ,sommeiller4 ,page #agd1 ,footnote #aa3 presumably ,fig4 #ib1 indicating the planes of the sections1 is from the same publication4 ,page #agf1 ,austrian method3 ,dresden and ,leipsic1 and the ,oberau ,tunnel1 are 7and were in #ahcg7 in ,saxony1 ,germany 7or ,prussia74 ,page #agi1 ,the short transverse beam c1 ,fig4 #ij3 there is no short transverse beam visible in ,fig4 #ij1 nor is it clear which other figure might be intended2 there is therefore no hyperlink to the illustration4 ,page #bgi1 ,stirtling boiler3 possibly an error for ,stirling boiler4 ,pages #ccg and #cdb1 ,arlberg3 possibly an error for ,aarlberg4 ,page #cdj1 ,wartha3 possibly an error for ,martha2 ,mertin3 possibly an error for ,merten4 ,changes made ,footnotes1 tables and illustrations have been moved out of text paragraphs2 some table data have been re-arranged for better legibility4 ,in some of the formulas brackets have been added for clarity4 ,several obvious minor typographical and punctuation errors have been corrected silently4 ,page #ab1 footnote #c3 ,chapter ,,ix4 changed to ,chapter ,x4 ,page #ce3 on page #aee changed to on page #ace ,page #cf3 on page #cd changed to on page #ce ,page #ec3 ,the lagging plank may be 444 changed to ,the lagging planks may be 444 ,page #aac3 7#a7 changed to 7,i7 7#b7 ,page #aag3 444 and it in this clearing 444 changed to 444 and it is in this clearing 444 ,page #acj3 as indicated by ,fig4 #eh changed to as indicated by ,fig4 #fa ,page #acf3 as indicated in the ,fig4 #fc changed to as indicated in the ,fig4 #fe ,page #adf3 as shown by ,fig4 #fc changed to as shown by ,fig4 #fi ,page #adi3 underpining changed to underpinning ,page #aej3 ,since the roof arch rests for some time 444 changed to ,since the roof arch rests are for some time 4442 as shown by ,fig4 #ff changed to as shown by ,fig4 #gb ,page #agb3 illustrated in ,fig4 #ab changed to illustrated in ,fig4 #aa ,page #age3 page #abg changed to page #abc ,page #agi3 as at b1 ,fig4 #ij changed to as at b1 ,fig4 #ig ,page #bjd3 ,the third type of section is shown by ,fig4 #aaf changed to ,the third type of section is shown by ,fig4 #aag ,page #bah3 ,malin changed to ,malm ,page #bfa3 ,fig4 #aah shows the hydraulic jacks changed to ,fig4 #acf shows the hydraulic jacks ,page #bhb3 shown by ,fig4 #aai changed to shown by ,fig4 #ada ,page #big3 towed down to the tunnel side changed to towed down to the tunnel site ,page #cae3 shown in ,figs4 #ada and #adb changed to shown in ,figs4 #aei and #afj ,page #cbd3 shown by ,fig4 #adh changed to shown by ,fig4 #aff ,page #cch3 given on page #ej changed to given on page #ee ,page #cdj3 ,scloss ,matrei changed to ,schloss ,matrei ,page #cda3 ,time4 changed to ,time4 ,page #cdh1 entry ,ryder3 page number #bif added2 ,sounstein changed to ,sonnstein 7#b74