,transcriber's note3 ,this is ,paper #da from the ,smithsonian ,institution ,united ,states ,national ,museum ,bulletin #bdj1 comprising ,papers #cd-dd1 which will also be available as a complete e-book4 ,the front material1 introduction and relevant index entries from the ,bulletin are included in each single-paper e-book4 ,italic emphasis denoted as ,text4 ,whole numbers and fractions3 shown as #a-a_/b1 #c-a_/d1 etc4 ,please see the end of the book for corrections and changes made4 ,smithsonian ,institution ,united ,states ,national ,museum ,bulletin #bdj ,illustration3 ,smithsonian ,press ,museum of ,history and ,technology ,contributions from the ,museum of ,history and ,technology ,papers #cd-dd ,on ,science and ,technology ,smithsonian ,institution 4 ,washington1 ,d4,c4 #aiff 99 99 99 99 99 ,publications of the ,united ,states ,national ,museum ,the scholarly and scientific publications of the ,united ,states ,national ,museum include two series1 ,proceedings of the ,united ,states ,national ,museum and ,united ,states ,national ,museum ,bulletin4 ,in these series1 the ,museum publishes original articles and monographs dealing with the collections and work of its constituent museums--,the ,museum of ,natural ,history and the ,museum of ,history and ,technology--setting forth newly acquired facts in the fields of anthropology1 biology1 history1 geology1 and technology4 ,copies of each publication are distributed to libraries1 to cultural and scientific organizations1 and to specialists and others interested in the different subjects4 ,the ,proceedings1 begun in #ahgh1 are intended for the publication1 in separate form1 of shorter papers from the ,museum of ,natural ,history4 ,these are gathered in volumes1 octavo in size1 with the publication date of each paper recorded in the table of contents of the volume4 ,in the ,bulletin series1 the first of which was issued in #ahge1 appear longer1 separate publications consisting of monographs 7occasionally in several parts7 and volumes in which are collected works on related subjects4 ,bulletins are either octavo or quarto in size1 depending on the needs of the presentation4 ,since #aijb papers relating to the botanical collections of the ,museum of ,natural ,history have been published in the ,bulletin series under the heading ,contributions from the ,united ,states ,national ,herbarium1 and since #aiei1 in ,bulletins titled ,contributions from the ,museum of ,history and ,technology1 have been gathered shorter papers relating to the collections and research of that ,museum4 ,the present collection of ,contributions1 ,papers #cd-dd1 comprises ,bulletin #bdj4 ,each of these papers has been previously published in separate form4 ,the year of publication is shown on the last page of each paper4 ,,frank ,a4 ,,taylor ,director1 ,united ,states ,national ,museum 99 99 99 99 99 ,,contributions ,,from ,,the ,,museum ,,of ,,history ,,and ,,technology4 ,,paper #da ,,tunnel ,,engineering--,a ,,museum ,,treatment ,robert ,m4 ,vogel ,,introduction #bjc ,,rock ,,tunneling #bjf ,,soft-,,ground ,,tunneling #bae ,,bibliography #bci ,,footnotes ,,index ,illustration3 ,figure #a4--,,mining ,,by ,,early ,,european ,,civilizations1 using fire setting and hand chiseling to break out ore and rock4 ,,mht model--#c_/d scale4 7,smithsonian photo #dibfj-;,h47 ,robert ,m4 ,vogel ,,tunnel ,,engineering--,a ,,museum ,,treatment ,during the years from #ahcj to #aijj1 extensive developments took place in the field of tunneling1 which today is an important1 firmly established branch of civil engineering4 ,this paper offers a picture of its growth from the historical standpoint1 based on a series of models constructed for the ,hall of ,civil ,engineering in the new ,museum of ,history and ,technology4 ,the eight models described highlight the fundamental advances which have occurred between primitive man's first systematic use of fire for excavating rock in mining1 and the use in combination of compressed air1 an iron lining1 and a movable shield in a subaqueous tunnel at the end of the #aith century4 ,,the ,,author3 ,robert ,m4 ,vogel is curator of heavy machinery and civil engineering1 in the ,smithsonian ,institution's ,museum of ,history and ,technology4 ,introduction ,with few exceptions1 civil engineering is a field in which the ultimate goal is the assemblage of materials into a useful structural form according to a scientifically derived plan which is based on various natural and man-imposed conditions4 ,this is true whether the result be1 for example1 a dam1 a building1 a bridge1 or even the fixed plant of a railroad4 ,however1 one principal branch of the field is based upon an entirely different concept4 ,in the engineering of tunnels the utility of the structure is derived not from the bringing together of elements but from the separation of one portion of naturally existing material from another to permit passage through a former barrier4 ,in tunneling hard1 firm rock1 this is practically the entire compass of the work3 breaking away the rock from the mother mass1 and1 coincidently1 removing it from the workings4 ,the opposite extreme in conditions is met in the soft-ground tunnel1 driven through material incapable of supporting itself above the tunnel opening4 ,here1 the excavation of the tunneled substance is of relatively small concern1 eclipsed by the problem of preventing the surrounding material from collapsing into the bore4 ,illustration3 ,figure #b4--;,,hoosac ,,tunnel4 ,,method ,,of ,,working ,,early ,,sections of the project2 blast holes drilled by hand jacking4 ,,mht model--#a_/b scale4 7,smithsonian photo #dibfj-,l47 ,in one other principal respect does tunnel engineering differ widely from its collateral branches of civil engineering4 ,few other physical undertakings are approached with anything like the uncertainty attending a tunnel work4 ,this is even more true in mountain tunnels1 for which test borings frequently cannot be made to determine the nature of the material and the geologic conditions which will be encountered4 ,the course of tunnel work is not subject to an overall preliminary survey2 the engineer is faced with not only the inability to anticipate general contingencies common to all engineering work1 but with the peculiar and often overwhelming unpredictability of the very basis of his work4 ,subaqueous and soft-ground work on the other hand1 while still subject to many indeterminates1 is now far more predictable than during its early history1 simply because the nature of the adverse condition prevailing eventually was understood to be quite predictable4 ,the steady pressures of earth and water to refill the excavated area are today overcome with relative ease and consistency by the tunneler4 ,in tunneling as in no other branch of civil engineering did empiricism so long resist the advance of scientific theory2 in no other did the practical engineer remain to such an extent the key figure in establishing the success or failure of a project4 ,the ,hoosac ,tunnel1 after #be years of legislative1 financial1 and technical difficulties1 in #ahge was finally driven to successful completion only by the efforts of a group who1 while in the majority were trained civil engineers1 were to an even greater extent men of vast practical ability1 more at home in field than office4 ,de,witt ,c4 ,haskin 7see p4 #bcd71 during the inquest that followed the death of a number of men in a blowout of his pneumatically driven ,hudson ,river ,tunnel in #ahhj1 stated in his own defense3 ,i am not a scientific engineer1 but a practical one 444 ,i know nothing of mathematics2 in my experience ,i have grasped such matters as a whole2 ,i believe that the study of mathematics in that kind of work tunneling has a tendency to dwarf the mind rather than enlighten it4444 ,an extreme attitude perhaps1 and one which by no means adds to ,haskin's stature1 but a not unusual one in tunnel work at the time4 ,it would not of course be fair to imply that such men as ,herman ,haupt1 ,brunel the elder1 and ,greathead were not accomplished theoretical engineers4 ,but it was their innate ability to evaluate and control the overlying physical conditions of the site and work that made possible their significant contributions to the development of tunnel engineering4 ,tunneling remained largely independent of the realm of mathematical analysis long after the time when all but the most insignificant engineering works were designed by that means4 ,thus1 as structural engineering has advanced as the result of a flow of new theoretical concepts1 new1 improved1 and strengthened materials1 and new methods of fastening1 the progress of tunnel engineering has been due more to the continual refinement of constructional techniques4 ,a ,,new ,,hall ,,of ,,civil ,,engineering ,in the ,museum of ,history and ,technology has recently been established a ,hall of ,civil ,engineering in which the engineering of tunnels is comprehensively treated from the historical standpoint--something not previously done in an ,american museum4 ,the guiding precept of the exhibit has not been to outline exhaustively the entire history of tunneling1 but rather to show the fundamental advances which have occurred between primitive man's first systematic use of fire for excavating rock in mining1 and the use in combination of compressed air1 iron lining1 and a movable shield in a subaqueous tunnel at the end of the #aith century4 ,this termination date was selected because it was during the period from about #ahcj to #aijj that the most concentrated development took place1 and during which tunneling became a firmly established and important branch of civil engineering and indeed1 of modern civilization4 ,the techniques of present-day tunneling are so fully related in current writing that it was deemed far more useful to devote the exhibit entirely to a segment of the field's history which is less commonly treated4 ,illustration3 ,figure #c4--;,,hoosac ,,tunnel4 ,,working ,,of ,,later ,,stages with ,burleigh pneumatic drills mounted on carriages4 ,the bottom heading is being drilled in preparation for blasting out with nitroglycerine4 ,,mht model--#a_/b scale4 7,smithsonian photo #dibfj-,m47 ,the major advances1 which have already been spoken of as being ones of technique rather than theory1 devolve quite naturally into two basic classifications3 the one of supporting a mass of loose1 unstable1 pressure-exerting material--soft-ground tunneling2 and the diametrically opposite problem of separating rock from the basic mass when it is so firm and solid that it can support its own overbearing weight as an opening is forced through it--rock1 or hard-ground tunneling4 ,to exhibit the sequence in a thorough manner1 inviting and capable of easy and correct interpretation by the nonprofessional viewer1 models offered the only logical means of presentation4 ,six tunnels were selected1 all driven in the #aith century4 ,each represents either a fundamental1 new concept of tunneling technique1 or an important1 early application of one4 ,models of these works form the basis of the exhibit4 ,no effort was made to restrict the work to projects on ,american soil4 ,this would1 in fact1 have been quite impossible if an accurate picture of tunnel technology was to be drawn2 for as in virtually all other areas of technology1 the overall development in this field has been international4 ,the art of mining was first developed highly in the ,middle ,ages in the ,germanic states2 the tunnel shield was invented by a ,frenchman residing in ,england1 and the use of compressed air to exclude the water from subaqueous tunnels was first introduced on a major work by an ,american4 ,in addition1 the two main subdivisions1 rock and soft-ground tunneling1 are each introduced by a model not of an actual working1 but of one typifying early classical methods which were in use for centuries until the comparatively recent development of more efficient systems of earth support and rock breaking4 ,particular attention is given to accuracy of detail throughout the series of eight models2 original sources of descriptive and graphic information were used in their construction wherever possible4 ,in all cases except the introductory model in the rock-tunneling series1 representing copper mining by early civilizations1 these sources were contemporary accounts4 ,the plan to use a uniform scale of reduction throughout1 in order to facilitate the viewers' interpretation1 unfortunately proved impractical1 due to the great difference in the amount of area to be encompassed in different models1 and the necessity that the cases holding them be of uniform height4 ,the related models of the ,broadway and ,tower ,subways represent short sections of tunnels only #h feet or so in diameter enabling a relatively large scale1 #a-a_/b inches to the foot1 to be used4 ,conversely1 in order that the model of ,brunel's ,thames ,tunnel be most effective1 it was necessary to include one of the vertical terminal shafts used in its construction4 ,these were about #fj feet in depth1 and thus the much smaller scale of #a_/d inch to the foot was used4 ,this variation is not as confusing as might be thought1 for the human figures in each model provide an immediate and positive sense of proportion and scale4 ,careful thought was devoted to the internal lighting of the models1 as this was one of the critical factors in establishing1 so far as is possible in a model1 an atmosphere convincingly representative of work conducted solely by artificial light4 ,remarkable realism was achieved by use of plastic rods to conduct light to the tiny sources of tunnel illumination1 such as the candles on the miners' hats in the ,hoosac ,tunnel1 and the gas lights in the ,thames ,tunnel4 ,no overscaled miniature bulbs1 generally applied in such cases1 were used4 ,at several points where the general lighting within the tunnel proper has been kept at a low level to simulate the natural atmosphere of the work1 hidden lamps can be operated by push-button in order to bring out detail which otherwise would be unseen4 ,the remainder of the material in the ,museum's tunneling section further extends the two major aspects of tunneling4 ,space limitations did not permit treatment of the many interesting ancillary matters vital to tunnel engineering1 such as the unique problems of subterranean surveying1 and the extreme accuracy required in the triangulation and subsequent guidance of the boring in long mountain tunnels2 nor the difficult problems of ventilating long workings1 both during driving and in service2 nor the several major methods developed through the years for driving or constructing tunnels in other than the conventional manner4#a ,rock ,tunneling ,while the art of tunneling soft ground is of relatively recent origin1 that of rock tunneling is deeply rooted in antiquity4 ,however1 the line of its development is not absolutely direct1 but is more logically followed through a closely related branch of technology--mining4 ,the development of mining techniques is a practically unbroken one1 whereas there appears little continuity or relationship between the few works undertaken before about the #ahth century for passage through the earth4 ,the ,egyptians were the first people in recorded history to have driven openings1 often of considerable magnitude1 through solid rock4 ,as is true of all major works of that nation1 the capability of such grand proportion was due solely to the inexhaustible supply of human power and the casual evaluation of life4 ,the tombs and temples won from the rock masses of the ,nile ,valley are monuments of perseverance rather than technical skill4 ,neither the ,egyptians nor any other peoples before the ,middle ,ages have left any consistent evidence that they were able to pierce ground that would not support itself above the opening as would firm rock4 ,in ,egypt were established the methods of rock breaking that were to remain classical until the first use of gun-powder blasting in the #agth century which formed the basis of the ensuing technology of mining4 ,notwithstanding the religious motives which inspired the earliest rock excavations1 more constant and universal throughout history has been the incentive to obtain the useful and decorative minerals hidden beneath the earth's surface4 ,it was the miner who developed the methods introduced by the early civilizations to break rock away from the primary mass1 and who added the refinements of subterranean surveying and ventilating1 all of which were later to be assimilated into the new art of driving tunnels of large diameter4 ,the connection is the more evident from the fact that tunnelmen are still known as miners4 ,,copper ,,mining1 ,b4,c4 ,therefore1 the first model of the sequence1 reflecting elemental rock-breaking techniques1 depicts a hard-rock copper mine 7fig4 #a74 ,due to the absence of specific information about such works during the pre-,christian eras1 this model is based on no particular period or locale1 but represents in a general way1 a mine in the ,rio ,tinto area of ,spain where copper has been extracted since at least #ajjj ,b4,c4 ,similar workings existed in the ,tirol as early as about #afjj ,b4,c4 ,two means of breaking away the rock are shown3 to the left is the most primitive of all methods1 the hammer and chisel1 which require no further description4 ,at the right side1 the two figures are shown utilizing the first rock-breaking method in which a force beyond that of human muscles was employed1 the age-old fire-setting method4 ,the rock was thoroughly heated by a fierce fire built against its face and then suddenly cooled by dashing water against it4 ,the thermal shock disintegrated the rock or ore into bits easily removable by hand4 ,illustration3 ,figure #d4--;,,hoosac ,,tunnel4 ,bottom of the central shaft showing elevator car and rock skip2 pumps at far right4 ,in the center1 the top bench is being drilled by a single column-mounted ,burleigh drill4 ,,mht model--#a_/b scale4 7,smithsonian photo #dibfj-,n47 ,the practice of this method below ground1 of course1 produced a fearfully vitiated atmosphere4 ,it is difficult to imagine whether the smoke1 the steam1 or the toxic fumes from the roasting ore was the more distressing to the miners4 ,even when performed by labor considered more or less expendable1 the method could be employed only where there was ventilation of some sort3 natural chimneys and convection currents were the chief sources of air circulation4 ,despite the drawbacks of the fire system1 its simplicity and efficacy weighed so heavily in its favor that its history of use is unbroken almost to the present day4 ,fire setting was of greatest importance during the years of intensive mining in ,europe before the advent of explosive blasting1 but its use in many remote areas hardly slackened until the early #bjth century because of its low cost when compared to powder4 ,for this same reason1 it did have limited application in actual tunnel work until about #aijj4 ,direct handwork with pick1 chisel and hammer1 and fire setting were the principal means of rock removal for centuries4 ,although various wedging systems were also in favor in some situations1 their importance was so slight that they were not shown in the model4 ,,hoosac ,,tunnel ,it was possible in the model series1 without neglecting any major advancement in the art of rock tunneling1 to complete the sequence of development with only a single additional model4 ,many of the greatest works of civil engineering have been those concerned directly with transport1 and hence are the product of the present era1 beginning in the early #aith century4 ,the development of the ancient arts of route location1 bridge construction1 and tunnel driving received a powerful stimulation after #ahjj under the impetus of the modern canal1 highway1 and1 especially1 the railroad4 ,the ,hoosac ,tunnel1 driven through ,hoosac ,mountain in the very northwest corner of ,massachusetts between #ahea and #ahge1 was the first major tunneling work in the ,united ,states4 ,its importance is due not so much to this as to its being literally the fountainhead of modern rock-tunneling technology4 ,the remarkable thing is that the work was begun using methods of driving almost unchanged during centuries previous1 and was completed twenty years later by techniques which were1 for the day1 almost totally mechanized4 ,the basic pattern of operation set at ,hoosac1 using pneumatic rock drills and efficient explosives1 remains practically unchanged today4 ,the general history of the ,hoosac project is so thoroughly recorded that the briefest outline of its political aspects will suffice here4 ,hoosac ,mountain was the chief obstacle in the path of a railroad projected between ,greenfield1 ,massachusetts1 and ,troy1 ,new ,york4 ,the line was launched by a group of ,boston merchants to provide a direct route to the rapidly developing ,west1 in competition with the coastal routes via ,new ,york4 ,the only route economically reasonable included a tunnel of nearly five miles through the mountain--a length absolutely without precedent1 and an immense undertaking in view of the relatively primitive rock-working methods then available4 ,illustration3 ,figure #e4--;,,burleigh ,,rock ,,drill1 improved model of about #ahgj1 mounted on frame for surface work4 7,catalog and price list3 ,the ,burleigh ,rock ,drill ,company1 #ahgf47 ,the bore's great length and the desire for rapid exploitation inspired innovation from the outset of the work4 ,the earliest attempts at mechanization1 although ineffectual and without influence on tunnel engineering until many years later1 are of interest4 ,these took the form of several experimental machines of the full area type1 intended to excavate the entire face of the work in a single operation by cutting one or more concentric grooves in the rock4 ,the rock remaining between the grooves was to be blasted out4 ,the first such machine tested succeeded in boring a #bd-;foot diameter opening for #aj feet before its total failure4 ,several later machines proved of equal merit4#b ,it was the ,baltimore and ,ohio's eminent chief engineer1 ,benjamin ,h4 ,latrobe1 who in his ,report on the ,hoosac ,tunnel 7,baltimore1 ,oct4 #a1 #ahfb1 p4 #abe7 stated that such apparatus contained in its own structure the elements of failure1 444 as they require the machines to do too much and the powder too little of the work1 thus contradicting the fundamental principles upon which all labor-saving machinery is framed 444 ,i could only look upon it as a misapplication of mechanical genius4 ,illustration3 ,figure #f4--;,,hoosac ,,tunnel4 ,flash-powder photograph of ,burleigh drills at the working face4 7,photo courtesy of ,state ,library1 ,commonwealth of ,massachusetts47 ,latrobe stated the basic philosophy of rock-tunnel work4 ,no mechanical agent has ever been able to improve upon the efficiency of explosives for the shattering of rock4 ,for this reason1 the logical application of machinery to tunneling was not in replacing or altering the fundamental process itself1 but in enabling it to be conducted with greater speed by mechanically drilling the blasting holes to receive the explosive4 ,actual work on the ,hoosac ,tunnel began at both ends of the tunnel in about #ahed1 but without much useful effect until #aheh when a contract was let to the renowned civil engineer and railroad builder1 ,herman ,haupt of ,philadelphia4 ,haupt immediately resumed investigations of improved tunneling methods1 both full-area machines and mechanical rock drills4 ,at this time mechanical rock-drill technology was in a state beyond1 but not far beyond1 initial experimentation4 ,there existed one workable ,american machine1 the ,fowle drill1 invented in #ahea4 ,it was steam-driven1 and had been used in quarry work1 although apparently not to any commercial extent4 ,however1 it was far too large and cumbersome to find any possible application in tunneling4 ,nevertheless1 it contained in its operating principle1 the seed of a practical rock drill in that the drill rod was attached directly to and reciprocated by a double-acting steam piston4 ,a point of great importance was the independence of its operation on gravity1 permitting drilling in any direction4 ,while experimenting1 ,haupt drove the work onward by the classical methods1 shown in the left-hand section of the model 7fig4 #b74 ,at the far right an advance heading or adit is being formed by pick and hammer work2 this is then deepened into a top heading with enough height to permit hammer drilling1 actually the basic tunneling operation4 ,a team is shown double jacking1 i4e41 using two-handed hammers1 the steel held by a third man4 ,this was the most efficient of the several hand-drilling methods4 ,the top-heading plan was followed so that the bulk of the rock could be removed in the form of a bottom bench1 and the majority of drilling would be downward1 obviously the most effective direction4 ,blasting was with black powder and its commercial variants4 ,some liberty was taken in depicting these steps so that both operations might be shown within the scope of the model3 in practice the heading was kept between #djj and #fjj feet in advance of the bench so that heading blasts would not interfere with the bench work4 ,the bench carriage simply facilitated handling of the blasted rock4 ,it was rolled back during blasts4 ,illustration3 ,figure #g4--;,,hoosac ,,tunnel4 ,,group ,,of ,,miners descending the west shaft with a ,burleigh drill4 7,photo courtesy of ,state ,library1 ,commonwealth of ,massachusetts47 ,the experiments conducted by ,haupt with machine drills produced no immediate useful results4 ,a drill designed by ,haupt and his associate1 ,stuart ,gwynn1 in #aheh bored hard granite at the rate of #e_/h inch per minute1 but was not substantial enough to bear up in service4 ,haupt left the work in #ahfa1 victim of intense political pressures and totally unjust accusations of corruption and mismanagement4 ,the work was suspended until taken over by a state commission in #ahfb4 ,despite frightful ineptitude and very real corruption1 this period was exceedingly important in the long history both of ,hoosac ,tunnel and of rock tunneling in general4 ,the merely routine criticism of the project had by this time become violent due to the inordinate length of time already elapsed and the immense cost1 compared to the small portion of work completed4 ,this served to generate in the commission a strong sense of urgency to hurry the project along4 ,charles ,s4 ,storrow1 a competent engineer1 was sent to ,europe to report on the progress of tunneling there1 and in particular on mechanization at the ,mont ,cenis ,tunnel then under construction between ,france and ,italy4 ,germain ,sommeiller1 its chief engineer1 had1 after experimentation similar to ,haupt's1 invented a reasonably efficient drilling machine which had gone into service at ,mont ,cenis in ,march #ahfa4 ,it was a distinct improvement over hand drilling1 almost doubling the drilling rate1 but was complex and highly unreliable4 ,two hundred drills were required to keep #af drills at work4 ,but the vital point in this was the fact that ,sommeiller drove his drills not with steam1 but air1 compressed at the tunnel portals and piped to the work face4 ,it was this single factor1 one of application rather than invention1 that made the mechanical drill feasible for tunneling4 ,all previous effort in the field of machine drilling1 on both sides of the ,atlantic1 had been directed toward steam as the motive power4 ,in deep tunnels1 with ventilation already an inherent problem1 the exhaust of a steam drill into the atmosphere was inadmissible4 ,further1 steam could not be piped over great distances due to serious losses of energy from radiation of heat1 and condensation4 ,steam generation within the tunnel itself was obviously out of the question4 ,it was the combination of a practical drill1 and the parallel invention by ,sommeiller of a practical air compressor that resulted in the first workable application of machine rock drilling to tunneling4 ,illustration3 ,figures #h #i4--;,,hoosac ,,tunnel4 ,,contemporary ,,engravings4 ,as such large general areas could not be sufficiently illuminated for photography1 the ,museum model was based primarily on artists' versions of the work4 7,science ,record1 #ahgb2 ,leslie's ,weekly1 #ahgc47 ,the ,sommeiller drills greatly impressed ,storrow1 and his report of ,november #ahfb strongly favored their adoption at ,hoosac4 ,it is curious however1 that not a single one was brought to the ,u4,s41 even on trial4 ,storrow does speak of ,sommeiller's intent to keep the details of the machine to himself until it had been further improved1 with a view to its eventual exploitation4 ,the fact is1 that although workable1 the ,sommeiller drill proved to be a dead end in rock-drill development because of its many basic deficiencies4 ,it did exert the indirect influence of inspiration which1 coupled with a pressing need for haste1 led to renewed trials of drilling machinery at ,hoosac4 ,thomas ,doane1 chief engineer under the state commission1 carried this program forth with intensity1 seeking and encouraging inventors1 and himself working on the problem4 ,the pattern of the ,sommeiller drill was generally followed2 that is1 the drill was designed as a separate1 relatively light mechanical element1 adapted for transportation by several miners1 and attachable to a movable frame or carriage during operation4 ,air was of course the presumed power4 ,to be effective1 it was necessary that a drill automatically feed the drill rod as the hole deepened1 and also rotate the rod automatically to maintain a round1 smooth hole4 ,extreme durability was essential1 and usually proved the source of a machine's failure4 ,the combination of these characteristics into a machine capable of driving the drill rod into the rock with great force1 perhaps five times per second1 was a severe test of ingenuity and materials4 ,doane in #ahfd had three different experimental drills in hand1 as well as various steam and water-powered compressors4 ,success finally came in #ahfe with the invention of a drill by ,charles ,burleigh1 a mechanical engineer at the well-known ,putnam ,machine ,works of ,fitchburg1 ,massachusetts4 ,the drills were first applied in the east heading in ,june of #ahff4 ,although working well1 their initial success was limited by lack of reliability and a resulting high expense for repairs4 ,they were described as having several weakest points4 ,in ,november1 these drills were replaced by an improved ,burleigh drill which was used with total success to the end of the work4 ,the era of modern rock tunneling was thus launched by ,sommeiller's insight in initially applying pneumatic power to a machine drill1 by ,doane's persistence in searching for a thoroughly practical drill1 and by ,burleigh's mechanical talent in producing one4 ,the desperate need to complete the ,hoosac ,tunnel may reasonably be considered the greatest single spur to the development of a successful drill4 ,the significance of this invention was far reaching4 ,burleigh's was the first practical mechanical rock drill in ,america and1 in view of its dependability1 efficiency1 and simplicity when compared to the ,sommeiller drill1 perhaps in the world4 ,the ,burleigh drill achieved success almost immediately4 ,it was placed in production by ,putnam for the ,burleigh ,rock ,drill ,company before completion of ,hoosac in #ahgf1 and its use spread throughout the western mining regions and other tunnel works4 ,for a major invention1 its adoption was1 in relative terms1 instantaneous4 ,it was the prototype of all succeeding piston-type drills1 which came to be known generically as burleighs1 regardless of manufacture4 ,walter ,shanley1 the ,canadian contractor who ultimately completed the ,hoosac1 reported in #ahgj1 after the drills had been in service for a sufficient time that the techniques for their most efficient use were fully understood and effectively applied1 that the ,burleigh drills saved about half the drilling costs over hand drilling4 ,the per-inch cost of machine drilling averaged #e4e cents1 all inclusive1 vs4 #aa4b cents for handwork4 ,the more important point1 that of speed1 is shown by the reports of average monthly progress of the tunnel itself1 before and after use of the air drills4 ,year ,average monthly progress in feet #ahfe #ee #ahff #dh #ahfg #ii #ahfh -- #ahfi #ach #ahgj #abf #ahga #ade #ahgb #abd ,illustration3 ,figure #aj4--,,trinitroglycerine ,,blast at ,hoosac ,tunnel4 7,leslie's ,weekly1 #ahgc47 ,the right portion of the model 7fig4 #c7 represents the workings during the final period4 ,the bottom heading system was generally used after the ,burleigh drills had been introduced4 ,four to six drills were mounted on a carriage designed by ,doane4 ,these drove the holes for the first blast in the center of the heading in about six hours4 ,the full width of the heading1 the #bd-;foot width of the tunnel1 was then drilled and blasted out in two more stages4 ,as in the early section1 the benches to the rear were later removed to the full-tunnel height of about #bj feet4 ,this operation is shown by a single drill 7fig4 #d7 mounted on a screw column4 ,three #h-;hour shifts carried the work forward3 drilling occupied half the time and half was spent in running the carriage back1 blasting1 and mucking 7clearing the broken rock74 ,illustration3 ,figure #aa4--;,,hoosac ,,tunnel survey crew at engineering office4 ,the highest accuracy of the aboveground and underground survey work was required to insure proper vertical and horizontal alignment and meeting of the several separately driven sections4 7,photo courtesy of ,state ,library1 ,commonwealth of ,massachusetts47 ,the tunnel's #ajbh-;foot central shaft1 completed under the ,shanley contract in #ahgj to provide two additional work faces as well as a ventilation shaft is shown at the far right side of this half of the model4 ,completed so near the end of the project1 only #ae percent of the tunnel was driven from the shaft4 ,the enormous increase in rate of progress was not due entirely to machine drilling4 ,from the outset of his jurisdiction1 ,doane undertook experiments with explosives as well as drills1 seeking an agent more effective than black powder4 ,in this case1 the need for speed was not the sole stimulus4 ,as the east and west headings advanced further and further from the portals1 the problem of ventilation grew more acute1 and it became increasingly difficult to exhaust the toxic fumes produced by the black powder blasts4 ,in #ahff1 ,doane imported from ,europe a sample of trinitroglycerine1 the liquid explosive newly introduced by ,nobel1 known in ,europe as glonoin oil and in the ,united ,states as nitroglycerine4 ,it already had acquired a fearsome reputation from its tendency to decompose with heat and age and to explode with or without the slightest provocation4 ,nevertheless1 its tremendous power and characteristic of almost complete smokelessness led ,doane to employ the chemist ,george ,w4 ,mowbray1 who had blasted for ,drake in the ,pennsylvania oil fields1 to develop techniques for the bulk manufacture of the new agent and for its safe employment in the tunnel4 ,mowbray established a works on the mountain and shortly developed a completely new blasting practice based on the explosive4 ,its stability was greatly increased by maintaining absolute purity in the manufacturing process4 ,freezing the liquid to reduce its sensitivity during transport to the headings1 and extreme caution in its handling further reduced the hazard of its use4 ,at the heading1 the liquid was poured into cylindrical cartridges for placement in the holes4 ,as with the ,burleigh drill1 the general adoption of nitroglycerine was immediate once its qualities had been demonstrated4 ,the effect on the work was notable4 ,its explosive characteristics permitted fewer blast holes over a given frontal area of working face1 and at the same time it was capable of effectively blowing from a deeper drill hole1 #db inches against #cj inches for black powder1 so that under ideal conditions #dj percent more tunnel length was advanced per cycle of operations4 ,a new fuse and a system of electric ignition were developed which permitted simultaneous detonation and resulted in a degree of effectiveness impossible with the powder train and cord fusing used with the black powder4 ,over a million pounds of nitroglycerine were produced by ,mowbray between #ahff and completion of the tunnel4 ,illustration3 ,figure #ab4--,,works ,,at ,,the ,,central ,,shaft1 ,,hoosac ,,tunnel1 for hoisting1 pumping and air compressing machinery1 and general repair1 #ahga4 7,photo courtesy of ,state ,library1 ,commonwealth of ,massachusetts47 ,illustration3 ,figure #ac4--;,,hoosac ,,tunnel4 ,,air-,,compressor ,,building on ,hoosac ,river near ,north ,adams4 ,the compressors were driven partially by waterpower1 derived from the river4 7,photo courtesy of ,state ,library1 ,commonwealth of ,massachusetts47 ,illustration3 ,figure #ad4--,,west ,,portal ,,of ,,hoosac ,,tunnel before completion1 #ahfh1 showing six rings of lining brick4 7,photo courtesy of ,state ,library1 ,commonwealth of ,massachusetts47 ,when the ,shanleys took the work over in #ahfh1 following political difficulties attending operation by the ,state1 the period of experimentation was over4 ,the tunnel was being advanced by totally modern methods1 and to the present day the overall concepts have remained fundamentally unaltered3 the ,burleigh piston drill has been replaced by the lighter hammer drill2 the ,doane drill carriage by the more flexible jumbo2 nitroglycerine by its more stable descendant dynamite and its alternatives2 and static-electric blasting machines by more dependable magnetoelectric4 ,but these are all in the nature of improvements1 not innovations4 ,unlike the preceding model1 there was good documentation for this one4 ,also1 the ,hoosac was apparently the first ,american tunnel to be well recorded photographically4 ,early flashlight views exist of the drills working at the heading 7fig4 #f7 as well as of the portals1 the winding and pumping works at the central shaft1 and much of the machinery and associated aspects of the project4 ,these and copies of drawings of much of ,doane's experimental apparatus1 a rare technological record1 are preserved at the ,massachusetts ,state ,library4 ,soft-,ground ,tunneling ,so great is the difference between hard-rock and soft-ground tunneling that they constitute two almost separate branches of the field4 ,in penetrating ground lacking the firmness or cohesion to support itself above an opening1 the miner's chief concern is not that of removing the material1 but of preventing its collapse into his excavation4 ,the primitive methods depending upon brute strength and direct application of fire and human force were suitable for assault on rock1 but lacked the artifice needed for delving into less stable material4 ,roman engineers were accomplished in spanning subterranean ways with masonry arches1 but apparently most of their work was done by cut-and-cover methods rather than by actual mining4 ,not until the ,middle ,ages did the skill of effectively working openings in soft ground develop1 and not until the ,renaissance was this development so consistently successful that it could be considered a science4 ,,renaissance ,,mining ,from the earliest periods of rock working1 the quest for minerals and metals was the primary force that drove men underground4 ,it was the technology of mining1 the product of slow evolution over the centuries1 that became the technology of the early tunnel1 with no significant modification except in size of workings4 ,every aspect of #afth century mining is definitively detailed in ,georgius ,agricola's remarkable ,de re ,metallica1 first published in ,basel in #aeef4 ,during its time of active influence1 which extended for two centuries1 it served as the authoritative work on the subject4 ,it remains today an unparalleled early record of an entire branch of technology4 ,the superb woodcuts of mine workings and tools in themselves constitute a precise description of the techniques of the period1 and provided an ideal source of information upon which to base the first model in the soft-ground series4 ,illustration3 ,figure #ae4--;,,centering ,,for ,,placement ,,of ,,finished ,,stonework at west portal1 #ahgd4 ,at top-right are the sheds where the lining brick was produced4 7,photo courtesy of ,state ,library1 ,commonwealth of ,massachusetts47 ,the model1 representing a typical ,european mine1 demonstrates the early use of timber frames or sets to support the soft material of the walls and roof4 ,in areas of only moderate instability1 the sets alone were sufficient to counteract the earth pressure1 and were spaced according to the degree of support required4 ,in more extreme conditions1 a solid lagging of small poles or boards was set outside the frames1 as shown in the model1 to provide absolute support of the ground4 ,details of the framing1 the windlass1 and all tools and appliances were supplied by ,agricola1 with no need for interpretation or interpolation4 ,the basic framing pattern of sill1 side posts and cap piece1 all morticed together1 with lagging used where needed1 was translated unaltered into tunneling practice1 particularly in small exploratory drifts4 ,it remained in this application until well into the #bjth century4 ,the pressure exerted upon tunnels of large area was countered during construction by timbering systems of greater elaboration1 evolved from the basic one4 ,by the time that tunnels of section large enough to accommodate canals and railways were being undertaken as matter-of-course civil engineering works1 a series of nationally distinguishable systems had emerged1 each possessing characteristic points of favor and fault4 ,as might be suspected1 the ,english system of tunnel timbering1 for instance1 was rarely applied on the ,continent1 nor were the ,german1 ,austrian or ,belgian systems normally seen in ,great ,britain4 ,all were used at one time or another in this country1 until the ,american system was introduced in about #ahee4 ,while the timbering commonly remained in place in mines1 it would be followed up by permanent masonry arching and lining in tunnel work4 ,overhead in the museum ,hall of ,civil ,engineering are frames representing the ,english1 ,austrian and ,american systems4 ,nearby1 a series of small relief models 7fig4 #ai7 is used to show the sequence of enlargement in a soft-ground railroad tunnel of about #ahee1 using the ,austrian system4 ,temporary timber support of tunnels fell from use gradually after the advent of shield tunneling in conjunction with cast-iron lining4 ,this formed a perfect support immediately behind the shield1 as well as the permanent lining of the tunnel4 ,,brunel',s ,,thames ,,tunnel ,the interior surfaces of tunnels through ground merely unstable are amenable to support by various systems of timbering and arching4 ,this becomes less true as the fluidity of the ground increases4 ,the soft material which normally comprises the beds of rivers can approach an almost liquid condition resulting in a hydraulic head from the overbearing water sufficient to prevent the driving of even the most carefully worked drift1 supported by simple timbering4 ,the basic defect of the timbering systems used in mining and tunneling was that there was inevitably a certain amount of the face or ceiling unsupported just previous to setting a frame1 or placing over it the necessary section of lagging4 ,in mine work1 runny soil could1 and did1 break through such gaps1 filling the working4 ,for this reason1 there were no serious attempts made before #ahbe to drive subaqueous tunnels4 ,in that year1 work was started on a tunnel under the ,thames between the ,rotherhithe and ,wapping sections of ,london1 under guidance of the already famous engineer ,marc ,isambard ,brunel 7#agfi-ahdi71 father of ,i4 ,k4 ,brunel4 ,the undertaking is of great interest in that ,brunel employed an entirely novel apparatus of his own invention to provide continuous and reliable support of the soft water-bearing clay which formed the riverbed4 ,by means of this shield1 ,brunel was able to drive the world's first subaqueous tunnel4#c ,illustration3 ,figure #af4--,,west ,,portal ,,upon ,,completion1 #ahgf4 7,photo courtesy of ,new-,york ,historical ,society47 ,the shield was of cast-iron1 rectangular in elevation1 and was propelled forward by jackscrews4 ,shelves at top1 bottom1 and sides supported the tunnel roof1 floor1 and walls until the permanent brick lining was placed4 ,the working face1 the critical area1 was supported by a large number of small breasting boards1 held against the ground by small individual screws bearing against the shield framework4 ,the shield itself was formed of #ab separate frames1 each of which could be advanced independently of the others4 ,the height was #bb feet #c inches3 the width #cg feet #f inches4 ,the progress was piecemeal4 ,in operation the miners would remove one breasting board at a time1 excavate in front of it1 and then replace it in the advanced position--about #f inches forward4 ,this was repeated with the next board above or below1 and the sequence continued until the ground for the entire height of one of the #ab sections had been removed4 ,the board screws for that section were shifted to bear on the adjacent frames1 relieving the frame of longitudinal pressure4 ,it could then be screwed forward by the amount of advance1 the screws bearing to the rear on the completed masonry4 ,thus1 step by step the tunnel progressed slowly1 the greatest weekly advance being #ad feet4 ,in the left-hand portion of the model is the shaft sunk to begin operations2 here also is shown the bucket hoist for removing the spoil4 ,the ,v-type steam engine powering the hoist was designed by ,brunel4 ,at the right of the main model is an enlarged detail of the shield1 actually an improved version built in #ahce4 ,the work continued despite setbacks of every sort4 ,the financial ones need no recounting here4 ,technically1 although the shield principle proved workable1 the support afforded was not infallible4 ,four or five times the river broke through the thin cover of silt and flooded the workings1 despite the utmost caution in excavating4 ,when this occurred1 masses of clay1 sandbags1 and mats were dumped over the opening in the riverbed to seal it1 and the tunnel pumped out4 ,i4 ,k4 ,brunel acted as superintendent and nearly lost his life on a number of occasions4 ,after several suspensions of work resulting from withdrawal or exhaustion of support1 one lasting seven years1 the work was completed in #ahdc4 ,despite the fact that ,brunel had1 for the first time1 demonstrated a practical method for tunneling in firm and water-bearing ground1 the enormous cost of the work and the almost overwhelming problems encountered had a discouraging effect rather than otherwise4 ,not for another quarter of a century was a similar project undertaken4 ,the ,thames ,tunnel was used for foot and light highway traffic until about #ahgj when it was incorporated into the ,london ,underground railway system1 which it continues to serve today4 ,the roofed-over top sections of the two shafts may still be seen from the river4 ,a number of contemporary popular accounts of the tunnel exist1 but one of the most thorough and interesting expositions on a single tunnel work of any period is ,henry ,law's ,a ,memoir of the ,thames ,tunnel1 published in #ahde-ahdf by ,john ,weale4 ,law1 an eminent civil engineer1 covers the work in incredible detail from its inception until the major suspension in late #ahbh when slightly more than half completed4 ,the most valuable aspect of his record is a series of plates of engineering drawings of the shield and its components1 which1 so far as is known1 exist nowhere else4 ,these formed the basis of the enlarged section of the shield1 shown to the right of the model of the tunnel itself4 ,a vertical section through the shield is reproduced here from ,law for comparison with the model 7figs4 #ba and #bc74 ,illustration3 ,figure #ag4--,,soft-,,ground ,,tunneling4 ,the support of walls and roof of mine shaft by simple timbering2 #afth century4 ,,mht model--#c_/d scale4 7,smithsonian photo #dibfj-;,j47 ,illustration3 ,figure #ah4--,,soft-,,ground ,,tunneling4 ,the model of a #afth century mine in the ,museum of ,history and ,technology was constructed from illustrations in such works as ,g4 ,e4 von ,loehneyss' ,bericht vom ,bergwerck1 #afij1 as well as the better known ones from ,de re ,metallica4 ,illustration3 ,figure #ai4--,,the ,,successive ,,stages in the enlargement of a mid-#aith century railroad tunnel1 using the ,austrian system of timbering4 ,,mht model4 ,illustration3 ,figure #bj4--,m4 ,i4 ,,brunel',s ,,thames ,,tunnel1 #ahbe-ahdc1 the first driven beneath a body of water4 ,,mht model--#a_/d scale4 7,smithsonian photo #dibfj-;,f47 ,,the ,,tower ,,subway ,various inventors attempted to improve upon the ,brunel shield1 aware of the fundamental soundness of the shield principle4 ,almost all bypassed the rectangular sectional construction used in the ,thames ,tunnel1 and took as a starting point a sectional shield of circular cross section1 advanced by ,brunel in his original patent of #ahah4 ,james ,henry ,greathead 7#ahdd-ahif71 rightfully called the father of modern subaqueous tunneling1 surmised in later years that ,brunel had chosen a rectangular configuration for actual use1 as one better adapted to the sectional type of shield4 ,the ,english civil engineer1 ,peter ,w4 ,barlow1 in #ahfd and #ahfh patented a circular shield1 of one piece1 which was the basis of one used by him in constructing a small subway of #acej feet beneath the ,thames in #ahfi1 the first work to follow the lead of ,brunel4 ,greathead1 acting as ,barlow's contractor1 was the designer of the shield actually used in the work1 but it was obviously inspired by ,barlow's patents4 ,the reduction of the multiplicity of parts in the ,brunel shield to a single rigid unit was of immense advantage and an advance perhaps equal to the shield concept of tunneling itself4 ,the ,barlow-,greathead shield was like the cap of a telescope with a sharpened circular ring on the front to assist in penetrating the ground4 ,the diaphragm functioned1 as did ,brunel's breasting boards1 to resist the longitudinal earth pressure of the face1 and the cylindrical portion behind the diaphragm bore the radial pressure of roof and walls4 ,here also for the first time1 a permanent lining formed of cast-iron segments was used1 a second major advancement in soft-ground tunneling practice4 ,not only could the segments be placed and bolted together far more rapidly than masonry lining could be laid up1 but unlike the green masonry1 they could immediately bear the full force of the shield-propelling screws4 ,barlow1 capitalizing on ,brunel's error in burrowing so close to the riverbed1 maintained an average cover of #cj feet over the tunnel1 driving through a solid stratum of firm ,london clay which was virtually impervious to water4 ,as the result of this1 combined with the advantages of the solid shield and the rapidly placed iron lining1 the work moved forward at a pace and with a facility in startling contrast to that of the ,thames ,tunnel1 although in fairness it must be recalled that the face area was far less4 ,the clay was found sufficiently sound that it could be readily excavated without the support of the diaphragm1 and normally three miners worked in front of the shield1 digging out the clay and passing it back through a doorway in the plate4 ,this could be closed in case of a sudden settlement or break in4 ,following excavation1 the shield was advanced #ah inches into the excavated area by means of #f screws1 and a ring of lining segments #ah inches in length bolted to the previous ring under cover of the overlapping rear skirt of the shield4 ,the small annular space left between the outside of the lining and the clay by the thickness and clearance of the skirt--about an inch--was filled with thin cement grout4 ,the tunnel was advanced #ah inches during each #h-;hour shift4 ,the work continued around the clock1 and the #ijj-;foot river section was completed in only #ad weeks4#d ,the entire work was completed almost without incident in just under a year1 a remarkable performance for the world's second subaqueous tunnel4 ,illustration3 ,figure #ba4--;,,enlarged ,,detail of ,brunel's tunneling shield1 vertical section4 ,the first two and part of the third of the twelve frames are shown4 ,to the left is the tunnel's completed brick lining and to the right1 the individual breasting boards and screws for supporting the face4 ,the propelling screws are seen at top and bottom1 bearing against the lining4 ,three miners worked in each frame1 one above the other4 ,,mht model--#c_/d scale4 7,smithsonian photo #dibfj-;,g47 ,illustration3 ,figure #bb4--;,,broadside ,,published ,,after ,,commencement ,,of ,,work on the ,thames ,tunnel1 #ahbg4 7,,mht collections47 ,,open ,,to ,,the ,,public ,,every ,,day 7,sundays excepted7 from ,seven in the ,morning1 until ,eight in the ,evening1 ,,the ,,thames ,,tunnel4 ,fig4 #a shows a transverse section of the ,thames1 and beneath it a longitudinal section of the ,tunnel1 as it will be when completed2 with the ascents in the inclinations in which they will be finished4 ,fig4 #b shows the two arched entrances of the ,tunnel from the shaft4 ,fig4 #c is a representation of the iron shield1 and shows a workman in each of the compartments4 ,the ,entrance to the ,tunnel is near to ,rotherhithe ,church1 and nearly opposite to the ,london-,docks4 ,the nearest landing place from the river is ,church ,stairs4 ,the ,greenwich and ,deptford coaches which go the lower road1 start hourly from ,charing-cross1 and ,gracechurch-street1 and pass close by the works at ,rotherhithe4 ,books relative to the ,tunnel may be had at the works4 ,the ,public may view the ,tunnel every day 7,sundays excepted7 from ,seven in the morning until ,eight in the ,evening1 upon payment of ,one ,shilling each ,person4 ,the extreme northern end of the ,tunnel is for the present secured by a strong wall2 but visitors will find a dry1 warm1 and gravelled promenade1 as far as to almost the centre of the river1 and brilliantly lighted with oil gas4 ,the entrance is from ,rotherhithe ,street1 and by a safe1 commodious1 and easy stair case4 ,h4 ,teape ,son1 ,printers1 ,tower-hill1 ,london4 ,illustration3 ,figure #bc4--,,vertical ,,section ,,through ,,brunel',s ,,shield4 ,the long lever1 x1 supported the wood centering for turning the masonry arches of the lining4 7,,law1 ,a ,memoir of the ,thames ,tunnel47 ,illustration3 ,figure #bd4--,,thames ,,tunnel4 ,,section ,,through riverbed and tunnel following one of the break-throughs of the river4 ,inspection of the damage with a diving bell4 7,,beamish1 ,a ,memoir of the ,life of ,sir ,marc ,isambard ,brunel47 ,the ,tower ,subway at first operated with cylindrical cars that nearly filled the #g-;foot bore2 the cars were drawn by cables powered by small steam engines in the shafts4 ,this mode of power had previously been used in passenger service only on the ,greenwich ,street elevated railway in ,new ,york4 ,later the cars were abandoned as unprofitable and the tunnel turned into a footway 7fig4 #cb74 ,this small tunnel1 the successful driving due entirely to ,greathead's skill1 was the forerunner of the modern subaqueous tunnel4 ,in it1 two of the three elements essential to such work thereafter were first applied3 the one-piece movable shield of circular section1 and the segmental cast-iron lining4 ,the documentation of this work is far thinner than for the ,thames ,tunnel4 ,the most accurate source of technical information is a brief historical account in ,copperthwaite's classic ,tunnel ,shields and the ,use of ,compressed ,air in ,subaqueous ,works1 published in #aijf4 ,copperthwaite1 a successful tunnel engineer1 laments the fact that he was able to turn up no drawing or original data on this first shield of ,greathead's1 but he presents a sketch of it prepared in the ,greathead office in #ahie1 which is presumably a fair representation 7fig4 #cc74 ,the ,tower ,subway model was built on the basis of this and several woodcuts of the working area that appeared contemporaneously in the illustrated press4 ,in this and the adjacent model of ,beach's ,broadway ,subway1 the tunnel axis has been placed on an angle to the viewer1 projecting the bore into the case so that the complete circle of the working face is included for a more suggestive effect4 ,this was possible because of the short length of the work included4 ,henry ,s4 ,drinker1 also a tunnel engineer and author of the most comprehensive work on tunneling ever published1 treats rock tunneling in exhaustive detail up to #ahgh4 ,his notice of what he terms submarine tunneling is extremely brief4 ,he does1 however1 draw a most interesting comparison between the first ,thames ,tunnel1 built by ,brunel1 and the second1 built by ,greathead #bf years later3 ,,first ,,thames ,,tunnel ,,second ,,thames ,,tunnel 7,,tower ,,subway7 ,brickwork lining1 #ch feet ,cast-iron lining of #h feet wide by #bb-a_/b feet high4 outside diameter4 #abj-ton cast-iron shield1 #b-a_/b-ton1 wrought-iron shield1 accommodating #cf miners4 accommodating at most #c men4 ,workings filled by irruption ,water encountered at almost of river five times4 any time could have been gathered in a stable pail4 ,eighteen years elapsed between ,work completed in about start and finish of work4 eleven months4 ,cost3 #c1jjj1jjj4 ,cost3 #ajj1jjj4 ,illustration3 ,figure #be4--,,transverse ,,section ,,through ,,shield1 after inundation4 ,such disasters1 as well as the inconsistency of the riverbed's composition1 seriously disturbed the alignment of the shield's individual sections4 7,,law1 ,a ,memoir of the ,thames ,tunnel47 ,illustration3 ,figure #bf4--,,longitudinal ,,section ,,through ,,thames ,,tunnel after sandbagging to close a break in the riverbed4 ,the tunnel is filled with silt and water4 7,,law1 ,a ,memoir of the ,thames ,tunnel47 ,illustration3 ,figure #bg4--;,,interior ,,of ,,the ,,thames ,,tunnel shortly after completion in #ahdc4 7,photo courtesy of ,new ,york ,public ,library ,picture ,collection47 ,illustration3 ,figure #bh4--,,thames ,,tunnel in use by ,london ,underground railway4 7,illustrated ,london ,news1 #ahfi87 ,illustration3 ,figure #bi4--,,placing ,a segment of cast-iron lining in ,greathead's ,tower ,subway1 #ahfi4 ,to the rear is the shield's diaphragm or bulkhead4 ,,mht model--#a-a_/b scale4 7,smithsonian photo #dibfj-;,b47 ,,beach',s ,,broadway ,,subway ,almost simultaneously with the construction of the ,tower ,subway1 the first ,american shield tunnel was driven by ,alfred ,ely ,beach 7#ahbf-ahif74 ,beach1 as editor of the ,scientific ,american and inventor of1 among other things1 a successful typewriter as early as #ahef1 was well known and respected in technical circles4 ,he was not a civil engineer1 but had become concerned with ,new ,york's pressing traffic problem 7even then7 and as a solution1 developed plans for a rapid-transit subway to extend the length of ,broadway4 ,he invented a shield as an adjunct to this system1 solely to permit driving of the tunnel without disturbing the overlying streets4 ,an active patent attorney as well1 ,beach must certainly have known of and studied the existing patents for tunneling shields1 which were1 without exception1 ,british4 ,in certain aspects his shield resembled the one patented by ,barlow in #ahfd1 but never built4 ,however1 work on the ,beach tunnel started in #ahfi1 so close in time to that on the ,tower ,subway1 that it is unlikely that there was any influence from that source4 ,beach had himself patented a shield1 in ,june #ahfi1 a two-piece1 sectional design that bore no resemblance to the one used4 ,his subway plan had been first introduced at the #ahfg fair of the ,american ,institute in the form of a short plywood tube through which a small1 close-fitting car was blown by a fan4 ,the car carried #ab passengers4 ,sensing opposition to the subway scheme from ,tammany1 in #ahfh ,beach obtained a charter to place a small tube beneath ,broadway for transporting mail and small packages pneumatically1 a plan he advocated independently of the passenger subway4 ,illustration3 ,figure #cj4--;,,contemporary ,,illustrations of ,tower ,subway works used as basis of the model in the ,museum of ,history and ,technology4 7,illustrated ,london ,news1 #ahfi47 ,,advancing ,,the ,,shield4 ,,fitting ,,the ,,castings4 ,illustration3 ,figure #ca4--;,,excavation ,,in ,,front ,,of ,,shield1 ,tower ,subway4 ,this was possible because of the stiffness of the clay encountered4 ,,mht model--front of model shown in fig4 #bi4 7,smithsonian photo #dibfj-;,a47 ,under this thin pretense of legal authorization1 the sub-rosa excavation began from the basement of a clothing store on ,warren ,street near ,broadway4 ,the #h-;foot-diameter tunnel ran eastward a short distance1 made a #ij-;degree turn1 and thence southward under ,broadway to stop a block away under the south side of ,murray ,street4 ,the total distance was about #cab feet4 ,work was carried on at night in total secrecy1 the actual tunneling taking #eh nights4 ,at the ,warren ,street terminal1 a waiting room was excavated and a large ,roots blower installed for propulsion of the single passenger car4 ,the plan was similar to that used with the model in #ahfg3 the cylindrical car fitted the circular tunnel with only slight circumferential clearance4 ,the blower created a plenum within the waiting room and tunnel area behind the car of about #j4be pounds per square inch1 resulting in a thrust on the car of almost a ton1 not accounting for blowby4 ,the car was thus blown along its course1 and was returned by reversing the blower's suction and discharge ducts to produce an equivalent vacuum within the tunnel4 ,illustration3 ,figure #cb4--;,,interior ,,of ,,completed ,,tower ,,subway4 7,,thornbury1 ,old and ,new ,london1 #ahhg1 vol4 #a1 p4 #abf47 ,the system opened in ,february of #ahgj and remained in operation for about a year4 ,beach was ultimately subdued by the hostile influences of ,boss ,tweed1 and the project was completely abandoned4 ,within a very few more years the first commercially operated elevated line was built1 but the subway did not achieve legitimate status in ,new ,york until the opening of the ,interborough line in #aijd4 ,ironically1 its route traversed ,broadway for almost the length of the island4 ,illustration3 ,figure #cc4--,,vertical ,,section through the ,greathead shield used at the ,tower ,subway1 #ahfi4 ,the first one-piece shield of circular section4 7,,copperthwaite1 ,tunnel ,shields and the ,use of ,compressed ,air in ,subaqueous ,works47 ,the ,beach shield operated with perfect success in this brief trial1 although the loose sandy soil encountered was admittedly not a severe test of its qualities4 ,no diaphragm was used2 instead a series of #h horizontal shelves with sharpened leading edges extended across the front opening of the shield4 ,the outstanding feature of the machine was the substitution for the propelling screws used by ,brunel and ,greathead of #ah hydraulic rams1 set around its circumference4 ,these were fed by a single hand-operated pump1 seen in the center of figure #cd4 ,by this means the course of the shield's forward movement could be controlled with a convenience and precision not attainable with screws4 ,vertical and horizontal deflection was achieved by throttling the supply of water to certain of the rams1 which could be individually controlled1 causing greater pressure on one portion of the shield than another4 ,this system has not changed in the ensuing time1 except1 of course1 in the substitution of mechanically produced hydraulic pressure for hand4 ,illustration3 ,figure #cd4--;,,beach',s ,broadway ,subway4 ,advancing the shield by hydraulic rams1 #ahfi4 ,,mht model--#a-a_/b scale4 7,smithsonian photo #dibfj-;,e47 ,illustration3 ,figure #ce4--,,vertical ,,section through the ,beach shield used on the ,broadway ,subway1 showing the horizontal shelves 7,c71 iron cutting ring 7,b71 hydraulic rams 7,d71 hydraulic pump 7,f71 and rear protective skirt 7,h74 7,scientific ,american1 ,march #e1 #ahgj47 ,unlike the driving of the ,tower ,subway1 no excavation was done in front of the shield4 ,rather1 the shield was forced by the rams into the soil for the length of their stroke1 the material which entered being supported by the shelves4 ,this was removed from the shelves and hauled off4 ,the ram plungers then were withdrawn and a #af-;inch length of the permanent lining built up within the shelter of the shield's tail ring4 ,against this1 the rams bore for the next advance4 ,masonry lining was used in the straight section2 cast-iron in the curved4 ,the juncture is shown in the model4 ,illustration3 ,figure #cf4--;,,interior of ,beach ,subway showing iron lining on curved section and the pneumatically powered passenger car4 ,view from waiting room4 7,scientific ,american1 ,march #e1 #ahgj47 ,enlarged versions of the ,beach shield were used in a few tunnels in the ,midwest in the early #ahgj's1 but from then until #ahhf the shield method1 for no clear reason1 again entered a period of disuse finding no application on either side of the ,atlantic despite its virtually unqualified proof at the hands of ,greathead and ,beach4 ,little precise information remains on this work4 ,the ,beach system of pneumatic transit is described fully in a well-illustrated booklet published by him in ,january #ahfh1 in which the ,american ,institute model is shown1 and many projected systems of pneumatic propulsion as well as of subterranean and subaqueous tunneling described4 ,beach again 7presumably7 is author of the sole contemporary account of the ,broadway ,subway1 which appeared in ,scientific ,american following its opening early in #ahgj4 ,included are good views of the tunnel and car1 of the shield in operation1 and1 most important1 a vertical sectional view through the shield 7fig4 #ce74 ,it is interesting to note that optical surveys for maintenance of the course apparently were not used4 ,the article illustrated and described the driving each night of a jointed iron rod up through the tunnel roof to the street1 twenty or so feet above1 for testing the position4 ,,the ,,first ,,hudson ,,river ,,tunnel ,despite the ultimate success of ,brunel's ,thames ,tunnel in #ahdc1 the shield in that case afforded only moderately reliable protection because of the fluidity of the soil driven through1 and its tendency to enter the works through the smallest opening in the shield's defense4 ,an ,english doctor who had made physiological studies of the effects on workmen of the high air pressure within diving bells is said to have recommended to ,brunel in #ahbh that he introduce an atmosphere of compressed air into the tunnel to exclude the water and support the work face4 ,this plan was first formally described by ,sir ,thomas ,cochrane 7#agge-ahfj7 in a ,british patent of #ahcj4 ,conscious of ,brunel's problems1 he proposed a system of shaft sinking1 mining1 and tunneling in water-bearing materials by filling the excavated area with air sufficiently above atmospheric pressure to prevent the water from entering and to support the earth4 ,in this1 and his description of air locks for passage of men and materials between the atmosphere and the pressurized area1 ,cochrane fully outlined the essential features of pneumatic excavation as developed since4 ,illustration3 ,figure #cg4--,,the ,,giant ,,roots ,,lobe-,,type ,,blower used for propelling the car4 ,in #ahci1 a ,french engineer first used the system in sinking a mine shaft through a watery stratum4 ,from then on1 the sinking of shafts1 and somewhat later the construction of bridge pier foundations1 by the pneumatic method became almost commonplace engineering practice in ,europe and ,america4 ,not until #ahgi however1 was the system tried in tunneling work1 and then1 as with the shield ten years earlier1 almost simultaneously here and abroad4 ,the first application was in a small river tunnel in ,antwerp1 only #e feet in height4 ,this project was successfully completed relying on compressed air alone to support the earth1 no shield being used4 ,the importance of the work cannot be considered great due to its lack of scope4 ,illustration3 ,figure #ch4--,,testing ,,alignment of the ,broadway ,subway at night by driving a jointed rod up to street level4 7,scientific ,american1 ,march #e1 #ahgj47 ,in #ahga ,dewitt ,c4 ,haskin 7#ahbb-aijj71 a west coast mine and railroad builder1 became interested in the pneumatic caissons then being used to found the river piers of ,eads' ,mississippi ,river bridge at ,st4 ,louis4 ,in apparent total ignorance of the ,cochrane patent1 he evolved a similar system for tunneling water-bearing media1 and in #ahgc proposed construction of a tunnel through the silt beneath the ,hudson to provide rail connection between ,new ,jersey and ,new ,york ,city4 ,illustration3 ,figure #ci4--;,,haskin',s pneumatically driven tunnel under the ,hudson ,river1 #ahhj4 ,in the engine room at top left was the machinery for hoisting1 generating electricity for lighting1 and air compressing4 ,the air lock is seen in the wall of the brick shaft4 ,,mht model--#j4c scale4 7,smithsonian photo #dibfj47 ,illustration3 ,figure #dj4--;,,artist',s ,,conception ,,of ,,miners escaping into the air lock during the blowout in ,haskin's tunnel4 ,it would be difficult to imagine a site more in need of such communication4 ,all lines from the south terminated along the west shore of the river and the immense traffic--cars1 freight and passengers--was carried across to ,manhattan ,island by ferry and barge with staggering inconvenience and at enormous cost4 ,a bridge would have been1 and still is1 almost out of the question due not only to the width of the crossing1 but to the flatness of both banks4 ,to provide sufficient navigational clearance 7without a drawspan71 impracticably long approaches would have been necessary to obtain a permissibly gentle grade4 ,haskin formed a tunneling company and began work with the sinking of a shaft in ,hoboken on the ,new ,jersey side4 ,in a month it was halted because of an injunction by1 curiously1 the ,d ,l ,w ,railroad1 who feared for their vast investment in terminal and marine facilities4 ,not until ,november of #ahgi was the injunction lifted and work again commenced4 ,the shaft was completed and an air lock located in one wall from which the tunnel proper was to be carried forward4 ,it was ,haskin's plan to use no shield1 relying solely on the pressure of compressed air to maintain the work faces and prevent the entry of water4 ,the air was admitted in late ,december1 and the first large-scale pneumatic tunneling operation launched4 ,a single #bf-;foot1 double-track bore was at first undertaken1 but a work face of such diameter proved unmanageable and two oval tubes #ah feet high by #af feet wide were substituted1 each to carry a single track4 ,work went forward with reasonable facility1 considering the lack of precedent4 ,a temporary entrance was formed of sheet-iron rings from the air lock down to the tunnel grade1 at which point the permanent work of the north tube was started4 ,immediately behind the excavation at the face1 a lining of thin wrought-iron plates was built up1 to provide form for the #b-;foot1 permanent brick lining that followed4 ,the three stages are shown in the model in about their proper relationship of progress4 ,the work is shown passing beneath an old timber-crib bulkhead1 used for stabilizing the shoreline4 ,the silt of the riverbed was about the consistency of putty and under good conditions formed a secure barrier between the excavation and the river above4 ,it was easily excavated1 and for removal was mixed with water and blown out through a pipe into the shaft by the higher pressure in the tunnel4 ,about half was left in the bore for removal later4 ,the basic scheme was workable1 but in operation an extreme precision was required in regulating the air pressure in the work area4#e ,it was soon found that there existed an #aa-psi difference between the pressure of water on the top and the bottom of the working face1 due to the #bb-;foot height of the unlined opening4 ,thus1 it was impossible to maintain perfect pneumatic balance of the external pressure over the entire face4 ,it was necessary to strike an average with the result that some water entered at the bottom of the face where the water pressure was greatest1 and some air leaked out at the top where the water pressure was below the air pressure4 ,constant attention was essential3 several men did nothing but watch the behavior of the leaks and adjusted the pressure as the ground density changed with advance4 ,air was supplied by several steam-driven compressors at the surface4 ,the air lock permitted passage back and forth of men and supplies between the atmosphere and the work area1 without disturbing the pressure differential4 ,this principle is demonstrated by an animated model set into the main model1 to the left of the shaft 7fig4 #ci74 ,the variation of pressure within the lock chamber to match the atmosphere or the pressurized area1 depending on the direction of passage1 is clearly shown by simplified valves and gauges1 and by the use of light in varying color density4 ,in the ,haskin tunnel1 #e to #aj minutes were taken to pass the miners through the lock so as to avoid too abrupt a physiological change4 ,despite caution1 a blowout occurred in ,july #ahhj due to air leakage not at the face1 but around the temporary entrance4 ,one door of the air lock jammed and twenty men drowned1 resulting in an inquiry which brought forth much of the distrust with which ,haskin was regarded by the engineering profession4 ,his ability and qualifications were subjected to the bitterest attack in and by the technical press4 ,there is some indication that1 although the project began with a staff of competent engineers1 they were alienated by ,haskin in the course of work and at least one withdrew4 ,haskin's remarks in his own defense indicate that some of the denunciation was undoubtedly justified4 ,and yet1 despite this reaction1 the fundamental merit of the pneumatic tunneling method had been demonstrated by ,haskin and was immediately recognized and freely acknowledged4 ,it was apparent at the same time1 however1 that air by itself did not provide a sufficiently reliable support for large-area tunnel works in unstable ground1 and this remains the only major subaqueous tunnel work driven with air alone4 ,illustration3 ,figure #da4--,,location ,,of ,,hudson ,,river ,,tunnel4 7,leslie's ,weekly1 #ahgi47 ,after the accident1 work continued under ,haskin until #ahhb when funds ran out4 ,about #afjj feet of the north tube and #fjj feet of the south tube had been completed4 ,greathead resumed operations with a shield for a ,british company in #ahhi1 but exhaustion of funds again caused stoppage in #ahia4 ,the tunnel was finally completed in #aijd1 and is now in use as part of the ,hudson and ,manhattan rapid-transit system1 never providing the sought-after rail link4 ,a splendid document of the ,haskin portion of the work is ,s4 ,d4 ,v4 ,burr's ,tunneling ,under the ,hudson ,river published in #ahhe4 ,it is based entirely upon firsthand material and contains drawings of most of the work1 including the auxiliary apparatus4 ,it is interesting to note that electric illumination 7arc1 not incandescent1 lights7 and telephones were used1 unquestionably the first employment of either in tunnel work4 ,illustration3 ,figure #db4--,,st4 ,,clair ,,tunnel4 ,view of front of shield showing method of excavation in firm strata4 ,incandescent electric illumination was used4 #ahhi-ij4 ,,mht model--#a scale4 7,smithsonian photo #dibfj-;,d47 ,,the ,,st4 ,,clair ,,tunnel ,the final model of the soft-ground series reflects1 as did the ,hoosac ,tunnel model for hard-rock tunneling1 final emergence into the modern period4 ,although the ,st4 ,clair ,tunnel was completed over #gj years ago1 it typifies in its method of construction1 the basic procedures of subaqueous work in the present day4 ,the ,thames ,tunnel of ,brunel1 and ,haskin's efforts beneath the ,hudson1 had clearly shown that by themselves1 both the shield and pneumatic systems of driving through fluid ground were defective in practice for tunnels of large area4 ,note that the earliest successful works by each method had been of very small area1 so that the influence of adverse conditions was greatly diminished4 ,the first man to perceive and seize upon the benefits to be gained by combining the two systems was1 most fittingly1 ,greathead4 ,although he had projected the technique earlier1 in driving the underground ,city and ,south ,london ,railway in #ahhf1 he brought together for the first time the three fundamental elements essential for the practical tunneling of soft1 water-bearing ground3 compressed-air support of the work during construction1 the movable shield1 and cast-iron1 permanent lining4 ,the marriage was a happy one indeed2 the limitations of each system were almost perfectly overcome by the qualities of the others4 ,the conditions prevailing in #ahhb at the ,sarnia1 ,ontario1 terminal of the ,grand ,trunk ,railway1 both operational and physical1 were almost precisely the same as those which inspired the undertaking of the ,hudson ,river ,tunnel4 ,the heavy traffic at this vital ,u4,s4--,canada rail interchange was ferried inconveniently across the wide ,st4 ,clair ,river1 and the bank and river conditions precluded construction of a bridge4 ,a tunnel was projected by the railway in that year1 the time when ,haskin's tribulations were at their height4 ,perhaps because of this lack of precedent for a work of such size1 nothing was done immediately4 ,in #ahhd the railway organized a tunnel company2 in #ahhf test borings were made in the riverbed and small exploratory drifts were started across from both banks by normal methods of mine timbering4 ,the natural gas1 quicksand1 and water encountered soon stopped the work4 ,illustration3 ,figure #dc4--,,rear ,,view ,,of ,,st4 ,,clair ,,shield showing the erector arm placing a cast-iron lining segment4 ,the three motions of the arm--axial1 radial1 and rotational1 were manually powered4 7,smithsonian photo #dibfj-;,c47 ,it was at this time that the railway's president visited ,greathead's ,city and ,south ,london workings4 ,the obvious answer to the ,st4 ,clair problem lay in the successful conduct of this subway4 ,joseph ,hobson1 chief engineer of the ,grand ,trunk and of the tunnel project1 in designing a shield1 is said to have searched for drawings of the shields used in the ,broadway and ,tower ,subways of #ahfh-i1 but unable to locate any1 he relied to a limited extent on the small drawings of those in ,drinker's volume4 ,there is no explanation as to why he did not have drawings of the ,city and ,south ,london shield at that moment in use1 unless one considers the rather unlikely possibility that ,greathead maintained its design in secrecy4 ,illustration3 ,figure #dd4--,,opening ,,of ,,the ,,st4 ,,clair ,,tunnel1 #ahia4 7,photo courtesy of ,detroit ,library1 ,burton ,historical ,collection47 ,the ,hobson shield followed ,greathead's as closely as any other1 in having a diaphragm with closable doors1 but a modification of ,beach's sharpened horizontal shelves was also used4 ,however1 these functioned more as working platforms than supports for the earth4 ,the machine was #ba-a_/b feet in diameter1 an unprecedented size and almost twice that of ,greathead's current one4 ,it was driven by #bd hydraulic rams4 ,throughout the entire preliminary consideration of the project there was a marked sense of caution that amounted to what seems an almost total lack of confidence in success4 ,commencement of the work from vertical shafts was planned so that if the tunnel itself failed1 no expenditure would have been made for approach work4 ,in ,april #ahhh1 the shafts were started near both riverbanks1 but before reaching proper depth the almost fluid clay and silt flowed up faster than it could be excavated and this plan was abandoned4 ,after this second inauspicious start1 long open approach cuts were made and the work finally began4 ,the portals were established in the cuts1 several thousand feet back from each bank and there the tunneling itself began4 ,the portions under the shore were driven without air4 ,when the banks were reached1 brick bulkheads containing air locks were built across the opening and the section beneath the river1 about #c1gaj feet long1 driven under air pressure of #aj to #bh pounds above atmosphere4 ,for most of the way1 the clay was firm and there was little air leakage4 ,it was found that horses could not survive in the compressed air1 and so mules were used under the river4 ,in the firm clay1 excavation was carried on several feet in front of the shield1 as shown in the model 7fig4 #db74 ,about twelve miners worked at the face4 ,however1 in certain strata the clay encountered was so fluid that the shield could be simply driven forward by the rams1 causing the muck to flow in at the door openings without excavation4 ,after each advance1 the rams were retracted and a ring of iron lining segments built up1 as in the ,tower ,subway4 ,here1 for the first time1 an erector arm was used for placing the segments1 which weighed about half a ton4 ,in all respects1 the work advanced with wonderful facility and lack of operational difficulty4 ,considering the large area1 no subaqueous tunnel had ever been driven with such speed4 ,the average monthly progress for the ,american and ,canadian headings totaled #dee feet1 and at top efficiency #aj rings or a length of #ae4c feet could be set in a #bd-;hour day in each heading4 ,the #f1jjj feet of tunnel was driven in just a year2 the two shields met vis-a-vis in ,august of #ahij4 ,the transition was complete4 ,the work had been closely followed by the technical journals and the reports of its successful accomplishment thus were brought to the attention of the entire civil engineering profession4 ,as the first major subaqueous tunnel completed in ,america and the first in the world of a size able to accommodate full-scale rail traffic1 the ,st4 ,clair ,tunnel served to dispel the doubts surrounding such work1 and established the pattern for a mode of tunneling which has since changed only in matters of detail4 ,of the eight models1 only this one was built under the positive guidance of original documents4 ,in the possession of the ,canadian ,national ,railways are drawings not only of all elements of the shield and lining1 but of much of the auxiliary apparatus used in construction4 ,such materials rarely survive1 and do so in this case only because of the foresight of the railway which1 to avoid paying a high profit margin to a private contractor as compensation for the risk and uncertainty involved1 carried the contract itself and1 therefore1 preserved all original drawing records4 ,while the engineering of tunnels has been comprehensively treated in this paper from the historical standpoint1 it is well to still reflect that the advances made in tunneling have not perceptibly removed the elements of uncertainty but have only provided more positive and effective means of countering their forces4 ,still to be faced are the surprises of hidden streams1 geologic faults1 shifts of strata1 unstable materials1 and areas of extreme pressure and temperature4 ,,bibliography ,,agricola1 ,,georgius4 ,de re ,metallica4 ,english transl4 ,h4 ,c4 and ,l4 ,h4 ,hoover 7,the ,mining ,magazine1 ,london1 #aiab74 ,basel3 ,froben1 #aeef4 ,,beach1 ,,alfred ,,ely4 ,the pneumatic dispatch4 ,new ,york3 ,the ,american ,news ,company1 #ahfh4 ,,beamish1 ,,richard4 ,a memoir of the life of ,sir ,marc ,isambard ,brunel4 ,london3 ,longmans1 ,green1 ,longmans and ,roberts1 #ahfb4 ,,burr1 ,s4 ,d4 ,v4 ,tunneling under the ,hudson ,river4 ,new ,york3 ,john ,wiley and ,sons1 #ahhe4 ,,copperthwaite1 ,,william ,,charles4 ,tunnel shields and the use of compressed air in subaqueous works4 ,new ,york3 ,d4 ,van ,nostrand ,company1 #aijf4 ,,drinker1 ,,henry ,,sturgess4 ,tunneling1 explosive compounds and rock drills4 ,new ,york3 ,john ,wiley and ,sons1 #ahgh4 ,,latrobe1 ,,benjamin ,h4 ,report on the ,hoosac ,tunnel 7,baltimore1 ,october #a1 #ahfb74 ,pp4 #abe-aci1 app4 #b1 in ,report of the commissioners upon the ,troy and ,greenfield ,railroad and ,hoosac ,tunnel4 ,boston1 #ahfc4 ,,law1 ,,henry4 ,a memoir of the ,thames ,tunnel4 ,weale's ,quarterly ,papers on ,engineering 7,london1 #ahde-df71 vol4 #c1 pp4 #a-be and vol4 #e1 pp4 #a-hf4 ,the pneumatic tunnel under ,broadway1 ,n4,y4 ,scientific ,american 7,march #e1 #ahgj71 pp4 #aed-aef4 ,report of the commissioners upon the ,troy and ,greenfield ,railroad and ,hoosac ,tunnel to his excellency the governor and the honorable the executive council of the state of ,massachusetts1 ,february #bh1 #ahfc4 ,boston1 #ahfc4 ,,storrow1 ,,charles ,s4 ,report on ,european tunnels 7,boston1 ,november #bh1 #ahfb74 ,pp4 #e-abb1 app4 #a1 in ,report of the commissioners upon the ,troy and ,greenfield ,railroad and ,hoosac ,tunnel4444 ,boston1 #ahfc4 ,the ,st4 ,clair ,tunnel4 ,engineering ,news 7in series running ,october #d to ,december #bg1 #ahij74 ,,footnotes #a ,there are two important secondary techniques for opening subterranean and subaqueous ways1 neither a method truly of tunneling4 ,one of these1 of ancient origin1 used mainly in the construction of shallow subways and utility ways1 is the cut and cover system1 whereby an open trench is excavated and then roofed over4 ,the result is1 in effect1 a tunnel4 ,the concept of the other method was propounded in the early #aith century but only used practically in recent years4 ,this is the trench method1 a sort of subaqueous equivalent of cut and cover4 ,a trench is dredged in the bed of a body of water1 into which prefabricated sections of large diameter tube are lowered1 in a continuous line4 ,the joints are then sealed by divers1 the trench is backfilled over the tube1 the ends are brought up to dryland portals1 the water is pumped out1 and a subterranean passage results4 ,the ,chesapeake ,bay ,bridge ,tunnel 7#aifj-aifd7 is a recent major work of this character4 #b ,in #aieb a successful machine was developed on this plan1 with hardened rollers on a revolving cutting head for disintegrating the rock4 ,the idea is basically sound1 possessing advantages in certain situations over conventional drilling and blasting systems4 #c ,in #ahjg the noted ,cornish engineer ,trevithick commenced a small timbered drift beneath the ,thames1 #e feet by #c feet1 as an exploratory passage for a larger vehicular tunnel4 ,due to the small frontal area1 he was able to successfully probe about #ajjj feet1 but the river then broke in and halted the work4 ,mine tunnels had also reached beneath the ,irish ,sea and various rivers in the coal regions of ,newcastle1 but these were so far below the surface as to be in perfectly solid ground and can hardly be considered subaqueous workings4 #d ,unlike the ,brunel tunnel1 this was driven from both ends simultaneously1 the total overall progress thus being #c feet per shift rather than #ah inches4 ,a top speed of #i feet per day could be advanced by each shield under ideal conditions4 #e ,ideally1 the pressure of air within the work area of a pneumatically driven tunnel should just balance the hydrostatic head of the water without1 which is a function of its total height above the opening4 ,if the air pressure is not high enough1 water will1 of course1 enter1 and if very low1 there is danger of complete collapse of the unsupported ground areas4 ,if too high1 the air pressure will overcome that due to the water and the air will force its way out through the ground1 through increasingly larger openings1 until it all rushes out suddenly in a blowout4 ,the pressurized atmosphere gone1 the water then is able to pour in through the same opening1 flooding the workings4 ,,index ,agricola1 ,georgius1 #bae1 #baf ,barlow1 ,peter ,w41 #bba1 #bbg ,beach1 ,alfred ,ely1 #bbd1 #bbg-bbi1 #bca1 #bcg ,brunel1 ,marc ,isambard 7the elder71 #bjd1 #bje1 #bag1 #bah1 #bba1 #bbd1 #bbi1 #bca1 #bcf ,burleigh1 ,charles1 #bab1 #bac ,burleigh ,rock ,drill ,company1 #bab ,burr1 ,s4 ,d4 ,v41 #bcf ,cochrane1 ,sir ,thomas1 #bca1 #bcb ,copperthwaite1 ,william ,charles1 #bbd ,doane1 ,thomas1 #baj1 #bab1 #bac1 #bae ,drinker1 ,henry ,s41 #bbd1 #bcg ,greathead1 ,james ,henry1 #bjd1 #bah1 #bba1 #bbd1 #bbi1 #bca1 #bce-bcg ,gwynn1 ,stuart1 #baj ,haskin1 ,de,witt ,c41 #bjd1 #bcb1 #bcd-bcf ,haupt1 ,herman1 #bjd1 #bji1 #baj ,hobson1 ,joseph1 #bcg ,latrobe1 ,benjamin ,h41 #bjh1 #bji ,law1 ,henry1 #bah ,mowbray1 ,george ,w41 #bac1 #bae ,nobel1 ,alfred ,b41 #bac ,putnam ,machine ,works1 #bab ,shanley1 ,walter1 #bab ,shanley ,bros41 #bae ,sommeiller1 ,germain1 #baj ,storrow1 ,charles ,s41 #baj ,tweed1 ,william ,marcy 7,boss71 #bbi ,weale1 ,john1 #bah 99 99 99 99 99 ,transcriber's ,notes ,all obvious typographical errors corrected4 ,formatting inconsistancies and spelling were standardized4 ,paragraphs split by illustrations were rejoined4 ,the text in the reproduced handbill for the ,thames ,tunnel was transcribed with a slight modification to the figure description portion4 ,the ,index was extracted from the full publication ,index4