,,earthwork ,,slips ,,and ,,subsidences ,,upon ,,public ,,works3 ,their ,causes1 ,prevention1 and ,reparation4 ,,especially ,,written ,,to ,,assist ,,those ,,engaged ,,in ,,the ,,construction ,,or ,,maintenance ,,of ,,railways1 ,,docks1 ,,canals1 ,,roads1 ,,waterworks1 ,,river-,,banks1 ,,reclamation ,,embankments1 ,,drainage ,,works1 c4 ,,by ,,john ,,newman1 ,assoc4 ,m4 ,inst4 ,c4,e4 ,,author ,,of 8,,notes ,,on ,,concrete ,,and ,,works ,,in ,,concrete20 8,,iron ,,cylinder ,,bridge ,,piers20 8,,queer ,,scenes ,,of ,,railway ,,life40 ,illustration ,,london3 ,e4 ,f4 ,n4 ,,spon1 #abe1 ,,strand1 ,,new ,,york3 #ab1 ,,cortlandt ,,street4 #ahij4 ---------------------------------------- -------------------------------- ,,preface4 ,the absence of any but fragmentary information on ,,earth-,,slips ,,and ,,subsidences ,,upon ,,public ,,works1 one of the most annoying and expensive occurrences in engineering construction1 has prompted the author to write this book as a vade-mecum for those in charge of such undertakings as ,railways1 ,docks1 ,canals1 ,roads1 ,waterworks1 ,river-banks1 ,reclamation embankments1 ,drainage works1 c41 and also to fill1 however imperfectly1 somewhat of an hiatus in engineering literature4 ,the theory of the lateral pressure of earthwork is not examined1 as it is well understood2 the intention being to concisely describe the chief causes of slips and subsidences in different earths and many points requiring attention1 to call to remembrance some soils especially treacherous and unstable1 and to name various preventive measures and effectual remedies4 ,a reference to the table of contents and the index will demonstrate the comprehensiveness of the subject1 for it involves in the various practical applications the science of geology1 physical geography1 meteorology1 the laws of pressure of earth1 some chemical and botanical1 and other scientific knowledge4 ,it is scarcely necessary to observe that no exhaustive treatise is herein attempted1 for that would indeed be an ,herculean task2 but in this volume the endeavour has been made to present reliable information1 the result of experience1 research1 considerable labour1 and lengthened observation4 ,j4 ,n4 ,,london4 ,march1 #ahij4 ,,contents4 ,,chapter ,i4 ,,pages ,,introduction--,,general ,,considerations--,,enumeration ,,of ,,the ,,primary ,,causes ,,of ,,slips ,,and ,,subsidences ,,in ,,cuttings ,,and ,,embankments1 ,,and ,,earthworks ,,constructed ,,to ,,contain ,,or ,,exclude ,,water--,,some ,,dominant ,,principles ,,to ,,be ,,remembered ,,in ,,determining ,,the ,,location ,,of ,,earthworks #a-ab ,,chapter ,,ii4 ,,the ,,probability ,,of ,a ,,slip--,,time ,,of ,,the ,,most ,,frequent ,,occurrence--,,some ,,conditions ,,under ,,which ,,slips ,,and ,,subsidences ,,in ,,cuttings ,,and ,,embankments ,,may ,,be ,,expected ,,in ,,different ,,earths1 ,,such ,,as ,,rock1 ,,chalk1 ,,sand1 ,,gravel1 ,,clay1 ,c41 ,c4--,,notes ,,on ,,the ,,slopes ,,of ,,repose #ac-di ,,chapter ,,iii4 ,,the ,,general ,,effect ,,of ,a ,,slip ,,in ,a ,,cutting ,,or ,,an ,,embankment--,,enumeration ,,and ,,consideration ,,of ,,some ,,protective ,,and ,,remedial ,,works--,,treatment ,,of ,,the ,,slipped ,,earth #ej-fd ,,chapter ,,iv4 ,,notes ,,on ,,the ,,percolation ,,of ,,water--,,systems ,,of ,,drainage ,,of ,,cuttings ,,and ,,embankments ,,in ,,different ,,kinds ,,of ,,earth ,,and ,,under ,,diverse ,,conditions--,,the ,,construction ,,of ,,culverts1 ,,pipe-,,drains1 ,,trenches1 ,,ditches1 ,,and ,,catchwater ,,drains #fe-hf ,,chapter ,v4 ,,approximate ,,safe ,,maximum ,,load ,,upon ,,different ,,earths--,,normal ,,pressure ,,of ,,the ,,earth--,,the ,,safe ,,maximum ,,load ,,upon ,,deposited ,,earth--,,approximate ,,safe ,,maximum ,,height ,,of ,,an ,,embankment #hg-ig ,,chapter ,,vi4 ,,slopes1 ,,general ,,considerations--,,table ,,showing ,,the ,,general ,,range ,,of ,,slopes--,,table ,,of ,,coefficients ,,of ,,friction--,,notes ,,on ,,the ,,cohesion ,,of ,,earth--,,form ,,of ,a ,,slope--,,some ,,conditions ,,governing ,,the ,,necessary ,,inclination--,,widening ,,earthworks ,,within ,,the ,,original ,,fences #ih-aad ,,chapter ,,vii4 ,,notes ,,upon ,,the ,,preservation ,,of ,,the ,,foot ,,of ,a ,,slope--,,various ,,methods ,,of ,,covering ,,and ,,supporting ,a ,,slope--,,protection ,,from ,,snow-,,drifts--,,the ,,formation ,,width ,,of ,,cuttings ,,and ,,embankments--,,the ,,deleterious ,,effects ,,of ,,vibration #aae-ada ,,chapter ,,viii4 ,,earthworks ,,in ,,or ,,upon ,,sidelong ,,ground--,,some ,,insecure ,,conditions--,,precautionary ,,measures--,,embankments ,,upon ,,soft ,,ground--,,embankments ,,composed ,,of ,,soft ,,earth--,,the ,,promotion ,,of ,,stability ,,and ,,consolidation #adb-aee ,,chapter ,,ix4 ,,the ,,deposition ,,of ,,an ,,embankment--,,preparation ,,of ,,the ,,ground ,,upon ,,which ,,an ,,embankment ,,has ,,to ,,be ,,deposited--,,methods ,,of ,,procedure--,,consideration ,,of ,,some ,,of ,,the ,,different ,,systems--,,the ,,effect ,,of ,,the ,,height ,,of ,a ,,tip ,,and ,,the ,,length ,,of ,a ,,lead--,,the ,,steam ,,navvy ,,and ,,embankments #aef-agj ,,chapter ,x4 ,,notes ,,upon ,,the ,,location1 ,,preservation1 ,,and ,,protection ,,of ,,sea1 ,,estuary1 ,,reclamation1 ,,canal1 ,,and ,,reservoir ,,embankments ,,of ,,earth ,,constructed ,,to ,,contain ,,or ,,expel ,,water #aga-aig ,,chapter ,,xi4 ,,notes ,,upon ,,the ,,failure ,,of ,,dock ,,and ,,other ,,walls ,,from ,a ,,forward ,,movement ,,of ,,the ,,earth ,,filling ,,or ,,backing--,,consideration ,,of ,,the ,,causes ,,of ,,such ,,action ,,and ,,some ,,preventive ,,and ,,remedial ,,measures #aih-bae ,,chapter ,,xii4 ,,notes ,,upon ,,slips ,,of ,,earth1 ,,subsidences1 ,,and ,,movement ,,in ,,foundations ,,caused ,,by 8,,boils10 ,,or ,,an ,,upward ,,rush ,,of ,,water ,,in ,,loose ,,earths--,,consideration ,,of ,,some ,,precautionary ,,and ,,remedial ,,operations #baf-bbe ,,earthwork ,,slips ,,and ,,subsidences ,,upon ,,public ,,works4 ,,chapter ,i4 ,,introduction--,,general ,,considerations--,,enumeration ,,of ,,the ,,primary ,,causes ,,of ,,slips ,,and ,,subsidences ,,in ,,cuttings ,,and ,,embankments1 ,,and ,,earthworks ,,constructed ,,to ,,contain ,,or ,,exclude ,,water--,,some ,,dominant ,,principles ,,to ,,be ,,remembered ,,in ,,determining ,,the ,,location ,,of ,,earthworks4 ,earthslips and subsidences may be caused by the terrible power of an earthquake or other dreaded subterranean destroying force1 upheaving1 cracking1 and shattering the earth's crust and dealing death and havoc in its awe-inspiring course4 ,they may also originate from the untiring efforts of the meanest rodents or the most minute crustaceous animals burrowing passages for aqueous action1 the chief agent of the instability of the surface soils of the earth4 ,the ceaseless mutability of the created elements has been thus magnificently described3-- 8,for know1 whatever was created needs ,to be sustain'd and fed2 of elements ,the grosser feeds the purer1 earth the sea1 ,earth and the sea feed air1 the air those fires ,ethereal1 and as lowest first the ,moon2 ,whence in her visage round those spots1 unpurg'd ,vapours not yet into her substance turn'd4 ,nor doth the ,moon no nourishment exhale ,from her moist continent to higher orbs4 ,the ,sun1 that light imparts to all1 receives ,from all his alimental recompense ,in humid exhalations1 and at even ,sups with the ocean40 ,it is the constant absence of peace and rest in the earth that produces instability1 however great1 however small1 for the disastrous landslips that have occurred in ,switzerland and other parts of ,europe1 in ,india1 and recently at ,quebec1 and in all regions of the world were caused by the same disintegrating operations as those which generate an earth-slip of comparative insignificance4 ,in proceeding to a practical consideration of earthslips and subsidences1 it may be well to call attention to the complexity of the subject1 the character and conditions of earth and the impairing elements being so very variable and numerous that it is impossible to determine any rules even for a particular soil2 and1 moreover1 it is necessary to separately consider slips in cuttings and those in embankments1 as movement is somewhat differently created1 and it does not necessarily follow because earth stands well in a cutting that it will do so in an embankment1 or vice vers4 ,it may be said every kind of earth will slip or weather under certain conditions1 even the hardest rock if superimposed upon an unstable stratum2 therefore1 some of the main questions to be considered are3-- ,i4 ,,the ,,probability ,,of ,,the ,,occurrence ,,of ,a ,,slip4 ,,ii4 ,,the ,,effect ,,of ,a ,,slip4 ,,iii4 ,,should ,,every ,,precaution ,,be ,,taken ,,to ,,prevent ,a ,,slip ,,when ,a ,,cutting ,,is ,,being ,,excavated ,,or ,,an ,,embankment ,,being ,,deposited2 ,,or ,,is ,,it ,,better ,,to ,,repair ,a ,,slip ,,as ,,it ,,happens8 ,it is obvious in railway cuttings and embankments a mere crumbling of the surface may be disregarded1 but in dock1 canal1 or any works containing or expelling water1 the smallest movement1 crack1 or aperture must immediately receive due attention4 ,in order to effectually remedy a disease it is necessary to ascertain its character4 ,many of the primary causes of slips in cuttings and embankments are1 therefore1 here enumerated2 but1 of course1 they are not named in their order of importance1 which cannot be established4 ,,heads ,,of ,,the ,,chief ,,causes ,,of ,,slips ,,and ,,subsidences ,,in ,,cuttings4 #a4 ,the want of uniformity of the earth1 particularly as regards percolation1 cohesive power1 and resistance to change by the action of water or meteorological influences4 #b4 ,the temporary or permanent exposure of the earth to the effects of the atmosphere1 rain1 frost1 and snow4 #c4 ,the opening to the air and weather1 c41 of thin seams of an unstable character1 which1 when unsupported1 gradually crumble away and cease to support superimposed strata4 #d4 ,the tapping of springs4 #e4 ,the lower portion of a slope being impaired or undermined through an infiltration and flow of water4 #f4 ,the erosion of the slope4 #g4 ,the earth having intermediate unstable seams4 #h4 ,the unprotected surface of a cutting in light soil being loosened and blown away by a storm of wind1 especially when it is accompanied by rain4 #i4 ,the slopes being honey-combed and disturbed by rodents1 particularly in clay soils1 clay marls1 and clay loams2 and upon submerged earthwork1 and in certain districts in the tropics by a mollusk which will penetrate and even destroy rocks4 #aj4 ,from one portion of a cutting being more exposed than another to disintegrating meteorological influences4 #aa4 ,by the discharge of water from land drains following the old drainage course1 and by the localisation of the surface or land water flow4 #ab4 ,the improper or imperfect drainage of land outside a railway fence1 causing land water to accumulate in and discharge itself through the slope1 thus disturbing the established equilibrium4 #ac4 ,by an interference with the natural flow of any underground waters4 #ad4 ,by allowing water to accumulate in the gullet1 or upon the formation during the process of the excavation of a cutting4 #ae4 ,the local percolation of water through the slopes of a cutting from the defective construction1 wrong location1 or permeability of the surface of a drain upon the cess4 #af4 ,an accumulation of water caused by the unevenness of the slopes4 #ag4 ,the acceleration and inducement of a flow through the slope of any water contained in land outside a railway fence1 and consequent incitement to the land-water to exude4 #ah4 ,vibration4 #ai4 ,insufficient flatness of a slope either at the time of excavation or after exposure to meteorological influences4 #bj4 ,the strain upon the face from lumps of earth being allowed to remain upon a slope during the construction of the works1 or the gullet being excavated for a considerable distance in advance2 the cohesion of the soil being thereby unduly and unequally strained4 #ba4 ,by overweighting4 #bb4 ,by unequal loading4 #bc4 ,the establishment of spoil banks upon the cess1 or the additional loading of the ground near and outside a railway fence1 in soft soils having practically no cohesion or tenacity4 #bd4 ,the excavation removed destroying the continuity of support1 especially in soils partaking of a semi-fluid character4 #be4 ,the want of uniformity of the covering of a slope causing unequal percolation or exudation of water4 #bf4 ,the neglect to fill up1 or otherwise remedy1 cracks or fissures in the slopes or cess4 #bg4 ,by artificial or irregular consolidation either of the formation or slopes superinducing movement and weathering in any portion not so compacted4 #bh4 ,from an accumulation of water behind a retaining wall at the foot of a slope1 resulting in the stability of the wall being overcome by pressure4 #bi4 ,by unequal pressure upon the foundations of a retaining wall at the foot of a slope caused by lateral over-pressure tilting it1 or by its unequal settlement4 #cj4 ,in sidelong ground1 by the removal of support against the action of sliding1 which1 without artificial aid1 may not be arrested until the slope of a cutting on the higher side approaches the steepest inclination of the face of the hill4 #ca4 ,by blasting laminated rock dipping at a considerable angle towards a cutting in the side of a hill2 the result sometimes being that a cavity is made depriving the upper beds of support and causing them to overhang1 and a mass extending to the top surface of the hill to slip along the unsupported stratum4 ,the first ten 8heads of the chief causes of slips in cuttings0 might be classed as ,,natural1 i4e4 produced or effected by nature and1 therefore1 beyond the power of man to entirely prevent2 the remaining heads as ,,artificial1 and therefore1 in some degree to be prevented1 unless obviously the result of the unavoidable exigencies of construction4 ,,heads ,,of ,,the ,,chief ,,causes ,,of ,,slips ,,and ,,subsidences ,,in ,,embankments4 #a4 ,the percolation of surface water into the toe and under an embankment upon the original surface of the ground1 and also downwards through the formation4 #b4 ,unequal percolation of water through the formation or the slopes4 #c4 ,the surface of the ground upon which an embankment is tipped inclining in one direction1 or falling on each side from the centre4 #d4 ,the effects of rain1 frost1 snow1 and the atmosphere on the deposited earth4 #e4 ,by a crumbling of the lower portion of a slope4 #f4 ,by a hurricane or extreme wind force1 especially when accompanied by rain and the location is that of a narrow1 steep valley1 blowing away or dissipating the top and the surface of an uncovered embankment4 #g4 ,by a slope becoming honey-combed by rodents1 and in some few countries by an embankment in a river or the sea being bored and disturbed by crustacea4 #h4 ,insufficient slope for permanent stability at the time of or after deposition4 #i4 ,the want of adhesion between the surface of the ground upon which an embankment is tipped and the deposited material4 #aj4 ,by the accumulation at the foot of an embankment of boulders or lumps having no cohesion1 and no adhesion to the surface of the ground upon which they are deposited4 #aa4 ,the weight being too great upon the ground upon which an embankment rests4 #ab4 ,by unequal loading4 #ac4 ,an accumulation of water1 caused by the unevenness of the surface of an embankment1 or by the ground not being prepared so as to prevent a lodgment of water4 #ad4 ,by obstructing the established discharge of land-water or by attempting to divert the natural flow of underground waters4 #ae4 ,the localisation of the surface drainage4 #af4 ,water percolating into a benching trench1 made to receive the toe of a slope1 thereby impairing the cohesion of the soil and reducing its weight-carrying capacity and stability4 #ag4 ,vibration4 #ah4 ,the different nature and state of the earth tipped into an embankment and the consequent localisation of water in the more pervious soil1 causing unequal settlement1 subsidence and movement4 #ai4 ,an embankment being tipped of material in a different state of dryness1 moistness1 hardness1 softness1 or in a frozen condition4 #bj4 ,the size and character of the earth1 as excavated in the cuttings2 for instance1 whether picked and shovelled soil1 or lumps of excavation simply barred away and deposited in small masses with earth approaching a state of dirt or mud4 #ba4 ,overpressure upon the material forming an embankment4 #bb4 ,the different conditions of the weather1 when an embankment is tipped1 causing portions to become dry1 wet1 or frozen4 #bc4 ,the lead or distance from a cutting to the place of deposition being of considerable length4 #bd4 ,the earth being loosened from vibration and concussion during transit in the wagons1 and in the process of deposition1 thus causing it to be non-homogeneous4 #be4 ,by the earth being tipped with greater impetus at one part than at another place4 #bf4 ,an embankment not being tipped to its full width as it progresses1 whether in one or more wagon roads4 #bg4 ,first tipping the central portion of an embankment1 and completing the width and slope by side deposition after some time has elapsed4 #bh4 ,tipping the contents of earth wagons from a considerable height1 thereby loosening and separating the soil1 causing the larger and heavier material to be near the foot of a slope and in lumps1 and an embankment to have interstices and be temporarily or permanently unstable4 #bi4 ,irregular consolidation1 artificial or otherwise4 #cj4 ,unequal exposure1 particularly in embankments upon sidelong ground4 #ca4 ,insufficient width of the formation1 especially in high and exposed embankments4 #cb4 ,the junction of two embankments tipped from cuttings in different kinds of earth4 #cc4 ,no time being allowed for subsidence or consolidation before the deposited earth is subject to varying loads and vibration4 #cd4 ,by allowing water to collect upon the formation and to form channels down the slopes4 #ce4 ,the neglect to fill1 or otherwise remedy1 cracks or fissures4 #cf4 ,the want of uniformity of the covering of the slopes or top of an embankment causing unequal percolation of water4 #cg4 ,by a retaining wall at the toe of a slope preventing the discharge of water that has percolated through the formation and the slope4 #ch4 ,by an abnormal increase of the load upon the foundation of a wall caused by lateral thrust and tilting forward1 or fracture of the footings or the concrete bed4 ,the first seven heads of 8the chief causes of slips in embankments0 might be classed as ,,natural1 i4e41 produced by nature1 and1 therefore1 beyond the power of man to entirely prevent2 the remainder as ,,artificial1 and1 therefore1 more or less to be prevented4 ,in the case of earthworks made to contain or exclude water for the purposes of docks1 canals1 waterworks1 reclamation of land1 irrigation or drainage1 c41 may be added1 without reference to their construction3-- #a4 ,leakage along a discharge culvert1 sluice1 or tunnel in an embankment1 or through the earthwork4 #b4 ,erosion of the land slope or backing of a retaining wall by waves1 or spray falling thereon and necessarily passing over the top of an embankment4 #c4 ,from abrasion and damage1 caused by vessels or barges rubbing or colliding against a slope4 #d4 ,from erosion caused by wave action produced by the passage of boats or ships propelled by machinery2 or by wind waves4 #e4 ,variation in the water level1 causing unequal pressure4 #f4 ,in the case of a reclamation embankment1 it being closed from the ends1 and not by raising in layers1 from the ground level4 #g4 ,variation of the submerged area1 and consequent change in the degree of exposure to deteriorating influences4 99 99 99 99 99 ,to sum up1 the principal causes of slips in earthwork may be stated to be air1 water1 frost and thaw1 over-pressure1 and vibration2 the chief agent both in cuttings and embankments being water1 which forces forward the surface of the slopes and destroys the cohesion of the soil1 and impairs its frictional resistance until the earth is unable to sustain the weight upon it2 vibration aiding and completing the movement1 as it not only tends to loosen the soil1 but may disturb the equilibrium of earthwork which is almost moving1 and only requires a slight shock to set it in motion3 in fact1 vibration is frequently the complementary agency that causes a slip1 and is obviously felt most in loose soils2 but if there should be fissures in earth of a tenacious character1 or boulders in clay to disconnect it1 the effect of vibration will be more serious in the latter case1 as whole masses of earth may become detached1 instead of an equal settlement proceeding as with soils1 such as sand and gravel1 which may become consolidated by shaking1 owing to wedging of the particles1 should the slopes be sufficiently flat to prevent lateral movement2 but it may detach portions of the slopes in soil having little or no cohesion1 and thus initiate a slip4 ,in the following chapters the chief causes of slips in cuttings and embankments are considered1 together with others bearing upon a solution of the subject1 which is so interwoven that it is impracticable to preserve a successive order1 but an endeavour has been made to separately indicate the cause and some remedies that may be adopted3 but before proceeding to particularise1 it may be well to name a few dominant principles of the alignment of public works1 which if duly regarded may tend to prevent slips of serious importance4 ,consequent upon financial and other causes1 an engineer is usually required to so quickly prepare the necessary parliamentary plans and sections of public works1 more particularly for railways1 that it is beyond the power of the most experienced to set out in a few hours the best line of railway1 c41 across a country1 giving due consideration to the parliamentary1 constructional1 economical working1 district and through traffic1 and financial requirements of the undertaking4 ,there are1 however1 a few points which he may be able to regard respecting the stability of earthworks1 some of which are now enumerated4 #a4 ,avoid cuttings or embankments in drift soil in or upon the side of a hill4 #b4 ,avoid all damming back or flow of the natural drainage waters1 or heaping of snow by the erection of an embankment1 especially in mountainous1 hilly1 or sidelong ground1 and in an undrained district4 #c4 ,when any excavation is in the side of a hill1 observe the natural configuration of the ground in the wettest part1 and remember that the slope of a cutting may not stand unless at the same inclination1 or the toe of the slope is supported by a massive retaining wall and extensive draining1 and that any disturbance may cause it to require a flatter inclination4 #d4 ,avoid river or stream diversions in earth of a very porous character2 and should an embankment have to be erected near to a deep river having a steep bank1 locate the line a sufficient distance from the edge that the slope of the river bank may be flattened when required1 as an extraordinary flood may cause it to be unstable and to fall in1 and in order to restore it to a condition of stability1 it may be necessary to widen the river and reduce the angle of inclination of its banks4 #e4 ,in treacherous earth do not locate a railway close to a road1 except at a station1 as if the line be placed above the road1 a slip upon the railway may result in a slip upon the road2 and should the line be below a road1 the extra weight or vibration may cause the road to follow the railway and act1 as it were1 in unison with it4 #f4 ,in treacherous soil1 where practicable1 have stations nearly upon the surface of the natural ground4 #g4 ,remember that upon one side of even the narrowest gorge or valley the earth may be much more solid than upon the other4 #h4 ,in exposed situations in a hilly country ascertain upon which side snow remains the longer1 note which receives the greater amount of sunshine1 and is the wetter and more covered with trees and vegetation4 ,in a hill or mountain1 the side to leeward of the prevailing winds almost invariably receives the greater rainfall4 #i4 ,in mountainous or hilly districts it may be advantageous to place a railway or road at a high level upon the sunny side of a hill or valley1 as obviously it dries quicker2 snow does not accumulate with the same facility1 unless it happens to be exposed to the direction of the prevailing storms2 the sunny side may be practically clear of snow1 the shady almost impassable2 but there is one drawback to the sunny side1 namely--the more frequent occurrence of snow-slips1 which may or may not be serious in extent4 ,on the whole1 experience seems to show that the wooded side of a valley is the best to select--sometimes one side is bare and the other wooded--unless there are special reasons to the contrary4 ,in the winter season in certain districts abroad1 for instance1 in parts of ,afghanistan and the adjacent mountain passes1 the days are sometimes as hot as the summer of ,european countries1 but at night the thermometer may fall below freezing-point1 hence the value of tree-protection4 ,it is obvious that in such climates the soil is peculiarly liable to disintegrating forces1 and likely to slip1 unless of a solid character1 and that upon one side earthworks may be stable1 and upon the other treacherous4 #aj4 ,in many countries it may be advisable to adopt a valley in preference to a hill-side line1 especially if the district is free from floods1 or if the waters flowing down the side of the hills are considerable and suddenly appear1 and there is a river and ample means available of controlling the hill-side torrents and conducting them to the river4 ,if not1 and the line must be on the mountain side1 it may be advisable1 in exposed places where water rapidly accumulates and becomes a torrent1 to adopt the system of short tunnels round the hill spurs1 in preference to deep cuttings1 drainage1 and slope protection works1 and to place the railway or road at the highest level1 so as to be free from the influence of floods4 #aa4 ,bear in mind that in high mountainous districts the drift deposit is generally torrential alluvium4 #ab4 ,avoid as much as possible high embanked approaches to a river bridge1 especially when a deep river1 which frequently changes its course1 is in a flat country4 #ac4 ,consider if the simple erection of an embankment may in time cause its destruction1 by the arrest or attempted diversion of the usual flow of the land waters4 #ad4 ,in treacherous soils1 on the side of a cliff facing the sea1 determine whether it is preferable to erect timber trestles at its base instead of a solid embankment1 or to place the line in a tunnel4 ,the trestles can either be erected upon sills1 resting on the ground and on short piles well secured from movement1 or on piles driven some distance into the ground4 ,the system may also be adopted if the ground be of a yielding character4 #ae4 ,it has been noticed in some mountainous districts that the clouds break against the highest main ranges1 discharge themselves on the smaller ranges1 and generally do not reach the inner ranges which rise on the high table-lands2 therefore1 consider whether by locating a railway or road near the latter1 there is much less probability of a slip in the earthworks and less provision required for surface and flood waters4 #af4 ,the configuration of a district through which a railway or road must be aligned1 may be such that its location becomes one more based upon placing it on soil which is less bad or treacherous1 than upon firm or stable ground4 ,this is especially the case in hilly countries contiguous to the sea or large rivers4 ,it may be optional to construct the works upon low or valley ground upon the side of a mountain or hill1 or close to the sea shore or a river bank1 which may require continuous defence works to protect it from waves and erosion2 or on table-land which1 however1 if impervious and retentive of moisture may act as a catchment reservoir between hills1 and cause the ground to be always in a damp state4 ,the character of the soil1 the magnitude1 and especially the average height of the embankments1 or the depth of the cuttings1 the easy drainage and discharge of the rainfall1 and an economically constructed1 maintained1 and worked line are the chief conditions to inseparably bear in mind in determining the location4 ,,chapter ,,ii4 ,,the ,,probability ,,of ,a ,,slip--,,time ,,of ,,the ,,most ,,frequent ,,occurrence--,,some ,,conditions ,,under ,,which ,,slips ,,and ,,subsidences ,,in ,,cuttings ,,and ,,embankments ,,may ,,be ,,expected ,,in ,,different ,,earths1 ,,such ,,as ,,rock1 ,,chalk1 ,,sand1 ,,gravel1 ,,clay1 ,c41 ,c41--,,notes ,,on ,,the ,,slopes ,,of ,,repose4 ,it is of importance to know when serious slips are most likely to happen and under what conditions they are probable1 for the process of disintegration may commence immediately the earth is excavated1 and be very gradual1 although the soil may remain stable for many months1 or even a year or two1 because the earth has not had time to be affected to the point of instability4 ,the history of recorded slips appears to indicate that the most serious movements of earth and those most difficult to remedy occur in the following soils4 ,,drift ,,earth upon rock in sidelong ground4 ,,chalk ,,soils1 as witness the slips in the early part of #ahgg in the cuttings near ,folkestone1 and the more recent on the ,calais-,boulogne ,railway1 and that in an embankment of chalk at ,binham's ,wood1 near ,balcombe1 in ,october #ahec1 when in a length of about #bjj yards some #gj1jjj cubic yards of earth slipped towards a valley4 ,probably this is one of the most extensive recorded slips of a railway embankment of chalk2 however1 in this case the traffic was not stopped1 but only delayed4 ,,clay ,,soils1 especially the yellow clay2 illustrated by the notable slip at ,new ,cross1 near ,london1 when some #ij1jjj cubic yards of yellow clay moved upon the smooth surface of a shaly clay bed and covered the formation3 also the brown1 and boulder clay1 and the lias clays1 as witness the well-known recorded slips in the ,midland counties of ,england1 in which either aluminous or calcareous material may preponderate4 ,there are few1 if any1 earths in which the cohesion1 weight-sustaining power and ability to resist the action of water and meteorological influences are practically the same at all depths1 the different conditions1 arrangement1 and character in which they are found being almost infinite1 and there are earths which may become consolidated and watertight if in a constantly moist and protected state1 that when dry and exposed will shrink1 fissure1 and soon become unstable4 ,consequent upon cohesion1 a cutting may stand for some time almost vertically2 nevertheless stability cannot be considered as solely regulated by the cohesion of earth1 for an embankment of gravel1 sand1 or broken rock with a proper slope and protected from erosion will usually safely bear more load than an embankment of clay1 although the former material may be said to have no cohesion2 but the lateral thrust of dry1 firm sand is known to be small1 provided the sand is not disturbed2 also no earth can be said to be immovable under every condition1 but consideration of the soils particularly liable to disturbance or mutation is1 under ordinary circumstances1 the main question to be determined4 ,with few exceptions the exterior or faces of cuttings and embankments will1 at certain times1 become impaired or soddened by the infiltration of water4 ,in cuttings there is the additional danger1 owing to the geological formation1 of the excavation reaching the depth at which water is generally found in the locality1 and it is therefore advisable to ascertain this level1 and also to decide whether the ground must be excavated below it1 as necessarily there will be a downward flow1 and the slopes and formation will consequently have to sustain a pressure due to the difference between the normal level of the water-bearing stratum in the neighbourhood and that of any depth beneath it4 ,in such a case1 in addition to the usual softening and loosening aqueous action1 there is the particular insecurity of the formation and slopes being undermined and eroded by springs3 also in pervious soil in a drained district a cutting will be found to be comparatively dry to about the level of the bottom of the existing contiguous drains1 but below that depth water will be present1 probably in considerable quantity4 ,land drains also frequently cause slips1 as they localise the flow of the surface or underground waters1 and when in excavating a cutting they are intercepted1 the discharge should be led away from the slopes2 but difficulty may be encountered in effecting this1 as water will usually follow its original course1 and it may be impossible to entirely divert the direction of the flow1 and the only thing to do may be to gently conduct the water down the slope by means of pipes1 rubble1 burnt brick1 gravel surface drains1 or timber ducts4 ,an important question to determine is1 when are slips in earthwork most likely to occur4 ,in ,europe they are most frequent in the autumn and winter months2 but no rule can be established1 nor is it reasonable to conclude1 because any earthwork has remained stable during the usual period when slips may be expected1 that1 therefore1 none will happen1 for the heaviest rain may descend at an unusual season1 and as moisture is the chief cause of the instability of all earths1 it is rather to the quantity of the rainfall at any time than to the fixed seasons that attention should be directed4 ,spring being the driest season in ,england and autumn the wettest1 ,october and ,november being the months of heaviest rainfall1 slips are more probable in the latter than the former season2 but the first heavy and continuous rainfall after a period of estival drought is that particularly to be feared1 or the first rainy weather after a dry period irrespective of the season of the year2 but serious slips may not occur for many days or until the expiration of even a month or two after such rainfall1 as the ground waters require time before they percolate to or reach the site of a cutting1 and1 therefore1 all danger may be thought to be past when it is steadily approaching4 ,the autumnal rains have to replace the moisture that has evaporated during the summer1 and this may not1 and usually does not if it slowly proceeds1 produce instability in earthwork2 but immediately the rainfall approaches or becomes in excess of the power of the natural absorption of the soil1 the rain must flow away1 for the earth being fully charged cannot contain it1 the surface becomes wet or the mass soaked1 according to the degree of the permeability of the soil1 and the quantity of rain necessary to produce saturation2 therefore1 the state of the earth that induces a slip is that most desirable to know2 this cannot be absolutely established in every case1 for it depends upon so many influences1 and obviously varies according to the character of the earth1 the varieties and conditions of which are practically infinite4 ,in countries that have dry and wet seasons1 which cause the earth to become parched and then to be rapidly saturated1 mere surface waters to become streams1 and rivers torrents1 slips are probable soon after the commencement of the rainy season4 ,when frost follows rain or a fall of snow1 and the latter has descended upon a frozen surface and a thaw sets in1 particularly if it be accompanied by a warm wind causing it to be very rapid in action1 the earth is severely tried1 for the frozen water in the ground becomes suddenly liberated1 while the surface is in a state of saturation4 ,probably the worst event that can occur for causing floods is when a sudden and rapid thaw follows a heavy snowfall upon frozen earth1 as then the snow will melt1 and water cannot gently percolate the earth1 as the surface will be in a more or less frozen and impermeable condition1 and the snow-water consequently must flow away4 ,should any excessive or violent rainfall succeed a period during which the heat of the sun has caused fissures in the surface of the earth1 allowing water to enter1 the state of the soil is favourable to movement4 ,land has also become unstable in mountainous countries because a district has been deforested1 or tree-protection much reduced1 movement of the earth usually happening after the first heavy rains or thaw succeeding frost or snow4 ,it has also been noticed that when an earth has become completely saturated or water-charged1 a sudden fall of the barometer to a low pressure will liberate the pent up water which the soil cannot contain and cause it to burst out1 the equilibrium having been so delicate4 ,under such circumstances slips are nearly sure to ensue1 and to be serious from their sudden action4 ,extensive slips in earthwork seldom occur during the excavation1 or a short time after the completion of a cutting2 on the other hand1 movement in an embankment frequently happens during deposition4 ,in the case of an embankment1 time may cause the earth to become consolidated1 but in a cutting the disintegrating and disturbing forces1 and the combined action of air and water percolating until they force forward the earth1 are usually gradual in their operation1 and often require a year or two to cause a state of instability2 in fact1 the history of slips1 with a few exceptions1 in soils whose condition is very readily changed by water1 indicates that serious movement in cuttings does not generally occur until a cycle or two of the seasons has elapsed1 during which period meteorological influences1 aided by vibration and other deteriorating operations1 are slowly and regularly proceeding1 until at length such a change in the general condition is caused that a slip happens1 apparently from some sudden agency1 whereas the stability of the earth has been gradually and surely wasting away for a long time2 hence the importance of continual careful observation in cuttings even of moderate depth in doubtful soil4 ,in canals and works of a similar character constructed to contain water1 if any movement or slip of earthwork takes place1 it usually occurs within a short time of the water being admitted1 and generally within a few months and seldom after so long a period as a year1 the ground in a short time becoming consolidated1 being exempt from severe vibration and many of the disturbing agencies present in railway cuttings and embankments4 ,in endeavouring to ascertain the probability of a slip occurring1 not only should the superficial strata be considered1 but also the original formation of the country2 for instance1 drift-soil1 which is generally met with upon the surface of sloping rocks1 may consist of various earths intermixed in endless variety1 and in every conceivable shape1 and is not necessarily produced by a weathering of the rock upon which it lies1 for it may have been brought from a distance4 ,in any case1 drift-soil is the result of decomposition and disintegration1 and from its nature is unreliable and ever subject to change1 to slip1 and to subside1 and so are most of the glacial deposits and moraine found in mountainous countries2 and whenever the contour of a district is irregular and has numerous clefts1 soft and marshy places1 valleys and hills1 earthworks will require to be protected against slips2 also1 should a cutting be at the base of a cliff or hill1 it will probably have to be excavated in drift deposit and1 perhaps1 in silt if below the water-level of adjacent sea or river1 and the ground dips towards the natural outfall of the land-waters4 ,such drift-soil may be alternately dry and charged with water from the rocks above1 especially if they are much fissured and water-bearing and permit easy percolation of water1 and must always be in a state of mutability4 ,,rock4 ,with regard to slips in rock1 or earth generally classed as rock1 the unstratified or igneous rocks1 although they are sometimes traversed by mineral veins and dykes1 are the less likely to slip2 but rocks liable to surface decomposition and disintegration1 such as some varieties of basalt and clay-slate1 which latter by atmospheric and aqueous action will partly return to its original state of being fine mud1 thrown down from the metamorphic rocks1 may change their condition and are likely to slip2 and also limestone rock1 which however resists the eroding action of water better than sandstone1 may become separated by frost although its surface soon dries4 ,simply knowing the general character of a rock without ascertaining the proportion1 state of the different particles of which it is composed1 and whether any metamorphic action has taken place1 is not necessarily a reliable guide to its stability4 ,in districts situated at a high level1 rocks are usually less permeable than in low-lying lands1 and the surface discharge is greater and quicker because of the increased rainfall1 and less absorption and retention of water4 ,it should be noticed whether there are dips in the surface of rock1 as they often contain unreliable material1 such as pockets and pot-holes of clay1 sand1 mud1 silt and detritus2 and movement may be expected if it be carelessly tipped with the rock into an embankment4 ,rocks which oppose vegetation are usually hard and weather-resisting1 and the faults and fissures local2 but it is not so much the equal weathering of the face of rocks that is to be feared1 as the presence and interspersion of seams1 breaks and fissures1 and it should always be borne in mind that the condition of a rock varies considerably--it may be sound in one place1 and be fissured1 disintegrated1 and quickly weather in others--and that all laminated and fissile earths are liable to slip because of the percolation of water down veins and crevices4 ,the durability of a rock may be approximately known by a careful examination1 commencing at the surface of the ground and proceeding until it is reached1 the thickness and character of the different top soils being noted1 and particularly whether the degradation is uniform2 but rock1 such as some sandstone1 which allows water to ooze1 permeate1 or force a passage1 is of doubtful stability4 ,weathering may be possible only upon the surface or may gradually extend downwards1 and as it can hardly be called a slip1 the point to ascertain is not so much that it is sound and weather-resisting1 as to know that there is no chance of any portion becoming detached or sliding1 through the cohesion of the joints being impaired or destroyed by water1 frost1 or other agencies2 for in the case of rocks which show irregularities of stratification1 much cleavage1 or are separated by upheaval1 or have synclinal and anticlinal folds1 masses become detached along the line of cleavage and independently of the normal stratification1 therefore fissures or faults1 weak veins between masses of rock and crevices1 or inclined beds through which water may flow and always be present2 the direction and inclination of the dip of the strata1 effects of weather upon the veins1 and to know the weight upon sloping ground which the rock will bear without sliding down a hill are the main considerations2 for rocks may be distorted1 upraised1 contorted and tilted at every angle1 and even horizontal beds may repose upon the upturned edges of other strata4 ,an inclined water-bearing stratum between rock loosely bedded and inclined towards a cutting1 unless drained and supported1 will probably cause a slip consequent upon the action of water or frost2 on the other hand1 veins may alone hold the masses together1 and1 therefore1 when they are affected the cementing medium is destroyed2 however1 inclined water seams are a frequent cause of slips1 for where any water-bearing earth meets a closer and consequently less pervious stratum1 damp surfaces are produced1 and an unstable condition2 consequently1 mixtures of rock1 clay1 and sand1 are usually troublesome4 ,also in a cutting in sidelong ground if a stratified rock dips parallel1 or nearly so1 to the slope of a hill1 slips are probable1 as it may slide towards the cutting4 ,similarly1 in a cutting in drift or alluvial soil1 or any that will quickly weather1 resting upon rock1 especially should it have a smooth bed inclining towards the formation1 the superimposed earth will usually be unstable1 and even the act of penetrating the top stratum1 or the erection of a retaining wall or the weight of a small embankment upon it1 may cause it to move2 and when motion has commenced it is difficult to arrest it2 and should water trickle upon the surface of the rock1 it may cause the upper stratum to slide2 also when water flows or remains upon rock having a superimposed bed of shale or clay1 the top stratum may not remain at rest even though the surface of the rock may be nearly level and practically waterproof1 and where rock beds overlie shale which is liable to become softened by time and water and to perish1 particularly when the beds are twisted or contorted2 as1 for instance1 limestone or sandstone upon shale or marly-shale1 the latter becoming softened by the action of the atmosphere1 water1 or frost will form a sliding medium upon which the rock may move1 or should shale overlie rock1 as it frequently does1 it may slide upon the hard surface4 ,all alternate beds of shale or any softer earth than the rock1 particularly broken shales when found mixed with sand and clay and the lias shales1 and rock should be regarded as treacherous and liable to slip4 ,also some of the slate rocks1 as they frequently have veins of limestone1 c41 and as the latter decomposes it mixes with the clay and becomes of a marly character4 ,dark blue shale or indurated slaty clay is sometimes difficult to excavate1 but when exposed to atmospheric and aqueous action it breaks into pieces and becomes little better than a treacherous clay4 ,the cohesion of shale becomes less as it approaches a greasy clayey condition1 and1 therefore1 one readily affected by water or air1 and it may then not stand at a steeper slope than #c to #a4 ,rock and shale1 which may stand at a steep inclination provided the beds are horizontal1 it has been found1 do not permanently repose when they dip towards a cutting until as flat a slope as #b to #a is given2 and where clay and shale beds in cuttings are present1 a slope of #a to #a has been insufficient1 and they have not been stable till an inclination of #b to #a has been adopted4 ,as cuttings in rock are frequently in the side of a hill1 the dip of the strata should be ascertained1 and in the case of an unstratified rock1 it should be known whether it is fissured or lies upon a solid and firm bed considerably below the level of a cutting1 so that it may be prevented from movement4 ,it should also be ascertained if the top stratum is a mere crust1 such as a capping of conglomerate resting upon clay-rock1 through which water may burst and cause it to separate1 and sometimes the rock may be more solid in the valleys than upon the hill-side because of greater diluvial action1 and induration caused by exposure4 ,the crystalline rocks are the least easily destroyed and are generally rough and jagged4 ,the science of geology shows that limestones1 sandstones and clays1 were originally heaps of mud deposited1 removed or arranged by water2 and that boulders are transplanted masses from the parent rock1 and are worn and rounded by mechanical attrition4 ,consideration of the manner in which rocks have been formed affords a fair indication of their stability in earthwork2 for instance1 many clay rocks are reduced to a pasty condition by the action of water and air1 but with different results according to their nature1 some requiring blasting to excavate them4 ,on the other hand1 there are sandstones which although soft in the quarry become hardened when exposed to the atmosphere4 ,a dock cut in red sandstone when exposed to the atmosphere may slip and fail1 but if the rock be protected from the weather or constantly covered with water it may be reliable4 ,as cuttings are near the surface and seldom at greater depths than #ajj feet1 it is hardly possible to know the angle at which a rock dips or whether there are faults and fissures in it1 unless an examination is made upon the site1 and this notwithstanding the geological character may be thoroughly understood4 ,local conditions may cause peculiarities which no law can determine1 and although at considerable depths1 deeper than railway or any works with the exception of well-sinking and mining are likely to reach1 the nature of the earth is accurately ascertained2 the surface soil may be in almost every conceivable variety1 and also so dislocated1 denuded and rearranged1 that usually horizontal strata may be nearly vertical4 ,its character may be accurately known1 but the lie of the surface beds or dip of the upper strata1 or the order of supraposition cannot be invariably absolutely established2 for instance1 when crevasses1 fissures and veins are frequent in earth upheaved and disintegrated by volcanic action1 earthquakes and other disturbing causes1 as in parts of ,south ,america1 ,japan1 and other eastern countries1 ,italy1 the ,tyrol1 ,spain1 c41 c41 slips of earthwork are to be expected1 and the soil is likely to be much inclined1 full of faults and probably water-bearing seams4 ,under the comprehensive name of rock is usually included any earth from the hardest mass to be found to that which will crumble in the hand1 as soft sandstone rock4 ,the chief absorbent rocks with which engineers have to do are the limestones1 sandstones1 chalk1 and clay rocks4 ,rock may also be simple or present the appearance of being homogeneous1 or it may be a mass of different substances1 be flat bedded1 have open or close joints1 and be what is called-- ,solid rock4 ,hard rock4 ,dense1 or compact1 rock4 ,loose rock4 ,rock in loose layers4 ,loose rock with cavities1 caverns1 and pot-holes of various earths4 ,fissured rock4 ,friable rock4 ,indurated earth liable to be disintegrated by atmospheric influences4 ,decomposed rock4 ,rotten decomposed rock4 ,or any mass of earth cemented together by a substance1 weather-resisting or not1 requiring blasting or that can be excavated by means of bars and picks4 ,the slope of repose required may range from overhanging or vertical to that of the earth of which it consists when disintegrated and dissolved2 therefore the angle of repose varies considerably1 but the following cardinal principles may be followed without fear under ordinary circumstances and conditions4 ,granite4 ,quartz1 if not fissured1 and when little mica is present in it1 and most of the igneous rocks1 ,overhanging1 vertical1 ,,to to #a4 ,also porphyry1 gneiss1 trap1 but their stability varies considerably4 ,compact hard sandstone and limestone and other solid sedimentary rocks producing stone sufficiently hard and weather-resisting that it can be used in construction1 ,perpendicular1 ,,to to #a4 ,but1 if non-weather-resisting1 to #a ,,to #a to #a1 ,the slope becoming flatter as the rock becomes softer and more easily disintegrated4 ,friable rock1 consisting of hard particles1 to #a ,,to to #a4 ,loose rock1 to #a ,,to #a to #a4 ,soft shaly limestone and the argillaceous rocks may not be permanently stable until the slope is1 #a to #a ,,to #b to #a4 ,schistose rock is troublesome in earthwork1 being fissile in structure and deleteriously affected by rain and the atmosphere4 ,on the ,panama canal works in the ,culebra cutting1 maximum depth #ccc feet #f inches1 numerous slips occurred1 displaced the roads1 and overturned the excavators4 ,mica-schist is variable and frequently has numerous water-bearing fissures4 ,its hardness depends upon the quantity of quartz it contains2 when the proportion of mica is greater than the quartz it is soft and very fissured and contains veins1 sometimes of clay1 often yielding a considerable flow of water4 ,should the percentage of quartz be large it becomes hard1 holds little water1 and is of a gneissose character4 ,as water is the chief disintegrating agent and cause of instability1 it may be well to mention that ,professor ,prestwich has stated that 8hard quartzites1 slates and grits 7,silurian71 purple and grey shales1 schists and fissile sandstones with hard compact limestones and dolomites 7,devonian71 rarely contain any levels of water1 and that it is only encountered in fissures02 hence the importance of knowing the position of the fissures1 and taking the necessary precautions to promote stability4 ,where rocks1 especially if generally known as water-bearing1 crop out at a high angle1 and are in well-defined beds1 water may be expected1 as although it may not percolate vertically1 it will along the inclined beds4 ,sandstone and limestone bands in rock usually cause small springs4 ,the stability of a sandstone for earthwork and purposes of construction is dependent upon the material which cements or holds it together1 whether iron rust1 lime1 free silica1 alumina1 c41 c41 c41 its quantity and condition1 and the degree of hardness imparted when it was formed1 and the nature of the agglutinant2 therefore the varieties and degrees of fineness and hardness are numerous4 ,sandstones are generally found to be laminated when hard2 and bare of vegetation if pure and free from marls2 they contain and part with water in different proportions1 and sometimes have watertight bands crossing them1 severing water communication1 which may cause earthworks to be of unequal stability4 ,the firmest and strongest are close-grained and fine in texture1 the weaker are coarse and gritty1 and have a sandy appearance4 ,they may be white1 yellow1 green1 black1 red1 grey1 brown1 or other colour1 and although of the same hue1 their character may not be identical2 for instance1 the red sandstone is hard and also very soft4 ,sandstone of a greenish hue is generally hard1 much fissured and full of water4 ,when firm1 greensand may stand at a steep slope1 the surface being protected2 but it varies considerably1 and may at one place be close and yet be gradually deteriorated until it is of the character of fine loose sand4 ,should it be found upon excavating sandstone that it is not upon its natural bed1 but distorted1 upheaved1 or vertical1 it will probably split and become detached under the destructive action of air and water4 ,in tropical climates it has been found that sandstones generally dissolve and become disintegrated when used in damp foundations4 ,limestone also varies much in character1 and is treacherous1 whether it is hard or soft1 when pockets of clay or sand are present and beds of clay are contiguous4 ,percolated water having carbonic acid in it may also soften or dissolve it4 ,the softer kinds if in fragments as ballast1 or when deposited in an embankment1 often become quickly disintegrated by frost and the weather1 as do sandstones4 ,should any rock strata be vertically inclined instead of horizontal1 although it may be known in the latter case they are generally watertight1 fissures in the upheaved beds may become channels for the passage of the subsiding or rising waters1 and may cause saturation of the soil over a considerable area and induce a flow through the slopes or the seat of an embankment4 ,upon such a site no reservoir1 dock1 canal1 or any earthen structure to hold water should be placed2 but although the nature of the ground may be fatal to the stability of such an embankment1 so long as the underground waters do not rise to the level of the seat of a railway embankment or flood a cutting or burst the slopes1 they may not seriously affect the stability2 for1 unless the head level of supply is great1 more danger maybe expected from downward percolation saturating the ground upon which the embankment is placed than from an upward flow4 ,the insecurity of erecting a reservoir or similar work upon such a site1 in which water is brought into a district in greater quantity than its natural flow1 is obvious1 as the earth may gradually become saturated from the constant leakage down the upheaved fissures1 until it becomes in an unstable condition and finally slips and subsides4 ,,chalk4 ,as in most public works1 with the except3on of tunnels1 wells and mines1 the chalk with which an engineer has to deal is surface chalk1 or the top layers of that deposit known as the upper chalk1 almost invariably containing much more water than the lower chalk1 although it rises quicker in the lower beds1 as it is under greater pressure1 and which vary in hardness1 purity1 and solidity and may have frequent fissures and holes1 with or without flints1 and be anything from hard1 compact chalk rock to mere marly calcareous earth2 considerable judgment is required to successfully determine the slope of stability and the precautionary works that may be necessary to attain repose2 for some of the upper beds soon weather1 and being soft1 friable1 and fissured are permeable and liable to slip2 in fact1 the ,oolitic series1 as it consists of alternating bands of limestones and clays and occasionally sandstone1 is frequently fissured and has loose joints and therefore requires to be carefully treated4 ,the range of the slope of permanent stability obviously depends upon the nature of the chalk1 whether it is denuded or covered or mere loose-jointed strata1 the effect ground and surface waters may have upon it1 and also the position of the beds1 and whether a cutting or embankment is on the side or the base of a hill1 and consequently at the place where it is likely to be in a wet condition4 ,the ,needle-rocks in the ,isle of ,wight and ,beachy ,head may be mentioned as familiar examples1 showing that firm and comparatively pure chalk will stand practically perpendicular1 even when much exposed1 if pure and free from faults and homogeneous in texture2 and in blocks with beds inclined away from a cutting it will permanently stand ,almost vertically ,,to to #a1 at a great height1 a slow regular crumbling of the surface or falling down of small fragments1 which seldom produce serious movement in such material1 being the only deleterious effect of weather influences4 ,as the chalk becomes broken and less evenly bedded1 about #a to #a4 ,loose1 friable chalk in surface beds will often not permanently stand at a less slope than from #a to #a ,,to #a to #a1 according to the depth and degree of exposure4 ,the most usual slopes being to #a ,,to #a to #a4 ,impure wet chalk and marly chalk will require a slope not less than #a to #a4 ,much depends upon its freedom from faults1 crevices1 and pot-holes1 as they hold water1 and the surrounding soil may fall away1 for water quickly passes in quantity through the fissures and crevices which are generally numerous in the upper chalk1 especially at the bottom of a bed of flints which in consequence of their impermeability lessen the upward flow2 but flint beds in soft chalk are an advantage1 as they act as drains4 ,the affinity chalk has for water1 which has been considered a reason for the absence of important rivers in that formation1 as water does not flow away freely upon it1 causes it to be readily affected by rain and disintegrated from the effects of the expansive and contracting action of frost and thaw2 hence draining and covering the surface may be important1 but care must be taken not to interfere with natural springs4 ,this property of chalk1 viz41 its affinity for water1 although a disturbing cause in earthwork in that formation is of value for covering or filling in open trenches1 counterforts1 or drains in other soils1 as the chalk attracts water1 and therefore dries the surface of other earths4 ,anything that localizes the percolation or flow of water1 or helps to make water seams1 veins1 fissures1 and hollows1 which are sometimes filled with sandy gravel1 loam1 and detritus readily admitting water1 will tend to break the chalk into separate masses and cause it to become loose and unstable by the action of rain1 frost and thaw1 and vibration4 ,should flint beds occur in chalk1 and they frequently do in the upper beds if they are horizontal or nearly so1 much more water may be expected to flow along their bed1 as it forms a water-passage1 than when they are in inclined or vertical seams4 ,as chalk absorbs much water1 but does not readily exude it1 although it may soon become dry upon the surface after rain1 it is advisable to lessen percolation in order to prevent slips4 ,it is known that the angle of friction of water in chalk will affect the flow and that the discharge varies greatly according to the character1 fracture1 and other conditions of the soil2 for instance1 it has been proved that a hydrostatic pressure due to a gradient of about #a in #acb is required to enable water to pass through the chalk as found at ,dover1 whereas in the ,hertfordshire beds much less is required1 namely1 that equal to a gradient of about #a in #cej to #a in #dbj4 ,this is named as showing1 even when unfissured1 the varying perviousness and character of chalk1 and that it cannot be treated as a material of even approximate consistency of texture4 ,the power of capillary attraction of chalk has been proved to be great and the evaporation from the surface practically unlimited4 ,these properties and its known affinity for water render it liable to constant change2 also the particles of calcareous soils being affected by moisture and to a certain extent soluble1 water will take up lime in them1 and therefore they are treacherous earths and liable to slip and subside4 ,professor ,ansted has shown that a cubic foot of the upper chalk when dried will absorb #b gallons or #dj per cent4 of its bulk of water2 the lower chalk #b gallons1 or #cc per cent4 of its bulk2 and that the pores of a cubic foot of chalk are equal to #dj per cent4 of the bulk1 and are therefore equivalent to the area of a pipe about #i inches in diameter4 ,ordinary drainage will not remove the water1 hence chalk is a difficult soil to treat successfully1 and slips and subsidences may result in such large areas as the surface of cuttings and embankments simply through the difficulty of preventing it becoming saturated4 ,another characteristic of chalk1 which requires careful observation to prevent slips1 is that water does not generally issue through a mass1 or equally over a consider able area1 but is discharged through fissures1 and crevices1 and flint beds2 hence one of the chief means of preventing slips cannot be adopted1 namely1 to disallow a localization of the flow of any water2 therefore1 the disturbing element of water seams is in greater or less degree present in all chalk-earth that is not solid and homogeneous in texture4 ,the flow from such water-veins or seams should not be interfered with1 as any obstruction1 and possibly diversion1 which is likely to fail1 will only result in the spring saturating the adjacent soil1 and in its bursting out at another place4 ,there is no safe remedy but to gently lead away the water1 for where springs occur1 either in chalk or rock1 they will find the line of least resistance2 consequently the waters of percolation will tend to flow to one place1 and cause a spring4 ,chalk is found in regularly stratified and separated masses1 sometimes caused by beds of flints1 and although the position of the layers may indicate their successive ages1 age can hardly be taken as an absolute indication of the increased stability of chalk in earthwork4 ,when overlaid with clay it is usually harder than when bare1 probably owing to pressure1 non-exposure to atmospheric influences1 and to the absorbed water being of a different character1 which has been proved by analyses4 ,it is especially advisable in chalk soils to know the head level of water in the district1 and to note if the bottom of a cutting is below the usual water-bearing line in the open wells1 which may not necessarily be at the same depth2 their average level being ascertained1 an idea can be formed of the probability of springs bursting out1 and according as the rainfall is excessive or not1 so usually will be the flow4 ,if chalk beds incline across a valley1 and have an impervious stratum of clay upon them1 it has been found that the most water issues at or about the point where the impervious seam first overlies the chalk1 i4e41 at the edge of the basin1 and the greater its depth1 the less the flow2 therefore1 should a cutting be located at a place where this stratum is thinnest1 more water from springs may be expected than at any point where the impervious layer is thicker4 ,it is also well to remember that the line of water-flow is not necessarily a horizontal plane1 for it frequently follows the contour of the chalk1 and that the causes of surface irregularities of subterranean water are unknown2 but rain-water accumulating in chalk principally rises and issues most rapidly along the bed lines2 consequently the flow along these must be gently discharged1 or slips will occur2 but chalk uniform in character and of solid and close texture1 without flints and fissures1 usually is not water-bearing1 and will stand almost vertically4 ,as a rule the cohesion of the upper beds1 if they are homogeneous1 is greater than the lower beds1 although the mass may be softer4 ,should the drainage or natural outlet of the land waters of a chalk district be obstructed or dammed back1 from the quantity of water being in excess of that the fissures or water seams in a chalk hill can discharge1 and the pent up waters be unable to escape1 hydrostatic pressure1 in addition to a weakened condition of the chalk through excess of moisture1 will be caused1 and extensive slips may be expected along the escarpment1 the displacement being gradual1 the ground separating and fissuring until at length it is pushed out by hydrostatic pressure4 ,such a slip usually occurs in large masses1 resembling a fallen cliff1 for the disturbing agent is all-powerful1 and the area affected very considerable1 and particularly so if the chalk is superimposed upon different soil1 or harder ground1 as then the whole mass will probably move forward4 ,although some approximate inclinations have been previously given1 the varieties of chalk are so numerous that no absolute slopes of repose can be named1 for chalk or calcareous earth may be3-- ,marble or crystalline limestone4 ,ordinary limestone rock4 ,hard1 compact chalk rock4 ,lower white chalk4 ,upper white chalk4 ,hard grey chalk4 ,ordinary grey chalk4 ,pure white chalk4 ,friable white chalk4 ,yellow1 light and dark blue1 soft chalk becoming of marly character4 ,hard chalk marl4 ,grey marly chalk4 ,grey clayey chalk4 ,,note4--,the preceding chalk marls contain so large a proportion of argillaceous matter as to become almost clays so far as regards treatment in earthworks4 ,many serious slips have occurred in chalk soils1 and their history indicates that the chief disturbing element was water1 whether held back over a large surface until the hydrostatic pressure became too great for the slopes to withstand it1 or from its bursting out in springs1 and so separating and disintegrating masses of the earth4 ,near the entrances to tunnels slips appear to be most frequent in cuttings in chalk4 ,this would seem to lead to the belief that in places where it is known the chalk soil is likely to be troublesome from land-water and springs1 it would be advantageous to prolong tunnels beyond the economic depth of a cutting1 and even to continue them until such a depth as #dj feet is reached1 to so arrange the gradients that they drain the interior1 and to provide a complete system of pipes and drains1 even if side galleries have to be driven to tap the water1 before it reaches the lining1 to relieve the sides1 crown1 and invert of a tunnel so that no water can pour down the roof or walls unless under control4 ,in a tunnel so situated and liable to water-pressure1 the thrust of the soil will be very variable1 and cannot be foreseen4 ,at one place during construction1 the walls and lining may be finished without movement of the earth1 at another1 the pressure maybe great and act unequally1 either upon the side walls or the arch4 ,as a rule1 at the entrances to tunnels the pressure is greater upon the arch than the sides1 for then the whole of the wedge-shaped mass within the boundary of the angle of repose of the soil is disturbed1 and its cohesion impaired or destroyed1 and therefore it presses upon the arch1 this pressure tending to counteract the lateral pressure2 but as the depth increases1 the load from this wedged-shaped mass becomes less upon the arch1 although generally greater than any lateral pressure1 because the earth above is not disturbed or impaired1 consequent upon the depth of the hill being greater and the cohesion and side-pressure of the earth tending to support it1 but the lateral pressure is increased because the normal pressure of the soil due to the depth is augmented4 ,it is this disturbance of such friable soil as chalk at tunnel entrances1 causing the particles to be loose and separated1 and in a state especially disposed to percolation of water1 that probably causes the earth to be in a condition favourable to slips1 and for them particularly to occur at or about the entrances to tunnels4 ,when1 therefore1 the depth of open cutting at the entrances is reduced1 any slip cannot be of the same magnitude as it would be if it happened at a greater depth4 ,the circular or one closely approaching it would appear to be the best form for the lining1 where variable or great pressure1 vertical or lateral1 is to be expected2 for the pressure in a tunnel will always be unequal1 and the surface of the earth must be supported4 ,in some experiments to join substances by pressure it was found that though great pressure forms chalk into hard blocks1 the particles are not firmly united1 and that they separate along the surfaces of contact of the original particles and not through them2 these tests tend to show that masses of chalk are usually in a state not indisposed to separation4 ,the same result occurred in similarly testing pulverised sandstone4 ,,sand ,,and ,,gravel4 ,in fine sand-cuttings springs may be expected1 and the earth become in a semi-fluid state if there is water at a higher level to filter through it2 also in the case of all porous and open soils4 ,any drawing away of the sand must be prevented1 as it will induce a slip1 and cause the earth to become running sand1 especially dangerous near buildings1 for its egress must be prevented1 or subsidence will ensue1 and serious erosion4 ,the excavation in such cases should be in as short lengths as practicable1 so that the surfaces are not unsupported1 and walls and structures should be quickly erected4 ,the sands that are met with in estuaries are frequently in such a condition1 that a slight obstruction to the tidal flow will cause movement1 the equilibrium being easily destroyed4 ,should there be a break in the continuity of a clay stratum1 overlying light loose soil1 the latter will probably boil up1 and in determining the depth of a cutting1 care should be taken that this impervious stratum is not broken or injured4 ,marl1 clay and sand beds are likely to slip when they are superimposed1 and there are some districts in which sandy soil is so charged with water that1 unless the drainage of the slopes and formation suffices to drain for some distance the land outside a cutting1 the sand will become overcharged with moisture and will act as a fluid and slip1 the lateral support being removed by the act of excavation and its normal condition altered4 ,being so delicately balanced the least additional disturbing force1 such as a spoil bank being tipped upon the surface1 or the inducement or acceleration of a flow of water1 will set it in motion and make it a quicksand4 ,for instance1 small sand islands have been removed by making cuts in them from #ae to #bj feet in width1 and by men shaking bars1 c41 inserted in the soil2 the sand along the edge becomes loose1 falls1 and the current sweeps it away4 ,as an example of the changeability of the condition of sand may be named that in sinking pits by congelation in loose sand it has been found that the grains during the freezing of the water1 by means of tubes containing a freezing mixture1 were additionally separated about #e to #g per centum4 ,as the sand met with in public works is seldom in very deep beds1 it has not been subject to the steadying forces which many earths have undergone1 and it may have been constantly moving until its final deposition1 and therefore it is easily set in motion2 and although sand will subside less from a load after it is saturated with moisture1 the water in it trying to escape may cause it to slip upon an unsupported surface such as a slope4 ,many experiments have shown that the power of absorption of sand decreases with the fineness of the grain1 and that sand when thoroughly wet will contain water equal to about one-third to two-fifths of its bulk1 and that almost all this can be drained2 hence its varying condition and instability4 ,if a well be sunk in sandstone and regularly pumped it will drain the rock around for some distance1 the drainage space being conical1 its vertex the bottom of the well1 and its base the surface1 varying in extent according to the nature of the soil and depth of well1 showing the porous nature of sand4 ,the interstices of silicious sea-sand1 when not compressed1 have been ascertained by ,mr4 ,j4 ,watt ,sandeman1 ,m4 ,inst4 ,c4,e41 to amount to about #dj per cent4 of the volume of sand4 ,for coarse or fine sand1 or a mixture of the two1 the interstices did not vary much4 ,when it was compressed by a rammer in water1 its bulk could be reduced to the extent of #ab per cent4 ,the interstices of broken red sandstone1 varying in size to that which would pass through an #h-;inch ring1 were found to be #cf per cent4 of the whole volume1 but as the stones were in contact #aj per cent1 must be added1 and if under water #ae per cent4 ,per cent4 of the interstices4 ,broken ,welsh limestone to pass a #c-;inch ring #eji ,gravel1 free of sand4 ,small pebbles to pieces gauged by a #ccf #be-;inch ring ,welsh limestone and gravel as above mixed in equal #cdj proportions ,mason's shivers of ,anglesey limestone1 small gravel to #dhj pieces gauged by a #d-;inch ring ,runcorn red sandstone1 large1 varying in size from pieces #ejj to pass a #d-;inch ring to an #h-;inch ring ,ditto1 small1 varying in size from sand to pieces gauged #cdj by a #d-;inch ring ,the two preceding when mixed in equal proportions #cfj ,the experiments clearly show the known great capability of subsidence in sandy and open sandy gravel soils1 their clear water space1 and how easily fine sand may1 by a current of water1 become running sand1 and their adaptability for ramming and consolidation by moisture4 ,tipped sand when rammed will subside if saturated with water nearly as much as it can be beaten down1 which shows how greatly its bulk is affected by water1 and although its rapid consolidation is an advantage in embankments1 it is of importance that percolation should be equal4 ,the chief conditions of a safe foundation upon pure sand1 namely1 that it cannot escape laterally or be undermined1 are obviously not to be attained in either cuttings or embankments1 as the lateral support is removed1 and the slopes are liable to be undermined and unequally charged with water1 and the influence of water on sandy soils is the principal cause of their instability1 for in excavating cuttings the face will frequently stand at a very steep slope if dry1 but upon its becoming saturated the sand may flow1 and in the case of gravel and sand1 although the stones forming gravel do not change1 the whole subsides4 ,as gravel is found in various conditions1 it may be well to classify it as it is herein regarded4 ,clean gravel is considered as that which nearly approaches the condition of a pebbly beach4 ,if an appreciable quantity of sand is present1 it is sandy gravel4 ,if loam1 or marl1 or clay1 it is loamy1 marly1 or clayey gravel4 ,gravel hills are large accumulations of water-worn rocks1 and may have boulders in them intermixed with the freshwater deposits of sands and marls1 and by means of natural cementing material between the particles seem to be firmly set and to be so conglomerated as to appear to be in a similar condition to weak concrete2 but there is always a chance of the matrix becoming dissolved1 therefore it is advisable to test a mass by the application of water and to expose it to the atmosphere before relying upon its permanent stability1 and with the view to determine whether it is hard cemented gravel or not4 ,gravel may be made more compact and will subside if water is pumped upon it and allowed to filter through1 and in making an artificial foundation of gravel1 it is not reliable without water percolation and consolidation by ramming4 ,all earth consisting of particles having rounded surfaces is liable to become loose1 and upon weight being placed upon it the grains are inclined to roll and become detached1 but if they are angular fragments1 which seldom is the case1 this tendency will be lessened1 and the angle of repose will be steeper4 ,with regard to the slopes necessary in sand and gravel1 the more angular1 rough1 hard1 and clean the particles1 the steeper the inclination4 ,earth that can be properly called gravel seldom requires a flatter slope than #a to #a1 and usually a less inclination is sufficient1 but if loose it will not stand vertically even for a depth of a few feet4 ,solid indurated masses of gravel will stand perpendicularly and as rock4 ,if the gravel consists of quartz or sandstone boulders1 or is very coarse with stones of considerable size1 or like a clean pebbly beach1 #a to #a ,,to #a to #a4 ,ordinary clean gravel of uniform size at about #a to #a4 ,thoroughly compressed1 hard1 clean sand1 about #a to #a4 ,looser sand and light gravel1 #a to #a ,,to #a to #a4 ,irregular beds of sand1 gravel1 clay1 and fragments of rock1 #a to #a ,,to #a to #a4 ,sand mixed with vegetable matter1 argillaceous or loamy sand1 about #a to #a4 ,as the proportion of mould or clay in the sand becomes greater a flatter slope is necessary according to the nature of the earth with which it is incorporated1 the degree of wetness1 and also the exposure of the surface4 ,clay loams require slopes from #a to #a ,,to #c to #a1 and shifting sand when a current of water reaches it will become a quicksand1 and not be stable even when horizontal1 but if drained and the toe is secured it will usually stand at an inclination of from #c to #a ,,to #d to #a4 ,on the other hand1 an embankment of hard1 clean1 angular sand1 rammed but left bare1 when exposed to tidal action with little wave disturbance1 has reposed at #b to #a ,,to #b to #a slopes4 ,loamy soil and vegetable mould will1 for any height not exceeding about #e feet1 stand nearly vertically for a reasonable time4 ,,clay4 ,with respect to cuttings and embankments in clay soils1 perhaps no earth is more affected by water and air1 or more difficult to treat1 as it will expand if only exposed to the atmosphere and without contact with water1 #f inches being no unusual dimension to allow for expansion in tunnel-work4 ,this property and its contraction upon drying alone make it an earth particularly liable to slip and induce fissures and cracks through which water can trickle1 notwithstanding the surface of the clay may be almost impermeable4 ,if clay could always be kept dry or in its natural condition it would be stable and free from slips2 but this cannot be effected1 for water is held in suspension in clay for a considerable period1 its plastic nature preventing gravitation1 and evaporation is known to be a very slow process2 and as the same clay under different circumstances may stand nearly vertically or only at a very flat slope1 its liability to constant change makes it very treacherous1 and it should be classed as a most deceptive earth of a dangerously unstable and unsafe description1 for it may be so hard as to nearly turn a pick1 and yet water and air will rapidly cause its disintegration1 but if weather influences can be prevented from reaching it when in such a hard compact state it will afford a firm foundation4 ,london clay in its natural condition usually contains about #aj per cent4 of water4 ,the more permeable the clay the more likely are slips to occur and the face to become soft1 loose and disintegrated1 slimy beds being thus produced which are difficult to prevent or remove2 therefore a covering of close grass turf1 or layer of burnt ballast1 ashes1 or chalk1 upon any damp place or fissure after it has been filled is advantageous4 ,solid blue clay1 which generally requires the use of the pick1 of the clays is1 perhaps1 the most stable1 being almost impermeable if free from delaceration2 but yellow and most other clays are unequal in texture1 faults and breaks are frequently numerous1 and water penetrating converts the surfaces and the mass into a muddy and semi-fluid condition resting only when horizontal1 which has been painfully experienced in the crushing in1 during construction1 of some tunnels in the ,london district4 ,the trickling of water down fissures forms a slimy and easy-sliding surface most difficult to treat or prevent1 and so long as the natural contour of the ground does not offer resistance to movement1 a slip may extend for a long distance1 either in deep or shallow cuttings1 and there may be considerable hydrostatic pressure4 ,the disruptions1 variableness of character1 and existence of fissures cause any but the most homogeneous clays to be treacherous and likely to slip1 particularly the yellow and any laminated clays1 as they allow water to enter by the veins which are usually frequent in the mass4 ,yellow clay has a greater tendency to crack upon drying than blue clay and does so much more quickly1 hence its dangerous nature1 and although a mass may be only damp1 fissures will enable water to penetrate and reduce it to a state of instability2 it is also not infrequently in a plastic state1 having fissures and cavities full of water4 ,it should1 however1 not be forgotten that in the endeavour to prevent the deleterious effects of aqueous action upon clay soils that they may be over-drained1 so that they become too dry1 as then the clay will shrink1 crack1 and fissure2 the chief aim should be to keep it always in a sufficiently moist state so as to obviate the formation of cracks and fissures1 and at the same time cause it to be dry enough to be firm1 and never in a pasty or pulpy condition2 in other words1 to maintain its natural state if one of stability1 and prevent any excess of water penetrating it or reaching its surface4 ,the lias clays are treacherous chiefly owing to the presence of much calcareous matter1 and therefore approach a marly state2 heavy slips have occurred in the has formation in the midland counties of ,england1 notwithstanding that a slope was adopted which experience had shown produced stability1 namely #c to #a4 ,a slight variation in the composition of this soil or an unfavourable position will cause a slip in such treacherous earth4 ,pure clay shrinks some #e per cent4 in drying1 the contraction being less as sand is present in it1 for when it is mixed with twice its weight of sand it is reduced to #c per cent41 and as impurities increase in clays the less impervious they become4 ,most clays have silicious earth in them1 but if sand is present the clay is then more open1 and water will permeate and drain more freely2 but mixtures of clay and sand may assume a pulpy condition when impregnated with water1 consequently it is always advisable to test such earth4 ,the varieties of sandy clay are many1 and all are usually more or less unstable4 ,among them may be named red clay with sand and mica1 blue sandy clay1 sandy green clay1 stiff red sandy clay1 the loamy clays of various hues1 dark grey1 red sandy1 and black clayey loams4 ,if clay could be kept in a moist state fissures would seldom occur4 ,the constant alternation of wetness and dryness creates the fissures1 and water completes the disintegration4 ,there are a few clays which are stable when kept in solid masses1 as then only a small surface is affected by air and water1 but if they are loosened and broken up1 as in the process of excavation and deposition1 they readily become in a muddy condition4 ,any mud or silt which may be soft and readily pressed when wet1 but cakes and shrinks in to detached lumps when dry or upon being exposed to the atmosphere1 is a treacherous soil1 as it will return to its original state upon becoming wet4 ,clays or any soils that cake should always be regarded with suspicion1 as although having the appearance of solidity and the possession of weather-resisting qualities in their natural position1 when disturbed1 quickly become worthless for earthwork purposes1 and may stand in one situation almost as a soft clay1 and when disturbed and wet assume a horizontal surface4 ,such ground may repose at a #d to #a ,,to #h to #a slope1 because its crust has become caked or case-hardened1 yet when it is broken it may become1 upon being exposed1 simply fluid mud4 ,to prevent clay soil weathering upon the surface1 a layer of gravel #a foot or so in thickness has been placed upon it1 the idea being that it is not only a protection1 but the weight of the covering upon the clay will cause the water to be pressed out from the soil into the gravel through which it can percolate to the drains4 ,a crude test to indicate the probable character of a clay as regards its stability in earthwork is to burn a piece of it and notice the colour4 ,if it becomes white or of a whitish tint1 the clay is generally less likely to slip than when it is of a reddish or yellowish tinge4 ,another rough experiment can also be made4 ,get a piece of clay1 place it in water1 and note the time taken and the depth to which the surface has become saturated1 and whether it is very slimy and will easily slide down a slightly inclined plane2 its tenacity may then be approximately judged4 ,also by weighing1 an idea of the amount of sand may be imagined2 the more sand there is in clay the lighter it will be1 all other conditions being identical4 ,a comparison between two clays will enable some opinion to be formed of their relative stability in earthwork1 though1 of course1 there are many other features to be considered4 ,all impure clays1 such as shaly clay1 sandy clay1 loamy clay1 and marly clay require to be carefully treated1 although they may be easier to manage than yellow or brown clay4 ,when two retentive clay beds overlap or overlie1 and have no intermediate permeable stratum1 they must be in a humid state1 as is the case in the ,fen country1 unless they are constantly drained2 but serious slips are not so likely to occur in them as when two masses of clay have an interposing seam of sand or silt liable to be eroded by water falling down fissures in the clay1 which probably extend to considerable depths1 with the result that two slimy surfaces are formed and the clay slides4 ,clay underlying gravel often contains numerous pockets and seams filled with running sand1 and should there be a permanent head of water the discharge will be in large quantities and at a considerable velocity4 ,a cutting in wet sandy clay is generally treacherous and difficult to manage4 ,as a clay bed near the surface of the ground is sometimes upheaved1 if a permeable stratum such as gravel or sand overlies it1 the drainage of water through or down the slopes will be arrested1 and the earth at the back of the slope will be constantly wet and may ultimately become saturated through the damming back of the water2 then a slip may be expected4 ,all upheaved1 dislocated1 and twisted superficial beds of clay1 which will generally be of varying consistency and therefore settle unequally2 over or underlying seams of sand or gravel1 are likely to slip and subside1 and their stability much depends upon whether or not the lie of the beds obstructs the permeation of water4 ,if the dip of the clay-beds is towards the natural outfall1 most probably an adjacent river1 slips are probable because of the creation of sliding surfaces and the continuity of the beds being destroyed by a cutting and the consequent loss of support4 ,should permeable soil lie between the top stratum and a bed of clay1 water will accumulate upon the clay1 make it slimy and cause a flow upon the bed2 for example1 when a thin bed of vegetable earth rests upon gravel1 sand1 or peat1 and that upon clay1 water will percolate1 and perhaps air1 through the top soils1 and may cause them to slip upon the clay-bed4 ,also should a layer of clay overlie permeable strata1 as clay upon sand1 or clay upon gravel1 unless it is sufficiently thick and solid to prevent infiltration1 it may slide upon the permeable soil as its lower surface becomes wet4 ,when clay-hills have veins1 water may accumulate in them and flow1 and if very dark yellow clay overlies light yellow calcareous clay1 which may rest upon hard blue clay1 it is obvious each stratum is somewhat differently affected by weather and air1 and therefore movement is to be expected4 ,the edges of clay-hills are always likely to slip1 especially should they be in the form of spurs4 ,boulder-clay is seldom reliable1 because1 although it may be hard and stand vertically in dry weather1 in wet it swells1 weathers quickly1 becomes soft and cakes upon drying4 ,the stability of such soil is governed not only by the nature of the clay1 but by that of the boulders and their effect upon the earth in which they are embedded1 and much depends upon the degree of changeableness upon exposure to air and moisture of all the particles of which they are composed2 hence boulder-clay1 although hard to excavate1 may quickly dissolve4 ,on the contrary1 it may occasionally be so hard that it seems to be solid rock1 and may even resist erosion and weathering as well as if it were rock2 but care must be taken to prevent indurated mud being mistaken for solid clay-rock1 and therefore it is advisable to test the soil with water4 ,seams of silt1 soft pasty soil1 or soapy earth met with in clay1 which have become decomposed by atmospheric and aqueous action1 are to be feared1 and the brown clay1 especially when soft3 red1 or dark yellow clays that break into lamin and crumble upon exposure to the air1 and although tenacious in the flakes and when fresh-cut are loosely held together in bulk1 often have thin veins of sand in them2 and when water percolates it remains1 and is very difficult to drain4 ,it has also been found that when minute non-adhesive particles of mica are present in clay that it will become disintegrated by water1 although it may be hard to excavate4 ,some of the gault clays1 although stable when dry1 become soapy when wet and are not easily managed1 but the bluish grey gault is usually tenacious and almost impermeable4 ,the gault clays have little sand in them but much calcareous matter1 and1 as a rule1 they do not swell and bulge like the ,london clays4 ,some clays1 when dry1 appear to be stable and firm1 though they are often drift or dried-up mud simply requiring the influence of water and the atmosphere to cause them to return to their original state2 the brown and boulder-clays are of this nature and are distinctly perishing1 and therefore treacherous clays4 ,as in clay and all retentive soils1 water is always present1 and as the impervious nature of clay prevents water gravitating and being drained1 and as owing to wet seasons the permeable portion of the clay may gradually become overcharged and be reduced to a muddy condition1 slips may occur years after a clay cutting has been excavated or an embankment deposited4 ,in clay embankments the greater weight upon the centre may gradually press water towards the slopes and cause them to slip2 hence the value of covering the formation in order to lessen percolation4 ,cracks and fissures may be so produced in clay embankments1 and the danger is that they form sliding surfaces and cavities from the presence of water1 and gradually soften the interior until it fails from the thrust of the earth and want of uniform support2 therefore1 clay earths are more difficult to treat than granular soils1 as local weakness is the cause of failure1 a mass may be sound1 but a crack or fissure may soon become large and pass through an embankment to the seat or the slopes4 ,although the filtration of still water may not cause an embankment to slip as long as the water merely restores it to its normal absorbing power1 when that is exceeded the percolating water will be dammed-up and cause hydrostatic pressure and a soddened surface1 destroy cohesion1 and disintegrate the particles4 ,when clay is contained within the walls of a building1 injurious action and unequal settlement may arise1 as the earth inside and outside may be in a different condition2 consequently in soils that expand and contract there may be external or internal pressure according to the state of dampness or dryness1 consequent upon the ground outside being subject to weather influences and the contained earth being comparatively free from such operation4 ,shale1 whether black or brown1 may become decomposed by water and be softened by time1 and is either loose or firm4 ,if loose1 it requires protection1 and the surface should not be exposed to the weather4 ,the presence of iron pyrites in shale has been found to be a cause of its becoming treacherous when water has access to it1 as the mass becomes decomposed4 ,marly soils are of various hues1 red1 blue1 grey1 and yellow1 and consist principally of clay and lime1 and are usually called clay-marls when clay preponderates1 and marl-clays or chalk-marls when chalk is in excess4 ,they are dry to the touch and will effervesce with acids1 the presence of lime being thus made evident by the ebullition produced1 and some idea of the relative quantity may be judged by comparing results with different lumps3 they vary in character according as lime or clay predominates4 ,chalk-marl may act as an almost impermeable stratum and arrest the percolation of water from more permeable soil1 but it is liable to slip because of fissures being present in it1 which are common to most calcareous earths2 and when these crevices are bared in cuttings by the ground being excavated1 the flow from the previously-confined or diverted springs is facilitated1 and perhaps the harmless underground passage of water is prevented1 and consequently the earth may become loosened and unstable owing to the changed condition4 ,although marl may be so hard that it cannot be excavated by picks and bars1 but requires blasting1 some varieties crumble and become soft under weather influences1 and the slopes need protection1 or a constant trickling and wearing away of the surface will result4 ,grey marl generally weathers quickly1 and if there is much clay in it1 it often falls to pieces upon exposure to the air1 and becomes broken and so split into disjointed pieces as to admit water1 and as it sometimes contains a considerable quantity of sand it is soon reduced to an unstable state1 for marl-clay and sand beds are always likely to slip4 ,the variegated marls are treacherous1 but red marl is usually stable1 still it must be lined in tunnels2 and so are those that are impermeable or closely approach that condition1 but any marl in which the lime may separate from the mass is unstable4 ,all clay or marl soils that soon work into 8slurry0 may be classed as treacherous1 or any earth that quickly becomes in a liquid state2 for instance1 some of the hard 8pan0 soil met with in ,canada melts away by the action of air1 rain1 snow and frost1 and becomes unmanageable and like blue paint1 and will quickly fill drains and run down the slopes and cover the formation of a cutting4 ,also the top black cotton soil found in ,india expands by aqueous action1 and contracts in drying as clay1 and is of doubtful stability4 ,as might be expected1 the more argillaceous or clayey marls when exposed to weather influences expand1 contract1 and act almost as clays1 becoming decomposed1 disjointed and separated1 and when superimposed upon rock1 especially if it be inclined1 are very likely to slip1 and are treacherous and unstable soils1 as they soon become in a muddy state and have slimy surfaces1 which1 when resting upon any dipping bed1 cause them to be disposed to move upon the smallest disturbing element being present or becoming increased1 such as water or vibration4 ,when a comparatively permeable stratum overlies even hard marl1 water will penetrate to the latter earth and the superimposed layer will rest upon an unstable bed1 and therefore be likely to slip4 ,blue1 or any marl when found mixed with layers of small gravel and sandy clay is very treacherous1 as air and water cause it to swell and crumble1 and it becomes in a soft state requiring a very flat slope4 ,all clay marls that swell when wet1 and crack and fissure when dry1 are unstable1 as water percolates to them1 and should sand veins occur in marl1 water may trickle to a considerable depth and cause the ground to be in a loose and doubtful condition below the formation or bottom of a cutting4 ,such soil when tipped into an embankment is worse to treat than in a cutting1 as it will absorb and retain water so that it is practically impossible to drain or extract it4 ,professor ,ansted has classed clay soils as under3-- ,when combined with #cj or #dj per cent4 of sand they are ,,clay ,,loams4 ,when combined with #dj to #gj per cent4 of sand they are ,,true ,,loams and ,,loamy ,,soils4 ,but not until they have #ij per cent4 of sand in them are they ,,sandy ,,soils4 ,when combined with from #e to #bj per cent4 of lime1 the soils become ,,marly4 ,but not until they have more than #bj per cent4 of lime in them are they ,,calcareous ,,soils4 ,with respect to the slope of repose in clay earths1 it may be anything from #a to #a ,,to #ab to #a1 and when the clay is mere dried mud and becomes saturated it may not be at rest until it is horizontal4 ,in cuttings1 strong compact clay1 if not seriously impaired by air and moisture1 will stand at from1 #a to #a ,,to #a to #a4 ,ordinary clay1 such as the blue clay1 with protected slopes and proper drainage1 and firm boulder clay1 about #a to #a ,plastic clay from1 #b to #a ,,to #c to #a4 ,lias clays of doubtful character1 #c to #a ,,to #d to #a4 ,superficial beds of ,london clay1 #c to #a1 and not less for any weak clay4 ,in embankments1 much depends upon the height1 mode of tipping1 state of the soil when deposited1 the protection afforded and uniform character of the mass1 the larger it is the more difficult it will be to drain4 ,although firm clay may for a short time stand at nearly a vertical slope for any height of face not exceeding about #aj to #ab feet1 few clays will permanently stand at a less slope than1 #a to #a1 for moderate heights1 although they may for a time do so at #a to #a in unsubmerged work1 but if the slope is covered with water1 as in a canal1 and subject to wash or wave action1 however shallow the depth1 it is seldom they repose at a less inclination than #a to #a4 ,should an embankment be more than about #cj feet in height #b to #a1 average4 ,firm clay from1 #a to #a ,,to #b to #a1 according to the depth4 ,plastic-clay1 consequent upon the percolation and pressure of water in cuttings1 may stand at a steeper slope in a surface protected embankment1 and if carefully tipped1 it will repose at from #a to #a ,,to #b to #a1 but from hydrostatic pressure the same clay may require from #b to #a ,,to #c to #a slopes in cuttings1 and even an inclination of #e to #a has been found to be necessary4 ,the varying slope-system is referred to in ,chapter ,,vi41 as also the range of slopes4 ,it is always well to bear in mind that in the case of clay1 loamy or marly soils1 or any possessing soluble particles1 the quantity of water in them governs the required flatness of the slope1 and as it may be variable1 a clay that will repose at a certain angle may slip upon receiving an additional amount of water1 hence the importance of drainage and protection4 ,the cohesive strength of clay also varies greatly2 and as it is likely to be impaired1 and1 perhaps1 destroyed by water and other causes1 it should be considered as of fluctuating value1 and therefore as generally unreliable4 ,the slopes of repose required in river-banks have a wide range according to the degree of exposure and opposition to the free flow of water1 and the protection given to the surface4 ,in canals1 and drainage-channels1 or ordinary rivers1 they range from #a to #a1 when protected1 to #e to #a2 but there are numerous small1 shallow1 and sluggish streams with almost vertical banks4 ,as the earth of river-banks is frequently of a clayey nature the slopes are referred to under the head of ,clay2 usually it is mixed in character1 and1 therefore1 the slope of stability cannot be determined from that of any particular and unalloyed soil4 ,towards the mouth the land often consists of detritus liable to be washed away by a stronger flood than that by which it was deposited2 it may also be eroded by constant or increased wave action4 ,ordinary clayey1 loamy1 tenacious1 or not easily moved1 silt and sand river-banks1 in a current that will not erode them at moderate depths1 if the face is protected1 will stand at an inclination of about #a to #a1 when the channel is freshly cut4 ,if not covered or protected at from #b to #a ,,to #c to #a1 but when in clay soil of a doubtful character and non-homogeneous1 or boulder-clay1 about #d to #a4 #b to #a ,,to #c to #a is the most general slope2 but in marsh land1 unless the surface is protected1 they may not permanently stand at #e to #a4 ,fascine-work may be the easiest and most convenient protection1 or a gravel or turf-covering may suffice1 and should new channels have to be created1 the question to decide is1 will it be cheaper to make the slopes sufficiently flat so that they can be left unprotected1 or is it preferable to have a steep inclination1 such as #a to #a1 and to carefully cover and protect the surfaces1 the probable cost of maintenance of the protecting cover being duly considered8 ,as a rule in homogeneous earth1 such as clay1 underground excavation is the most free from water1 and therefore from slips2 but the enormous force clay possesses upon swelling--and this disturbance of the soil may occur many times by the action of air and moisture--and its contraction upon drying1 cause tunnels in clay to be risky undertakings4 ,the chief precautions against failure are to allow plenty of space for the expansion of the clay1 reduce the uncovered lengths to the least dimensions1 have dry1 yet hard and compressible1 filling between the arch and the walls and the clay1 use the strongest bricks1 or material with great compressive strength for the lining1 adopt a form giving as equal support as possible in every direction1 i4e41 one closely approaching the circular1 leave plenty of weep-holes to prevent any accumulation of water1 and thoroughly drain and gently conduct to the proper drainage channels all water as it exudes4 ,,chapter ,,iii4 ,,the ,,general ,,effect ,,of ,a ,,slip ,,in ,a ,,cutting ,,or ,,an ,,embankment4--,,enumeration ,,and ,,consideration ,,of ,,some ,,protective ,,and ,,remedial ,,works4--,,treatment ,,of ,,the ,,slipped ,,earth4 ,with regard to the effect of a slip the chief consideration is1 will it be dangerous and prevent traffic or the unrestrained use of the work8 ,a problem most difficult to solve4 ,upon railways experience seems to show that slips of earthwork in cuttings of a depth exceeding about #aj to #ae feet are more to be feared as likely to interfere and stop the traffic than slips in embankments1 and particularly as1 except on sidelong ground1 slips in embankments seldom occur in which the whole of the formation is moved1 or becomes too unstable for a slow train to pass over1 and a temporary road can usually be maintained by timber trestles and baulks1 or other usual means4 ,when a slip happens in a cutting the fallen earth may cover the formation1 and it is certain that it can move in no other direction4 ,the permanent way may be entirely buried1 and it may be undesirable to excavate the slipped earth until other remedial works have been completed1 and therefore the traffic is stopped until they are effected4 ,in cuttings of little depth where a #c or #d to #a slope assumed by a cutting originally excavated to1 say1 #a to #a slopes1 will not touch the ballast1 the serious consequences of a slip are reduced to a minimum1 and may not interfere with the traffic1 and can be remedied by the road-men on the section2 but not so in the case of embankments4 ,consequently the depth of a cutting or height of an embankment must be regarded as a governing condition apart from other considerations hereinafter named4 ,the height or depth at which a slip in an embankment or cutting becomes disastrous cannot be ascertained by any rule1 but knowledge of the flattest slope at which any particular earth has remained stable in the same state as the embankment or cutting under deliberation1 will enable a close approximation to be determined of the point to which a slip in a cutting is likely to reach1 and that to which an embankment will subside4 ,for instance1 a cutting #ae feet in depth1 having originally slopes of #a to #a1 can assume practically #b to #a slopes without covering the rails1 and1 similarly1 a #aj-;feet cutting1 a slightly flatter inclination than #b to #a4 ,taking into consideration that for some little depth from the surface a cutting1 except in loose or treacherous soil1 will stand at a steeper slope than #b to #a1 perhaps1 on the whole1 apart from the formation of proper water-tables1 an engineer is not justified in making expensive provision in cuttings1 even in doubtful soil1 unless upon an inclined bed towards the cutting1 of a less depth than from #aj to #ae feet1 as they can be more economically remedied after they occur1 and meteorological influences have shown the location of the unstable portion4 ,nevertheless heavy slips have taken place even in cuttings of such a moderate depth as about #aj feet1 particularly in clay earths1 and it has been necessary to entirely suspend the traffic consequent upon a continuous mass of earth of shallow depth moving forward upon an unguentous stratum slightly inclined towards the formation1 and completely blocking up the cutting2 but this was an exceptional case4 ,there are many cuttings in all parts of the world under very different conditions of weather and climate1 and in every conceivable variety of earth1 in which nothing has been done to prevent movement1 with the exception1 perhaps1 of a surface-drain inside the fence and a water-table1 self-formed or otherwise1 near the foot of the slope2 and there are many cuttings and embankments without any precautionary works4 ,nevertheless they stand or require but little attention4 ,this fact naturally leads to the question3 when ought any works to be executed with the view of preventing movement in earthwork8 ,expenditure in precautionary and preservative works1 where they are not required1 and the serious consequences of a slip are reduced to a minimum1 cannot be defended2 nor can the absence of such preventive measures in treacherous earth or soil so placed as to induce instability1 and where the effect of a slip may be temporarily or permanently disastrous1 notwithstanding that economy in construction has now become the watch-word of railway-extension2 as then the expense of restoration and maintenance will be very considerably increased and far exceed the comparatively small cost of initial protection1 for public traffic may be stopped and injury caused to life and property4 ,the preceding and the following pages have been written in the hope that they may afford some assistance in arriving at a correct decision1 with regard to the necessity of precautionary works1 and with the view of calling to remembrance many of the principal points to be considered in order to remedy slips1 a matter usually demanding prompt decision4 ,with respect to the measures that should be adopted to prevent slips1 and the works required when they have occurred1 it would be a mistake to generalize from any successful application of one method of reparation1 as it is necessary to consider each soil separately1 and to discover the reason of a slip2 for an attempt to arrest the forward movement of a large mass will be futile2 the disturbing cause must be ascertained and removed1 or so lessened and controlled as to obviate further motion or deterioration2 sand or porous strata1 which may emit water uniformly1 must be treated differently to earth which sets free water in a particular place1 as also the same soil if it should be in a dissimilar condition4 ,the object of all such works is to support1 maintain1 and drain the earth and prevent any accumulation of water in the slopes and formation1 so that movement is improbable2 therefore1 water flowing towards the slopes must be intercepted and led away before it has time to percolate2 and the method of discharging it must be governed by the position and nature of the soil1 the chief aim of draining operations being to cause the earth to be always in its most consolidated condition4 ,without obstruction to the drainage1 a general preservative is to cover the surface1 and protect it against the deleterious effects of rain1 frost and thaw1 particularly in the case of soils which disintegrate rapidly under the influence of weather4 ,some of the means that can be adopted to prevent slips and subsidences in cuttings and embankments may be enumerated as follows4 #a4 ,systematic drainage of a cutting1 and the natural ground and deposited earth in an embankment1 so as to augment its weight sustaining power and general stability4 #b4 ,a side ditch near to the foot of each slope1 and at the top of the slope adjacent to the fence line4 #c4 ,catchwater drains upon the slopes4 #d4 ,wells1 filled with broken filtering material1 contiguous to the fence line and connecting drains with them4 #e4 ,open timber trenches1 strutted at intervals1 and acting as drains and counterforts1 at the toe of a slope4 #f4 ,a channel for the discharge of any water issuing from an intercepted field drain4 #g4 ,tapping springs in the slopes or formation of a cutting1 or that exist in the ground upon which an embankment has to be deposited4 #h4 ,the profile of the formation being made higher in the centre1 so that water will flow into the side drains or water-table and not remain1 due provision being made for its discharge4 #i4 ,side drains being made before the excavation is commenced or deposited4 #aj4 ,no accumulation of water being allowed upon the ground upon which an embankment has to be deposited4 #aa4 ,covering a slope with rammed earth1 burnt ballast1 chalk1 gravel1 ashes1 or other protective material4 #ab4 ,turfing a slope1 or sowing it with grass seed4 #ac4 ,depositing layers of material1 consolidated by ramming or otherwise1 upon a slope at right angles or diagonally to the line of the foot of a slope4 #ad4 ,by benching1 or a terrace or cess upon a slope4 #ae4 ,covering the toe of a slope with stone pitching4 #af4 ,dividing a slope by trenches filled with stones or absorbent material4 #ag4 ,weighting a slope to counteract the pressure of the internal water1 and to restore the equilibrium4 #ah4 ,a breast-high retaining wall at the toe of a slope4 #ai4 ,covering part or the whole of a slope with fascine mattresses or brushwood1 systematically laid in combination with gravel1 stone1 broken bricks1 ashes1 c4 #bj4 ,counterforts of gravel1 chalk1 burnt ballast1 ashes1 rubble1 c41 at the toe and upon a slope4 #ba4 ,a dry wall at the toe of the slope of a stratum of unstable soil1 found above the formation level and superimposed upon rock or firm earth4 #bb4 ,varying or increasing the flatness of a slope towards the bottom of a cutting or embankment4 #bc4 ,in cuttings1 by retaining walls1 with or without overhead struts4 #bd4 ,systematic planting upon the cess and slopes1 trees1 shrubs1 or bushes having deep wide-spreading roots4 #be4 ,the removal of any spoil bank that may have been tipped or cast out near the top of the slope of a cutting4 #bf4 ,removing the turf and all loose or decaying matter from the natural ground before the earth is deposited4 #bg4 ,clearing away all snow and frozen soil before tipping or excavating1 and taking care that no frozen earth is deposited4 #bh4 ,forming the ground upon which an embankment has to be tipped1 at an inclination downward from the toe of a slope1 towards the centre1 and the construction of a dry drain along the centre line so as to cause percolating water to flow away1 or prevent it reaching the slopes4 #bi4 ,benching the ground upon which an embankment has to be deposited4 #cj4 ,covering the ground upon which an embankment is to be tipped with a hard permeable layer4 #ca4 ,trenches filled with stones or other hard permeable material across the base of an embankment4 #cb4 ,covering the toe of the slope of an embankment with sods or making a counterfort of turf4 #cc4 ,running to spoil all saturated earth1 and suspending operations for a day or two after heavy and continuous rain or a fall of snow1 or frost4 #cd4 ,filling any large fissures as they appear4 #ce4 ,weighting the earth so as to condense it4 #cf4 ,increasing the area of the base of an embankment according to the bearing power of the soil4 #cg4 ,by the exclusion of all boulders1 roots1 turf1 branches of trees1 or bushes in forming an embankment4 #ch4 ,by aiding consolidation and preventing separation at the junction of two embankments4 #ci4 ,tipping an embankment in such a way as to promote consolidation4 ,in subsequent chapters many protective and remedial measures are specifically named4 ,here reference is made to the more general principles4 ,the purpose for which a cutting has been excavated1 or an embankment deposited must be taken into consideration in providing protective works1 for the surfaces may only be temporarily bared1 as in trenchwork for walls1 or be partly covered with water1 as in canals1 and entirely unsubmerged upon one side as in canal1 reservoir1 and reclamation embankments2 or be fully exposed to meteorological influences as in railway and road cuttings and embankments4 ,there can be no stereotyped system of operations for treating a slip1 but experience indicates that a frequently successful initiatory method is to divide the earth into small portions1 and to proceed to equally consolidate them4 ,however1 in the case of deep cuttings1 especially when excavated in the side of a hill1 it may be necessary to drive a heading beneath the formation and to connect it with a shaft upon the higher side1 so as to tap the water-bearing soil1 and to convey the water away to prevent it reaching the slopes2 this may be considered as a slip requiring an exceptional remedy4 ,should a cutting be in moving ground or permeable soil of doubtful stability1 such a system of wells and covered galleries1 which are generally successful even in the worst soil1 may be required4 ,the wells should1 if possible1 be sunk a few feet into an impermeable stratum1 their diameter being the least a man can excavate1 to any size required1 and their distance apart1 say1 from #cj to #fj feet1 according to the quantity of water to be collected4 ,they should be connected by drifts4 ,smaller intermediate wells can be made between the main wells4 ,in order to be effectual such works must be carefully and uniformly constructed1 or an accumulation of water will arise4 ,when a slip is known to have occurred1 simply from want of drainage1 a sufficient remedy may be the removal of the slipped earth and the insertion of drains4 ,an advantage of the loose counterfort system of drainage as compared with rigid and fixed drains1 is that open drains will follow a slight subsidence of the earth1 and yet maintain their efficiency1 but care must be taken that they do not become choked4 ,in shifting or doubtful soil all works should be quickly finished1 and in sidelong ground it is best to commence drainage operations on the valley side so as to tap the water1 as if they are begun on the hill-side they may1 until through drainage is effected1 form channels for the accumulation of water1 and cause a slip4 ,the repairs of a slip can be commenced at several places simultaneously if at short distances apart1 such as #bj feet or so1 and1 as a rule1 it is preferable in an embankment that the work proceeds towards the centre1 and not from the central portion to the slopes4 ,it is advisable to make ditches or galleries in short lengths1 not only to disturb the ground as little as possible1 but also to ensure perfect supervision1 as if the work is not carefully and uniformly constructed1 localization of water will ensue4 ,the extent of a slip will to some extent govern the remedy4 ,simple open stone-filled drains1 #b to #d feet in width1 and #a foot to #b feet in depth1 extending from the base to the top1 may be sufficient for shallow cuttings or embankments1 such as #aj to #ae feet1 and larger and deeper trenches above those depths or heights1 and complete drainage of and around the slipped earth1 and division of it by means of drains and pipes4 ,in countries where there is an excessive rainfall in a short time1 it has been found necessary to catch as much of the surface flood waters and torrential streams as possible1 and to reduce their velocity before passing through an embankment or down a cutting1 and to provide a pond or 8tumbling bay0 at the base of a waterfall for such purpose1 or to erect dams1 when the force is not too great1 so as to arrest and lessen the velocity of the flow4 ,without such precautions1 flood waters will erode the earth1 and the beds become gradually deeper2 and walls at the toe1 culverts1 and dry stone filling across the whole width of an embankment1 and stone covering upon the slopes where water issues or flows may be required4 ,catchment reservoirs have also proved of use in controlling the surface waters before they reach a cutting or embankment1 and in permitting them to be controlled4 ,many of the chief causes of slips in embankments are enumerated in ,chapter ,i41 c4 ,some of the most important operations to prevent slips in an embankment are to thoroughly drain its seat1 prevent a flow upon the surface of the original ground1 percolation of drainage waters into its lower part and filtration of rain-water at the crown1 and to generally protect the surface4 ,the stability of an embankment is not regulated by the cohesiveness of the soil1 as a sand or gravel embankment1 or that formed of any material whose particles are not deleteriously affected1 will stand with a sufficiently flat slope if protected against erosion1 and be more stable than a clay or any embankment in which the particles are soluble and soon impaired by water1 however great their original tenacity4 ,if any part of an embankment has become saturated1 the internal water must be tapped and drained2 as the lower surface portion is almost certain to be the wetter1 the drains should be made at the base1 trenches filled with open porous material upon the slopes1 and1 perhaps1 it may be necessary to sink a few shallow wells4 ,the slopes and formation should be covered so that when the excess of moisture is extracted from the mass it cannot be replaced4 ,porous earth counterforts can be adopted1 #f to #aj feet in width1 placed at intervals depending upon the nature and condition of the soil and height of an embankment1 or a continuous bank of similar material at the toe to support the embankment during the temporary weakening from drainage operations4 ,one of the worst cases that may have to be treated in embankments is in clay or marl soils1 when the central portion has been first tipped in a wet state in the winter months1 and after an interval the embankment completed to its required width in a frozen condition1 or nearly so1 or one in which the earth becomes frozen when deposited4 ,in ,russia it has been found that rain-water percolating into such an embankment cannot drain away1 but accumulates and finally bursts the slopes1 and that water will exude from frozen soil when it thaws1 a considerable time elapsing before all the frozen earth has thawed2 water is thus1 as it were1 taken into the mass1 which in all retentive soils will be difficult to drain without turning over the earth2 and it will cause slimy surfaces and general instability4 ,it will always be an expensive operation to make such an embankment secure1 and it cannot be made as firm as one properly deposited4 ,after subsidence has ceased1 an approved remedy in such a case is to cover the formation with an impermeable layer1 and to raise the embankment to the rail level with sand1 which is ultimately alone used for repairs1 the slopes being carefully trimmed and sown4 ,although not considered in the usual acceptation of the word as a slip1 the trickling of the surface soil is mentioned as it is a movement which may1 if allowed to proceed1 cause a slip1 and frequently necessitates attention because of the soil becoming in a liquid condition and flowing upon land beyond that acquired for any works1 and also because it obstructs and chokes drains4 ,it may be expected when a thaw occurs after severe frost1 or heavy rain succeeds drought1 or subsequent to a rapid change of weather in any earth of a clayey or calcareous nature1 as1 for instance1 in clay marl and argillaceous chalk cuttings or embankments1 and if the configuration of the ground should be favourable to its passage to land outside that purchased1 such issue must be prevented by protecting the slopes by means of a covering1 by draining1 or by the consolidation of the surface of the earth1 which latter operation may be difficult1 or by the erection of a small mound near the fence line4 ,in ground containing salt or other solvents in appreciable quantity1 care should be taken that water does not reach it2 if it should1 the soil immediately becomes damaged and subsides2 also it is found that the earth from which soda nitrate is manufactured in ,north ,chili must be kept perfectly dry to be secure as a foundation4 ,all soils of a salifiable character should be considered as likely to subside and slip4 ,in the salt-producing districts in ,england it is found that when the brine1 which is about #be per cent4 of the mass1 is pumped up to the surface to be made into white salt1 the land will subside1 as in effect it is pumping up the underground supporting stratum or rock salt bed2 and when a river is contiguous or copious springs1 the rock-salt will be supplied with water to make it brine4 ,the experience of those who have had to maintain embankments in these districts indicates that so long as subsidence is uniform embankments can be raised and maintained2 but when water penetrates into an old pit previously comparatively dry1 unequal and dangerous slips and subsidences may be expected1 and on so large a scale as to require much expenditure for restoration4 ,if the settlement is uniform1 the easiest way is to simply raise an embankment2 the rate of sinking varies considerably1 averaging1 say1 from #b to #e feet per annum1 and depending upon the amount of brine extracted and the percolation of water1 c4 ,it is obvious that embankments upon such land require constant attention to prevent serious slips4 ,at the edge of a cliff or hill where loose rock exists and is joined by clayey soil1 but is sufficiently stable not to slip in a mass1 it may be necessary to have a cover shed over a railway or road to prevent detached pieces of rock falling upon the surface1 the slopes from being injured1 and larger masses sloping down4 ,covering a slope in such a case is useless1 but an open deep trench1 specially constructed to catch pieces of rock1 may suffice4 ,important questions to determine when a slip has occurred are3-- #a4 ,should the whole or part of the earth that has slipped be removed8 #b4 ,how are the voids to be filled that have been caused by the slip8 #c4 ,can the disturbed material be again used8 #d4 ,what protective measures should be adopted8 ,a thorough examination of the site of a slip and the slipped earth is absolutely necessary before the most effectual and economical means of restoration can be determined1 for weakness or the presence of a disturbing agent in the upper or lower portion of a cutting or embankment may be the cause of movement4 ,an embankment may be solid in the mass and only portions may slip and subside1 but then may become unstable and require different treatment1 or local restoration may alone be necessary1 and the slipped earth to be removed be small in quantity4 ,extensive slips of the whole of an embankment usually occur from springs in its seat or the existence of a flow of water upon the ground under the base1 producing a greasy surface4 ,should it happen that an embankment of pervious soil is tipped upon impervious ground having a depression resembling a basin1 water will accumulate until it reaches the level of discharge1 and a serious slip may result4 ,in such a case the slipped earth must be removed and the water tapped and permanently drained4 ,the upper portion of an embankment may slip and the lower be stable2 if so1 it is not so serious as when movement commences at the toe and the slope bulges outwards and the embankment subsides2 in the former case1 provided the lower portion is not affected or its drainage obstructed1 it may not be necessary to remove the slipped earth1 but it is advisable to drain it1 and any localization or lodgment of water between the slipped mass and the firm part of an embankment must be prevented1 or the toe of the slope will be made in an unstable condition4 ,in cuttings in order to keep open the formation the whole of the slipped earth may have to be excavated1 but in embankments1 so long as the soil does not extend outside the fencing1 its entire removal becomes optional1 and is unnecessary provided further movement be prevented1 and the soil drained2 but in most treacherous earths1 although a slip may be arrested1 it will generally be a place requiring constant watching1 and be one of doubtful stability4 ,earthwork slips require to be remedied as soon as possible after they occur1 not only to repair them and obviate an interruption of traffic1 but in order that the unslipped portions may not be deleteriously affected and movement be induced4 ,when the earth is very soft1 silty1 and difficult to drain1 the only course may be to remove the slipped material1 although it may not be necessary to excavate all of it1 as it may form a reservoir for the accumulation of water1 and is certain to be liable to disturbance from the effects of weather2 but in firmer soil a portion of the slipped earth may be excavated1 and be rammed in layers inclining at right angles1 or nearly so1 to the surface of the slope1 and a drain can be inserted at about the bottom of the line of the slip to prevent any water that may percolate from the unslipped mass flowing into the rammed earth or any counterfort so constructed2 but counterforts may afford insufficient support in very treacherous soil1 and it may be necessary to remove either the whole or a considerable part of a slope and replace it with the best available material watered and rammed3 however1 the simple ramming of the earth and depositing it in inclined layers may not be sufficient to ensure stability1 and should it be found that the slipped material is very soft and cannot be readily drained1 it must be excavated1 and solid and firm earth put in its place4 ,when the base of a slip is level with the bottom of any side ditch that may have existed before movement occurred1 the drain should be below the level of the ditch1 or a flow of water may be induced at the seat which will probably cause further unsettlement2 and if a slip extends below the bottom of a cutting it is necessary to remove the slipped earth as far as the solid ground1 and to fill the void with dry material of sufficient weight to prevent the surface being uplifted1 and to cause solidity in order to avoid any movement of the toe of a slope4 ,when the slipped soil is clay or shale it can be burnt in situ down to the solid ground1 or upon an incombustible bed1 and be converted into a kind of brick rubbish and then be restored to its original place2 but this may be an expensive method1 and it may be cheaper to procure firm earth1 nevertheless1 should no other material be available it may be the only economical means of repairing a slip4 ,before deciding whether clay or shale shall be burned in situ it may be advisable to test the amount of ballast that can be made by1 say1 #a ton or more of coal1 and the cost including every item of expenditure3 #aj or #ab cubic yards of ballast may be obtained for every ton of coal burnt1 but this quantity may be so reduced that the cost of burning may prohibit the use of such a method for replacing the slipped earth when made into firm soil4 ,it much depends upon the quantity of water in the material1 and also upon the nature of the earth2 for instance1 burning becomes more difficult as the amount of silica in the clay becomes greater1 and the ballast is not so good as the quantity of lime increases in the clay2 therefore pure clay makes the best burnt ballast4 ,should it be decided to burn the slipped earth1 it is necessary that it be placed upon firm ground1 and that it rests upon an open layer of stone or material that will not kindle in order to obtain the necessary draught4 ,the thickness of the layers must be regulated by the degree of wetness of the soil1 from #a to #b feet being required for thorough burning1 and should layers of a less thickness than #a foot be required1 the process of making the slipped earth into burnt ballast will usually be too expensive1 but of course much depends upon the price of the coal upon the site4 ,the burnt ballast may cost anything from #as4 to #bs4 #f;d4 a cubic yard2 when the latter price is reached1 it may be cheaper to procure sound earth4 ,if the slipped earth approaches the condition of carbonaceous shale1 black or dark brown in colour1 it may kindle easily2 the more argillaceous shales will require a little coal to convert them to burnt ballast1 the quantity increasing as they gradually become of a clayey character4 ,blue clay1 when thoroughly burnt1 generally makes better ballast than most other clays1 but as a drain the ballast is not equal to clean gravel4 ,in considering whether it is only necessary to simply replace the dried earth in its original position1 it should be determined whether the undisturbed portion of an embankment will support the weight when unaided by counterforts with a foundation in solid ground at the toe of the slope1 trenches and drains upon the slopes1 and perhaps a rough stone bed below the seat of the slip acting as an open drain over part or the whole of it4 ,in any case provision must be made that there is no localization of water between the original embankment and the filling or the counterfort4 ,in some soils1 particularly those having seams of sand or silt1 the slipped earth frequently becomes displaced in layers1 and if allowed to remain1 each bed will form a water seam upon which any stratum can slide1 and then the earth may not be at rest until the slope is very flat4 ,the removal of the whole mass is the cheapest remedy4 ,the surface left bare by the slipped earth should be trimmed1 and all fissures in it be filled so as to prevent any accumulation or lodgment of water1 but the slipped earth should only be excavated in short lengths1 as it may render support and keep part of the face covered1 and it should be remembered that although the upper portion of the fallen earth may be the drier it may not be the most stable4 ,the system of removing the slipped earth1 erecting rough rubble walls at intervals of #bj to #cj feet projecting as far as the face of the original slope1 and then filling the intervening space with the material that has slipped1 when turned over and punned1 has been successfully adopted4 ,it is advisable to cover with turf the replaced earth in the slope1 unless some other protection is supplied4 ,when any signs of movement afterwards take place a few additional counterforts1 which1 may also be made to act as drains1 will generally restore the equilibrium4 ,this system relies upon preventing movement in earth by separating the masses of the slipped soil1 and draining and supporting them in detail4 ,the foundations of the counterforts must be in the solid ground and not merely below the seat of the slip4 ,it may be impossible to drain the site of a slip or the soil that has moved without dividing it into portions1 the chief object being to thoroughly drain the site and the slipped earth1 so that it is practically encircled with drains and any water prevented from collecting in or upon it4 ,when the land is of little value and a cutting is in a mountain or hill-side1 it may be advisable to assist an extensive slip1 provided it happens before any public works are opened for traffic2 and to remove the earth by loosening it by the action of a stream of water until it slides away1 as draining or supporting it may be insufficient4 ,under such circumstances it is the best course to adopt1 especially if a stream of water can be readily diverted to it as the unstable soil is finally disengaged4 ,,chapter ,,iv4 ,,notes ,,on ,,the ,,percolation ,,of ,,water4--,,systems ,,of ,,drainage ,,of ,,cuttings ,,and ,,embankments ,,in ,,different ,,kinds ,,of ,,earth ,,and ,,under ,,diverse ,,conditions4--,,the ,,construction ,,of ,,culverts1 ,,pipe-,,drains1 ,,trenches1 ,,ditches1 ,,and ,,catchwater ,,drains4 ,with respect to the percolation and drainage of water in cuttings and embankments1 in cuttings the chief consideration is to gently extract and conduct the water so as to avoid any accumulation or localised flow beneath the original surface of the ground in order to prevent the surface water eroding the slopes or collecting or forming a course1 saturating the ground outside them1 and to ensure that the earth is not more charged with water than when in its normal condition2 for1 as soon as the state of absorption has reached that of dissolving or separating the particles1 however fine1 aqueous action is likely to produce slips1 and a flow of water or vibration will supply the disturbing force necessary to commence a movement4 ,in embankments one of the chief precautions is to obviate any flow of water upon or at a few feet beneath the land upon which an embankment has to be deposited1 as it will disturb the feet of the slopes and the base1 reduce the adhesion to and the friction of the tipped earth upon the ground and form a sliding surface4 ,an accumulation of water upon the formation must be prevented1 and1 as in the majority of cases a railway or road is not level1 any collection of water at the commencement of an incline or at a change of gradient should be provided against1 and especially any localisation of flow down the slopes from the formation2 the main point being to keep a cutting or embankment in a uniform state so that settlement is equable4 ,by carefully watching the effect of heavy rain upon the slopes and the formation1 the places where water amasses can be traced1 and means used to restore the surface to the same condition as the other portions of a cutting or embankment4 ,as water is the chief cause of slips1 the friction and cohesion of earth being impaired and1 perhaps1 destroyed by it1 it is obvious that at the time percolation1 which varies greatly with the seasons1 is at its maximum1 i4e4 when the earth becomes in a damp or wet state1 slips are to be most expected1 and particularly soon after the commencement of the wet season4 ,it is known that upon the thawing of a heavy fall of snow1 and of quickly succeeding and separate falls of snow1 percolation is great2 also after heavy and continuous rains1 especially if the strata dip towards a river1 and in the case of springs whose yield depends more upon percolation than the amount of rainfall1 a wet winter will cause an increased flow some time after1 when the earth may become saturated4 ,if it could be determined at what depth in any earth in any state percolation1 evaporation1 and meteorological influences would cease1 and also their effects1 rules could be deduced for guidance in draining cuttings and embankments4 ,the manner of the execution of ordinary cuttings and embankments is so dissimilar to that of filter-beds of waterworks1 that the experiments made for such purposes are only of comparative value for the former works1 for the condition as well as the character of the soil affects its permeability by water4 ,for instance1 in cuttings1 with the exception of some surface disturbance during the process of excavation1 the removal of vegetation or a covering1 and the exposure of the ground to the atmosphere1 c41 the normal state of the earth is not much altered2 but in embankments different soils may be intermingled in a manner almost unknown in nature1 the varieties of mixtures of earth being most numerous1 and they may be in every condition of compactness1 dryness1 and dampness amounting almost to saturation1 and in any case1 therefore1 percolation is temporarily or permanently increased consequent upon the earth having been disturbed and loosened4 ,the general principles of the percolation of water are here only briefly referred to1 as they particularly concern slips in earthwork3 but obviously the quantity of percolated water greatly affects the stability of a slope1 for the surface water should not be guidelessly allowed to soak into or be absorbed by the ground at the top1 and so proceed through and down the slopes1 as then the pent-up water tends to press out the face which may be temporarily sun-dried4 ,as in excavating cuttings the surface is bared and vegetation removed from the soil1 water has easier access1 and unless the ground when excavated is immediately covered as before1 its normal state is not preserved4 ,one point of considerable importance is to ascertain whether in any cutting or embankment percolation is uniform and regular2 some infiltration will necessarily take place1 as water will gravitate from the top to the bottom and will find the easiest course or line of least resistance1 which may not be at the lowest level4 ,as the amount of the annual rainfall varies greatly according to the country1 and1 even in ,england1 considerably in a small area1 the earth will be more affected in one place than another2 for instance1 #dh to #ej inches is approximately the annual average rainfall upon the extreme ,s4,s4,w4 coast of ,england1 being greatest at the highest level nearest the sea and to leeward2 it diminishes gradually from ,w4 to ,e4 to from #bf to #bd inches1 the minimum of about #bj inches being in ,essex4 ,the differences of quantity must therefore be regarded2 but such rainfall is as nothing compared with that of tropical lands1 for the fall often continues many hours1 and yet equals and perhaps exceeds an inch per hour4 ,the heaviest fall and its usual time of appearance should be ascertained1 as earthworks may have to be constructed in a peculiar district where the rainfall may be more than double that of the average wettest district1 and it will often be much greater at the foot or the top of neighbouring hills than on a flat coast4 ,local information from reliable sources is the best guide when confirmed by general knowledge4 ,in the tropics #ajj to #bjj inches in depth of rain instead of #bj to #cj inches has to be treated1 and frequently half the total annual rainfall in ,england comes down in twenty-four hours4 ,it is almost superfluous to name that the protective works which would be amply sufficient in one country may be useless in another1 simply because of the variation in the amount of the rainfall and the capacity of different earths to resist or invite the percolation of water4 ,obviously percolation will vary considerably with the seasons1 and a succession of wet periods or a continuous downpour will increase the quantity of infiltrating water2 but the effect of a fall may not be experienced until some time after it occurs1 as in districts or rivers that are fed with water from the thawing of snow upon surrounding or distant hills water reaches the lower tracts of country in hot and sunny1 and therefore generally dry weather1 when evaporation is the greatest1 and not in winter4 ,again1 there is generally very little rainfall over flat deserts1 but an excess upon mountain ranges which may surround a desert1 and especially in tropical countries experience has proved that storms and rainfall are often local and extend over a small area1 one district being more liable to such a visitation than another2 they are also1 as usual1 of irregular duration and severity4 ,the position of a river may also affect the percolation of water more upon one side of a valley than another1 for a river seldom has its course in the centre of a vale1 but is generally nearest to the steeper and higher side of a hill4 ,the configuration of a country governs to a great extent the flow and quantity of the rainfall that sinks into the earth1 as in a hilly country and in impervious soil the water is quickly discharged into an adjacent river1 taking the easiest course4 ,in a flat country and pervious soil rain percolates the earth and saturates the ground1 or reappears in springs4 ,as by drainage the retentive power of the soil is not allowed free operation1 water rapidly flows into the drains instead of being chiefly held by the earth and watercourses1 and channels are sometimes created2 and where the rainfall is heavy or occurs in a comparatively short time floods may be caused1 although the soil when drained1 and therefore in a drier state1 absorbs more water than when undrained and in a damp condition1 water will pass through it quicker1 and the discharge is thus increased in volume and velocity4 ,earth may be in a damp state1 either from mere surface percolation and accumulation of water1 or from springs which may never cease to flow2 on the contrary1 in rainless districts1 from the almost perpetual daily drying power of the sun1 the earth is sometimes found to be firmest and hardest upon the top1 and for a few feet below it1 than at greater depths4 ,separate masses of vegetation usually indicate damp places in a bare country4 ,as rain flows more quickly from non-absorbent soil1 such as rock1 and slowly permeable earth1 as the clays1 than from porous soil1 the surface discharge is greater2 and unless the water is guided1 pools are likely to be formed and weak places created1 especially if the ground dips towards a cutting4 ,it is well to remember that a cutting being excavated upon the side of a hill or upon table-land may change the direction of the flow of the drainage waters1 and an embankment may obstruct and interfere with them1 and should the strata incline towards the excavation1 it obviously favours a discharge of water into it4 ,if water permeates the soil or trickles down through fissures or veins1 it will continue to do so until an impervious layer is reached1 when it will be deflected and may become a current2 therefore1 whenever a permeable stratum overlies an impermeable1 and the impermeable earth inclines1 an increased flow may be expected1 as also near the junction of tributary waters with streams or rivers4 ,in a drained district1 water will not usually be encountered in large quantities until a depth is reached below the level of general drainage1 i4e41 about the invert of the nearest drains or sewers1 especially in porous soils1 but in the case of a pervious subsoil1 such as sand or gravel1 or if the tides rise in an adjacent river or the sea to the level of any foundations or above it1 more water may percolate over the site or drainage area than has time to flow away between tides1 the water will then rise1 and systematic pumping becomes a necessity1 unless the volume of the ingressing waters can be sufficiently reduced by the deposition of an impervious layer upon or in the river-bed or sea-shore1 or by sheet-piling or other means1 or the flow confined1 which may be a risky operation in loose soil1 depending upon its resistance to scour4 ,in clay soils1 so far as slips are concerned1 the action especially to be feared is the trickling of water down fissures which may extend to depths below the bottom in cuttings and create slimy surfaces1 disconnecting masses of earth1 and finally offering a ready means of movement1 which swelling of the clay or vibration may complete4 ,the experiments of ,mr4 ,baldwin ,latham1 ,m4 ,inst4 ,c4,e41 on the absorption and retention of water by clay soils1 gave the following results3--,the stiffest clays retained the greatest quantity of water4 ,clay soils can absorb and retain from #dj to #fj per cent4 of water by weight4 ,marly clays hold less water than the pure clays4 ,in the case of loamy soils1 the percentage of water retained varied from #ce to #fj per cent4 by weight1 the mixture of sand and clay1 therefore1 limited the amount of water which it would naturally hold4 ,as in chalk soils fissures occur1 the percolation of water and the effects of the atmosphere through the pores causes movement1 and even crevices and breaks in rocks are not to be disregarded with impunity1 as they are channels of disintegration4 ,most earths when dry attract water1 but if they are regularly irrigated1 they require less moisture1 depending upon the nature of the earth1 and slope and relative level of the land4 ,all soils when broken1 as in embankments1 absorb more water than when in an unbroken state1 as in cuttings2 for instance1 it has been found by experiment that clayey and retentive earths will absorb about #g per cent4 more water1 and light porous soils about #f per centum4 ,of course1 the increment varies4 ,even wet retentive soil1 if handled1 becomes considerably less impervious to moisture4 ,mr4 ,evans1 ,f4,r4,s41 has proved by experiment that percolation through pure chalk is much greater than through ordinary top soil consisting of gravel1 loam1 and mould1 both being covered with turf1 and that in winter the average proportions of percolation are as about #a for soil to #ae for chalk2 in summer #a for soil to #bf for chalk4 ,the depth also to which chalk will allow a passage of water is some #fj per cent4 more than ordinary top soil4 ,rain will percolate through chalk or any open soil until it meets an impervious stratum1 or to that place which is in a state of saturation1 when the water must either flow away or the level of saturation must gradually rise4 ,this causes rivulets to burst out in places after heavy rain1 when the water has had time to percolate1 and the rainfall has exceeded the average1 but such springs will cease when the local excess has terminated4 ,however1 in cuttings it is the flow from fissures that is to be feared1 and their size may indicate the quantity of water that may be expected to issue from them4 ,it seems to be generally agreed that the supply of water from chalk is derived from rain1 which percolates through innumerable fissures1 and that in all rocks1 whether limestone1 sandstone1 granite1 sand1 or clay1 it is by means of the fissures1 seams1 and veins that the supply of water is obtained from rain1 and springs created4 ,with regard to the percolation of water through sand1 it may always be expected to be very considerable1 and the soil may under certain conditions become water-charged4 ,mr4 ,greaves1 ,m4 ,inst4 ,c4,e41 has shown by experiments that the average percolation through ordinary top soil is only about one-third of that of sand1 but the evaporation from a surface of ordinary soil was about four times more than from a similar surface of sand1 and also the amount of percolation in ordinary top earth was small on the whole1 and1 perhaps1 the percolation through ordinary ground would be about #be per cent4 of the rainfall1 but #hj per cent4 in average sand4 ,experiments have also shown that the absorbent capacity of sand decreases regularly according to the fineness of the grain1 and that 8some sandy soils will not absorb more than #bj per cent41 but sandy soil containing peat1 as moorland1 as much as #hj per cent41 both computed by weight40 ,the quantity of water absorbed by loamy soil will vary considerably according as clay or sand preponderates in the mass4 ,earth may become so mixed with coarse or fine sand that1 when saturated1 it approaches the condition of a quicksand4 ,the general effect of percolation has been briefly described as follows4 ,upon water entering the pores of an earth it displaces the air or liquid previously present1 forcing the former upwards into the atmosphere1 and the latter downwards4 ,having briefly referred to the percolation of water in cuttings and embankments1 the drainage is now considered4 ,it must be either precautionary1 i4e41 to prevent a slip1 or remedial1 i4e41 to drain a slip4 ,the aim of any draining operations to prevent slips in earthwork is to search for the source of water discharge1 to tap and gently conduct it away and prevent it reaching1 accumulating1 percolating1 or being confined within the slope of a cutting1 which it may then reduce to a pulpy condition2 its free effluxion being most important1 as also the lessening of the percolation of rain and surface-waters4 ,the drainage of cuttings or embankments may consist of wells1 culverts1 closed or open channels1 pipes1 and tile drains of every reasonable and economical form1 and may be placed in various positions4 ,to describe them and the different systems of draining is to open up a subject requiring several volumes2 here the endeavour is made to indicate whether elaborate or ordinary drainage is required1 or mere water-tables and surface drains1 and care in the process of excavation and deposition1 protection of the slopes1 and in giving them sufficient inclination to prevent movement4 ,if possible and time allows1 the drainage in treacherous soils should always be commenced before the main excavation1 and1 in any case1 simultaneously4 ,rock and solid impermeable earth may merely require to be surface drained1 but all treacherous and porous soil1 deep draining2 and granular soils1 which usually exude water from the whole mass1 demand different treatment to those earths which discharge water at particular places2 but it may be most difficult to drain a mixed soil1 such as sandy loam and silt4 ,with the exception of a counterfort and drain at the foot of a slope1 and an impermeable catchwater drain upon the slopes and top drains1 to prevent and lessen surface percolation1 the best method to adopt in earth of this description may be to sink wells at intervals to intercept the flow or percolation of any ground waters2 to attempt to drain or draw out the water in the soil will end in comparative failure4 ,to reduce the volume of the percolating waters is the object to be attained1 and then evaporation1 vibration1 which tends to shake down water1 and time may gradually convert the earth to the desired drier condition4 ,the wells can be filled with broken stone or coarse gravel to support them1 and prevent their closing4 ,it is an advantage to prevent the percolation of water into soil that will not readily part with it1 such as the clay earths1 as it may be economically impossible to drain or restore the earth to its normal condition1 and should the strata be upheaved1 intermixed1 and of a permeable and impermeable character1 a scientific application of drainage can alone succeed4 ,when the source of the water is ascertained1 it can be seen whether a complete system of drainage is necessary over the whole of a cutting or only a portion of the slopes4 ,dampness and the egression of water may be merely local2 if so1 by boring a hole and inserting a drain into a slope to tap the flow it may be cured1 the surface being made dry by a layer of ashes or other absorbent material4 ,pipes or tile drains may be sufficient when springs exist1 or the flow of water is local1 and in loose soils it is especially advisable to provide openings for cleaning any covered drains4 ,brickwork1 masonry1 concrete1 pipes1 or other rigid drains1 may not be suitable for ground likely to unequally subside1 as they will probably crack or leak1 and loose-jointed pipes or over-lapping tile drains may be required4 ,in treacherous clay soils surface longitudinal and transverse drains will most probably be insufficient1 and deep draining of the mass be necessary1 also the ground upon which earth is deposited will require to be drained and a layer of rubble stone placed upon it1 a cutting or embankment being divided into small drainage areas by deep open dry stone trenches4 ,water may not sufficiently percolate into a hill1 either because of its surface being covered with vegetation1 or the soil being of an impervious nature4 ,it may then flow down the slope of a cutting which will probably be bare and unprotected4 ,to prevent slips the discharge must be carefully controlled and led away1 particularly when the formation is drift soil upon rock1 or the earth will be liable to saturation and degradation2 also to prevent a flow of water under its seat1 and upon the natural ground1 should an embankment be deposited upon it4 ,when a slope upon the hill-side of a cutting is of considerable length and steepness1 it is advisable to bench it and divide it into a series of terraces and short slopes1 and to provide catchwater drains1 with impermeable surfaces so as to prevent any surface water attaining a high velocity1 and scouring power4 ,all surface water upon the side of a hill should be controlled1 and catchwater drains may suffice to do this4 ,should an impervious stratum be upheaved so as to make a reservoir wall for water under the seat of an embankment1 it is useless to surface-drain the valley side of it in sidelong ground1 as it will not affect the waters that trickle down the hill1 which will be dammed up to the top level of the impervious stratum1 and may saturate the seat of an embankment and cause a slip4 ,in such a case through drainage must be created from the hill to the valley1 and the impervious upheaved cap must be pierced so as not to interfere with the passage of water4 ,in countries where there is a certain dry and rainy season1 the necessary provision required for drainage must not be computed from the visible effects of the rainfall soon after the wet season has commenced1 but the maximum flood may be discerned when the earth has absorbed or retains the moisture evaporated during the dry season1 and becomes water-charged4 ,in the tropics or exceptionally wet districts the only effectual method of draining may be to divide the area into small portions1 as the rainfall may be so great1 sudden1 and continuous that unless it naturally flows into a channel1 which should not be diverted or its course be materially altered1 it will be impossible to control the waters4 ,in an exceptional situation where a railway must be located in a ravine and close to a river1 and the material of which an embankment is made is compact earth or the ground firm1 it may be advisable to allow the overflow waters of a river1 or the flow of surface water towards it1 when the extreme flood level is known1 to gently pass over a line of railway1 it being kept at such a level as not to impede free working1 and to ensure that any back water is not prevented from escaping4 ,if not1 an embankment may slip and require extensive and frequent bridges1 culverts1 or drainage channels in order to provide sufficient waterway1 and to attain permanent stability of the embankment4 ,in all cases it is necessary to determine the depth to which the drains must be placed to be effectual1 and their position1 extent and number1 and it should be remembered that the fewer there are the greater will be the velocity and discharge2 also if many small drains are inserted the soil may stand1 but if only one or two are made the surface may succumb to the erosive action of the flowing waters4 ,the provision of a water-table or the mere surface drainage of a cutting1 or the seat of an embankment may be of little use1 as the superimposed soil may slide upon a stratum1 and unless this bed is thoroughly drained rain may quickly destroy the equilibrium4 ,of course1 in the case of a slip1 the drains to be effectual must be placed below its level and down to the layer upon which movement has occurred1 especially in clay and retentive and impervious earths1 for instance1 surface drainage in yellow clay is almost useless4 ,should the source be known from which the water issues the drainage may be local1 and if a spring be unsealed it may be necessary to insert pipes in the slope1 for until the spring is tapped and guided no system of drains may be effectual4 ,by inserting a stand-pipe over a spring1 the height to which the water will rise will approximately show the head-level of the supply4 ,if possible1 this should be ascertained1 as it may happen that the water can be drained by gravitation in pipes without much excavation being required in the slopes or formation2 but care should be taken that no water is allowed to settle or accumulate for the purpose of its being conducted away unless upon a protected surface4 ,with regard to catchwater drains upon the cess at the top of the slopes1 they should be cut before the excavation is commenced2 and it is important to remember that instead of their affording protection by guiding the surface waters1 which would otherwise proceed towards the slopes1 they may increase the percolation by localizing the water and allowing it to accumulate and find its way to the slope2 and in sidelong ground it may1 therefore1 be necessary to protect their valley more than their uphill side1 as the surface water will impinge against it2 but when they are practically impervious and gently direct the surface water they are advantageous1 and in permeable soil1 unless they are so constructed as to be impervious1 perhaps it is better to have none4 ,they should be as reasonably distant from the top of the slope as is convenient without weakening the foundations of the posts supporting any fencing1 and in order to quickly discharge the water and lessen the chance of their becoming choked by detritus or ice1 they should have considerable inclination4 ,as the adoption of even a moderate fall in the drains may erode the side ditches and cause water to percolate to the slopes and make a water-seam1 it may be necessary to protect the bottom1 and as the depth of the side drains in order to be effectual may be considerable1 according to the character of the soil1 the sides may also require to be covered and supported4 ,in cuttings in many soils sufficient stones can be picked out to cover the surfaces of the side drains1 and they can be roughly packed1 the smaller stones being rammed into the interstices between the larger1 which will gradually become filled2 also a covering of brushwood1 rammed earth1 or puddled clay can be used1 or other expedient which occasion may suggest4 ,the inclination must not be steeper than the natural or protected bed can bear without the water scouring it1 and yet should be sufficient to prevent any deposit or choking1 and the drains should be cleared regularly1 and especially in the autumn in ,england or before the wet season commences1 and all depressions in which water can accumulate should be levelled in order to assist easy discharge4 ,small open drains become choked somewhat easily1 and it is therefore advisable to make them according to the nature of the soil1 situation1 and requirements not less than #a foot #f inches to #c feet in width at the top and #a foot at bottom2 they may be from #a foot to #c feet in depth4 ,care should be taken that the bends are not too abrupt or the water may make its own course4 ,a gentle curve considerably increases the flow4 ,the angle of a bend should be as easy as possible1 and not exceed #bf or #b to #a4 ,in sandy and loose soils1 if unprotected1 open drains may be difficult to maintain even when filled with broken stone1 and covered or pipe drains be necessary1 and those loosely filled with stones or faggots may not succeed2 in any case no run of the sand must be allowed1 and it is advisable to rapidly construct them4 ,in peaty soils1 from subsidence of the ground consequent upon draining1 the drains often become choked4 ,the depth of a drain in the formation may require to be deeper than elsewhere1 as at the toe of the slope1 the weakest part1 the water will generally be most abundant4 ,upon railways1 the advantage of thorough drainage of the formation as regards the stability of the permanent way and reduction of the cost of repairs is proverbial1 but here is only named in its relation to the prevention and the reparation of slips4 ,when field drains are intercepted in the slopes1 drain pipes or timber ducts should be joined to them and be connected with the general drainage of a cutting4 ,draining the slopes1 providing outlets for the water1 and also support to the earth can be effected by means of a counterfort of permeable material at the toe of the slope1 with its foundation a few feet below formation level1 with open drains at right angles or obliquely to it extending from the foe to the top of the slope4#a ,these open drains and trenches can be filled with stones1 gravel1 hard chalk1 ashes1 brushwood and gravel1 broken bricks1 burnt clay or other suitable material2 and a simple covering of picked ashes1 c41 over a moist place in a clay cutting of little depth may be sufficient4 ,the distance apart of such trenches in clay cuttings generally ranges between #aj and #cc feet2 their location must be governed by the consideration that they exist in order to prevent a localization of water in the slopes3 their width is usually from #b feet to #h feet1 and most frequently #d to #f feet1 and the depth from #a foot #f inches to #c feet and upwards1 below the surface of the slope1 but in very wet embankments a width from #f to #aj feet and of such a depth as the soil will allow without extensive support4 ,if the earth has not slipped1 and it should be found that the ground is wet for from #f to #h feet or so beneath the surface1 and the depth of the trench is made about half that of the wetted soil1 it is sufficient to collect the water1 but if it has slipped most probably such drains will not be effectual until carried down below the seat of movement4 ,at the foot of a slope these drains should be connected with longitudinal channels parallel to the formation to gently convey the water to the nearest outlet4 ,the location1 distance apart1 depth1 width1 and direction of the trenches must be governed by the nature of the soil1 the depth of a cutting or height of an embankment1 the area of the surface to be drained1 the quantity of water in it1 the presence of water-seams and weak places1 and by other minor considerations4 ,footnote #a3 ,vide ,chap4 ,,vi41 pp4 #aaa1 #aab4 ,with respect to the material with which the trenches should be filled1 a uniform substance having considerable power of absorption1 and but few particles between the interstices1 is to be preferred1 as the trickling of water and vibration causes the smaller material to fall towards the bottom of the trench1 which1 therefore1 may become partly choked1 and free drainage be interrupted at the toe of the slope1 the most vulnerable place4 ,as sand is always present in unwashed gravel1 it will gradually flow or fall to the base of the trench and will prevent equal drainage1 but properly burnt clay1 being a more uniform and fragmentary substance1 is better than sandy gravel1 as it is dry and porous2 but much depends upon it being well burnt or it may weather4 ,ashes and chalk are excellent collectors of water and are usually of an even character1 but ashes are better than chalk1 as the latter material1 unless very hard1 is liable to become disintegrated by the action of the atmosphere1 rain1 and frost4 ,the difficulty with respect to ashes is to obtain them in sufficient quantity1 free from dust1 and of the requisite size4 ,when weight is required as well as drainage1 burnt clay1 gravel1 or chalk is to be preferred to ashes4 ,burnt clay1 although burned upon the site1 is generally a more expensive material than gravel1 but the amount of moisture in the clay will principally determine the quantity of fuel necessary to burn it1 and therefore the cost4 ,if shale is present1 by thoroughly igniting it the expense of burning may be nearly reduced to that of lighting and turning over1 as it will usually burn unaided4 ,all trenches should drain into pipes placed below the formation or into open drains at a sufficient distance from the toe of a slope as not to deleteriously affect it1 in order that the water may be controlled and gently conveyed to an outlet4 ,the chief objection to open drains is that all excavated trenches or inserted drains in the slopes destroy the cohesion of the earth and aid in detaching portions of the surface4 ,if the cohesion and adhesion of the soil were the same under every condition1 this would be a cogent reason against the system1 but1 as in earthwork1 every degree of moisture from dampness to saturation may be attained1 the cohesive power is a very variable quantity1 apart from the effects of vibration2 and also open drains undoubtedly do cause a slope to be drier1 and moderate local humidity1 and therefore increase the cohesion and general stability of the part drained2 the only fear being that from inattention they may become choked2 then they are dangerous1 as they will permanently collect and retain water instead of temporarily retaining and gently guiding it4 ,a careful consideration of the circumstances may much reduce this objection by indicating whether it is advisable to have only a few deep1 or several small surface drains4 ,provided proper precautions are taken1 experience indicates that filled-in trenches in the slopes are generally successful1 and certainly are simpler and cheaper than a retaining wall at the toe of a slope4 ,in pervious soil it may be economically impossible to drain the slopes unless they are divided into sections1 and should the material in the trenches be well-packed and pressed down1 it may even increase the friction between the separated portions4 ,in connection with the drainage of cuttings may be named that excavation should not be allowed to be cast upon the cess unless some distance from the edge of a slope1 and only temporarily for purposes of ballasting and metalling2 as such spoil-banks increase the load and localize the water to be drained4 ,a more complete system of drainage may be necessary than those previously named1 consisting of a combination of wells1 open1 or holding filtering material2 pipe-drains or filled-in trenches1 wells with a pipe leading to a catchwater drain1 c41 or other usual methods of land drainage4 ,for instance1 it may be discovered that water issues from a spring outside the fence or cutting2 if so1 in order to drain the slopes it may be necessary to sink a well to a stratum below the formation level so as to tap the spring1 thereby preventing an exudation of water upon the slope2 this is a better plan than drawing the water into the slope and then draining it4 ,when pervious earth overlies an impervious stratum1 i4e41 gravel or sand upon clay1 rough-filled wells at intervals inside the fence extending #c or #d feet into the clay1 with an outlet drain1 may be required to prevent a flow of water upon the clay and a wetted surface upon which the gravel can slide2 and it may be necessary to have a cess on the slope between the top of the clay and the bottom of the gravel or sand1 with a catchwater drain upon it1 particularly in a cutting in sidelong ground4 ,should the soil be silty sand1 or be charged with water1 consequent upon the formation of the country1 it may be impossible to drain a cutting without a complete system of wells1 catchwater drains and pipes1 and even then it may be difficult to separate the water from the earth4 ,in building a drain-shaft it should be remembered that it may not only be subject to a compressive strain1 but also to transverse strain and flexure from different pressures of the earth at various depths1 especially when the soil is not the same throughout1 and unequally damp4 ,when 8boils0 occur in sand-cuttings1 perhaps the cheapest expedient is to place a shaft over the boil1 weight the bottom sufficiently to prevent a movement of the sand1 but to allow the water to escape1 and make a discharge outlet after having ascertained its head level3 vide ,chapter ,,xii4 ,on no account should a spring be stopped1 as such action will result in its diversion to some other place2 but the water flowing from it should be guided and discharged4 ,weighting may arrest a slip in any sandy soil1 also clay or any impervious material placed upon the sand1 or sinking a well outside a cutting to a depth of some #e feet below the bottom may effect a remedy by abstracting the surplus water1 but care must be taken not to disturb the sand4 ,slips in embankments frequently occur from the percolation of water through the formation to the slopes1 and so to the toe1 the lower portions become disintegrated by moisture and the effects of weather1 and cause the upper parts to slide or move4 ,to lessen percolation and to prevent an accumulation of water upon the formation1 it is usual for its centre to be raised a few inches above the level of the top of the slope4 ,this is undoubtedly a good practice1 as it also tends to drain the ballast1 but it may be nullified in time if the entire width of the formation be not covered with an impermeable layer or with ballast2 for when an unprotected space remains between the toe of the slope of the ballast and the top of the slope of an embankment1 water is liable to percolate through the cess and cause a slope to become wet and unstable2 particularly so if the ballast is broken rock and has side walls instead of slopes1 as then a depression will probably be made by the platelayers or signalmen walking upon the cess4 ,in all cases where the material is treacherous or likely to slip1 it is advisable to cover the top of embankments of considerable height throughout their width with ballast or some impervious soil1 provided the permanent way is also properly drained4 ,this is the simplest precaution to take respecting the preservation of the formation level or summit of an embankment4 ,all grass1 dirt1 and refuse should be regularly removed from it and anything that obstructs free drainage4 ,the nature of the ballast also affects the evenness of the surface of the formation1 as if it consists of broken rock1 the equal and regular packing of the sleepers is not so easily effected as with gravel ballast2 the sleepers are frequently not uniformly supported throughout their length1 the pressure upon the formation is localized1 depressions are formed and water collected1 and slips and subsidences in soils of a treacherous nature may be induced from this cause1 as the equilibrium is soon disturbed4 ,the formation should be so drained and constructed that water cannot percolate to or cause the surface to become soft and work up into or through the ballast1 or a state of unsettlement will be produced by water soaking through the ballast to an embankment1 and so saturating part of it and forcing out the upper portion of a slope4 ,in all close granular ballast cross channels should be made to lead away the surface water4 ,transverse open tile-drains may be required leading to an impervious channel4 ,water has been known to percolate through a considerable depth of ballast when added to restore a sunken embankment1 even through as much as #g to #aj feet when two falling gradients induced a flow of the surface waters to one place4 ,in certain situations it may be necessary should an embankment be of clay or treacherous soil when wet1 to cover the formation with an impervious stratum to prevent percolation to the embankment1 and to thoroughly and separately drain the ballast placed upon it4 ,at the base of an embankment a ditch should be cut upon the higher side1 or both sides1 as near as convenient to the fence4 ,when in addition to the interception of any surface waters by an embankment the ground is very retentive of moisture1 it may be necessary to drain the seat2 with this object trenches can be excavated at intervals at right angles or obliquely to the centre line of the embankment1 and be filled with some hard filtering substance1 such as stone or gravel1 so as to effect and control the discharge of the waters4 ,should this be too expensive a method to adopt1 and always provided the surface waters are prevented from flowing or trickling into the base of an embankment1 the ground might be excavated so as to equally incline downwards towards the centre1 the level at that point being #a foot to #b feet below the toe of the slope on each side1 according to the width of the base of the embankment2 a small trench being cut in the centre and filled with stones1 and covered at the top with brushwood or hurdles or other provision necessary to ensure it being permanently an effectual water channel1 with occasional or other drains to lead the water to the nearest culvert or side ditch4 ,when it is found that water passes over the surface of firm soil upon which an embankment is deposited1 the water must be intercepted and led away2 and should an embankment be of retentive earth1 in order to tap the water that has flowed and percolated into it1 and to restore the earth to its normal condition and prevent slips and subsidences1 it may be necessary to sink shafts to a depth of a few feet below the seat of an embankment until the mass is drained4 ,with regard to culverts1 a settlement or slip of an embankment over a culvert may unequally strain1 fracture1 and displace portions of it1 and therefore interrupt the flow of the drainage waters1 which may then reach the seat of an embankment and cause it to be in a dangerous condition4 ,they are usually necessarily placed at the deepest point of an embankment1 and consequently the most difficult to make repairs4 ,in such a situation they should be built sufficiently large to allow of the easy passage of a man1 in order that due inspection may be made1 and be constructed of materials of a durable character4 ,should a naturally firm bank exist on one or both sides of a stream1 it should be stripped of all plant growth and decaying matter1 and be preserved in order to form a natural wall to relieve a culvert from side pressure1 but firm or hard material must be inserted between the back of the wall and the face of the stream bank so as to support the wall against the pressure it receives from the arch4 ,this leads to a consideration of the best form of culvert4 ,in clay soils1 and those which exert pressure from expansion1 especially if the culvert is surrounded by clay earth1 the circular is generally considered to be the best form1 and this has been proved to be so in tunnels in similar soil1 with splayed wing-walls to assist and guide the flow and help to keep a clear entrance4 ,in granular soils1 such as dry sand or gravel1 the earth acts differently and more in accordance with the angle of repose theory of pressure1 therefore the strain upon the arch would be the greatest1 and its thrust must be counterbalanced at the sides1 the strain upon the invert being probably very little and due to the tendency to an overturning movement of either of the straight walls4 ,however1 in culverts as in tunnels1 it is impossible to say the exact amount or direction of the strain1 although it may be approximately computed4 ,should it be necessary to erect a culvert upon soft ground1 as much of it as practicable should be excavated and a concrete foundation be placed thereon2 it is also advisable to allow an extra length to that required by the calculated slope4 ,a culvert should have an invert unless upon a hard rock bed1 and care should be taken that there shall be no leakage at the springing of the inverted arch or under it1 or beneath the sidewalls at the level of the surface of a flat stone drain or below it4 ,the banks of a stream or watercourse should be inspected occasionally1 especially on the up-stream side of a culvert1 in order to note whether they are stable or crumbling away1 as then the course of the stream may be widened or diverted1 and so erode the toe of an embankment and cause a slip of earth4 ,splayed wing-walls are a protection against such a danger besides aiding the flow of water through them1 and they also lessen the chance of a damming back of the water and undermining1 as they increase the discharge2 for instance1 a splay of #ec has been found to increase the flow about #be per centum4 ,the surface of the material of which a culvert is constructed should be as smooth as practicable1 so as to reduce the friction of water flowing past it1 which1 in the case of unplaned timber1 cast and wrought ironwork1 ashlar masonry1 brickwork1 and concrete1 is about the same1 but is some #cj per cent4 more when the surface consists of rubble masonry4 ,when an embankment crosses a narrow valley1 in which no watercourse exists1 instead of a culvert1 a bed of loose stones has been placed upon the ground under the whole area of the seat of an embankment at its greatest depth1 a proper fall and bed being given to it4 ,the toe of the slope on the up-stream side should be protected from any wash1 and the stone layer be carried a few feet beyond the foot of the slope on the lower side4 ,the following general principles it is well to remember in designing culverts4 ,when a culvert is of uniform section1 which is almost invariably the case1 it should have the same inclination throughout4 ,avoid1 or ease1 all bends as much as possible4 ,have splayed wing-walls4 ,make provision against undermining by scour or percolation of water4 ,have smooth and even surfaces so as to reduce the friction and increase the discharge4 ,have an arched invert to a culvert1 and a flat bed stone to all small surface drains1 with complete connection to the side walls4 ,in some countries having a severe climate1 or in high mountainous districts where the soil is rock and a heavy discharge of flood-waters occurs1 instead of placing a culvert and gathering the waters at or about the level of the toe of an embankment1 in deep hillsides or ravines an unlined tunnel is made under the embankment in the rock1 thus avoiding a masonry or brickwork structure1 which could only be set in the summer months1 and preventing the waters touching the seat of an embankment and promoting a slip4 ,when the level of a rivulet allows1 and the waters are simply surface discharge1 the system has been used of making two open channels1 one upon each side of a steep valley1 thus retaining the waters1 allowing the adoption of two short span open culverts and two channels instead of one large culvert at the deepest place1 and saving expense1 the original bed of watercourse being filled with the surplus excavation4 ,the embankment consisting of broken rock or hard granular soil1 any little percolation of water along the old bed will not deleteriously affect it1 but will find a passage4 ,,chapter ,v4 ,,approximate ,,safe ,,maximum ,,load ,,upon ,,different ,,earths4--,,normal ,,pressure ,,of ,,the ,,earth4--,,the ,,safe ,,maximum ,,load ,,upon ,,deposited ,,earth4--,,approximate ,,safe ,,maximum ,,height ,,of ,,an ,,embankment4 ,there is no limit to the depth of a cutting except a due regard to economical construction1 provided the slopes are sufficiently flat1 and the lateral and upward fluid pressure in the slope1 and formation and quantity of water not too great for the stability of the earth2 but1 in the case of embankments1 the load upon the ground and the deposited material in great measure restricts the height1 or necessitates an embankment being gradually spread out1 so as to enlarge the bearing area as the weight is increased4 ,the following values of the safe maximum compressive load have been compiled from actual practice1 but are1 of course1 only intended as a guide to the safe load for foundations excavated in ground not artificially deposited4 ,the condition of the earth in each case should be considered1 and in works of magnitude it is advisable to make experiments extending as long as practicable1 and for at least a month1 and it is false economy not to carefully ascertain the character1 condition and other circumstances of a foundation destined to support any part of a structure1 a failure of which may result in serious consequences2 and it should be borne in mind that a continuous surface possesses greater sustaining power than the same area in detached portions1 as the adhesion of the sides is not destroyed2 similarly1 the load that a tenacious earth will support upon a small area is somewhat greater than over a large area1 because the lateral surfaces are relatively larger in proportion to the area1 and1 therefore1 the effect of cohesion is proportionately greater2 but in loose soils it is not so1 for cohesion exists but in name1 and the ground around would be upheaved upon an excessive load being superimposed4 ,in testing the weight any earth will support1 it is not so much the first settlement1 provided it is not excessive1 that it is desirous to know1 but whether after the first settlement it ceases or the earth1 as it were1 reacts and rebounds1 which it may do in firm ground to the extent of one-eighth to half an inch4 ,if so1 the ground is not overloaded4 ,after ascertaining by experiment the pressure any earth will bear over a given area1 the object should be to make the soil neither drier nor wetter than that of its natural state when experimenting1 and it should be maintained in that condition4 ,in testing the weight which a soft earth will support1 some days should be allowed for the sinking of the test platform1 and such subsidence should be ascertained periodically by careful levels4 ,a month is not too long for a reliable and complete test1 as many soft soils continue to yield4 ,in soft clay soils considerable depression often proceeds for weeks after a load has been applied1 but except in peculiar earths such settlement will ultimately be imperceptible1 and will practically cease4 ,a considerable margin of stability should in all cases be allowed4 ,although it may not be absolutely necessary to experiment when the nature of the ground is well known1 wherever stability is of great importance1 the cost of a practical experiment being so small1 there is no sufficient reason why an actual test of the sustaining power of the soil should not be made in the majority of instances1 for there are many earths whose friction and cohesiveness can alone be depended upon for resistance to displacement4 ,in such cases the initial pressure upon the earth should not be much exceeded4 ,description of ,earth4 ,approximate ,safe ,maximum ,load in ,tons per ,square ,foot4 ,bog1 morass1 quicksand1 peat moss1 marsh-land1 silt #j to #jbj ,slake and mud1 hard peat turf #j to #jbe ,soft wet pasty or muddy clay1 and marsh clay #jbe to #jcc ,alluvial deposits of moderate depths in river beds1 c4 #jbj to #jce ,,note4--,when the river bed is rocky and the deposit firm they may safely support #jge ton1 but not more4 ,diluvial clay beds of rivers #jce to #ajj ,alluvial earth1 loams and loamy soil 7clay and #dj to #gj per cent4 of sand71 and clay loams 7clay and about #cj #jge to #aej per cent4 of sand7 ,damp clay #aej to #bjj ,loose sand in shifting river bed1 the safe load increasing #bej to #cjj with depth ,upheaved and intermixed beds of different sound clays #cjj ,silty sand of uniform and firm character in a river bed #cej to #djj secure from scour1 and at depths below #be feet ,solid clay mixed with very fine sand #djj ,,note4--,equal drainage and condition is especially necessary in the case of clays1 as moisture may reduce them from their greatest to their least bearing capacity4 ,when found equally and thoroughly mixed with sand and gravel their supporting power is usually increased4 ,sound yellow clay containing only the normal quantity of #djj to #fjj water ,solid blue clay1 marl and indurated marl1 and firm boulder #ejj to #hjj gravel and sand ,soft chalk1 impure and argillaceous #ajj to #aej ,hard white chalk #bej to #djj ,ordinary superficial sand beds #bej to #djj ,firm sand in estuaries1 bays1 c4 #dej to #ejj ,,note4--,the ,dutch engineers consider the safe load upon firm clean sand as #e tons per square foot ,very firm1 compact sand foundations at a considerable #fjj to #gjj depth1 not less than #bj feet1 and compact sandy gravel ,,note4--,the sustaining power of sand increases as it approaches a homogeneous gravelly state4 ,firm shale1 protected from the weather1 and clean gravel #fjj to #hjj ,compact gravel #gjj to #ijj ,,note4--,the relative bearing powers of gravel may be thus described3-- #a4 ,compact gravel4 #b4 ,clean gravel4 #c4 ,sandy gravel4 #d4 ,clayey or loamy gravel4 ,sound1 clean1 homogeneous ,thames gravel has been weighted with #ad tons per square foot at a depth of only #c to #e feet below the surface1 and presented no indication of failure4 ,this gravel was similar to that of a clean pebbly beach4 ,in loose non-cohesive earths the load may be increased1 when the depth is considerable1 as the soil has been subject to a greater normal pressure due to the weight of the soil upon it at any depth2 but it is not advisable to consider such increase of bearing power of the soil1 unless at any depth it is found that the normal pressure augments the bearing power and makes the earth more dense1 which may be approximately ascertained by experiment4 ,in such event the load upon the base can be increased by the weight of the normal pressure removed4 ,supposing #e tons per square foot was known to be the safe load upon the surface of the ground1 and at any depth it was found that the normal pressure of the soil was #b tons2 #e #b #g tons placed at that depth would equal #e tons at the surface4 ,in the worst case1 when the loose earth is of great depth1 and it is certain that it cannot be tapped or disturbed at the depth at which it is decided to place the foundations of a structure1 provided the load is not more than the normal pressure1 it is not probable that it will subside or slip1 as no additional weight is imposed4 ,in foundation and general work1 rocks are usually not loaded with a greater weight than from #h to #ah tons per square foot1 according to the character of the rock4 ,as the crushing strength has been principally ascertained from cubes1 and not from prisms1 rectangular blocks1 or irregularly shaped pieces1 and as the resistance of rocks to transverse strain or breaking across is considerably less than the compressive strength1 and varies greatly and not always according to the crushing resistance of the material1 from #h to #bj tons per square foot is a prudent limit for the safe load1 and should not be exceeded unless under exceptional circumstances2 as unequal bearing may greatly intensify the strain1 and irregularity in the texture may reduce the resisting powers to that of the weakest part4 ,sandstone rock that can be crumbled in the hand should not be loaded with more than #a to #a ton per square foot1 or it will probably begin to flake and disintegrate4 ,the strength of sandstone varies very greatly1 and in experiments it has been found that when fine close grained1 it supported before being crushed five times the weight that very coarse gritty sandstone1 having a sandy appearance1 would sustain2 the respective crushing pressures per square foot being #cfb and #fg tons4 ,reference to authorities on the resistance of stones to crushing1 tension and transverse strain1 will give the approximate safe load per square foot2 but in foundations1 i4e41 upon the rock in its natural location1 it should not exceed one-tenth of the ultimate resistance1 and the compressive strength should not alone be taken as a guide to the safe load1 but the resistance of the rock to tensional and transverse strain should be considered4 ,the value given for crumbling sandstone is for the softest material that can be called rock1 and is merely stated to show that although some earths may be generally classed as rocks their bearing power may be limited4 ,the safe load upon an artificial rubble mound foundation depends upon its character1 and firmness and solidity when deposited1 and upon that of the ground on which it is placed4 ,no general values can be named1 although it may be classed as clean or compact gravel4 ,in a cutting1 by excavation1 the normal pressure of the earth1 which varies with the depth and weight of the soil1 is removed4 ,let ,d the depth in feet of a cutting from the original surface of the ground1 ,w the weight of a cubic foot of earth in decimals of a ton1 ,p the normal pressure in tons per square foot at any given depth1 ,then ,p ,d ,w4 ,on the other hand1 in the case of an embankment the normal load upon the earth is not affected1 but an additional weight is superimposed2 consequently1 to prevent slips or subsidence from overweighting1 there is a limit to the height of an embankment1 apart from economical considerations of its deposition4 ,the problem to determine is1 therefore1 the limit of the height to which an embankment may be deposited without exceeding the safe load that the natural ground will permanently sustain4 ,the safe load upon the earth of which an embankment is composed is referred to in due course4 ,let ,s the safe load in tons per square foot upon the original ground or earth not artificially deposited4 ,h the theoretical limiting height in feet of an embankment4 ,w the weight in tons of a cubic foot of the deposited earth4 ,,note4--,when the earth is of a mixed character1 the safe load should be that of the weakest soil4 ,the condition of equilibrium is that the height is not greater than the safe load divided by the weight of the ground1 and is consequently given by the expression-- ,h ,s_/,w4 ,in order to prevent a reference to other books1 a table is appended of the approximate weights of different earths in their ordinary condition1 compiled from the best authorities4 ,the weights are those of solid rock1 therefore1 when it is deposited they will be lighter according to the volume of the interstices4 ,name of ,earth4 ,weight4 ,decimals of a ,tons4 ,ton4 ,cubic ,yard4 ,cubic ,foot4 ,basalt1 solid #jjhc #bbe ,bath stone1 solid #jjeb #adj ,chalk1 damp to wet1 loose to close #jjef to #jjgd #aej to #bjj ,clay #jjed to #jjei #ade to #afj ,flint1 solid #jjgd #bjj ,granite #jjgh #baj ,gravel and shingle #jjdf to #jjee #abe to #aej ,limestone4 ,lias to compact mountain #jjfg to #jjgh #aha to #baj ,marl #jjdd to #jjeb #abj to #adj ,mud1 at surface #jjdd #abj ,mud1 at about #ae feet in depth #jjdh #acj ,peat1 hard1 and top mould #jjcf #jih ,portland stone1 solid #jjfe #age ,quartz1 solid #jjgf #bje ,sand1 dry river #jjda #aaj ,sand1 damp and shaken #jjee #aej ,sandstone1 solid #jjfc to #jjgb #agj to #aie ,shale #jjgd #bjj ,slate1 solid #jjhj #bae ,trap1 solid #jjgh #baj ,in determining the safe load upon deposited earth it is well to remember that3 #a4 ,excavated earth cannot be restored in bulk to its original condition4 #b4 ,when the earth is simply deposited from a tip head1 it cannot be immediately consolidated by the act of deposition4 #c4 ,until subsidence may1 for all practical purposes1 be considered at an end1 no deposited earth can be regarded as stable2 but a mere uniform weathering of the surface1 which cannot be prevented when the exterior is uncovered1 will generally not cause instability of the mass4 #d4 ,upon most public works the earth in an embankment is exposed in thin layers4 #e4 ,the earth is loaded1 in the great majority of cases1 soon after it is deposited and before it has settled or become consolidated1 and is also subject to vibration from earth waggons1 locomotives1 c4 #f4 ,the comparative dry or wet state of the deposited earth and its power of resistance to meteorological deterioration4 ,vide also ,chapter ,,ix4 ,taking into consideration these and other deteriorating influences1 the problem to be solved is1 what deduction must be made from the safe load upon unexcavated earth in foundations1 in order to know the safe sustaining power of the same earth when deposited in an embankment8 ,much depends upon the liability of the soil to become saturated or in a damper state than that in which it is known to be stable4 ,for this reason the height of embankments in clay soils1 which are so deleteriously affected by the weather1 is generally made as little as possible4 ,of course1 temporarily an embankment will stand with a greater pressure1 i4e41 at a greater height than the safe height1 and1 provided no lateral movement took place1 an embankment would be stable until the earth was nearly crushed2 but permanent stability and freedom from slips and subsidence is the object to be attained1 and everything must be subject to local conditions1 such as the amount of rainfall1 the situation1 the care exercised during deposition1 the protection given to the surface1 and the general drainage1 and these must always govern the application of any general rule4 ,it is1 therefore1 necessary to divide earths into two kinds1 namely3--granular and non-granular2 the former is assumed to have particles1 for purposes of earthwork1 insoluble in water1 the latter to be liable to be dissolved by aqueous action1 or to be so affected by it as to lessen the stability4 ,it is impracticable to determine by a formula the permanent safe maximum height of an embankment2 the values named are1 however1 an approximately reliable indication of the height1 and are based upon the assumption that the slopes are sufficiently flat to be stable1 and that the embankments are deposited in the ordinary way1 the width of the formation or top being not less than about #ae feet4 ,it is seldom economical to make an embankment more than #gj to #ij feet in height1 except for short lengths1 and where deep cuttings cannot be avoided1 and it becomes a question of tipping spoil banks or main embankments1 or the foundations for a viaduct are known to be of a treacherous and doubtful character4 ,the heights named have been calculated under the worst conditions1 i4e41 that any weight upon the formation will be directly communicated to the base as in the case of a column1 and not through the cross-section of an embankment1 and over the whole area of the base2 however1 there is always the danger that the central portion may subside1 as the weight upon it is the greatest1 and that the slopes may be disturbed and pressed out1 especially in soft or soluble earth likely to be quickly affected by moisture4 ,the soil is considered to have no reliable cohesion4 ,in this country the limits of general practice for the height of embankments when unaided by retaining walls or other support1 but with the slopes soiled1 covered with grass1 and only externally drained1 has been as follows3-- ,surface soils1 about #bj to #cj feet4 ,boulder clay from #be to #cj feet4 ,yellow1 or ordinary clay1 #cj to #dj feet4 ,ditto1 ditto1 in cuttings1 #fj to #fe feet4 ,chalk1 #cj to #dj feet4 ,gravel and sand1 about #fj feet4 ,ditto1 in cuttings1 #hj feet4 ,these have1 however1 been exceeded in many instances1 especially upon the lower side of an embankment upon sidelong ground4 ,probably the highest artificial embankments unsupported by walls or any protective works1 are quarry and mining-tips1 and ballast-heaps4 ,these have been cast out in all weathers1 and allowed to assume any slope or shape1 and to a height as great as #ajj to #abj feet1 and have remained stable1 although usually in an exposed situation1 but almost free from vibration4 ,in ,chapter ,,vi4 a railway embankment #ij feet in height1 in treacherous clay-soil is instanced1 and there are many embankments of various earths from #gj to #ij feet in height on the centre line1 but a railway embankment exceeding #ajj feet in height on the centre line is rare1 although the height from the toe of the slope to the formation level in sidelong ground may be frequently exceeded4 ,a short and very high embankment may stand where one of considerable length would slip1 consequent upon variations in the character and condition of the earth1 the bearing capacity of the ground1 the state of the weather1 the flow of the surface water1 general homogeneousness1 the configuration of the ground1 and other deteriorating influences2 but draining1 careful deposition1 and a judicious adoption of the varying slope system1 and other precautionary works1 will conduce to stability4 ,unless in exceptional circumstances1 it is advisable to avoid very high embankments1 as a slip of earthwork seldom gives much prevenient notice1 and the works of reparation can scarcely be effected by any means than manual labour4 ,the quantity of earth to be treated may be so large that before the remedial works can be completed a wet season may arrest operations and cause additional movement and subsidence of the earth4 ,,granular ,,earths4 ,description of ,earth ,embankment4 ,approximate safe permanent maximum height in feet1 of an embankment in earth1 conditions as described4 ,feet4 ,indurated compact gravel1 cementing material #abj imperishable4 ,clean ballast ,clean gravel1 unwashed #aaj ,sharp compact clean sand #ajj ,firm1 clean1 angular1 large-grained sand #ij ,ordinary nodular sand1 slightly loamy #fj to #gj ,loamy sand #ej to #ee ,,note4--,clean fragmentary rock of uniform size1 carefully tipped1 would stand permanently at any height within reasonable approach to the safe compressive load2 but in deposited earth1 as in cuttings1 in addition to the contingency that the natural ground at the base may not be able to bear the strain1 the effect of water pressure must be considered as it may become of sufficient force to cause the face of the slopes to become loose and finally separate and slip4 ,at a height of only #ej feet clear head1 the pressure would be about #bb lbs4 per square inch2 therefore1 it is not so much the weight the deposited earth will bear as the effects of water upon the earth1 and the water pressure that have to be considered4 ,,other ,,earths4 ,description of ,earth ,embankment4 ,approximate safe permanent maximum height in feet1 of an embankment in earth1 conditions as described4 ,feet4 ,peat moss1 marsh earth1 consolidated mud1 silt1 #j to #g hard peat turf ,alluvial soil obtained from a river bed #e to #h ,,note4--,when the river bed is rocky and the deposit firm1 the height may be increased to #ae feet4 ,soft wet pasty clay1 and marsh clay1 moist and #e to #f difficult to drain ,diluvial clay soil of river beds1 according to its uniform character1 degree of firmness and #f to #bj hardness ,alluvial soil4 ,loam and loamy earth4 7,clay and #dj to #gj per cent4 of sand47 ,clay loams 7clay and #ae to #cj about #cj per cent4 of sand7 ,damp clay soil4 ,equably damp1 that can be drained #be to #cj and will partly drain itself ,,note4--,the earths named will generally have their bearing power increased by careful deposition in an embankment1 for the act of equal separation of the mass will cause a decrease in the quantity of water contained in them3 and they will be relieved of the water-pressure to which they were liable in their natural position4 ,on the contrary1 when carelessly tipped they may be deteriorated4 ,vide ,chapter ,,ix4 ,in the case of all earths that are readily impaired by water1 it is the degree of permanent uniform dryness or wetness that governs the safe height of an embankment2 for even the surface of the most impervious clay will be liable to become in a muddy state1 although in the mass it may be dry or in a condition conducive to stability4 ,almost all aluminous or calcareous earths hold or retain water in varying quantity1 and as in embankments this may constantly change1 no safe permanent height of an embankment in such soils can be established4 ,the most solid impermeable clay when separated into small pieces and impregnated with water to any quantity above that it normally contains1 will have its bearing power and general stability reduced1 until1 when saturated1 it becomes as mud4 ,impure and argillaceous chalk1 marly clay1 marl1 and shale1 are all more or less weakened by aqueous action1 and their safe permanent height may be anything not exceeding the crushing strength of the earth1 with a due allowance for the deteriorating influences of weather1 vibration1 and internal water-pressure4 ,in this chapter reference has been made to certain limits of the safe height of embankments2 but were these to be adopted as the maximum safe height in each earth it would be an indefensible edict1 for by the adoption of the required precautionary measures named in the several chapters of this book the height can be considerably increased1 and what is more1 has been much exceeded with impunity in numerous instances4 ,the inclination that any earth assumes1 after being exposed to the weather a sufficient time for it to be affected by it1 will afford a good indication of the safe load it will support4 ,as the slope of repose becomes flatter1 the bearing power of the soil in an embankment will be reduced1 all the deteriorating influences being identical4 ,for the best information 8,on the actual lateral pressure of earthwork10 vide the paper by ,sir ,b4 ,baker1 ,m4 ,council ,inst4 ,c4,e41 ,minutes of ,proceedings of the ,institution of ,civil ,engineers1 ,london1 vol4 lxv41 part iii4 ,,chapter ,,vi4 ,,slopes1 ,,general ,,considerations4--,,table ,,showing ,,the ,,usual ,,range ,,of ,,slopes4--,,table ,,of ,,coefficients ,,of ,,friction4--,,notes ,,on ,,the ,,cohesion ,,of ,,earth4--,,form ,,of ,a ,,slope4--,,some ,,conditions ,,governing ,,the ,,necessary ,,inclination4--,,widening ,,earthworks ,,within ,,the ,,original ,,fences4 ,with regard to the inclination and the form of a slope1 and the prevention of slips in earthwork1 in any slip the surface must be affected2 therefore1 to determine the slope of permanent stability of any earth1 whether in a cutting or an embankment1 is of great importance4 ,an unnecessarily flat slope is not only a monetary waste but may be a cause of instability1 for it exposes a larger surface to deterioration by the weather4 ,by what means is a correct decision to be attained8 ,experience has shown that certain earths under known conditions will repose at particular inclinations2 however1 to empirically assume that any earth will always stand under any circumstances is clearly imprudent and untenable4 ,as a guide1 a table of slopes for earths is valuable1 but consideration of the consequences of movement1 and the distinctive features of each case should govern a decision4 ,should the earth be treacherous and require a flat slope1 it may be advisable to reduce the quantity of excavation by the erection of a retaining wall1 not only to effect a saving in expenditure1 but also to permanently support the soil1 and prevent instability4 ,an inspection of neighbouring quarries and the waste tips1 sand or gravel pits1 hills and cliffs1 cuttings and embankments for roads1 river banks1 c41 will afford an indication of any local peculiarities caused by the climate or otherwise2 and a comparison of the natural slopes assumed when the soil has to withstand vibration1 and when not so disturbed1 will enable a judgment to be formed of its deleterious effect upon the earth2 but above all1 an examination of the cuttings and embankments passing through or upon the same geological formation4 ,reliable evidence can be so obtained upon which the slope of permanent repose can be determined according to the dictates of science and experience1 but the probable consequences of instability will demand a due regard to provision against contingent deteriorating influences which may almost destroy cohesion and render it necessary to rely solely upon frictional resistance1 the remaining resisting power against movement of the earth1 except in solid rock1 which may stand with an overhanging or vertical face1 whereas mud and quicksand may not be in a state of rest even when horizontal4 ,the following table of slopes for different earths has been carefully compiled to indicate the probable permanent slope1 but it should not be separately considered from the other chapters in this book1 as circumstances modify even a considerable range of inclinations2 for instance1 earths that will be stable at a certain slope in temperate climates will require a much flatter slope in tropical or very cold countries4 ,those named are more especially for artificially deposited or embanked earths subject to vibration1 and1 therefore1 in cuttings the slope might be steeper1 although not so in aluminous soils or those in which the particles become decomposed upon exposure4 ,in ,chapter ,,ii41 under the head of each kind of earth1 the approximate slopes of repose are more exactly named1 as they would occupy too much space in a table4 ,when not mentioned in ,chapter ,,ii4 the slope is given4 ,,general ,,note4--,the slopes must be flatter according to the amount of water in the same soil or to which it may be subject1 the depth of a cutting and height of an embankment1 and the presence of all other disturbing influences4 ,vide ,chapter ,v4 for the safe maximum depth of cuttings or height of embankments4 ,,table ,,showing ,,the ,,general ,,range ,,of ,,slopes4 ,description of ,earth4 ,inclination4 ,peat moss1 marsh earth1 consolidated mud1 silt1 ,horizontal to #d to #a hard peat turf1 when loaded ,alluvial soil #b to #a ,,to #c to #a ,ditto4 ,when wet about #d to #a ,soft wet pasty clay in superficial beds #c to #a ,,to #d to #a ,diluvial firm clay of river beds #b to #a ,,to #c to #a ,alluvial soil4 ,loam and loamy earth4 7,clay and #dj #a to #a ,,to #b to #a to #gj per cent4 of sand7 ,ditto4 ,clay loams4 7,clay and about #cj per cent4 of sand7 ,ditto4 ,when wet and crumbling #c to #a ,,to #d to #a ,damp clay soil #c to #a ,upheaved and intermixed beds of different sound #b to #a ,,to #c to #a clays ,solid clay mixed with very fine sand #b to #a ,sound yellow clay containing only the normal quantity of water1 the surfaces covered after #b to #a ,,to #c to #a deposition ,brown laminated clay1 quickly affected by weather3-- ,surface covered #f to #a ,surface exposed #ab to #a ,solid blue and firm clays1 marl and indurated #a to #a ,,to #b to #a marl1 and boulders imbedded in sand and gravel ,soft chalk1 impure and argillaceous #a to #a ,,to #b to #a ,ditto4 ,in cuttings to #a ,,to #a to #a ,hard white chalk1 having greater density than the #a to #a ,,to #a to #a preceding4 ,ditto4 ,in cuttings ,nearly vertical ,,to to #a ,ashes #a to #a ,very fine dry sand #a to #a ,,to #b to #a ,firm sand1 surface not completely protected #a to #a ,,to #a to #a ,firm sand in embankments1 surface protected by #b to #a 7least7 ,,to #c fascine mattresses1 as in ,holland2 and exposed to #a to moderate sea ,ditto1 on land side4 #a to #a 7least7 ,firm shale1 surfaces covered to #a ,,to #a to #a ,,note4--,when the shale is greasy and becomes unguentous upon being exposed to the weather1 it must be considered as a clay4 ,clean gravel and dry shingle #a to #a 7dry7 ,,to #a to #a 7wet7 ,ordinary clean coarse sea beach1 #c to #a at top1 graduating according to the depth1 size1 range1 set of the tide1 and exposure1 to #e to #a ,,to #h to #a at moderate depths1 and at the base to #bj to #a ,,to #cj to #a1 the curve of the slope being parabolic if the waves alone disturb it4 ,the angle of repose will be less as the size of the particles become smaller1 and between high water and a few feet below low-water mark will seldom be less1 if not sheltered1 than #d to #a to #f to #a2 but coarse firm sand that has become consolidated will often stand at a steeper inclination than a mass of rolling stones1 however hard they may be4 ,compact gravel #a to #a ,ordinary road metalling1 moderate height #a to #a 7clean71 ,,to #a to #a 7stacked1 as excavated from road47 ,large concrete blocks4 ,sheltered position and carefully deposited4 to #a ,harbour side ,large concrete blocks4 ,exposed site and carefully #a to #a deposited ,rubble mound4 ,sheltered position #a to #a ,,to #a to #a 7harbour side47 ,rubble mound4 ,exposed to sea #b to #a 7sea slope47 ,,note4--,if an exposed coast1 the rubble may require from #d to #a to #g to #a slope1 depending upon its size1 the currents1 depth1 and 8fetch0 of the sea1 and solidity of the mass4 ,the usual slopes adopted for cuttings and embankments may be said to range from #a to #a for firm earth1 having particles not seriously affected by water or weather1 to #d to #a1 and the most frequent1 #a to #a ,,to #a to #a in cuttings and #a to #a in embankments4 ,with respect to the chief organ of stability in earths other than rock1 namely1 the frictional resistance2 friction during motion is generally considered to be less than the force necessary to overcome it when at rest1 and undoubtedly this is the case when the surfaces are similar1 and are smooth and hard and not easily impressed1 as iron1 granite1 concrete1 and metals generally2 but when they are comparatively soft and incapable of resisting indentation at any pressure that they may have to bear1 the difference between the coefficient of friction during motion and that at the commencement of motion or of repose will not be so marked1 for other resistances may come into action not due solely to surface friction of the mass4 ,a surface may become indented or roughened thus offering opposition to motion not existing at the commencement of movement1 and particularly so in any earth of a mixed character possessing hard particles1 such as boulders1 or sand in clay4 ,on the other hand1 in the case of hard rock1 solid clay1 or other homogeneous earth1 the difference between friction during motion and that of friction at rest may be reliably determined4 ,in soils of a granular or gritty nature small particles become detached during motion1 and by pressure occupy or become wedged into any cavities upon the surfaces1 and therefore offer resistance which is not alone due to friction of a mass upon a like mass4 ,from this cause friction during motion may seemingly even become greater than during rest1 but with material consisting of rounded particles that will not wedge1 the friction upon a sliding surface may be lessened by reason of the grains revolving4 ,in deducing a slope of repose for earth1 the lowest value of frictional resistance1 whether during motion or at rest1 should be taken1 and always as if the surfaces were wet4 ,the coefficients of friction1 ,f1 during motion usually range between #jbe to #aaj1 and the slope of repose1 ,s to #a1 is consequently found by the expression-- ,s #a_/;,f1 therefore1 ,s would equal to #a_/jbe to #a_/aaj #d to #a ,,to #jia to #a1 say1 #a to #a4 ,this is the required inclination to prevent movement provided no pressure is exerted upon the surface1 and not taking into consideration the disturbing and weakening effects of vibration and all other deteriorating influences1 such as the variable degree of moisture of the soil1 the irregularity of its character1 the destruction of the continuity of the surface by trenches or drains in a slope1 the effect of gravity to detach a mass1 the process of excavation or deposition1 and the expansion and contraction of soils of an argillaceous nature4 ,when any earth becomes suddenly water-charged or deteriorated by any of the agencies previously and subsequently mentioned1 movement may be expected1 and it should be remembered that in the same soil the resisting powers to disintegration frequently vary1 consequent upon inequality in the quantity of moisture1 the roughness1 evenness1 smoothness1 compactness1 looseness1 the degree of fineness of the earth1 and also the manner in which strain is applied4 ,friction upon a dry surface is almost invariably greater than that upon a wetted surface1 and is so beyond all question upon any plane lubricated with an unguent4 ,the disturbing and enfeebling effect of water may be judged from a careful analysis of many reliable experiments to ascertain the frictional resistance in the case of the same material in a dry and in a wet state on an unplaned surface of cast iron and on timber piles4 ,it shows the following results in addition to those given in the table of coefficients of friction of earth upon earth in the next page4 ,the surface friction of masonry or brickwork upon dry clay is reduced by from #be to #cj per cent4 when the clay is wet4 ,the frictional resistance of an unplaned surface of cast iron upon wet sand is about #af per cent4 less than the resistance upon the same material when dry4 ,in the case of timber piles1 it is about #ab per cent4 less1 and about #dj per cent4 less in sandy clay and gravelly clay soil4 ,in sandy gravel the difference in the resistances is small1 being only from #e to #aj per cent4 less when the earth is wet4 ,sand has about #bj per cent4 more friction than sandy gravel1 both materials being in a wet state2 and below a depth of from #aj to #ae feet1 the frictional resistance increases little in gravelly sand and gravelly soils4 ,in lieu of a sufficient example under similar conditions and circumstances1 the most reliable method to ascertain the slope of repose of any earth is that of ,s1 the slope of repose1 to #a1 #a_/;,f1 any cohesion of the soil being disregarded and considered as a margin of stability liable to be much impaired2 and1 therefore1 except in a mass1 it is prudent to look upon it as non-existent in the whole of a slope2 and when motion has commenced1 as even a means of accelerating movement by causing lumps to become displaced instead of mere particles4 ,the following coefficients of friction during motion are here given in confirmation of the frictional resistance of an earth being an indicator of its slope of repose4 ,they have been tabulated from different authorities1 are the average results of practical experiments1 and have been compared with the inclination of slopes actually assumed under the ordinary conditions of work4 ,description of ,earth or ,material4 ,coefficient ,corresponding ,earth upon ,earth4 of ,friction ,slope4 during ,s ,,to #a #a_/;,f4 ,motion--,f4 ,damp vegetable or loamy earth #jej to #jfgb to #a ,,to #a to #a ,clean dry shingle or ballast1 nearly #jge to #jhja to #a ,,to #a to #a without sand ,clean wet shingle or ballast1 nearly #jfg #a to #a without sand ,shingle or ballast with ordinary #jhj #a to #a quantity of sand ,,note4--,the presence of sand in gravel increases the frictional resistance because it makes it gritty4 ,excavated hard road metalling1 cast #jhj #a to #a into a mound ,fine dry sand #jge #a to #a ,hard clay1 slightly damp #jfg #a to #a ,hard clay1 damp to wet #jdj to #jejb to #a ,,to #b to #a ,damp lias1 yellow1 and most upheaved #jbe to #jcc #d to #a ,,to #c to #a clays in superficial beds ,wet rubble on wet rubble1 ordinary size#jfg to #jhja to #a ,,to #a to #a and character ,do41 do41 when the surfaces are unclean #jfg #a to #a ,do41 do41 ,large to very large size4 #jhj to #aj #a to #a ,,to #a to #a ,surfaces clean ,,note4--,all rubble carefully deposited4 ,rough-faced granite on gravel and sand1 #jed #ahe to #a both dry ,rough-faced granite on gravel and sand1 #jdh #bji to #a both wet ,rough-faced granite on sand1 both dry4 #jgj #a to #a ,rough-faced granite on sand1 both wet #jec #ahh to #a ,,constructed ,,material ,,on ,,earth4 ,rubble masonry1 or brickwork on clay1 #jej #b to #a dry ,rubble masonry1 or brickwork on clay1 #jcc #c to #a wet ,,note4--,vide ,chapter ,,ii4 ,friction is the chief cause of stability in granular soils and those readily affected by moisture which have for practical purposes no immutable cohesion4 ,in few earths are both cohesion and friction of considerable and reliable value1 one or the other quickly becoming impaired or destroyed4 ,movement is caused by such various means that each earth must be separately considered1 and also the circumstances under which it is placed4 ,the particles of the earth may be dissolved by water and become in a muddy state1 or they may be considered insoluble as in clean sand and gravel1 although in compact sand or gravel the cementing material may crack and weather4 ,provided it was certain any earth would always remain as originally formed1 a condition which it is impossible to guarantee in work1 the cohesion and frictional resistance being known1 the correct slope could be mathematically determined1 but as all earths are subject to varying deteriorating influences1 such a deduction is only valuable as a guide for reasonable inference4 ,cohesion may be more quickly impaired by certain action than friction1 and vice vers4 ,probably1 of all soils1 that to be most distrusted is one that expands and contracts1 such as clay earth1 which although possessing considerable cohesion may become upon drying a mere congregation of disconnected lumps ready to move upon the return of wet weather1 thus its considerable power of cohesion may practically be one of the chief causes of a slip4 ,on the contrary1 clean sand1 although devoid of cohesion1 will not crack or have a greasy surface1 but the particles may be washed away4 ,to ascertain that any earth is uniformly affected throughout the mass1 and to prevent or provide against deteriorating influences is the chief aim4 ,it is useless to declare any earth possesses considerable cohesion when the power can be quickly dissipated by ordinary atmospheric action and even become a cause of movement1 and to rely for permanent stability upon such property4 ,in ordinary earths1 not rock1 it will generally be found that cohesion is small or insignificant in soil having a coefficient of friction of some moment1 and the reverse4 ,in most earths friction1 although it is affected in a greater degree by vibration1 has to be relied upon1 and not cohesion1 as the latter is variable and may exist almost unimpaired in a lump1 which nevertheless may become detached because of fissures4 ,the coefficients of friction of different earths are also better known than the cohesion2 but how easily even friction is impaired may be gathered from the sudden manner in which bridge cylinders will sink after having hung for days by surface friction1 or been held by the transitory expansion of clay4 ,mr4 ,wilfrid ,airy1 ,b4,a41 in a series of experiments on the cohesion of earth1 found that in strong brick loam it is about #afh lbs4 per square foot1 in compact clay and gravel it may reach #hjj lbs4 per square foot of section1 and in clean sand it is practically nihil4 ,in rock the slope of repose depends whether the earth is unstratified or stratified2 and if stratified1 upon the dip of the strata and their resistance to the effects of the weather4 ,a vertical face may be stable in unstratified or stratified rock1 provided in the latter case it does not dip towards a cutting2 or the requisite slope may range from to #a to such an inclination that the cohesion and friction1 which vary greatly1 are sufficient to prevent movement4 ,in sidelong ground should the rock dip parallel to the surface the hill slope may require to be flat1 whereas the valley slope may stand vertically4 ,although1 perhaps1 in many instances the slopes of cuttings and embankments have been arbitrarily fixed1 it may be said1 on the whole1 no very serious interruptions to traffic have been caused from the sole want of sufficient initial flatness of a slope1 as that will soon become known4 ,in determining the inclination it is not the angle at which the earth will stand at the time of excavation or deposition1 and for a few months after that is required to be ascertained1 but that which will permanently suffice to prevent movement4 ,it is well known that almost all freshly cut soil stands nearly vertically for a small depth for a few days in ordinary weather but then begins to crumble and finally break away4 ,what then will be the slope of permanent stability8 ,this chiefly depends upon the degree of exposure1 the effects of the weather1 water1 and vibration upon the soil1 and the depth or height of a cutting or embankment4 ,each earth requires to be duly considered2 for instance1 gravel and sand are pieces of rock1 however small1 and for earthwork purposes the particles may be regarded as insoluble in water2 nevertheless in the case of sand1 should it be charged with water1 it may be necessary to treat it as a fluid1 the same as mud1 although water does not change the particles2 however1 slips in cuttings and embankments in sandy or gravelly soils are not usually caused by their becoming gradually saturated throughout their mass1 but by a flow of water which creates water seams3 the stability1 therefore1 is dependent upon equal percolation and drainage and protection of the surface2 and the slope that should be given to a sand cutting is also governed by the quantity of water it will have to hold1 and whether the sand is pure or loamy4 ,the depth of a cutting in sand has a considerable influence upon the slope of stability1 for frequently sand is in a dry state in the upper portion of a cutting1 but beneath it is wet1 and partakes more of a silty character1 and therefore may stand at a steeper inclination in the upper part1 but require a flat slope in the lower portion4 ,the same conditions are found in all soils1 and the sides of a cutting vary1 one may be comparatively compact and free from water1 the other in a wet state and disintegrated4 ,they will not permanently repose at the same angle1 the slope varying according to the degree of dryness1 size1 and uniformity of the particles4 ,in all earths in which cohesion is liable to be quickly destroyed1 a straight slope is the best as having an even surface1 which prevents the formation of depressions and causes the water to drain away1 and also offers the least surface to the weather4 ,in all earth such as shingle1 gravel1 or sand1 consisting of pieces of rock or rubble1 or having round particles1 it is important to remember that any surface disturbance may cause serious movement1 particularly should it commence at the bottom of a slope1 as then the revolving action may not cease until a flatter inclination is produced by material rolling from the top and not reposing until it nearly reaches the base4 ,the quantity of moisture is the chief governing condition of the slope of repose in clay soils1 and it should not be forgotten that this may vary considerably4 ,clay when only slightly moist may stand at a #a to #a or #a to #a slope1 but as it gradually becomes in a wet state will require a flatter inclination1 and may not be at rest until the slope is at least #c to #a1 and it is not safe to rely upon a steeper slope than #c to #a in the case of almost any surface clay beds liable to become charged with water1 and even #d to #a1 should the excavation be on the side of a clay hill and near houses1 or the ground be loaded2 but clay having some powers of cohesion which usually are greater as the clay is harder1 is not so quickly disintegrated as in the case of more porous soil1 and the form of the slope it assumes is not a straight line2 that most usually approached by sand or gravel or a granular soil consisting of particles of the same character1 although the lower part of the slope may be flattened consequent upon the erosion of the finer particles which crumble and become deposited at the base4 ,as a rule1 the greater the cohesion of the soil the more curved is its natural slope1 the greatest pressure being at the base where the inclination is flatter1 and is steeper towards the top1 as the ground may be held together by cohesion at a vertical face4 ,the harder and looser the particles the straighter will be the slope1 and if the ground gradually increases in firmness it will usually be nearly straight2 but if the contrary condition exists1 the natural slope will be flatter towards the base although nearly vertical for a few feet from the top4 ,as a proof how quickly clay becomes less stable and loses its cohesive power with the usual quantity of moisture in it1 when first tipped it may assume a slope of #a to #a ,,to #a to #a1 but upon exposure to the weather1 which causes the lumps to waste away and the clay to swell from moisture and other agencies1 the firmest clay in cuttings and embankments may be said to be unstable until a slope of at least #a to #a is reached in moderate depths1 and #b to #a ,,to #c to #a in high embankments or deep cuttings4 ,in all earths the chief cause of movement of earth is water1 and the main questions to be decided are so far as regards the inclination of the slope4 #a4 ,should the surfaces of a cutting be drained and protected and be excavated to a comparatively steep slope2 or1 #b4 ,should they be left undrained and uncovered and be excavated to a flat slope4 ,provided a cutting can be readily drained and covered and there is no probability of any sudden or permanent increase of moisture1 perhaps the first method is the more economical2 but much depends upon the quantity of water held by the earth in its normal state1 whether it is of the same character throughout1 and the depth of a cutting4 ,should the beds be upheaved or intermixed1 then a flat slope is necessary and no covering except a wall may make it stable at a steep slope1 and1 for instance1 should clay be always in a semi-saturated condition1 #c to #a is the least slope at which it will permanently stand1 and it will usually require a more moderate inclination4 ,a medium course to adopt is that of varying the inclination of the slopes1 the steepest1 of course1 being at the top and the flattest towards the toe2 this is in accordance with the laws of pressure and a mathematical investigation of the theoretically correct slope1 which nearly corresponds with the actual slope a high embankment will assume when allowed to weather and settle3 for by varying the inclination of the slope the latter becomes practically a curved line and approximates to that of the curve of equilibrium4 ,in almost all slips the surface from which the fallen mass has become detached is curved1 the upper part being concave and the lower slightly convex1 the outline being caused from the upper portion falling1 the lower receiving it and being pressed outwards2 however1 it may happen that the lower part of a slope has remained intact1 and only the upper slipped and become deposited upon it4 ,the varying slope system has recently been adopted by ,mr4 ,francis ,fox1 ,m4 ,inst4 ,c4,e41 upon the ,scarborough and ,whitby ,railway1 where an embankment about #ij feet in height in treacherous clay had slopes of #a to #a for the upper #cj feet in height1 #b to #a for the middle #cj feet1 and #c to #a for the bottom #cj feet4 ,formation width #bh feet4 ,a calculation of the insistent weight per square foot1 without a train1 at stated heights gives the following results2 taking the weight of the earth at #jjee of a ton a cubic foot1 or #a ton a cubic yard1 and assuming the worst case1 that of the earth for the width of the formation1 viz41 #bh feet1 to act simply as a column #a foot square and the load as not being distributed over the area of the entire base at any point4 ,at the base of the upper #cj feet1 #a to #a slopes1 it would be about #afe ton per square foot4 ,at the base of the middle #cj feet1 #b to #a slopes1 it would be about #ccj tons per square foot4 ,at the base of the lower #cj feet1 #c to #a slopes1 it would be about #die tons per square foot4 ,if the weight of #a foot lineal of the embankment is taken and considered as equally distributed over the whole area of the base at the #cj feet divisions1 the strain per square foot would be as follows3 ,at the base of the upper #cj feet1 #a to #a slopes1 about #a ton per square foot4 ,at the base of the middle #cj feet1 #b to #a slopes1 about #a ton per square foot4 ,at the base of the lower #cj feet1 #c to #a slopes1 about #b tons per square foot4 ,,note4--,the actual strain is probably approximate to a mean between the two values1 and is nearer the latter than the former4 ,there is no reason why the varying slope system should not be adopted in embankments of clay or soil having considerable powers of cohesion1 as the expense of trimming the slopes is very little more than making them to a straight line4 ,to trim a slope to an elliptical1 parabolic1 or cycloidal curve would be a needless refinement requiring a template2 moreover1 the surface is better when it consists of straight lines1 provided that at the junction of any two inclinations the point of meeting is sufficiently rounded to prevent a lodgment of water4 ,in cuttings in non-weathering tenacious soil the upper part might be left at a steep slope for #e or #f feet from the surface of the ground4 ,it is evident that the depth of a cutting or the height of an embankment affects the stability of the slopes1 but some soils are so weak that an embankment of even little height will not be at rest until the toe of the slope is supported4 ,if the slopes were not pressed out the earth in the central portion of an embankment would stand at any weight less than that which would crush it when in its weakest condition2 therefore1 as the load increases downwards it is a logical deduction that the slope should be flatter as it approaches the base4 ,in slips the form generally assumed in soils having considerable cohesive power nearly approaches that of a parabolic curve1 which shows that a straight slope is not the correct one in tenacious soil1 and theory confirms it4 ,in the case of cuttings of considerable depth1 apart from the question of the best form of slope1 in order to lessen the velocity of the surface water and the extent of a slip1 and cause supported weight upon the slopes1 they can be divided by broad terraces or benchings1 about #f feet in width1 and at vertical distances of #ae to #bj feet1 upon which can be impermeable catchwater drains4 ,it is important not to allow a flow in a straight line or nearly so1 as the velocity of the water may erode the slope4 ,if the nature of the earth and its resistance to erosion will allow1 the benches or steps should be abrupt1 in order to cause the greatest resistance and deviation from a direct discharge4 ,the slopes of the catchwater drains may require to be covered in a flood district or one having a heavy rain or snowfall4--,vide ,chapter ,,iv4 ,in excavating a cutting in soil likely to slip1 care should be taken that the surfaces are not strained by lumps being left upon them which are only retained by reason of the cohesion of the earth1 as they will cause weak places less able to bear any pressure brought upon the slopes through the sides being deprived of continuity of support4 ,therefore1 in such cases1 the slopes should always be rough trimmed as quickly as possible after the gullet has been excavated4 ,also when the slope of a cutting is furrowed so that its surface consists of separate and unsupported masses of earth clinging to it1 continuity of support is destroyed and the earth is more exposed to meteorological dissipation2 and in non-cohesive soils such as sandy or gravelly earth1 in which especially a straight and uncut surface is of importance1 movement is incited4 ,therefore1 when it is found necessary to insert open trenches in a slope1 they should be at right angles to its foot1 and the inserted material should be well packed so as to support the sides and to interfere as little as possible with the slope4 ,even in clay soils or any having considerable cohesion1 trenches diagonally or transversely cut in the surface are generally inexpedient as disturbing and destroying the continuity of support of the surface and increasing its exposure to the action of the weather2 and although they may be temporarily effectual as drains1 such division of the inclined face cannot but induce a disunited condition which will at once be apparent should the trench become choked and it miscarry as a drain2 and a temporary failure may so destroy the existing delicate equilibrium as to cause movement4 ,such trenches should be regarded with suspicion1 as any stability caused by their draining or conducting away water may be effected at the cost of continuity of support1 the deterioration of the resistance of the soil to weather1 and the impairment of its frictional and cohesive properties4 ,if placed upon a slope at right angles to the formation the preceding objections are removed4 ,it may become necessary to excavate or trim a slope to a steeper inclination than that which would otherwise be adopted and is considered to be its angle of repose1 in order to widen a railway between the fences1 or enlarge a station4 ,then1 pre-eminently the question of the effects of a slip demand attention4 ,the great majority of railway stations are located prior to the commencement of1 or as the works progress1 but additional accommodation which1 for reasons of economy must proceed pari passu with the development of a district1 is usually required some time after a railway has been opened for public traffic1 and it may be imperatively necessary to confine the works within the boundaries of the land originally purchased4 ,consideration of the several chapters in this book will recall to the mind the chief points to be regarded4 ,fortunately1 stations are seldom placed in deep cuttings or upon high embankments2 but frequently when a station is opened1 houses will be erected around it1 thus causing any movement of the ground to be of serious moment and dangerous4 ,assuming the railway must be widened within the original fences1 the position of the toe of the slope is fixed1 and also that of the top of the slope4 ,the questions then in the case of a cutting are principally3-- #a4 ,will the slope be too precipitous for the earth to stand at one inclination8 #b4 ,can it be made sufficiently steep for #e or #f feet from the top to obtain an inclination for the lower portion at which it will have permanent stability8 #c4 ,can the earth be made to repose if the face is evenly protected under circumstances #a and #b8 #d4 ,is it necessary to erect a retaining wall to a distance a few feet from the original surface of the ground8 #e4 ,if a wall be necessary1 what should be its lowest height consistent with the stability of the unsupported inclined earth above it8 ,provided there is no appreciable superincumbent weight to be borne nearer than #aj feet from the top of the slope1 and that the foundations of a building are at a considerable depth in the ground1 and the surface and back drainage waters properly controlled1 no retaining wall may be required1 assuming the original inclination under ordinary conditions to be proved to be the permanent slope of stability2 but should the distance of the face of a building from the toe of the slope after widening be insufficient to allow of the original slope being adopted1 a retaining wall will be necessary1 its height being chiefly governed by the proximity of any building1 and the necessity of nearly maintaining the originally established steepest slope of repose in the case of any unsupported earth4 ,the advantage of a sufficient cess in such a case is that it makes provision against deterioration of the surface1 and causes an imaginary slope of the same inclination as the original slope to be contained within the space between the face of the building and that of the retaining wall at formation level4 ,in sandy or loose soil if any buildings or wells near the site show signs of cracking1 the excavation should at once be stopped to see what preventive measures are requisite1 and pumping water out of a trench may be dangerous4 ,any retaining wall in such a position should be erected in short lengths1 so that the earth and foundations are exposed to the weather as little as practicable4 ,,chapter ,,vii4 ,,notes ,,upon ,,the ,,preservation ,,of ,,the ,,foot ,,of ,a ,,slope4--,,various ,,methods ,,of ,,covering ,,and ,,supporting ,a ,,slope4--,,protection ,,from ,,snow-,,drifts4--,,the ,,formation ,,width ,,of ,,cuttings ,,and ,,embankments4--,,the ,,deleterious ,,effects ,,of ,,vibration4 ,the protection of the toe of a slope is of importance1 as it is usually the most vulnerable and the weakest part4 ,when the earth is of the same character1 the quantity of water is usually greater at the lowest level than above it1 and the stability of the soil in its vicinity is therefore lessened4 ,in clay soils this softening action at the base may cause a slip and probably can only be prevented by reducing the percolation by surface drainage1 which has been referred to in ,chapter ,,iv42 the matter under consideration being the counteraction of movement in the toe by other means than draining1 although combined with it1 such as by-- #a4 ,an impervious retaining wall with a pervious backing of ashes1 gravel or sand1 and ample weep-holes1 at the foot of a slope1 which1 by preference1 should be of ,portland cement concrete1 a more homogeneous material than brickwork or masonry1 as it has no joints1 and is particularly to be preferred for retaining walls in clay soils1 as it approaches in a greater degree the condition of air-tightness and that of equal resistance4 #b4 ,by a pervious wall or counterfort of gravel1 burnt ballast1 hard chalk1 rubble1 strutted timber framework1 or a covering of other firm material4 ,in both the preceding cases1 to ensure stability and to prevent any protective works being pushed forward1 the foundations must be below the formation or ground level4 ,to lessen sliding action the foundation should incline at right angles to the face1 and should have a batter either for the whole width or for a distance not less than about one-third to one-half of the bottom thickness in the case of low retaining walls4 ,a wall having a steep batter upon each face1 and therefore a wide base as compared with its area1 causes the centre of gravity to be at a greater distance from the exposed face1 and therefore the resistance to overturning is increased2 but care must be taken that it does not slide forward4 ,a foundation for such a wall upon clay or tenacious soil is to be preferred1 provided there is no upheaval of the ground in front1 but it should not be upon a thin stratum1 or the latter may slide upon another4 ,in towns1 or where land is of considerable value1 the two sides of a cutting can be made to support each other1 and one of the following principal methods may be adopted4 #a4 ,an invert under the line4 #b4 ,a heavy flat platform1 arched on plan or solid throughout1 under the permanent way or formation1 to prevent a forward movement of the toe4 #c4 ,overhead arches and iron struts at intervals to resist and reduce the pressure upon a wall4 ,in such a situation1 should a tunnel or covered way be not required1 any subsidence of the earth may cause the destruction of valuable property1 and the erection of a retaining wall be imperatively necessary from a due consideration of prudential construction1 and altogether regardless of the character or condition of the earth or its liability to become water-charged4 ,in order to prevent movement of the earth different forms of support may be required4 ,in some cases1 owing to excessive pressure1 a counterforted wall with an invert under the permanent way may be essential1 or the invert may be flat and be arched on plan1 thus supporting the toe of a retaining wall between the intervals1 in combination with a vertical or inclined pilaster and a front counterfort system1 and in addition flat overhead struts of iron or other material between the walls acting as an auxiliary support above the required traffic space may have to be adopted where the walls have to sustain considerable thrust1 the thickness of the retaining wall being thus reduced2 or a simple retaining wall may be sufficient4 ,a non-jointed material as ,portland cement concrete of equal character is to be preferred to a mass consisting of hard materials yet incapable of possessing a joint equal to their strength or durability4 ,with regard to the protection of the toe or lower portion1 of a slope by means of a retaining wall1 it may be the only effectual support in one case1 and not succeed in an exposed country without a complete system of open or closed drains1 and then its adoption may be superfluous4 ,in the following few paragraphs an endeavour is made to indicate some situations in which retaining walls have or have not been completely successful when erected for such purpose4 ,first1 it is most important that ample provision be made for draining the back of the walls1 for if the egression of the surface waters be obstructed1 they must accumulate and cause hydrostatic pressure1 soften the lower portion of the earth1 thereby failing to partly effect one of the objects of their erection1 and cease to protect the surface2 the probable result being that the wall is pushed forward1 broken up1 or overturned4 ,the drainage must be regulated by the quantity and velocity of the flow1 and ample weep-holes should be provided to prevent an accumulation of water at the back4 ,in damp soil there should be one to about every three or four superficial yards1 and an outlet at each wet place1 or a wall may not stand4 ,the wall should be backed with a filtering medium such as coarse gravel1 hard ashes1 ballast1 and no retentive earth should be used4 ,in clay earths a retaining wall should always have a dry porous backing1 as it not only reduces any pressure due to a head of water1 but also allows of the earth swelling without affecting the stability of the wall1 as it probably would if the clay rested against the back of the wall4 ,retaining or breast walls are particularly useful in loose soil having no cohesion1 i4e41 those of a sandy character or consisting of very small grains1 and which upon saturation by water or by the action of its flow become in an unstable state or one of actual movement2 in such1 a case not only is it requisite to protect the surface of a slope1 but support at the toe is indispensable4 ,in cohesive soil1 such as clay or clay marls1 surface protection1 combined with systematic and thorough drainage1 may be all that is required to make a slope stable1 and the erection of an impervious or solid high wall be unnecessary1 always provided the earth cannot slide from being superimposed upon an inclined stratum4 ,in fact1 retaining walls in retentive soil have been found to induce a slip1 because they neither drain the earth nor prevent the additional impregnation of water1 and they have consequently been destroyed4 ,in countries where floods or very heavy and sudden rainfall1 frost and snow quickly succeed1 masonry or dry stone retaining walls at the foot of a slope soon become impaired1 and require constant supervision and careful maintenance1 and cannot be considered as economically or generally effectual2 and should the earth settle1 as they are comparatively solid they will not follow any subsidence of the surface2 therefore cracks occur and water accumulates in the hollows1 the slope has no longer uniform support1 a localization of the egression of water is caused1 owing to the fissures in the wall inducing a flow1 and the wall becomes a cause of a slip instead of a protection against movement4 ,should such a wall bulge after it has been restored to the condition of being a continuous support1 its forward movement may be arrested by the erection of counterforts with an inclined face in front from #aj to #cj feet apart according as weak places exist1 having joints at right angles to the batter2 and this is1 perhaps1 the cheapest and quickest remedy1 but the slope must be carefully drained and the number of weep-holes be increased4 ,in order not to obstruct1 but induce the through drainage of water1 retaining walls to prevent slips have been erected1 consisting of arches turned upon piers1 the intervening space being dry walling which allows a free flow of water1 the idea being to afford the necessary support without interfering with the drainage4 ,in some cases1 as it tends to condense the soil1 weighting the toe of the slope may prevent movement1 and on the side of a hill weight and mass1 apart from slope protection or drainage1 must be provided to arrest a slip or prevent further movement1 either by means of a continuous wall1 or by the addition of frequent counterforts1 #e or #f feet in width1 to an existing wall1 if space permits1 the back and front having a considerable batter3 the centre of gravity of such a mass being low and the base large1 overturning is improbable4 ,forward movement can be also guarded against by deep foundations1 and as the earth will rest on the inside they can have a flatly inclined base sloping towards the cutting1 as it will tend to prevent overturning1 the depth of the foundations at the face being two or three times that at the back4 ,such a structure can hardly be called a wall1 being really an extensive and massive concrete toe4 ,perhaps generally the most economical and secure way of preventing movement is to erect a low ,portland cement concrete wall at the toe of a slope with a considerable batter2 or to cut a trench at formation level outside the line of the slope1 and to shore it by means of old sleepers strutted at intervals when better and durable material cannot be readily obtained4 ,the chief object of a protection at the toe in clay soils is to prevent the bottom of a slope being softened by a lodgment of water1 or fissured by heat or drought2 this may be effected without a wall2 but in the case of sand or fine granular earth cuttings liable to become quicksand1 support at the base is absolutely necessary1 and the best way to prevent movement may be to erect a breast retaining wall at the toe a few feet in height1 say #c to #e feet1 the backing being of dry porous material such as ashes1 coarse gravel1 or broken stone1 increasing according to the depth or height of the earthwork and quantity of water1 the thickness being more than sufficient to contain the drainage waters1 and not less than #a foot #f inches1 in order that it may act as a filter and drain the slope1 c41 so as to lessen the percolation of water4 ,sheet-piling and a backing of rubble acting as a drain #b or #c feet square1 or a strutted timber duct1 both made out of old sleepers1 have been used with this object in quicksand where water rapidly percolated to and accumulated at the base4 ,instability of the toe may also be prevented by covering it with layers of gravel1 but one of the reasons that may cause a gravel counterfort to fail in loose porous soil is that sand or mould may be washed through the interstices in the stones forming the gravel2 hence a more impermeable covering is to be recommended in such a case4 ,a toe of rammed coarse gravel or broken stone may supply the required support in the case of coarse and fine sand1 when the latter is alone movable4 ,experiments have shown that sand rammed in layers of about #e inches and earth mould #b inches in thickness give the best results4 ,the less the weight is increased by ramming the more solid the original earth4 ,brushwood or fascine work weighted with gravel1 stone or broken bricks1 and stone pitching can also be used for sandy soils1 but a filtering layer must cover the sand1 or the latter will be eroded4 ,counterforts of well-rammed natural earth may be sufficient provided the soil is firm and is made compact and uniform in texture4 ,in otherwise stable soil1 when it is known that a sand vein is the cause of a slip because of water percolating through it1 it should be raked out as deeply as practicable if not too large1 and the space be filled with stones1 coarse gravel1 or dry material forming an open drain for the water to issue without a flow of sand1 thereby preventing any accumulation4 ,when a stratum of shifting sand overlies beds of conglomerate and gravelly or clayey sand it will be necessary to support the lower portion of its slope by a wall4 ,the wettest places in a slope should be noted and the surface be turfed or covered1 and should the depth of the unstable sand exceed #e or #f feet1 narrow benchings can be made #b or #c feet in width at every #e or #f feet of vertical height to divide the flow of water and prevent it following a continuous course4 ,it also sometimes happens that two treacherous earths have a stratum of stable soil between them such as rock2 in that event it is advisable to leave a cess between the bottom of the slope of the upper stratum of unstable soil and the underlying rock1 so as to allow of weighting or other works to resist movement of the toe4 ,with respect to the adoption of open surface rubble drains upon the slopes1 in ,chapter ,,iv41 page #gh1 special reference is made to them as drains1 and in ,chapter ,,vi41 pages #aaa1 #aab1 an objection is examined2 but they are generally effective if cut at right angles to the formation and not diagonally or transversely4 ,when a slip is repaired by replacing the slipped earth when dried and rammed between such drains1 it should be determined whether it would be better to cover the slope or increase the number of drainage channels4 ,a simpler remedy is the insertion of a dry rubble lining on the surface of the original ground upon which a slip has occurred1 and the restoration of the slope by means of firm earth or rammed and dried slipped soil2 but the system of rammed earth counterforts1 although it has succeeded when effected during the dry season1 the earth being wetted sufficiently to make it cohesive by ramming1 will not succeed in wet or winter weather1 as the soil cannot then be consolidated by ramming operations1 for it will be overcharged with water from the effects of rain1 frost1 or snow4 ,fair or summer weather is required to ensure success4 ,should it be considered advisable1 in addition to the erection of rammed earth counterforts to a height of from one-third to one-half of that of an embankment1 a porous layer or wall of broken stone can be inserted between the slipped material1 which is not touched1 so that the waters can filter away through it and the slope be restored2 and the counterfort have a channel at its base1 in order to prevent a lodgment of water1 to drain the slipped earth and the embankment1 and to prevent the counterfort becoming saturated4 ,this method may be insufficient in any but comparatively firm soil1 and it may be necessary to make a trench at the toe of the slope having its base #b or #c feet below the seat of the slip or firm ground1 it being filled with rock chippings1 shingle1 gravel1 burnt ballast1 broken bricks1 ashes1 coarse clean sand1 or other material having equable frictional stability and particles that may for earthwork purposes be considered as insoluble in water1 and therefore that form stable masses and yet act as drains2 and to drain the slopes by trenches varying in width according to the position and depth of cutting1 the depth of a trench may be little or have to be such that it extends to the solid ground through the slip1 or about #ej to #ge per cent4 of its depth1 which must be determined in each case1 may be sufficient4 ,such dry stone counterforts may be required at distances from centre to centre of #ae to #ff feet1 and are sometimes placed in the same right line and even through an embankment1 and are connected with a drain sufficiently deep to prevent any lodgment of water at the centre of the base of the embankment or near the foot of a slope4 ,with regard to covering a slope of a cutting or embankment1 its principal use is to lessen deterioration from meteorological action1 to keep the ground underneath in an equable condition1 to reduce percolation and make it uniform1 to diminish the danger arising from cracks and fissures caused by heat1 evaporation1 or drought1 to prevent the erosion of the surface by a flow of water or the production of unctuous surfaces1 and yet not interfere with effectual drainage4 ,it is known that percolation is decreased by vegetation1 and that it is less through turf than bare ground1 but varies greatly according to the kind of covering1 the season of the year1 the regular or irregular distribution of the rainfall1 and other causes4 ,if the surface has to be covered with vegetation it should be close1 uniform1 and vigorous throughout the whole year1 and nothing fulfils these conditions as well as grass or turf4 ,the protecting value of turfing earthwork may be judged from an inspection of fortifications in which steep slopes1 deep ditches1 and perfect maintenance are a necessity4 ,as a consequence of the binding and shielding of the earth by the roots of grasses and plants1 and their protection of the surface1 the slopes stand at a steeper inclination than they otherwise would1 and the system of clinching the exposed faces of the parapets of earthwork with a layer of sods laid header and stretcher is found to be a great support4 ,in earth possessing considerable cohesion1 such as the clays1 provided the covering is uniform1 grass having comparatively deep roots is not a particular advantage1 but the closeness of the growth of the plant and the unimpaired maintenance of a complete cover is of importance1 and the earth should be disturbed as little as possible so as to prevent any particles comprising the soil becoming disintegrated and dissolved4 ,when it is considered advisable to adopt a covering of grass1 plants1 shrubs1 or trees1 it should be remembered that some grasses1 such as the couch-grass1 are injurious to other plants4 ,to equally cover a slope with sods of turf they should be cut to a regular form and depth of about #f inches1 and be firmly pressed into their places so as to produce an even smooth surface4 ,a steep slope or any less than #a to #a1 if of considerable depth1 will not give a sufficiently flat surface for grass to properly grow upon it4 ,in sandy and gravelly ground1 as the particles may be considered insoluble in water and as possessing no cohesion1 grass1 if it will grow1 having deep roots is to be preferred1 even if passing through any earth that has been placed upon a slope1 in order to counteract the want of cohesion by a greater hold in the soil and any peeling of the turf or tufts forming or becoming detached1 rolling down and leaving an unbared surface4 ,bent-grass will usually grow on most sandy soils1 and a shrub known on the north-east coast of ,england as the sea buckthorn also rapidly vegetates1 but marine grasses must be used in ground impregnated with brackish or sea water4 ,to prevent light sand from being scattered by the wind or washed away a species of rush 7,bot4 ,ammophila arundinacea7 has been used in ,holland and ,england1 and is found to flourish in dry soils1 and as it has spreading roots which often grow to a length of #bj feet or more it binds the grains of sand4 ,experience in ,holland has shown that grass upon sea embankments does not grow well or flourish at a steeper slope than about #f to #a4 ,in countries where wind storms occur1 or the soil is of so light a character that the passage of a train at considerable speed raises the earth and moves it as dust1 a covering of fine grass indigenous to the country has been found to be a protection and necessary to economical maintenance4 ,planting the white basket willow1 or withy1 has been recommended as a means of preventing slips in loose soil1 as the roots form a network and bind the earth and cover the surface with shrub growth4 ,in damp ground the cuttings need not be planted as deeply as in dry earth1 but of course they will not flourish in all soils4 ,osiers have also been adopted with good results in damp places4 ,embankments of blown or drift sand1 easily moved by the wind1 have also been protected and maintained by branches of trees laid horizontally4 ,they were placed in regular courses alternately with a stratum of sand1 the ends projecting over and down the slopes1 which were sown with indigenous plants that it is known will flourish upon it4 ,great difficulty had been experienced in maintaining the embankment until its surface was so shielded4 ,sandy dunes have also been prevented from slipping and being eroded and destroyed by the sea and wind by reducing them to the same line1 level1 and slope1 by filling all openings or depressions1 or1 if curved1 by trimming them to a regular exterior and the largest radius1 and by a covering of fascine work in the exposed places1 and in any less exposed situation by planting them with grasses that will grow upon such soil1 the object being to remove all local obstruction to wind or wave force and cause equable resistance and protection4 ,in ,france1 the drifting of blown sea-sand into cuttings1 which not only may interfere with the free traffic but also be a destructive agent to the rolling stock1 has been prevented by planting pine trees upon the cess4 ,in embankments in loose soil and across valleys1 especially if they are narrow and deep1 repeated gusts of wind which have their maximum effect upon a flat surface at right angles to it1 will produce a hammering action upon the windward side1 and when the velocity is very great1 upon the leeward portion there may even be a partial vacuum created by the wind rushing over the top of an embankment4 ,an actual maximum momentary pressure of wind of #hj lbs4 per square foot was registered at the ,liverpool ,observatory in #ahfi1 equal to a hammering action of #jee lb4 per square inch4 ,it is here referred to in order to show that in exposed valleys the surface of all embankments of light soil should be covered so that the particles cannot be blown away at the top or from the slopes1 for a force of #hj lbs4 per square foot nearly equals the weight of a cubic foot of dry open sand which cannot be taken as weighing much more than #ij to #ajj lbs4 ,if seed be sown upon a slope it is evident that it should be of uniform kind in order to create a general equable condition1 and the growth of all rank vegetation should be prevented1 for an unevenly protected or covered surface will promote a localization of disturbing agencies1 and especially in treacherous ground when it has been covered1 neither the surface nor the turf should be allowed to be broken4 ,in ordinary cases where slips may be expected1 soiling with mould or top dressing1 and sowing the slopes may be sufficient1 and turfing in others of small extent2 but in retentive soluble soil1 a filtering layer under the turf may be required1 so as to prevent spreading1 particularly near the toe of a slope2 however1 in mountainous or hilly districts1 experience seems to indicate that it is advisable to allow earthwork to become consolidated by the natural effect of rain and atmosphere before finally trimming or covering the slopes3 on the contrary it may be advisable1 especially in treacherous ground1 to trim and cover with mould1 sow1 turf1 plant1 or cover the slopes as soon as possible after they are excavated or deposited1 in order to protect soluble soil from rain1 frost1 or snowstorms consequent upon the wet season being near4 ,of course1 when experience shows that slips are improbable1 the slopes can remain bare and simply be trimmed1 and a covering of grass be left to time to effect1 and this is now the frequent practice4 ,should settlement be expected or be unavoidable1 the face protection can be so made that it will not be disturbed or broken4 ,in such a case a short1 straight slope with a flat inclined berm or cess1 the length of the slope being divided into three or four short continuous straight portions1 has been adopted with success4 ,should sowing or planting the slopes be considered as too slow in producing a covering1 experiments can be made by mixing available soils1 or with one earth2 and by exposing the mixture or earth to the deteriorating weather influences it will have to resist1 the best protective covering to be readily obtained can be discovered4 ,respecting the planting of saplings or shrubs1 laws have been enacted to compel the planting of saplings and trees upon certain lands as a protection against landslips1 and it seems to be generally acknowledged that trees1 particularly when in plantations1 are a protection1 as they not only absorb moisture and bind the earth with their roots1 but also lessen any flow of water down the steep sides of a cutting or embankment2 and instances have been recorded in which trees have been shown to preserve the alluvial banks of rivers1 as when they were felled the sides were eroded1 or weakened1 probably by the increase of moisture and exposure1 with the result that the channel became widened4 ,the systematic planting of live slips of poplar or willow has been found to effectually protect soft banks of rivers1 washed by the stream1 against weathering and erosion4 ,also in treacherous clay marly-soils1 in which slips of earth were numerous1 acacia trees have afforded a good protection1 as their widely spreading roots conduced to hold the soil together1 and their foliage and branches gently regulated and lessened the effects of rain and prevented quick infiltration into the earth4 ,however1 care must be taken that the roots do not open or strain the surface of the ground by force of the wind or otherwise1 and increase and localize percolation2 but they tend to prevent cracking and fissuring of the surface in clay and argillaceous earth1 and form a protection against the effects of the sun's rays and drought4 ,quick-growing trees should be selected having large and deep roots and abundant foliage1 especially in non-cohesive earths4 ,acacia and birch trees appear to give satisfactory results4 ,unless in exceptional situations1 such as to protect a cutting from drifts of snow1 or where from local experience they are proved to act upon the earth as a holdfast1 it is questionable whether the indiscriminate and non-systematic planting of saplings or bushes is not more likely to aid disruption than promote stability1 and1 as a rule1 other and less expensive means of protecting a slope are to be preferred unless a uniform covering by trees or shrubs is practicable1 whether over a small or large unstable area4 ,isolated trees should not be allowed within the fences of a cutting1 although if just outside the toe of the slope of an embankment the roots may serve as a buttress1 and therefore be beneficial4 ,although in some dyke embankments in ,north ,europe no trees or plants are allowed to grow upon them1 so that any deterioration of the mass maybe clearly and quickly apparent2 in ,holland the defensive covering varies according to the character of the earth1 fascines1 wattling1 sodding1 a gravel coating1 benching at the top of a slope and planting it with reeds to protect an embankment from erosion and wash caused by traffic2 pitching1 plank facing1 and sheet planking at the toe1 when the ground is very soft1 have all been used with success4 ,on silty land willows generally grow rapidly1 and when planted a little distance from the toe of the land slope in enclosure embankments they are found to protect the ground4 ,in some situations it may be necessary to protect an embankment against boring by burrowing animals or crustacea4 ,clay and clay loams are soils especially liable to be burrowed4 ,usually as the quantity of sand increases1 the boring decreases2 a coating of hard ashes may afford the required protection3 however1 in the case of crustacea1 local experience alone can indicate the best protection1 probably nothing less than stone pitching may suffice1 but as a general rule in this country1 no precautions are necessary2 in warmer regions it may be otherwise4 ,with reference to fissures in a slope which tend to produce slips as they allow water to trickle down them1 which must either be absorbed by the earth or find an outlet2 a slippery surface is thus created and the tenacity and continuity of the soil impaired or destroyed2 separation also takes place in non-homogeneous earths such as boulder clay and in embankments formed of rock and earth tipped together4 ,it is practically impossible to fill or pun every fissure that may appear in a cutting or an embankment1 but as there are generally places where slips are more probable than others1 it may be advantageous in treacherous soils to adopt a regular system of filling the fissures1 especially before the wet season commences4 ,coverings can also be made of a thin coating of burnt ballast1 hard chalk1 or gravel1 which will reduce the number of cracks or crevices1 or a mattress of fascine work can be used at the toe of the slope in submerged work1 but care should be taken that the mattresses overlap and that there are no open places between them1 or1 instead of being a protection they will then be a source of danger by conducting water between the joints2 for this reason1 as with any other material having loose openings1 it is advisable to use them over a continuous surface so that percolation may be uniform and not simply for weak places or for the purpose of repairing a slip in an earth embankment4 ,the chief aim in fascine work is to thoroughly bind the work together so that it is of equal strength in all directions1 and a little time after construction should be allowed before deposition in order that the material may settle1 as an even surface is important4 ,the most durable material should be used in making a fascine covering1 willow being the best1 or it may require constant renewing4 ,alder1 aspen1 and the best available brushwood are also employed1 and straw and ordinary matting for shallow embankments1 say up to #h feet in height1 which lasts only six to twelve months4 ,the best time for cutting should be locally ascertained1 and when they commence to deteriorate after being hewn1 generally from three months to a year1 depending upon the season in which they are cut1 c41 c4 ,in ,england1 thorn switches have been used in lengths of #e to #f feet1 tied up with tarred rope in bundles having a diameter of about #a foot1 every endeavour being made to bind and interweave them4 ,care must be taken that the mattresses are well loaded or they will float2 the loading should commence at the centre1 and be equally continued in all directions1 as that has been found to be the best method2 they should be made to sink evenly if they have to be lowered through water1 and they must be prevented from curling up at the edges4 ,the props which fix them must not be too close to the border1 or near the centre1 as then the extremities will be torn away or bent upwards4 ,the system of fascine work may be very useful for protecting sandy and soft foundations in such situations1 to prevent slips in the slopes of an embankment and in providing a firm bed1 and also for making training banks1 groynes1 and spurs1 for correcting and directing a current in a desired channel1 and to secure freedom from slips in a river-bank4 ,depending upon the degree of looseness of the sand or sandy bed1 loaded fascine mattresses will assume a slope of from #a to #a ,,to #e to #a if allowed to sink in the bed1 and after they have settled and reached the angle of repose which the action of water will effect2 the large number of structures standing upon them for many years in considerable depths of water proves1 when they are properly made1 that they are to be trusted in comparatively unexposed situations4 ,a covering of stone pitching may be necessary1 but in unsubmerged work it has some disadvantages for1 having joints1 it allows unequal penetration of water through them and impedes the equal discharge of water from the earth1 although its weight is a recommendation as it opposes and may balance a pressure of water behind the slope4 ,however1 unless it is bedded upon a layer of soil of equal permeability1 such as gravel laid upon a nearly impermeable bed of clay1 which should always be mixed with sand to prevent it fissuring and bursting by heat or water1 so as to convey the water that has percolated and also that which exudes through the slope2 it may cause a localization of the flow1 and1 except in peculiar cases and provided the slopes are covered1 there is no occasion for pitching if merely used to prevent slips and not erosion1 as obviously weight and a secure protection may be obtained by other means and at less expense4 ,for the protection of the slopes of rivers or canals or submerged work the case is different1 as then pitching prevents erosion and may be the only secure preservative in exposed situations1 although generally the most expensive4 ,the pitching should rest upon a bed of permeable material1 and this layer should have a power of suction and distribution more than equal to the quantity of water that may penetrate the joints of the pitching2 there should be a bed of impermeable material next to the soil1 and in exceptional cases even two to carry off any water that has percolated1 so as to obviate any lodgment of water1 due provision being made for the land drainage discharge4 ,sir ,james ,brunlees1 ,past-,president ,inst4 ,c4,e41 found by experiment that at a slope of #b to #a pitching has the greatest resistance to extraction1 i4e41 it requires a greater effort to extract a brick at that slope4 ,taking the slope of #b to #a as unity1 the relative resistances were found to be as follows3-- #a to #a slope #jga #b to #a slope #ajj #c to #a slope #jig #d to #a slope #jff ,the resistances at #b to #a and #c to #a are practically the same4 ,should it be determined to pitch the lower part only of a slope1 in order to prevent slips1 the pitching must continue to such a height that a flow of water down the slope is impossible1 or it may become detached4 ,if the pitching is not rough squared on the joints1 but of various forms1 it is preferable that the face having the largest area be laid downwards1 smaller stones being carefully wedged in between the interstices4 ,any defective execution is usually followed by a falling of the stones1 and should this happen the surface will be broken and erosion and slips will ensue4 ,in laying the stones they should be so placed that if a few become removed those above or upon the sides will not be disturbed1 and in loose soil no pitching should be laid until an embankment has had time to settle and consolidate1 which the necessities of rapid execution may prevent1 for however even the pitching may be when first laid1 it will settle and become more or less uneven in such soil as sand or estuary slake1 and every effort should be made to leave no hole or exposed surface1 but to cause a continuous close covering4 ,fascine mattresses may have to be used in such a situation1 as they will follow the contour of the slope4 ,should the slope be subject to considerable wave action1 smooth surfaces offering the least frictional resistance1 obviously aid the travel of a wave1 which is undesirable1 and provided the embankment is sufficiently strong a rougher surface is to be desired4 ,projecting stakes tend to subdivide a wave4 ,should pitching be required to be placed partly upon the face of a cutting and partly upon the slope of an embankment1 as in the case of a canal upon sidelong ground1 care must be taken that it does not settle unequally1 and provision should be made by setting it upon a pervious layer1 so that any damming back of drainage waters may be prevented4 ,the weight of pitching upon a slope affords a counter-pressure to that of any water in the slopes which may be trying to emerge4 ,chalk rubble1 also hard chalk1 or gravel has been used in lieu of stone pitching for protecting slopes against erosion4 ,with the exception of retaining walls1 the preceding may be considered as the principal means1 used separately or in reasonable combination1 for covering the surface of a slope in a cutting or an embankment4 ,a frequent cause of instability of the slopes in countries having severe winters is the melting of unequal masses of snow1 the result of drifts1 and also from the thawing of a considerable snowfall4 ,the chief preventive measures against snowdrifts and consequent protection to the slopes1 although not a covering1 may be stated to be as follows3-- #a4 ,locate the line in a naturally sheltered position1 which it is most improbable can be done throughout its length4 #b4 ,adopt tunnels1 covered or sheltered galleries where the district is subject to avalanches or snow-slips4 #c4 ,prevent drifts by permanent or portable screens such as earth mounds1 trees1 hedges1 fences1 c4 #d4 ,obstruct drifts by having deep trenches some distance from the top of the slopes4 #e4 ,avoid cuttings as much as possible1 and make the line upon an embankment of such a height as to be above the depth of the drift snow in similar situations4 #f4 ,construct the embankments from side cutting1 instead of cutting1 so that the trenches may catch the snow before it reaches the railway4 #g4 ,make the slope much flatter than its angle of repose4 #h4 ,increase the width of the formation so as to lessen the depth of a drift1 and to enable a snow-plough to more readily discharge its excavation4 ,with regard to the preventive measures enumerated4 ,no4 #a4--;,as a rule this can only be practised to a limited extent consequent upon traffic requirements and the configuration of the country4 ,no4 #b4--,shelter-galleries are found to be generally effectual1 but obviously are expensive2 they may1 however1 be the only means to adopt1 as any obstruction to a snow-slip is avoided4 ,the slope of the top of a covered or shelter-gallery should not be steeper than that of the hill1 so as to offer no impediment to the free passage of the snow4 ,no4 #c4--;,experience has proved that permanent screens are to be preferred to portable shields1 and that ultimately they are the more economical4 ,the excavated material1 either from a cutting1 drains or fence-ditches1 is generally used for the earth mounds so as to save expense2 their height1 which is often from #g to #aj feet1 of course is governed by the greatest depth of the snowfall1 degree of exposure and usual direction of storms1 wind1 and drift4 ,should these vary much1 in an open air line it may be impracticable to entirely shut out or prevent drifts1 but the protective works will lessen drifting and may reduce it to manageable proportions4 ,a simple earth dam is seldom sufficient1 owing to the impelling power of the wind upon the snow-flakes and the considerable height at which it acts2 therefore1 fencing has been fixed in the top of the mound1 or trees and shrubs planted1 also old sleepers have been successful when simply closely driven into the surface of the original ground4 ,a screen1 consisting of one or more rows of trees or shrubs placed at a little distance from the top of the slope of a cutting1 is that most generally preferred4 ,it is made either double or single1 as may be thought necessary4 ,in ,germany1 hedges of fir trees similar to ,christmas trees have been found to afford excellent protection4 ,in ,france1 pine trees planted upon the cess have effectually prevented serious snowdrifts4 ,in sloping ground1 mounds or dams1 screens1 plantations of trees and hedges in very exposed places have been insufficient to prevent some drifting and accumulation of snow in a cutting1 and a mound or fence has consequently been erected upon the plateau at the top of the hill a sufficiently safe distance from its face that snow-slips1 which might be increased into avalanches1 were prevented from reaching the slopes or formation4 ,a drain should be cut upon the higher side of such a hill-dam or fence so as to carry away the snow-water upon a thaw1 and prevent the earth becoming in an unstable condition4 ,no4 #d4--,this system is generally used when an earth mound is also adopted and it has to be deposited from side cutting4 ,the trench1 of course1 should be on the side of the mound farthest from the main cutting4 ,as a snow-catcher it is successful1 especially in shallow embankments1 for it not only retains snow that would otherwise heap1 but drains an embankment4 ,no4 #e4--,this depends upon the configuration of the country1 but as cuttings act as traps to catch snow1 if possible they should be avoided2 and particularly when of little depth1 as it is found they quickly become choked1 and want as much protection as deeper excavations1 and from being more exposed to the cold air1 the snow in them becomes caked and frozen1 and requires breaking up before it can be removed4 ,embankments of a height a little above the ground1 and the greatest depth of the uniform snowfall of the country1 are to be preferred4 ,no4 #f4--;,generally approved1 as not only affording an advanced catch-trench1 but because it acts as a permanent drain4 ,no4 #g4--,this is a controverted system4 ,some engineers object to it as facilitating the deposition of snowdrifts2 others approve1 upon the ground that by flattening the slopes the snow can drift freely and will fall equally upon the formation4 ,the balance of experienced opinion seems to be rather against the adoption of flattened slopes1 unless they are made very flat1 such as from #d to #a ,,to #aj to #a1 at which latter slope snow it is found does not usually accumulate but passes on depositing only its general depth3 and additional means of protection are afforded1 and appears to indicate that the unaided system is only well adapted for countries in which winds of great force are generated1 such as the 8blizzards0 of ,north ,america4 ,no4 #h4--;,it is found that increased width of the formation of a cutting is an advantage1 as it retards choking1 facilitates clearing operations1 and provides room for shovelling snow from the permanent way1 whether effected by a snow-plough or by manual labour4 ,with regard to the formation width1 i4e41 the width of the bottom of a cutting or the top of an embankment1 and the prevention of slips in earthwork1 ample breadth is necessary in cuttings for the purposes of drainage1 although less in a rock cutting than in that of ordinary soil1 and the extent of the top of an embankment has some influence in the promotion of stability4 ,the required width of the formation must be principally regulated by the character of the earth1 the amount and suddenness of the rainfall1 the height of an embankment or depth of a cutting1 the degree of exposure1 the exigencies of the traffic1 and the required drainage4 ,in wet cuttings the formation should be wider than in dry earth1 and the side ditches should be made larger1 especially when there is a steep gradient in a long cutting1 in order to keep the formation and the permanent way in as dry a state as possible and aid traction1 for the coefficient of friction of the wheels of a locomotive will then be greater than when the rails are damp and greasy4 ,in cold climates the width of the formation is often increased so as to lessen the depth of snowdrifts1 and to enable a snow-plough or men to more readily deposit the excavated snow and clear the track1 as has been referred to in the immediately preceding pages2 and in severe climates in wet places ample width in cuttings is found necessary1 as drains frequently have to be cut in them as deep as #d to #e feet to afford a free flow for and to prevent an accumulation of water4 ,in temperate climates the width can be much reduced4 ,when the formation is narrow the simple percolation of water through the slopes of an embankment1 unaided by any aqueous action caused by fissures1 may gradually saturate the mass1 and as the wider the formation the larger the cross-sectional area of an embankment1 it follows that increased resisting power to deterioration is obtained by widening the formation1 as there is more earth to absorb the water4 ,a train upon the permanent way will make a force act downwards until it meets with sufficient resistance to cause reaction4 ,the direction of the resolution of these forces is towards a slope1 therefore1 the farther the surface of a slope is from the line of action and reaction1 the greater is its distance from the disturbing force and the lateral resistance it receives from the mass4 ,in the case of a solid rock foundation and a homogeneous embankment in the same state of consolidation throughout its mass1 the direction of the forces might be accurately delineated1 but as such a uniformly homogeneous and equable condition seldom exists in railway embankments1 it cannot be absolutely said that the forces act throughout upon certain lines2 however1 it is advisable to ascertain the probable direction of the forces4 ,the allowance for lateral settlement should be liberal and be regulated by the nature of the earth1 the height of an embankment1 and other local conditions of situation and rainfall that affect earth1 many of which are named in other chapters4 ,it will vary greatly1 and may be anything1 from #e per cent4 to #ajj per cent4 additional width of formation4 ,an addition of from #e to #aj per cent4 of the height of an embankment is usually sufficient1 but in clay sand and such soils an embankment may be slowly washed away by rain until it has shrunk to half its required width4 ,as an embankment settles or weathers the width of the formation should be maintained without having to steepen the slope1 widen the top1 or erect a wall upon the formation in order to hold the added earth4 ,the additional formation width of embankments is also a provision against the effects which the 8lurching0 of an engine may cause by its weight temporarily acting upon one rail1 and the pressure to be in the #d feet #h inches gauge at a distance of about #b feet #f inches from the centre of the permanent way4 ,for some distance upon each side of the point of junction of two high tip heads the top width should be increased1 vide ,chap4 ,,ix41 and in sidelong ground it is advisable to widen an embankment more on the upper side than the lower1 as slips seldom occur upon the higher side2 and in the case of railways1 should the lower slope move1 the rails can be placed towards the hill1 and perhaps away from the slipped portion of the embankment4 ,with respect to the deteriorating influence of vibration as regards the slope of a cutting or embankment1 it is well established that vibration will cause movement in a retaining wall which would otherwise be stable1 and that soils possessing considerable powers of cohesion are not so easily affected by vibration as those of a looser character consisting of particles having more or less rounded surfaces2 but the action of water may produce seams in such earths as clay1 and create a smooth greasy sliding surface upon which any reposing mass may but require the least disturbing force1 on the principle that the least impact is sufficient to impart motion to the largest body2 such as a man walking upon it or the tread of an animal1 to unbalance the delicate state of equilibrium4 ,this action may be gradual1 continuous1 and increasing1 as the earth will always be subject to changes of weather4 ,on the contrary1 vibration in soils having particles insoluble in water1 provided water does not dissolve any cementing material between them1 may cause them to equally settle and become firmer by being pressed together than if they were not subject to such operation1 and should the particles wedge by shaking and the slopes be sufficiently flat1 vibratory motion may1 under these circumstances1 tend to consolidate certain earths in an embankment2 but not so in the slopes of a cutting which vibration must disturb by reason of it agitating and loosening the surface and making it less dense4 ,for instance1 in sandy soils the surface friction on a cylinder1 when sinking operations are not being prosecuted and when the material is being raised from the interior1 is different2 the latter resistance being from #bj to #be per cent4 less than the former1 consequent upon the disturbance1 and although fine1 soft drift sand usually presents greater frictional resistance than firm sand1 it obviously cannot be taken as equal to that of firm sand1 as it is quickly dissipated4 ,the conditions of earth being so very diverse no rules can be deduced1 for even the effects of such stupendous force as that of earthquake vibrations vary according to the nature of the ground1 however1 the weakening effects of vibration are undoubtedly very considerable4 ,it is known that the lateral thrust of earth is thereby much augmented1 and1 therefore1 that the strain upon the frictional resistance and the cohesion of the earth is increased2 and experiments have shown that when a wall is nearly strained to the point of overturning1 slight vibration will quickly destroy the equilibrium1 thus demonstrating that it adds to the lateral pressure4 ,an analysis of some reliable experiments proves this increase to usually range from #aj to #fj per cent41 but it is evident that the practical effect of any increase may be very much greater than a mere computation of the increment1 for it may supply the additional strain1 however small1 necessary to initiate a movement1 hence the danger4 ,as collateral testimony to the important effects of vibration may be mentioned3-- ,a comparison of the coefficients of friction during motion and those at the commencement of movement or of repose4 ,the existence of a nearly vertical face generally assumed1 when unshaken by artificial means1 in the bared top earth in a quarry1 shallow well1 gravel or sand pit1 pond1 and even a river-bank or a cliff1 which experience has proved could not be maintained when subject to vibration4 ,the fact that timber piles1 which are chiefly supported by the frictional resistance of their surfaces1 will not sustain a rolling1 i4e41 a vibratory1 load equal to that of a fixed load1 and also that the method of driving in soils easily disturbed1 such as sand1 is also considered as reducing the safe load according to the percussive action and frequent vibration caused by a pile-driver1 whether worked by steam1 hand1 or by means of an explosive substance4 ,as further proof may be named that in pile-driving1 especially in open soil1 piles continually driven penetrate the earth considerably quicker and easier than if driven at intervals1 as the latter system allows the soil to settle round them and the loosening and friction destroying effects of vibration are lessened4 ,the experiments made by ,mr4 ,j4 ,a4 ,longridge1 ,m4 ,inst4 ,c4,e41 for ,mr4 ,g4 ,r4 ,stephenson1 ,past-,president ,inst4 ,c4,e41 in ,morecambe ,bay1 ,england1 showed that by vibration the bearing power of driven timber piles was reduced to one-fourth or one-fifth of that when subject to a steady non-vibratory load4 ,its deleterious effect on the structure of such a solid substance as iron1 c41 particularly when it is loaded beyond its elastic limit4 ,it is generally agreed that a substance is broken sooner when a load is intermittingly imposed than when the same load is permanently placed upon a structure4 ,the experiments of ,professor ,stokes1 #ahdi2 ,m4 ,phillips1 #ahee2 ,m4 ,renaudot1 #ahfa2 ,m4 ,bresse1 #ahff2 and recently of ,dr4 ,winkler and others1 show that the increase of the intensity of strain consequent upon the dynamic effect of a suddenly-applied moving load may be as much as #cc per cent4 more than that of the computed statical pressure4 ,the fact that in masonry piers of considerable height and small dimensions1 as in piers of viaducts1 the vibration caused by trains loosens the brickwork or masonry and necessitates frequent repairs4 ,the theory that the particles of all solid bodies may be in a state of continuous vibration and motion1 though there may be no means of rendering their motion visible1 has not been refuted by deductive reasoning2 but1 on the other hand1 it is in accord with the theory that 8motion communicates itself among material bodies1 and is never lost2 when it appears to be so1 it in fact only passes from the moving body into other bodies which are at rest1 or are endued with a less velocity1 and at length it becomes insensible in consequence of its enormous diffusion4 ,in fact1 motion can only be destroyed by motion2 resistances and friction disperse it1 but do not destroy it40 ,the laws of statics and dynamics are well established1 and are fully described in many admirable works upon mechanical philosophy2 so far as the subject of this book is concerned that which is required to be answered is the question4 ,have the deleterious effects of vibration upon earthwork in various conditions been determined so as to be of practical value8 ,not by experiment upon a large scale1 nor is it probable that they will be2 but they have been deduced from experience1 reasonable inference1 and experiments on a small scale1 as has been before mentioned4 ,the effect of vibration is usually more marked in cuttings than in embankments1 although it may nearly approach when they are of little depth or height3 because a train in a cutting is contained within the area excavated1 whereas in an embankment it is without the area deposited4 ,in a cutting vibration commences upon the formation level and the toe of the slopes1 the latter the most vulnerable parts and those most strained4 ,in an embankment it proceeds through the formation to the base and the toes of the slopes which are necessarily the most distant4 ,on the other hand1 the material in an embankment is generally in a looser and lighter condition1 and therefore more inclined to move and to suffer from vibration4 ,it may also be greater upon one side consequent upon the 8lurching0 of the engine and carriages4 ,obviously1 vibration is increased with the speed and weight of a train2 probably a short1 heavy train travelling at high speed causes a more deleterious effect than a long heavy train travelling at a slow speed3 also the higher an embankment or the deeper a cutting the greater the area of the cross section4 ,assume a train weighs #ajj tons1 and the weight of the earth is #aab lbs a cubic foot1 or #jje of a ton2 it might be considered that the effects of vibration would be less as the areas increased4 ,consider the formation to be #ah feet in width and the slopes #a to #a1 the respective areas of cross section would be as follows3-- ,height4 ,area4 ,weight of ,weight of ,ratio of ,feet4 the the ,train4 the ,weight ,embankment4 ,tons4 of #a ,foot ,tons per ,lineal of ,lineal an ,foot4 ,embankment to the ,weight of the ,train4 ,square ,lineal ,ton4 ,feet4 ,foot4 #aj #ccj #a #jje #afe #ajj #jafe to #a #bj #ifj #a #jje #dhj #ajj #jdhj to #a #cj #a1hij #a #jje #ide #ajj #jide to #a #dj #c1abj #a #jje #aefj #ajj #aefj to #a #ej #d1fej #a #jje #bcbe #ajj #bcbe to #a #fj #f1dhj #a #jje #cbdj #ajj #cbdj to #a ,,note4--,for the purpose of a comparison of ratios it is not necessary to consider the length of the train4 ,a simple inspection of the above ratios would lead to a supposition that the effects of vibration would be no less than #cbaj_/jafe #aif times greater in a #aj feet than in a #fj feet embankment4 ,merely comparing the weight of a train with that of an embankment1 and assuming that the results of vibration at the same rate of speed are so governed is incorrect1 for the effect of vibration at the formation level is not regulated by the height of an embankment or the depth of a cutting4 ,the weight of a train may bear a very small relation to that of the quantity of earth slipped1 yet the soil may have gradually become in such a state of delicate equilibrium that at last the least vibration will destroy it1 even a little of the top soil falling upon the slope2 and it frequently occurs that a slip commences by the detachment of a few small lumps and increases until it becomes of serious dimensions2 therefore1 the area of a cutting or embankment cannot necessarily be considered as reducing vibration although the source of disturbance may be more distant2 but1 of course1 the heavier the mass the greater the weight and speed required to cause the whole to vibrate4 ,lighthouses and such exposed works being constantly subject to vibration1 the experience gained through their behaviour may be considered as indicating the direction in which the stability of structures in analogous situations has to be sought4 ,it is generally agreed that it favours weight and bulk1 as they are unchangeable1 and shows that although the form1 execution1 and the material may be perfect1 a light fabric will gradually be deteriorated by constant tremor and vibratory motion1 at length culminating in the loosening and separation of the parts4 ,except from actual experiment in each case1 it is impossible to determine the greatest weight of and the speed at which a train should be allowed to travel so as to prevent any deleterious effect from vibration1 and the circumstances are so various that a practical rule cannot be deduced1 except by assuming conditions from experience alone1 which would so modify a formula as to make it show any desired result1 and cause it to be regarded as too complaisant to be trusted4 ,perhaps the best test of the effects of vibration that any earthworks can receive is when a temporary railway is laid upon the formation or cess for the carriage of materials1 and in a lesser degree a steam excavator1 as the weight and vibratory action may show the weak places in a cutting1 or so shake portions of an embankment that should the earth be unstable a slip will soon occur4 ,,chapter ,,viii4 ,,earthworks ,,in ,,or ,,upon ,,sidelong ,,ground4--,,some ,,insecure ,,conditions4--,,precautionary ,,measures4--,,embankments ,,upon ,,soft ,,ground4--,,embankments ,,composed ,,of ,,soft ,,earth4--,,the ,,promotion ,,of ,,stability ,,and ,,consolidation4 ,with regard to earthworks in or upon sidelong ground1 the configuration of the surface conduces to a movement of the hill-slope of a cutting1 and the centre of gravity of an embankment is not in the middle1 and in a narrow embankment may be outside the central portion1 the tendency1 therefore1 is for the slope of an embankment on the upper or hill-side to assume a steeper inclination than that on the lower1 as the earth is tipped against the inclined ground until the point is reached where a perpendicular erected upon the surface of the ground cuts the top of the inside slope4 ,this slope1 if protected from weathering1 might be allowed to stand at the inclination at which it remains when tipped1 and be simply trimmed and covered2 but the toe of the slope on the lower or valley side is especially likely to slip1 and therefore1 every precaution should be taken to prevent movement4 ,a retaining wall is a certain protection1 benching the ground1 weighting the foot of the slope1 dividing it into benches about #aj to #ae feet apart1 varying in width from #e feet and increasing according to the depth2 the benches having sufficient inclination to prevent an accumulation of water2 counterforting the slopes in dry and mild weather with simple earth counterforts #e to #ab feet in width at intervals1 and in length about twice their height with a reasonable slope1 the height being about half that of the embankment2 a dry retaining wall may also be erected in temperate climates and in a comparatively unexposed situation3 are all precautionary measures that can be adopted4 ,but in the case of a cutting in drift or permeable soil upon rock or an impermeable surface liable to become wet1 which not infrequently occurs1 the conditions of equilibrium may easily be destroyed1 and the slope upon the higher side may not stand at a less inclination than that of the hill4 ,obviously this slope cannot be obtained either in cuttings or embankments1 therefore1 provided the drift is of considerable depth and treacherous1 means must be taken to prevent movement1 and drains should be inserted so as to make the earth capable of standing at a steeper inclination than it naturally assumes2 and in order to drain the ground at the seat of an embankment1 a trench on the valley side filled with stones or supported by other means acting as a wall and drain can be made4 ,every precaution should be taken to prevent any accumulation of water in earthworks in sidelong ground1 and to gently control them1 and to promote this object it is well that lateral outlets be opposite to each other so as to afford through drainage and an unobstructed flow4 ,as drift soil upon the inclined surface of a rock may be held by friction1 the least change may impair it sufficiently to cause movement1 therefore it is advisable to have a narrow gullet or heading excavated in short lengths1 followed pari passu with protective works1 whether a retaining wall or not1 so that the earth is weakened as little as possible by exposure and deprivation of its usual support2 and there are many places in which1 unless the system of excavating in short lengths be adopted1 failure and slips must result4 ,in sidelong ground the formation is frequently partly in cutting and partly in embankment1 if so1 and the drain is impermeable and can be thoroughly relied upon1 it may be advisable to make the formation incline towards the hill1 so as to drain it1 lessen1 and perhaps prevent percolation into the semi-embankment or under its seat1 for the soil being loosened by the process of excavation and deposition is in the mass more porous than in a cutting4 ,the chief aim of all drainage operations for the preservation of earthworks in sidelong ground is to prevent the hill waters guidelessly flowing into1 upon1 or under them1 their accumulation1 or any obstruction to their easy discharge2 and to attain this object it is necessary to know the location of the sources of the supply1 the quantity1 and other particulars1 vide ,chap4 ,,iv4 ,a proper system of drains must therefore be made upon the hill-side to gather and gently guide the waters1 to lead them by channels across the formation and discharge them outside it1 care being taken to protect and line the surface of the drains so that no leakage occurs or any erosion of the face4 ,in countries where the rainfall is excessive or sudden at certain places or entirely1 it may be sufficient to protect the slopes so as to allow of a flow over them1 and particularly upon the valley slope of an embankment1 and in a lesser degree upon the hill-slope of a cutting4 ,when the configuration of the country allows1 it is advisable to avoid cuttings1 and particularly embankments1 in or upon drift soil lying upon an inclined surface of rock or impermeable soil1 because it can so easily be disturbed1 become unstable1 and of the difficulty of restoring it to a state of equilibrium2 in fact1 this may be impossible1 as vibration may cause it to move4 ,in such a case the only means of preventing a slip is by erecting a wall at the toe of the slope1 and as it is necessary that the foundations be in the rock beneath the surface earth1 the simple operation of excavating may impel the drift down the hill4 ,also should an embankment be required upon drift soil its weight may be sufficient to cause the mass to slide and a diversion of a railway may be imperative1 for the cost of a retaining wall1 because of its height and the great pressure it would have to sustain1 or be built to sustain1 would prohibit the adoption of such a remedy4 ,therefore1 an embankment is more to be feared than a cutting in such earth4 ,making benchings in the rock below the drift to resist movement of an embankment will most probably be impracticable1 and the soil may be in such a delicate condition that a shock or very little additional weight may make it slip1 and when once it has moved1 its stability may not be permanently restored4 ,such a case may be considered as one of the worst that can be encountered1 and certainly the simple removal of detached masses of rock that may slide upon the formation is easier to effect than to treat drift soil upon an inclined rock bed4 ,it is always well to remember that in sidelong ground a hill may be reposing at the steepest slope of stability1 and when the earth is rock it may dip in the direction of a cutting or be imposed upon a perishable stratum1 such as porous or inferior shale4 ,support upon the valley side is then absolutely necessary to restore its normal equilibrium1 and every care should be taken to prevent water reaching the embankment or trickling under its base1 and to control all water that may permeate through fissures in the rock face1 especially should it be loosely bedded4 ,earthworks in such positions require to be regularly watched4 ,in forming an embankment upon sidelong ground every means should be adopted to increase the friction between the tipped material and the soil2 consequently all turf or herbage should be removed in order that the embankment may be upon the bare earth1 care being taken that no loose top mould or turf is deposited1 but only the firm soil4 ,it may be advisable to only tip earth excavated from the solid hill-side1 and not top soil such as that obtained from side cutting1 and unless in rock or firm soil to avoid partly side cutting and embankment4 ,should an embankment have to be tipped upon rock1 care must be taken to prevent the surface water flowing under its base1 and to counteract sliding movement the ground should be benched and a drain made on the higher side2 also in a deep cutting the slope or face should be stepped1 or have a cess at about mid-height1 or where desirable1 to lessen the effect of the trickling of the surface water and to prevent a flow in a direct line1 which might make the velocity of any leakage waters dangerous1 especially after a rapid thaw4 ,on a mid-cess a catchwater drain should be cut to intercept the surface water1 which may not percolate but flow upon the slope1 and1 unless diverted and conducted to an outlet1 may saturate or erode the bottom4 ,before a cutting in drift soil upon the side of a hill can be drained1 it may be necessary to sink a shaft upon the higher side some distance from the slope and construct a complete series of drains under the formation4 ,also should an embankment in sidelong ground be near to a river1 the exposed river-bank face must be protected1 and in any case1 when a pier of a bridge has to be placed close to the edge of a rock1 the face of the earth should be preserved by a substantial ,portland cement concrete covering in order to prevent disintegration culminating in a slip or subsidence4 ,in setting out a line of railway or a canal care should be taken to avoid1 if practicable1 either cuttings or embankments in soil resting upon inclined rock1 as slips are almost sure to occur4 ,however1 should it be unavoidable1 their depth and height should be reduced to a minimum and1 if possible1 the formation be raised until the bare rock crops out1 and this can frequently be effected within the limits of deviation4 ,also deep cuttings in clay or earth1 having particles soon affected by weather1 should be avoided1 but they may be necessary2 and should any have to be located upon a sharp curve1 it is advisable to excavate the projecting spur on the convex side of the curve more than that required to obtain the formation width1 as it is peculiarly exposed1 and therefore more likely to slip4 ,when cuttings are upon the escarpment of a clay hill the slope upon the valley side need not be so flat as that against the hill4 ,an inclination of #c or #d to #a may be necessary upon the hill-side1 whereas a #a to #a slope may be sufficient upon the other4 ,when a slip may involve the destruction or injury of any adjacent buildings1 the best plan is to erect a retaining wall at the foot of a slope1 not less than about one-fourth of the height of an embankment or the depth of a cutting1 ample provision being made for drainage and the expansion of the earth4 ,it is a sure protection and support1 and the consequences of a slip may be most serious in such a position4 ,the protection of the slope and a breast wall may1 however1 be alone necessary upon the valley-side4 ,the construction of embankments upon soft soil is here referred to so far as regards lateral movement1 or where vertical settlement causes such action by drawing asunder4 ,whenever the surface of the ground bulges or upheaves upon earth being tipped upon it or pressure applied1 it shows that the disturbing harbingers of instability are in action and that its sustaining power has been reached1 its surface ruptured1 and any more soil placed thereon will only sink and displace the earth until it meets the solid ground beneath1 or the material becomes sufficiently compressed and dense for it to sustain the load2 such a condition of unrest generally proceeds from over-pressure and will loosen the soil1 increase percolation1 and aid disintegration4 ,when it is known that soft1 peaty1 muddy1 or silty earth overlies level solid ground1 and it is certain it cannot escape1 and can only be condensed by weighting until it will permanently bear the strain required1 it can be built upon2 although should there be more pressure at one place than another1 or the character of the soil vary1 in certain places be swampy and in others dry1 the surrounding ground will probably rise where the weight is the least2 therefore1 increased bearing area of an embankment maybe necessary until the sustaining power of the earth is not exceeded1 or slips and subsidences will occur1 for the weight of an embankment in such a situation cannot be diminished by retaining walls1 as stable foundations are not to be obtained4 ,it is obvious the width of the formation cannot be reduced and therefore the only way of lessening the load upon the base per square foot1 assuming the embankment to act as a mass1 and of distributing its weight1 is by flattening the slope and making a platform under the seat of an embankment4 ,all earths1 however1 that are not hard rock subside upon being weighted1 and in the case of tenacious clay soils1 upon a considerable load being applied over a small area1 a trifling contiguous uplifting of the ground will generally be noticed4 ,if such rise of the soil does not exceed about one-sixth of the settlement of the clay under the load it may be disregarded as not likely to cause a slip or serious lateral movement4 ,when the foundation consists of a firm stratum of gravel1 sand1 or solid earth overlying soft soil such as quicksand or silt1 i4e41 mud and sand2 or alluvial deposit1 care must be taken that the latter is not forced up at a weak place by the additional weight of an embankment1 and the firm stratum undermined1 as then it will sink1 fissure1 and be unsafe4 ,any disturbance of the bed or water of an estuary or lake other than by the tides1 currents1 or wind is an indication that the earth beneath the firm soil is overloaded1 and that subsidences and slips will ensue4 ,before determining upon the necessary precautions that must be taken1 the deposits should be thoroughly examined and tests made of the amount of soluble and insoluble material in a certain mass1 as although the earth may have the appearance of being mud1 it may contain a preponderating proportion of insoluble particles of sand1 and its character may hardly be that of mud or silt4 ,when a marsh rests upon clay it usually requires only reasonable care1 but if upon mud or loose sand it may always be in a more or less unstable condition4 ,the chief means of consolidation in the construction of embankments of soft soil upon soft ground may be stated to be as follows3-- #a4 ,draining1 which must be deep1 and should be effected before the earth embankment is deposited4 #b4 ,weighting the ground outside the slopes with firm material so as to consolidate the soil by intermixture with it4 #c4 ,the formation of terraces of earth1 and by allowing the ground to subside until movement is arrested1 but there may be a porous seam of harder soil1 such as gravel1 under the soft ground1 then care must be taken not to dam back the flow of the underground waters by the subsidence of the added earth or the whole embankment may slide1 become softened and finally be swept away2 therefore1 through drainage must be maintained under an embankment4 #d4 ,making the load as light as possible consistent with due consolidation4 #e4 ,constructing an embankment in equal and regular layers of ashes or other dry1 light1 stable soil1 and by drying the earth to be deposited by separation1 wind1 sun1 or by burning4 ,to prevent slips in such situations1 draining1 although causing subsidence1 should be executed as long as possible before the embankment is tipped1 is more effectual and certain in its action than any system of lessening the load or of counterweighting the soil1 which may thereby temporarily be brought to rest but afterwards give way2 and any damming back of water may cause additional sinking1 and change the condition of the earth from a state of dampness to that of saturation4 ,it may be easy to calculate the weight per square foot that will have to be sustained by the ground from an embankment and the heaviest train1 but to make the necessary allowance for the effects of vibration is not so readily computed4 ,the ground can be weighted to ascertain the limit of its sustaining power4 ,the test should extend for a period of several weeks to be thoroughly reliable1 which time can seldom be afforded upon works2 therefore a considerable excess of sustaining power over the load should be allowed4 ,in draining the site of an embankment in peat soil1 it is advisable first to ascertain the depth to which trenches can be cut without the sides falling in4 ,it generally varies from about #a foot #f inches to #c feet4 ,as the ground becomes firmer the drains can be deepened if required4 ,the width should not be less than #b feet #f inches to #c feet4 ,cross drains can be cut at every #bj to #dj feet according to the state of the soil4 ,peat usually drains freely at the surface when its level is not at or below the water-bearing line of the country4 ,a successful method of thoroughly draining the surface of peat moorland is to first make a drain about #a foot #f inches in width and the depth of an ordinary spade1 and leave it for a time until the top soil to that depth becomes firmer1 then repeat the operation until a depth of #c feet is obtained1 the sides being excavated to a perpendicular face1 the top turf being carefully cut and stacked upon the surface to dry4 ,along the centre of the bottom of the trench a small cut is made about #a foot in depth and #f inches in width1 leaving a #f-;inch ledge upon each side1 then the dry stacked turf #a foot #f inches in width previously excavated1 is placed upon the ledge1 the grass downwards and the layers reversed in rotation to the order in which they were excavated4 ,this system in moss peat land is cheaper and better than tile or rough stone drains1 as they often settle unequally4 ,the underneath drain will not close up provided the excavated turf is carefully deposited1 and water will not disintegrate the peat4 ,these drains should be cut about #bj feet apart4 ,a more extensive system may be necessary1 and a comparatively large area may be required to be drained in order to obtain a firm foundation and to prevent breaking away of the ground4 ,in such event the first drain on each side parallel to an embankment should be at a distance from the centre line of the formation at least equal to the bottom width of an embankment1 and as deep as the soil will allow1 so as to drain the land within the fences4 ,a cut should also be made outside the fencing at a distance of not less than #aj feet from the inside drain1 to catch the surface waters and prevent their flowing upon the enclosed land4 ,cross drains may be required at intervals of from #ae to #ej feet according to the character and depth of the bog4 ,the sides of the open drains may require to be supported4 ,branches of trees and rough fascine work laid in them have been used to an extent so as not to interfere with the flow2 and when a spoil or fence bank has to be deposited it should be made a reasonable distance from the drains or they may become closed4 ,every effort should be directed to make the drainage of the same degree throughout the area2 it is therefore necessary to know whether the water can be discharged into a channel or adjacent river1 or if the bottom of the drains will be above the general water-discharge level of the district so as to prevent the ground being in the condition of a sponge always full of water and becoming a floating mass4 ,when the peat soil is of little depth and rests upon sand or clay1 drainage can be effected by side drains reaching to the underlying stratum1 and the drains can be open and be filled with gravel to prevent the sides falling or the bottom rising4 ,few serious slips will take place in bog-land when the precautionary works named in this chapter are more or less executed2 subsidence is then the chief difficulty4 ,it cannot be entirely prevented1 but it may be lessened4 ,it is frequently very considerable1 depending principally upon the depth1 situation1 and character of the deposit and the proportion of water in it4 ,deep bog-lands upon being drained have subsided as much as #d to #e feet the first year1 and #aj to #ab feet the second1 and in the worst situations they will continue to subside until the earth is sufficiently compact to support the insistent weight1 and they have sunk as much as #cj feet before the ground became consolidated4 ,burnt ballast1 fine gravel1 or sandy gravel1 is to be preferred as ballast upon peat embankments1 as affording an even coating and tending to consolidate the earth1 whereas broken rock ballast breaks up the surface1 as the pieces are not uniform in size and are fragmentary4 ,the cost of maintenance on bog or marsh-land is sure to be heavy for two or three years1 but then the road will generally have become firm4 ,the chief points in maintenance are to cause equal loading and to promote thorough drainage4 ,baulks laid under the sleepers1 or the longitudinal system of permanent way1 is not advantageous in soft soil1 and even should a longitudinal bearer be placed upon the cross sleepers the road is difficult to lift or pack1 and less timber will be required by a reduction of the distance between the cross sleepers4 ,the rail joints should also be stiffened so as to make the depth of the undulations consequent upon the passage of a train as regular as possible1 and the number of the sleepers can be increased with this object4 ,the sustaining power of peat moss1 and peat which is sometimes found under a bed of gravel and upon a substratum of clay or marl2 and bog-land varies greatly4 ,as a rule high bog-land will bear the greater weight4 ,the only reliable method of ascertaining its sustaining capabilities is by an actual test1 and such experiments are the more requisite in unreliable soils such as mud and slake1 alluvial deposits1 peat and bog-land4 ,it is known that some mossy peat and bog-land will not even resist the weight of a stone of ordinary size1 but will upheave and shake upon very little pressure being applied4 ,by draining and other consolidating operations such land may be rendered capable of sustaining a load if the weight be spread over a considerable area upon a platform of poles1 timber1 or fascine work1 as it then as it were1 floats upon the surface2 but piling is not successful1 as the piles disunite the particles1 destroy the continuity of the layers and make a passage for water4 ,the elasticity of bog-land is manifest even when a road-bed has become sufficiently firm and even-bearing for traffic1 by the agitation of the water in any adjoining drains4 ,in low bog-land1 peat-moss1 or peat-land1 it is important to ascertain whether the deposit extends to a considerable depth1 as in ,holland it has been found that some marshes simply rest upon a bed of water1 being nothing but floating peat moss1 although having as great a thickness as #bj feet4 ,it has also been noticed that marsh-lands often rest upon peat mosses with a small layer or film of loam upon them1 and that they are floating masses1 although the water upon which they float may not be deep2 its depth may be known by the insertion of a bar or boring-tool1 for when it sinks suddenly it has probably reached the water1 and until its downward movement stops it shows that water exists4 ,peat bogs consist of decomposed mosses1 grasses1 aquatic plants1 and mud4 ,in mountainous districts when they are superimposed upon hard or non-weathering rock1 such as quartz1 they have little thickness2 if upon clay rock1 or any that decomposes under weather influences1 they are usually of considerable depth4 ,as a rule1 the greater the specific gravity of peat1 the firmer it is and also the darker4 ,the top layers are generally the most fibrous and the driest1 although spongy and containing vegetable matter1 and are of a light brown colour1 and of less specific gravity than the next deposit1 which is of a darker brown tint1 and is denser and more decomposed2 the peat then becomes brown black or black in hue and approaches a coaly condition4 ,compact turf usually contains little water1 but should it be of a mossy nature it is generally saturated4 ,wet bog1 peat1 or moorland may contain as much as #hj per cent4 of water1 and any soil having so large a proportion must necessarily subside and change upon being thoroughly and regularly drained1 and have its bearing power increased in a ratio approximate to the percentage of water in it before draining and that after such operation has been effected1 other conditions being similar4 ,the depth and character of the top layers will indicate the best method of procedure1 and whether it is advisable to excavate them and deposit an embankment upon the lower and firmer bed4 ,in ,holland1 where the peat is superimposed upon sandy soil1 in order to prevent slips in embankments it is found advisable to excavate a trench about #ae to #bj feet in width and as wide as the formation width of a railway or road1 until it reaches the subsoil1 and to fill it with sand2 and when an embankment has to be formed of very porous earth1 to make a trench at the toe of each slope1 and to fill it with sand so as to act as a counterfort4 ,peat and sand have been found to laterally spread the most1 clay and sand less1 and therefore the latter soil stands at a steeper slope4 ,on the ,south ,austrian system of railways marsh-land has been made firm1 and malaria-fever almost annihilated by depositing ashes over the earth4 ,when they are mixed with the bog or swamp deposit1 it is found that they cause it to become fertile4 ,peaty soils and peat bogs1 which latter it should always be remembered may be almost floating upon water and have a surface layer of vegetation and moss1 must be differently treated to other soft soils1 and thorough drainage may be economically impossible in deep deposits4 ,in such a situation1 as the peat is alone capable of bearing the pressure1 it should not be disturbed or the particles disunited1 for the continuity of the layers will then be destroyed1 and probably cause an upward flow or other passage of water upon pressure being applied4 ,this state is frequently met with where inland waters have existed1 as in that case the peat moss covering has sunk1 the depression depending upon the depth of the peat underneath it and the distance at which the firm ground is reached4 ,it is1 therefore1 advisable to ascertain this1 as then some idea of the probable subsidence may be known4 ,the system of a platform of poles1 hurdles1 or fascine-work is well known1 and has been proved to be effectual in preventing any dangerous lateral or vertical movement4 ,sand1 fine gravel1 ashes1 or other binding material1 spread over the surface of peat consolidates it and assists in preventing movement1 and it is well if such a covering extends for some distance in front and at the sides of an embankment to keep the ground from rising4 ,upon soft soil1 a thick layer of clean sand1 well wetted and consolidated1 #e feet or more in depth1 has been used in lieu of piles for forming a bed upon which to deposit a ,portland cement concrete foundation to receive heavy masonry piers of a bridge1 and at much less expense and with greater expedition1 and no slip or subsidence of the ground has occurred4 ,it is obvious the earth should be deposited in even layers1 similarly to the general method of closing reclamation embankments from the bottom upwards2 staging is1 therefore1 necessary for the waggons to run upon and discharge their contents1 but piles should not be driven1 as they disturb and upheave the earth and do not consolidate any soil4 ,a successful system of depositing embankments of bog or peat earth is to thoroughly cut up1 pun1 and tread down the soil in order that it may not shrink in cakes4 ,if an embankment subsides and must be raised1 only light earth or material should be used4 8,forming0 or embankments of little height are usually made from the drain excavation1 and when more earth is required the outer ditches are widened and deepened so that the fenced-in land is made as firm as possible upon which a railway or a road has to be maintained4 ,fascine mattresses1 to prevent slips and subsidence in an embankment in very soft ground1 such as loose sand1 are to be recommended1 and experienced engineers have expressed their belief that they are the best means of procuring a firm foundation and securing it from scour in loose sandy and soft deposits2 and their employment may become necessary when the earth is very wet1 and the contour of the district renders effective drainage or consolidation of the soil difficult or impracticable4 ,should the ground after drainage be only damp1 brushwood1 or heather1 so laid as to offer the firmest and most even bed may be sufficient2 and if sand can be used with it1 it is very advantageous2 but the fascine or a more solid method of distributing weight may have to be adopted4 ,fascines should be laid over the whole base of an embankment and extend some little distance upon each side1 beyond the toe of the slope1 and be made stronger according to the load they have to support1 which1 of course1 increases towards the centre of an embankment1 where it is greatest1 in order to prevent their breaking apart and becoming detached4 ,in peaty soils an embankment should be formed of light dry materials1 be spread out1 have equal bearing1 and be of as little height as possible1 and all hollows and depressions should be carefully filled4 ,the worst state of peaty or bog soils upon which an embankment has to be tipped is when they are no better than a floating mass4 ,where a stratum of sound firm soil1 such as gravel1 lies upon a soft bed of great depth1 by increasing the bearing area upon the firm earth and not interfering with it1 a stable foundation for an embankment may be obtained4 ,in such a case a cutting should be avoided1 for if care be taken not to impair or injure the firm top layer it may stand without serious subsidence1 but under other conditions it would be unstable1 and when a soft stratum is affected and its natural condition altered1 it may be very difficult to restore it to a state of permanent equilibrium in consequence of it being in almost a constant state of mutation4 ,,chapter ,,ix4 ,,the ,,deposition ,,of ,,an ,,embankment4--,,preparation ,,of ,,the ,,ground ,,upon ,,which ,,an ,,embankment ,,has ,,to ,,be ,,deposited4--,,methods ,,of ,,procedure4--,,consideration ,,of ,,some ,,of ,,the ,,different ,,systems4--,,the ,,effect ,,of ,,the ,,height ,,of ,a ,,tip ,,and ,,the ,,length ,,of ,a ,,lead4--,,the ,,steam ,,navvy ,,and ,,embankments4 ,with regard to the deposition of an embankment1 one of the chief objects to be accomplished is to make it homogeneous and prevent the formation of solid layers1 which may become detached along the line of stratification from less compact strata4 ,careless and intermittent tipping conducted in dry and wet weather and with different kinds of earth1 probably in various conditions1 will cause slips and subsidences2 as also any local disturbance of the soil1 which is always more porous and absorbent of water than when in its natural unexcavated state1 although it may be free from water-pressure which may exist in a cutting3 and particularly so when fresh-tipped1 as then the pressure and strain upon it is at the maximum1 its tendency to unstableness gradually decreasing as it becomes consolidated4 ,in hard granular soils this is almost certainly the case1 but consequent upon percolation of water into a mass deposited in a dry state that expands2 it may not be so in aluminous or other earth having particles affected by moisture1 for an additional or an unequal load after a settlement may cause further movement and irregular density4 ,in countries where the ground becomes caked or parched during the dry season1 the change to a wet or saturated condition affects them much more than in variable climates1 as they are then generally in a moist state4 ,it is easy to decree that no embankment shall be made of any earth of a treacherous character1 if the circumstances are known to conduce to instability1 and to rigidly specify what shall be done and what shall not be done1 but the exigencies of an undertaking may cause such stipulations to be impracticable4 ,for instance1 it may be found that no other earth may be available except that which is proscribed4 ,no one with a knowledge of earthwork would desire to erect an embankment of considerable height of yellow or sandy clay1 or excavate a deep cutting in such soil unless a considerable allowance be made to provide against contingencies2 nevertheless1 it has to be done1 and will have to be done4 ,the precisianism and delicate refinement of a specification replete with good intentions has1 therefore1 very frequently to be toned down in order to allow of the execution of work4 ,it is obvious the care that is bestowed upon a reservoir embankment1 such as the damping1 punning1 rolling1 mixing of the material1 and raising it in layers1 is not necessary in a railway or ordinary embankment2 however1 certain precautions should be observed and may be effected at a small cost1 and it is well to remember that errors of construction will cause undue strain upon particular parts4 ,a fruitful cause of a slip or subsidence in an embankment is the variation of the character and condition of the tipped earth4 ,it seldom happens that the soil of a cutting of considerable extent is the same throughout in character and condition2 and the earth in an embankment tipped at one end may be different to that deposited at the other1 and therefore the point of contact of the two earths will probably be troublesome4 ,when a seam of unstable soil occurs in a clay cutting1 it should not be tipped but be run to spoil4 ,such layers are usually of small extent1 yet in an embankment they may cause portions to run in rainy or frosty weather4 ,side cuttings are a protection against slips in embankments when they are sufficiently far from the toe of the slope1 as they form drainage channels1 but the excavation being top soil is loose and porous1 therefore1 when the lower portion of an embankment is made from side cutting and the upper from a cutting1 the firm material may be at the top and the more open earth at the base2 consequently1 if an embankment in soil of a doubtful character must be partly constructed from side cutting and partly from cutting1 especial care is required in forming it so as to prevent slips and subsidence1 and also1 in excavating any ground for such purposes1 it is advisable not to interfere with any ditches1 or join them1 as by concentration a stream may be created4 ,in countries where land is of little value1 contractor's plant expensive1 not to be obtained in the district1 and carriage costly1 embankments in most cases can be more cheaply and quickly deposited from side cutting than cutting1 the excavation from the latter being run to spoil instead of tipped by waggons into the embankment1 therefore1 their erection by such means becomes imperative for reasons of economy4 ,in depositing embankments it is well to remember that experience has proved that materials uniform in size and homogeneous in character form the most compact and impenetrable masses4 ,the great stability of breakwaters formed of materials of uniform size and the firmness of macadamized roads are proofs of this4 ,the same rule applies to soils4 ,it is the separation of the larger bodies from the smaller that causes a want of cohesiveness and weight-sustaining power4 ,to prevent embankments of little height as in 8forming10 spreading1 slipping or weathering1 as they are usually constructed from side cutting and loose top soil1 the sods over the site of the side cutting should be removed and a turf wall be made of them on each side of the formation1 the excavation being deposited within them1 when it will settle equally and become consolidated1 the wall preventing it spreading and also saving expense in maintenance4 ,in an embankment of soft earth that weathers quickly1 the tipped material should be allowed to take its natural slope1 and then every effort should be made to prevent its equilibrium being destroyed4 ,where heavy and sudden rainfall occurs the edges of the formation have been purposely tipped and maintained from #f to #ab inches above the height of the centre1 in order to prevent during construction gutters or eroded channels being formed upon the slopes1 the central portion being drained and the water led away4 ,however1 aqueous action may not deleteriously affect earth when tipped into an embankment notwithstanding that the soil cannot be made in the same state as before excavation1 and that deposited material is more open and subject to percolation than the solid unexcavated earth2 on the other hand1 although the percolation and degree of exposure to the atmosphere are greater1 in some soils this may tend to drain and render them harder and more stable4 ,in fact1 special circumstances may alter the general behaviour of any earth1 but the material forming an embankment should be regarded as in the same condition as if it had been exposed to meteorological influences1 and it should be remembered that in railway1 dock1 or canal works the deposited earth is seldom uniform throughout1 it being either soft at one place and hard at another1 or intermixed in a manner unknown in nature1 and that exceptionally difficult cases may occur which can hardly be treated by any particular method of procedure or even in the way which experience has proved to be effectual in several instances in similar soils under apparently like conditions4 ,the system of tipping has some influence upon the stability of an embankment and the prevention of slips and subsidences4 ,the first operation is the preparation of the ground upon which an embankment will be deposited4 ,solid hillocks or firm mounds that in any way tend to arrest motion should not be removed1 but vegetable or bush growth should be destroyed1 and where slips and subsidences are likely to occur1 turf and all soft soapy matter should be stripped so that the deposited earth rests upon a sound stratum4 ,in the dyke countries of ,north ,west ,europe1 before an embankment is deposited1 care is taken to remove all trees and roots so as to effect a thorough connection between the ground and the earth forming the embankment4 ,it is well if the ground be ploughed1 raked1 or harrowed1 so as to offer a rough and similar surface to the tipped material1 and also to obviate any arrest of the percolation of water1 which upon reaching a turf or smooth or less permeable surface1 may form a water seam at the foot of an embankment4 ,it may not be necessary to strip the turf for the full width of the base of an embankment1 but only for some #bj feet from the toe of the slope on each side4 ,as the earth is bared it should be covered in order not to expose it to the weather1 for should the surface be coated with mud1 water will accumulate1 as it cannot drain away or evaporate as quickly as when the ground at the seat is laid bare2 and also if the top soil be mere dust moisture will convert it into mud4 ,when the surface of the ground is inclined it can be benched or bared1 and it is open to question whether baring and harrowing the surface is not a better practice than benching1 as it gives uniform support and increases friction and prevents a sliding surface1 and is generally a quicker and cheaper method to adopt as the soil need not be so prepared for a greater depth than #f to #i inches4 ,benching may be the better system to adopt1 in loose and non-cohesive earths which require support to prevent rolling1 but it must be carefully made with the necessary slopes and inclination of cess to prevent a localization of water1 or the ledges may slip and carry away the material deposited upon them4 ,the ground at the seat of an embankment can also be prepared by ploughing over it and removing the disturbed earth with a scraper4 ,the drainage of the ground is most important in order that water cannot reach the seat of an embankment4 ,many systems are referred to in ,chapter ,,iv41 and others are herein named4 ,a complete system of drains may be necessary1 but much depends upon the character and sound condition of the earth and whether the slopes and formation are protected4 ,simply covering the whole area of the seat1 or that upon which the base of the slopes rests1 with broken stone obtained from the cuttings may suffice1 the stone being so deposited that water flows from the centre to the sides1 with a rough drain here and there1 or central1 diagonal1 and lateral drains may be required2 but the pressure of the deposited earth frequently causes land springs to issue in the seat of an embankment1 the existence of which was not conjectured1 hence the effect of tipping should be watched4 ,slips and subsidences are induced in embankments by the material being deposited when the soil is dry1 and in every state of humidity from dampness to saturation2 consequently the earth settles unequally1 is denser in parts1 and a stratification is caused as if it were composed of dissimilar earths4 ,should any soil be deposited in the same condition throughout1 and be punned or rammed in layers1 it becomes as near its original texture as is possible to quickly attain2 but in depositing railway embankments1 which cannot be punned or rammed1 the perfect incorporation of any soil is not effected by the simple operation of tipping from a spurn head1 and stratification of earth is disadvantageous1 inasmuch as the layers may not be homogeneous1 and in railway embankments are1 with a few exceptions1 in a different state owing to changes in the character of the soil1 the effects of weather1 mode of excavation1 and in a lesser degree the height and length of the lead or distance from the cutting to the tip2 the stratification1 therefore1 becomes varied and irregular1 and depressions are formed which may hold water1 and none should be permitted to accumulate in or upon a freshly tipped embankment1 for then it is in its most permeable condition1 and in retentive soil especially the existence of a wet place may cause it to become so deteriorated that it cannot be made stable without being drained1 and when the earth is liable to become alternately very wet and dry1 every means must be taken to lessen the deleterious effects4 ,provided an embankment is tipped of one kind of earth1 although it will be in a more open state than the solid unexcavated ground1 the slopes given to it are flatter than the angle of repose1 the weight brought upon it does not exceed the safe load1 that it is deposited upon level ground in regular and equal particles and the soil of ordinary character1 there is no reason that it should slip or subside unequally if it be not undermined by aqueous action4 ,under these conditions settlement would be equal1 or nearly so1 and as all deep embankments must necessarily subside from about #aj to #dj per centum1 and in extreme cases one-half1 the object to be gained is to cause the settlement to be even and regular towards the centre4 ,benching the ground so as to prevent a movement of the toe1 does not aid equal settlement nor keep the portion of an embankment above the level of the ground from spreading1 except from the resistance offered by the cohesion and friction of the soil2 whereas1 if the ground slopes inwards towards the centre the earth has a tendency to rest and come together1 and therefore not to slip upon the slopes4 ,this system is subsequently referred to4 ,all saturated or wet earth should1 if practicable1 be run to spoil1 but it is not easily effected1 as it cannot well be filled into one waggon of a set1 for it may be present throughout the whole surface of a cutting1 nor in variable weather can operations be conveniently suspended until the exposed faces of a cutting are dry1 but means are generally available by which any serious deterioration may be lessened4 ,no turf1 mould1 mud1 peat-moss1 soft pasty earth1 frozen soil1 or snow1 should be deposited in an embankment1 but only firm earth2 and no solid lumps of large size intermixed with shovelled material unless they are broken up and trimmed when tipped1 as the absorption of water will be greater in the earth having the smaller particles2 and should it happen that several waggon-loads of such material are tipped and are succeeded by others containing large lumps1 an embankment cannot be a homogeneous mass1 but will consist of more or less consolidated portions in a comparatively dry state1 and others which are less impervious and therefore more subject to the effects of water and settlement4 ,all snow or frozen soil or muddy earth should be cleared away from the spurn head1 and if it can be avoided no material should be tipped in bad weather4 ,with respect to the loosening of the soil by the process of tipping1 taking into consideration that railway embankments are almost invariably formed in masses of #b1 #c1 or #d cubic yards1 according to the capacity of a waggon1 it is obvious almost the whole bulk has been disturbed1 and that the condition of the solid earth in a cutting is not maintained1 for the soil in addition to being unbound by the process of excavation1 casting into waggons1 and shaking during transition1 is ejected with force down the slope of the tip1 the impetus having to be dispersed4 ,it is certain the size of earth waggons cannot conveniently be much increased1 and that little would be gained if a cubic yard or two were added to their contents2 and that the higher an embankment the greater the velocity of the soil down the slope of the tip and the loosening action which causes the earth to be lighter and to take a flatter slope than when deposited in layers from a moderate height1 also the greater the length of the lead1 the greater the vibration and agitation4 ,in the case of certain soils the particles of which become soft or dissolved when in a wet state1 such as sandy clay1 loamy soil1 and some varieties of clay1 vide ,chapter ,,ii41 the effect of a long lead or even a short one will be that the more solid portion of the contents of a waggon will settle1 leaving the loose or mud at the top1 and when a waggon is tipped the loose top 8slurry0 will roll down the tip almost as a fluid and proceed beyond the spurn head1 thus making a wet sliding surface1 the bottom toil frequently remaining in the waggons and requiring to be excavated from it4 ,nothing can be done in such a case but wait until the earth has had time to dry1 or preferably the wet mud should be run to spoil4 ,in fact a long lead1 especially when aided by deposition from a considerable height1 will cause friable soil possessing particles readily impaired or dissolved in water to become dust when in a dry state1 or mud if saturated4 ,the gradients and leads chiefly determine the manner in which earthwork can be economically executed1 and are1 in great measure1 governed by the configuration and roads of the country2 therefore1 it will usually happen that the length of the lead cannot be reduced1 and the only resource is to lessen the height of the tip1 and1 consequently1 the momentum of the earth down the slope1 and to reduce the inclination of the temporary road at the tip head to that sufficient to cause the contents of a waggon to be freely ejected and no more4 ,this cannot be effected at the same cost as depositing an embankment to the full height1 although in the case of an uphill lead a down gradient upon which the waggons will run freely by force of gravity can be made from the commencement of a cutting to the required width1 the embankment being raised to its desired height without extra expense but assuming the case of an embankment #fj feet in height1 and that in order to make it as dense and firm as possible it has to be tipped in three heights averaging #bj feet1 it involves the laying1 maintaining1 and removal of three temporary roads instead of one1 and cannot be erected without extra expenditure4 ,the large majority of railway embankments have been deposited to the full height and width1 and they stand2 although the effect of tipping loose soil upon loose soil1 which has not had time to consolidate1 is at each addition to cause a movement of the surface4 ,it is obvious the higher the tip the greater the disturbance1 but it may be said in firm and hard granular earth1 if always dry1 this unbinding1 although temporarily a disturbing element1 may really tend to produce ultimate homogeneity and stability2 on the other hand1 in tipping dry clay from a considerable height it often separates and becomes loose and mere dust4 ,in an embankment of moderate height the day's excavation from a cutting will increase its length several yards1 and the material from each set of waggons will only be exposed to the weather for a short time4 ,on the contrary1 in a high embankment1 the effect of the deposition of the contents of a set of waggons upon the tip head is hardly perceptible1 and is1 until the toe of the slope is approached1 the superimposition of a thin layer of earth which a shower of rain can convert into mud or cause to be in a soft or disunited condition1 especially in the case of soils having easily soluble particles4 ,the deteriorating influence of high deposition may be judged from the closing of an embankment of considerable height1 as it is often a tedious and somewhat anxious undertaking1 as might be expected from excavated1 shaken1 and loosened earth being deposited upon soil in a similar condition1 instead of upon the solid ground like the other portions of an embankment4 ,also water frequently percolates and trickles down the approaching slopes1 and penetrates them and loosens the soil1 whereas if one tip is proceeding1 any surface waters may flow away upon the slope and the solid ground1 and the earth has time to become in a similar state throughout4 ,to lessen these disintegrating effects1 if it can be done without interfering with the due progress of the works1 it is well to allow one tip end to consolidate for some time1 and to complete the closure of the embankment solely from the other1 suitable means being adopted to effect a firm junction4 ,should closing from a single tip head be impracticable1 the earth from the meeting point of the toe of the slopes of the tip heads should be similar in character and be deposited in the same condition2 in any case additional care should be taken to adopt every reasonable precaution to secure equal consolidation4 ,as evidence of the dissipation of earth at and near to the junction of two high tip heads may be stated that they require more material to close them than would appear to be necessary from a computation based upon measurements taken from cross sections4 ,in non-granular earths few cases will occur in which high tipping is an advantage2 one of the few is when loose rock and firm earth are deposited1 then the rock having larger particles1 and consequently being heavier1 will roll to the foot of the tip before the smaller material1 and so form a broken stone seat for the embankment4 ,in granular earths1 such as gravel or sand1 the height of a tip head is not a matter requiring much careful attention1 as the particles are not deleteriously affected by water4 ,when they are of nearly equal size1 an embankment will settle equally1 but in gravelly sand the stone will separate to some extent during transit and the process of deposition will be at the base2 a varying slope may then be assumed1 and it may here be named that it is known when sand is differently deposited1 although its appearance is unaltered1 it will exert dissimilar thrusts4 ,an embankment of little height may be deposited in bad weather without slipping or subsidence1 but when a high embankment is similarly tipped the surface of the earth is in an unfit state1 and operations should be suspended for a few days4 ,with regard to the systems of tipping and the prevention of slips1 as a general rule an embankment should be deposited to the full width1 for if it be not erected at one operation the earth may be of a different character in diverse conditions1 and will be more exposed to the vicissitudes of weather2 and in wide embankments1 should the system be adopted of tipping two outer roads and one central road1 the three tips should equally proceed in order that the earth may be in a similar state and be subject to equal exposure2 or weathered surfaces will be created down which water will more easily percolate than through the solid mass4 ,in the three tip system the two sides have a tendency to lean towards each other1 and cause the greatest pressure to be upon the inner material during construction1 and therefore the embankment is supposed to be more consolidated and less likely to slip2 but1 unless the conditions are exactly similar1 the advantage of this arrangement is more fanciful than real1 for should the inside slopes of the outer roads meet first1 the earth deposited from the centre tip has not an equal distance to descend and1 therefore1 the mass has not been tipped from the same height1 the looser material1 temporarily or permanently1 being upon the outer tips and the denser in the centre2 whereas the slopes1 being the most exposed1 should be the more compact1 and when they settle towards the centre without an outward movement at the foot1 so much the better for the stability of the embankment4 ,the pressure upon the seat is more regular when it is deposited to the full width1 as weight is then not irregularly added1 probably after some settlement4 ,instead of dividing the tips into two outer roads and one central road1 and in that way endeavouring to obtain permanent stability1 it is better to diminish the height the earth has to be cast1 and to deposit it as far as practicable in lifts1 and to the full width4 ,in treacherous soils such as some of the clays1 embankments that would not stand at a depth of #cj feet have been permanently stable when the seat was drained1 and they were tipped in lifts of #ae to #bj feet in soft clay1 and #bj to #be feet in firmer clay1 at double the height at which they previously slipped4 ,this method involves the expense of moving the temporary roads1 but allows more time for subsidence1 and the mass of an embankment is not so exposed to the weather2 however1 in a dry season1 an embankment can often be tipped to the full height1 whereas in wet or changeable weather it would not stand if so deposited1 and two lifts may be required4 ,care should be taken that the width is always sufficient to receive the top lift4 ,it is more in the direction of equally reducing the height the material has to be tipped1 especially in treacherous soils1 that solidity is to be attained1 than in an attempt to consolidate earth by endeavouring to cause it to fall together by deposition from two or more separate parallel roads at the same level4 ,many slips and failures of embankments have been caused by the central portion being deposited of one material1 such as clay1 and the slopes afterwards made of a different earth1 as rock4 ,the latter will then slip upon the greasy surface of the clay1 the porous nature of the broken rock readily admitting water and air4 ,in fact1 a more flagrant example of effecting that which on no account should be done is not easy to imagine4 ,in treacherous soil the system of tipping an embankment wider than that required from considerations of lateral and vertical settlement1 and allowing it to stand at a steeper slope than its permanent angle of repose1 and paring down the top unnecessary width is not to be commended1 as the earth is then strained1 and the lower portion is in the looser condition and the toe the weakest part3 however1 in the construction of a single line of railway with a narrow formation width1 it is very convenient as affording room for roads for loaded and empty waggons1 and in any soils other than aluminous and calcareous earths it may be done with impunity1 provided all slimy and slippery surfaces are removed4 ,no side tipping should be allowed in depositing a new embankment1 and any addition of soil to a slope should be avoided as much as practicable1 although in trimming some filling may be necessary1 but the slopes should be rough trimmed by the bank-head men as the earth is deposited so as to prevent hollows and depressions1 form a comparatively even and regular surface1 cause the mass to be equally exposed to the weather1 and prevent any lodgment of water4 ,the form a tip head naturally assumes will afford some indication of the stability1 for should it be regular and approach a semicircular shape it shows the earth is of a comparatively uniform character and is subsiding equally4 ,when it is uneven and jagged1 with streaks down the tip1 it indicates unevenness of soil and condition4 ,circumstances arise which necessitate a departure from any generally approved method1 for frequently an embankment must be widened to provide for increased traffic1 and tipping upon a consolidated surface must be effected4 ,chapter ,,viii4 and this refer to such a condition of work4 ,it sometimes occurs when a slip has taken place that only a narrow tip can be adopted1 as the soil may not temporarily be able to bear the weight of a larger mass unless equally diffused2 then there is no other reasonable course to pursue than to complete an embankment to the required width and slopes by dry side-filling1 such as ashes1 broken bricks1 or other absorbent firm material regularly and carefully deposited4 ,in order to prevent slips and subsidence and increase friction1 when an embankment must be widened by tipping upon its side1 the existing slope should be stripped of all turf or covering1 but only so as to leave no uncovered surface exposed to the weather2 and the bared earth should be made to present an even surface4 ,when the slope is benched1 care should be taken that the benchings do not localise water1 and that it cannot percolate down the face of the old bank at its point of junction with the new2 also in tipping an embankment upon sidelong ground or upon the slope of an old bank1 the seat should be bared1 particularly on the lower side1 as the earth meets with no resistance from the ground except from friction2 but upon the upper side1 the material being tipped partly against the hill has a less distance to travel1 and1 therefore1 the upper or lesser slope is not so loose as the lower or longer slope1 which latter is the more likely to admit water1 and requires a flatter inclination than the denser portion of the embankment4 ,in the absence of other protective works1 it is advisable to form on the lower side an earth wall or counterfort covered with turf at the toe of the slope in advance of the tip1 and to make it of the hardest and largest material deposited and with a foundation upon bared soil1 as it is the part most liable to injury4 ,this is a simple precaution against slips1 and will save its cost in lessening the expense of repairing and trimming the slopes4 ,as the steam navvy or excavator has now become necessary plant upon most large public works1 and greatly accelerates the speed at which cuttings can be executed1 always provided the excavation is not of a treacherous nature1 and is in such quantity that if not so used it would have to be run to spoil1 many narrow valleys in the near future will probably be wholly or nearly closed with an earthen embankment1 thereby effecting an important saving of time and expense2 or the number of spans of a viaduct will be lessened1 and only made sufficient to cross a road or allow the required waterway for a river or the discharge of any drainage or surface waters4 ,the tendency1 therefore1 will be to increase the height of embankments of earth2 and in countries where the first cost of an iron1 masonry1 or brickwork viaduct is too great1 and the use of timber rendered necessary1 earth embankments1 except in treacherous soil or upon soft ground1 are to be preferred to wooden pile and trestle bridges or culverts1 whose average life in ,america1 which probably now possesses as many as all other countries1 is from eight to ten years1 and that of timber truss bridges nine to eleven years4 ,in addition to other recommendations1 the steam navvy usually excavates the earth in small pieces of nearly uniform size1 and as it will perform the work of many men it may be most useful in treacherous soil1 as it may enable a cutting to be excavated in dry weather and be protected before the commencement of the wet season4 ,the slopes should be excavated in such earth as soon as possible after the gullet has been removed so as to prevent a slip1 and it may be necessary to close-sleeper or consolidate the ground in order that the weight of the machine can be supported upon soft ground4 ,,chapter ,x4 ,,notes ,,upon ,,the ,,location1 ,,preservation1 ,,and ,,protection ,,of ,,sea1 ,,estuary1 ,,reclamation1 ,,canal1 ,,and ,,reservoir ,,embankments ,,of ,,earth ,,constructed ,,to ,,contain ,,or ,,expel ,,water4 ,in the first place1 care should be taken in determining the site of an embankment across an estuary that there shall be no concentration or alteration of the general direction of the currents1 or scouring action will be created2 for the erosive and other deleterious effects of wave action upon a shore are influenced by the angle at which they are impelled against it4 ,a prudent course to adopt is to carefully preserve the usual channels by means of bridges1 particularly in ground of a loose character1 such as is usually found in partly landlocked waters2 for if the velocity is increased1 the earth which has been deposited by the original current being reduced or impeded resulting in the suspended matter in the water falling to the bottom1 will be subject to a force that will again disturb and cause it to return to its previous suspensory condition2 and any disturbance of the normal currents may destroy the equilibrium of stability and alter the flow1 and when they are affected it may be most difficult to restore them to their original state1 for water will always endeavour to obtain the easiest channel4 ,it is essential to know the heaviest flood discharge of any river that may flow into an estuary1 the greatest depth and velocity of the river1 the normal and flood channels1 their sectional area and direction1 and the extent and shape of the catchment area1 so as to establish the required opening to give the natural waterway2 for it is important not to interfere with the tidal capacity of an estuary or the volume or flow of any upland waters into the sea1 as a navigable channel may become filled with silt1 especially when the shore is flat or sandbanks exist2 and upon a sandy coast an embankment across an estuary with openings for a navigable channel will probably cause it to become difficult to navigate and1 perhaps1 impossible1 without constant dredging and other works of maintenance1 as an embankment may obstruct and deflect the currents and prevent them carrying away the suspended matter4 ,an open viaduct instead of an embankment is almost always to be preferred1 and may be necessary2 for the power of a current to scour or move particles is greatly augmented by a small increase of the velocity1 and the earth may be in such a delicately balanced condition that any increase of scouring action may destroy the seat of an embankment4 ,to prevent leakage and scour of the base of an embankment near a river resting upon loose soil1 curtain walls are sometimes inserted upon both sides extending to a considerable depth1 thereby affording security against an embankment merely resting upon a mound which may gradually erode1 with the result that it must finally slip and be destroyed2 and it may happen1 unless the foundations are carried down into impervious soil1 that water may escape underneath and undermine it2 such action is obstructed by carrying the slopes a few feet below the ground so as to prevent through surface percolation4 ,as a rule1 an embankment across an estuary with one or two openings in it is to be avoided1 and it should be most carefully considered whether it will not be better to expend a larger sum and erect a pile viaduct which will not interfere with the currents or channels and only require ordinary precautions to be taken against erosion1 instead of depositing an embankment with openings at the channels and the necessary protective works which may consist of pitching the slopes1 covering them with fascines1 mattress work1 or sods1 erecting short or long1 low or high1 groynes1 as the former may be ineffectual in causing a deposit or a shoal in front of the toe of the slope and in preventing scour1 for in loose silty and sandy soil of considerable depth and not sufficiently firm to resist erosion1 they will probably fail by reason of the space between them being washed away2 and a complete covering of the foreshore may be requisite1 or a protecting apron of homogeneous impermeable soil1 and continuous training walls to prevent the creation of shoals3 all of which protective works will constantly need to be repaired1 and the failure of any one may cause not only an embankment to give way but the remaining preservative works4 ,undoubtedly there are many estuaries upon which if an embankment even with many openings for channels had been deposited1 it would have failed1 the soil being in such a tender state that the least additional weight upon the surface would destroy the equilibrium4 ,also interference with the littoral currents is a risky operation in any but a hard rock bed as regards the foundations1 quite apart from injury to navigable channels4 ,when there are numerous ditches1 creeks1 or channels crossing the line of a proposed estuary embankment of variable stability1 especially should hills be near and the earth be so porous as to be saturated every tide1 without doubt the safer plan is to erect a low viaduct1 as the old waterways will be an endless source of trouble should the ground be anything but firm clay1 and interference with the currents will not be preventable1 as either their velocity will be increased or decreased1 the result being scour or fresh deposits which will affect the channels2 and such alteration may change the direction of the motion of the waters1 which must be prevented in front of an estuary embankment2 or waves will be created by the water travelling and rushing over shoals1 for the even configuration of the bottom is a wave lessener1 and should there be a deep channel near an estuary embankment severe wave action may be created4 ,the piers or piles of such a viaduct should be cylindrical1 thus offering no flat surface for the waves to break against1 and yet temporarily to divide them without serious shock to a structure4 ,when of very considerable length1 a projecting embankment deposited upon a flat shore of a tidal estuary has caused a heaping up of the water on one side at low tide1 and therefore it is unequally strained4 ,this was found to be the case with an estuary embankment on the ,scheldt1 #b miles in length4 ,the form of the slope has also to be considered1 but all the principles that determine the best profile in each case of a pier or breakwater do not necessarily apply to an embankment in an estuary4 ,the recoil of the waves washing away the ground in front and at the toe is particularly to be guarded against1 and the action of spray or a broken mass of water falling upon the formation1 as also the direct action of the waves4 ,a concave form should not be adopted throughout1 as waves roll up until they approach the top portion1 when they turn over and fall upon the flatter portion and often breach it1 but when the face is straight1 excepting for a few feet at the toe1 the waves are diffused in travelling up1 although they proceed to a higher point upon a flat slope than a steep one1 and the recoil is greatly diminished1 but with the view of avoiding direct wave action1 when the ground is inclined in front of a sea or estuary embankment1 it is well to curve the lower part of the slope and to make it cycloidal to the surface of the ground and the slope for a little distance1 so as to reduce obstruction to a minimum4 ,the method of making a level terrace or stepping the slope instead of a curved face has the advantage of checking the rising of the sea up the face1 altering its direction and acting as a wave-breaker1 and also combines these effects with giving as large an area of the base as can be obtained by a curved face1 and in bringing the centre of gravity of the cross section of the embankment nearer to the seat1 but the face must be securely protected4 ,the width of the cess should increase according to the degree of exposure4 ,if an embankment consists of earth the slope of the cess should be from #f to #aj to #a1 or the system is better avoided and a continuous face adopted4 ,short groynes will often protect the toe of an embankment and prevent any longitudinal current undermining it4 ,as a rule1 in a tidal estuary the cost of protecting the slopes is considerable1 and more above low-water level than below it4 ,in adopting groynes formed of single or double rows of piles1 in order to prevent erosion of the toe and a slip and subsidence in an estuary or sea embankment1 the littoral currents must be considered before determining their direction and position1 the object of their erection being to prevent the waves1 and especially the prevailing waves1 from scouring the shore1 and also to cause a general deposition of shingle1 and1 therefore1 they are usually placed at an angle to the set of the waves1 so as to cause the latter to be diffused4 ,the angle will vary2 the best guide is to examine the effects of any that may be erected in a similar position to that to be built4 ,an angle of #ej to #gj with the foreshore1 in a leeward direction is frequently adopted1 and with respect to the distance apart1 this depends principally upon the direction of the current and prevailing wind1 contour of the shore1 degree of exposure1 and the length of the groynes4 ,when the whole of an open coast has to be protected1 no natural defence existing1 the line of the prevailing set of the current and wind on a straight shore can be set off at the end of a groyne1 and before the point at which it meets the foreshore another can be erected4 ,they are generally successful when properly placed1 and are most frequently straight2 if not1 they have a concave face to the direction of maximum eroding force2 a convex must be avoided1 as it will not permanently retain the deposits2 their practical effect being that the breach is heaped up or retained upon the prevailing wind1 set of current1 or wind-wave side to a height of some feet above the leeward side1 therefore1 a groyne should be so constructed that planks can be added to it as required4 ,they have been proved to prevent the formation of bars when judiciously located1 but their success greatly depends upon their proper position and direction1 or in loose soils such as sand they may cause a deposit upon the windward and prevailing current side1 but an erosion and falling away upon the other2 and when placed in front of a reclamation embankment upon shifting sand until the ground at the back of the embankment becomes dry by the tidal waters being excluded1 or the surface is impermeably coated1 they may be of comparatively little use to prevent a slip or movement of the shore2 for as the tide recedes below the level of the toe of the slope1 a seaward flow of the tidal and land waters will be created in very porous soil under the seat of an embankment1 and may continue until the tide returns and rises to the level of the ground1 thus causing the shore to be constantly changing place and permanently established accumulation impossible4 ,short transverse spurs have been adopted to lessen this action but their effect is hardly noticeable4 ,as failure of a groyne will probably cause erosion of the foot of an embankment and a slip1 a cheap and effective means1 attested by the experience of nearly half a century1 of preserving the timber from the attacks of most marine worms may here be named4 ,it consists in scorching the piles1 thus preventing fermentation of the sap1 and immediately tarring them3 also in placing the wood in the opposite direction to that in which it grew2 the latter operation has been found to increase the durability #ej per cent41 the reason1 it is believed1 being that the capillary tubes in the trees are so adjusted as to oppose the rising of moisture when the wood is inverted4 ,in excavating for an enclosure embankment1 the earth should not be disturbed nearer than is economically necessary1 and a cess should be left of about #dj to #ej feet in loose permeable soil1 the width being governed by the character of the earth1 the depth of the excavation1 and the height of the embankment4 ,should dredging have to be executed near an embankment1 a considerable distance should be left between the toe of the slope and the line of operations4 ,before commencing an estuary or enclosure embankment1 it is advisable to notice whether a deposit is left upon the shore by the incoming tide1 and to ascertain whether it forms in some degree a protective covering1 for if this should be the case1 any increase of the velocity of the flowing water which might be caused by dredging or a concentration of the littoral currents should be avoided1 or the tidal matter in a state of suspension will not gradually sink to the ground4 ,the tidal deposit1 although the earth forming the embankment should not be tipped upon it1 may also be of importance as tending to prevent or lessen any percolation of water through the foreshore and under the seat of an embankment2 for instance1 on the ,nile1 the deposited slime is found to make a practically watertight covering on the loose sand4 ,mr4 ,thomas ,stevenson has also stated that1 according to the depth below the surface of low water that mud reposes1 may be approximately judged the force of wave disturbance and degree of exposure2 the less the depth1 the less the power possessed by the waves4 ,in the case of treacherous soil which circumstances compelled to be partly used in a reclamation embankment of moderate height1 but which it was found would gradually become firm by compression1 rough sheet piles with a plank at top have been inserted1 giving the outline of the finished slope of the material to be afterwards tipped upon it1 the piles and planking not being removed1 and1 therefore1 affording the required temporary support before the earth became consolidated and stable by compression and time4 ,in ,chapter ,,ix4 the deposition of embankments is referred to as it affects slips and subsidences in earthwork1 but in an enclosure embankment an additional precaution is particularly necessary1 namely1 that immediately tipping from the ends increases the velocity of the flow of the outgoing or incoming tidal water through the opening1 and consequently augments its scouring action2 its deposition from a spurn head should be abandoned1 and the embankment be uniformly raised from the base4 ,the employment of cofferdams1 piling and planking for effecting a closure is now generally discarded in favour of the horizontal system of equally raising the height of an embankment from its base2 and is even to be preferred to fascines1 unless the latter are merely used to distribute the weight over the base1 to protect the surface of a slope1 or form a shield against scour either temporarily or permanently4 ,in previous chapters the protection of a slope is examined2 here some reference is made to the particular preservation of the slopes of an estuary or reclamation embankment4 ,when the protection afforded is not uniform care must be taken that although it makes one part secure it does not weaken another4 ,in the case of river-banks in a soil that is in a delicate state of equilibrium1 it may occur that soon after one portion has been protected1 another is being scoured1 whereas previously it was stable2 therefore1 to prevent localization of the erosive action1 whether on the foreshore of an estuary1 reclamation1 or a river-bank1 and consequent slips and subsidences1 the covering should extend over a considerable length4 ,in a sheltered position simply sodding the slopes may be effectual4 ,some other means of protection are a hard chalk or gravel counterfort founded a few feet below the ground at the toe of an embankment1 and a covering of similar chalk or gravel upon the slope1 should the soil be favourable4 ,when an embankment of earth in an estuary or river is of firm soil and only requires to be made proof against wave action1 stones may be simply deposited evenly upon a slope and so that they will not be washed out1 and pitching be not required1 as the rough face will tend to break up the waves2 but where a simple covering is adopted1 whether close or comparatively loose1 the slope should be straight1 as a concave form causing a recoil of the waves will in time damage or separate the face shield4 ,a coating of clay about #b feet in thickness1 upon a slope with stakes driven into it1 and large bushy boughs of trees fixed thereon with the tops downwards1 is frequently used in ,india as a protective cover to a crumbling bank of a river1 and to training spurs erected to prevent erosion and slips4 ,mattresses1 fascine or wattled work1 besides being expensive1 will slide down a slope unless well secured to it1 and therefore a constant strain is produced as in all stake-held coverings2 it has also been observed by the experienced that although so largely and successfully used in ,holland and on its coast1 there is very little ground swell on the ,dutch shores1 and that in a very exposed situation1 or where heavy ground swells exist1 they may not answer1 and may become disintegrated by the much greater weight and force of the sea2 and this1 notwithstanding the surface breakers of thin water and little mass broken up by the wind may produce more visible agitation4 ,to prevent a river-bank slipping1 and also to maintain a channel in a muddy river1 half-tide longitudinal training walls made of wattled work or fascines have been used1 so as to cause the deposition of the suspended matter in the tidal water and to gradually restore the impaired slope and secure it from crumbling into the river4 ,the stones brought down by heavy floods have also been used to maintain a river channel and protect its banks from slipping1 the interstices gradually becoming filled with mud deposited by the water when the floods subside4 ,when sudden and unexpected scour of the slope or bed near an estuary embankment upon soft soil has to be immediately arrested to prevent a slip1 gunny bags filled with sand afford a ready means of repairing any cavities1 the interstices between the bags usually being filled rapidly4 ,material should be added as required and any concentration of the erosive currents should be avoided4 ,the required height has to be determined of an embankment in an estuary or the sea to prevent any flow over it or waves falling upon the inner slope2 #d to #e feet above the highest water mark appears to be adopted in the lower reaches of the ,thames and unexposed estuaries in ,england4 ,in ,holland #aj to #ae feet1 depending upon the degree of exposure4 ,it is of paramount importance to prevent any waves washing over the top1 as damage and1 perhaps1 a breach may be caused thereby4 ,the height of the highest known wave must therefore be ascertained4 ,should the shore be sandy and loose1 a characteristic of estuarine accumulations1 although its usual bed may be preserved in any storm1 when an embankment is erected the rapid and ceaseless process of wasting of the sand and loose soil by the recoil of the waves from the face may in time lay bare the toe of a steep slope and undermine it2 for it has been found where the foundation was sand and a rubble mound1 which should be so constructed that its interstices become filled in order to make it more solid and stable1 was placed upon it1 and the superstructure upon the mound1 that the sea being resisted by a vertical wall recoiled and made the soil a quicksand1 although the sand would be stable at its natural slope in still water4 ,obviously the less the action of the waves is impeded1 the less the looseness of the sand4 ,experiments have shown that a slope of #a to #a will reflect waves1 on a flatter slope they are broken4 ,in such situations light structures1 offering little resistance to the action of the waves and not causing an impediment to the current1 should be adopted in preference to a massive or solid erection2 but when an embankment is necessary1 it should have a long sloping mound or foreshore upon which the waves will gradually become lessened and dispersed1 the desired object being to prevent deep water close to the work4 ,when a railway or road follows the shore1 instead of erecting a retaining wall to protect an embankment1 a preferable plan to adopt may be to have open trestle-work offering the least possible obstruction1 and when the formation is at the base of a cliff of variable and doubtful soil it is the best construction1 as the cliff is not touched1 and slips and subsidences are avoided4 ,should the deposition of an artificial beach be considered necessary for the preservation of the foot of a cliff in addition to the trestle road1 experience seems to indicate that the contour affording the most protection is one in which the slope has a flat terrace or cess at not above three-fourths of the vertical height1 another short slope1 and a nearly horizontal space some distance from the foot of the cliff2 but a storm will straighten the face1 and it may be impossible to economically maintain it2 however1 should such a slope be assumed it should not be disturbed4 ,vide ,chapter ,,vi4 for information respecting slopes4 ,when a sea or an estuary retaining wall is necessary in order to prevent the slipping of an embankment consisting of loose soil1 an inner dwarf wall at the edge of the formation upon the land side should be erected so as to hold the embankment in a box1 and not allow any spray or water passing over the retaining wall to erode the inner portion4 ,deep water is generally required close to the work in railway piers or jetties to enable vessels to get alongside2 a heavy and monolithic wall must consequently be erected2 however1 in the case of loose soil1 the vertical system simply should not be used unless the foundation is thoroughly protected and below the reach or effect of wave action1 and no re-entering or right angles should exist1 as they increase the action of the waves4 ,when a rubble mound is cast in and a vertical structure placed thereon1 great care must be taken that there are no holes1 except the natural interstices between the stones1 and that they have a firm foundation and sink equally1 or the random mound may give way and the superstructure will then necessarily follow4 ,illustration3 ,,data4--,sand embankment3 ,width of formation1 #cj ft42 inclination of the slopes1 #c to #a2 height of embankment from the surface of the ground1 #cj ft42 depth of water1 #bj ft42 height of wave1 #e ft4 ,as an illustration of the deleterious effects of the recoil of waves may be mentioned that a high vertical wall with a parapet has been found to endanger the toe1 but when the parapet has been removed in order to allow the head of the waves to leap over the top of the work1 the structure remained stable4 ,to prevent the recoil of the sea and the scooping away of the base and the foreshore in much exposed situations1 and consequent slips and subsidences1 breakwaters which simply act as wave screens1 and not as wind screens1 are sometimes kept a little below high-water mark so that the heads of the waves may have free action1 although their onward motion is prevented4 ,on the contrary1 light open work1 such as a lattice screen1 although it may somewhat lessen wave action1 does not prevent it passing through4 ,the principal causes of the failure of vertical walls when placed upon an easily eroded foundation are by the scouring action of the recoiling waves1 therefore their magnitude should be reduced to the lowest limit3 by the impounded air driving out particles of the structure3 by waves travelling upon the top1 therefore their forward motion should be deflected and rendered vertical3 by the hammering action of the mass caused by its being alternately quickly submerged and unsubmerged2 the practical effect being that the foundation is intermittingly released of a portion of the load and then fully strained1 therefore the height of the waves should be reduced as much as possible4 ,respecting the action of falling water1 experiments were recently made in ,india1 which proved that 8the greatest intensity of pressure does not exceed that due to a column of water of a height equal to the fall20 the greatest intensity of pressure being always fractionally under the hydrostatic head4 ,as an illustration of the constant change of the load upon the foundations of an embankment in tidal waters1 the following calculations have been made4 ,the weight of a cubic foot of sea water is taken as #jjbh ton4 ,the weight of a cubic foot of sand is here taken as #jjef ton4 ,a4 ,the weight of a lineal foot of the embankment when unsubmerged equals #bjafj tons1 computed as follows3-- ,cubic ft4 ,the central portion #cj ft4 #cj ft4 #a ft4 #ijj ,the two inclined #ij ft4 #cj ft4 #a ft4 #b1gjj portions ---------- ,ton4 ,tons4 ,cubic contents #c1fjj #jjef #bjafj4 ,b4 ,at high water the weight of the embankment is reduced by the weight of the water displaced1 which equals #hd tons1 calculated as under4 ,the submerged contents of the embankment are-- ,cubic ft4 ,the central portion #cj ft4 #bj ft4 #a ft4 #fjj ,the two inclined portions #b_/cj ft4 #bj ft4 #a ft4 #a1bjj #fj ft4 #bj ft4 #a ft4 #a1bjj ---------- ,ton4 ,tons4 ,cubic contents #c1jjj #jjbh #hd4 ,from this must be deducted the weight of the water resting upon the two slopes1 which equals #ccfj tons-- ,cubic ft4 ,ton4 ,tons4 #fj ft4 x #bj ft4 ,x #a ft4 #a1bjj ,x #jjbh #ccfj4 ,c4 ,thus the insistent load at high water upon the whole area of the foundation is reduced by ,tons4 ,tons4 #hd - #ccfj #ejdj -------------------- ------------ #jbe 4 #bjafj #bjafj ,d4 ,at high water a vertical pressure is imposed upon the ground beyond the toe of the slope due to the #bj feet head of water-- #bj ft4 #a ft4 #a ft4 #jjbh #jef ton per square foot4 ,this latter weight and element of stability tends to prevent movement of the ground1 and also the toe of the slope1 but is entirely removed at low water when the insistent pressure at the foot of the embankment is the greatest4 ,for the purposes of illustrating the varying load upon the surface of the ground caused by a rise and fall of a tide1 it will be sufficient to take one slope of the embankment4 ,e4 ,the weight of a lineal foot of one slope1 if unsubmerged ,cubic ft4 ,ton4 ,tons4 #ij ft4 #ae ft4 #a ft4 #a1cej x #jjef #gefj4 ,f4 ,the weight of water resting upon the slope per lineal foot at high tide ,cubic ft4 ,ton4 ,tons4 #fj ft4 #aj ft4 #a ft4 #fjj #jjbh #afhj4 ,g4 ,the weight of the water displaced by a lineal foot of the submerged portion of one slope of the embankment at high tide ,unsubmerged portion of one slope ,cubic ft4 ,ton4 ,tons4 #a1cej - 7#cj ft4 #e ft4 #a ft47 #a1bjj #jjbh #ccfj4 ,h4 ,the area of the base of the slope per lineal foot #ij ft4 #a ft4 #ij square ft4 ,i4 ,therefore the insistent pressure upon the surface of the ground at the base of one slope at low water1 when the bed is presumed to be dry1 is1 ,e #gefj ---------- #jhd of a ton per square foot4 #ij ,h ,j4 ,at high water it is ,e ,f ,g 7#gefj #afhj7 - #ccfj #ehhj ---------------------------------------- ------ ---------- #jfe #ij #ij ,h of a ton per square foot1 or #bbfj per cent4 less4 ,it has been shown that the vertical pressure of the water upon the ground beyond the slope is #jef ton per square foot at high tide1 vide ,d41 therefore the weight upon the seat of the slope is only in excess of the normal weight of the water upon the ground beyond the slope1 ,j ,d #jfe - #jef #jji of a ton4 ,an inspection of the diagram shows that the flotation power of the whole of the shaded portion of the slope is balanced by the weight of water resting upon the whole of it1 the areas of the triangles being similar2 and that the portion ,w4 of the slope is that which loses weight by immersion4 ,calculating the pressures at low and high water upon the base of the portion ,w41 the relative vertical pressures would be-- ,,at ,,low ,,water4 ,cubic ft4 #cj ft4 #e ft4 #a ft4 #aej #cj ft4 #bj ft4 #a ft4 #fjj ------ #gej #jjef #db tons4 ,k4 ,the area of the base #cj ft4 #a ft4 #cj square ft41 consequently the pressure upon it #db_/cj #adj ton per square foot4 ,,and ,,at ,,high ,,water4 ,l4 ,the unsubmerged portion ,cubic ft4 ,ton4 ,tons4 #cj ft4 #e ft4 #a ft4 #aej #jjef #hdj ,the submerged portion #cj ft4 #bj ft4 #a ft4 #fjj 7#jjef - #jjbh7 #afhj_/bebj #bebj ,consequently the pressure ---------- #jhd ton per square foot1 #cj ,k a difference of #jef ton per square foot1 or #dj per cent4 less load4 ,m4 ,and upon the base of the central portion-- ,,at ,,low ,,water4 ,cubic ft4 ,ton4 ,tons4 #cj ft4 #cj ft4 #a ft4 #ijj #jjef #ejdj4 #ejdj ,the pressure is1 therefore1 equal to ---------- #afh ton per square foot4 #cj ,k ,,at ,,high ,,water4 ,n4 ,the unsubmerged portion ,cubic ft4 ,ton4 ,tons4 #cj ft4 #aj ft4 #a ft4 #cjj #jjef #afhj ,the submerged portion #cj ft4 #bj ft4 #a ft4 #fjj #jjbh #afhj_/ccfj #ccfj ,consequently the pressure ---------- #aab ton per square foot2 #cj ,k also a difference of #jef ton per square foot1 or #cc per cent4 less load4 ,the difference in weight1 assuming a wave of #e feet in height1 measured downwards from high water level1 to simultaneously roll against the embankment upon both slopes and completely recoil1 would be equivalent to the displacement of #e feet depth of water for a strip 7#cj ft4 #cj ft4 #cj ft47 7#de ft4 #cj ft4 #de ft47 ---------------------------------------- ---------------------------------------- ------------------------------ #aje ft4 in width4 #b ,the cubic contents per lineal foot are-- #aje ft4 #a ft4 #e feet #ebe cubic ft4 ,o4 ,the flotation power #ebe cubic ft4 #jjbh ton #adgj tons4 ,for the purposes of this calculation1 this weight is taken as if it were spread over the whole area of the seat of the embankment at a depth of #ae feet from the top #de ft4 #cj ft4 #de ft4 #abj ft4 #a ft4 #abj square ft4 ,the vertical pressure per square foot therefore #adgj_/abj #jabc ton #bge lbs41 which is equivalent to a hammering action upon the foundations of #bge_/add say1 #b lbs4 per square inch occurring each time the #e feet waves recoil4 ,the weight1 #aje ton upon each slope1 of the water upon that portion of the slope which is alternately submerged and unsubmerged is not considered4 ,this wave action may1 and generally will1 happen upon one side only of an embankment owing to the direction of the wind1 the current1 and the 8fetch0 of the water4 ,in that event the lateral pressure upon the embankment will also constantly change1 and there will be a varying horizontal force from the #e feet in height wave and its percussive action upon the slope tending to produce unequal strain and movement4 ,the object of the preceding calculations is to show the variation of pressures an embankment in an estuary or a tidal river has to sustain in addition to those of an ordinary embankment upon dry land1 and its especial liability to slip and subside2 and also to demonstrate that the vertical and necessarily the horizontal pressures may be in a perpetual state of mutation and vary considerably1 and that the vertical pressure of the water outside an enclosure embankment may reach a point when the water may be forced upward upon the land side4 ,usually1 subsidence is greatest in the wet seasons and at the time of the lowest tides4 ,in choosing between two materials for submerged work practically equal in other respects1 the heavier should be preferred1 as by reason of its own weight it has greater power to resist the action of the waves and scour1 and the decrease of its specific gravity by the weight of the bulk of water displaced is relatively not so large4 ,with respect to the earthwork of canals and embankments constructed to hold water1 each chapter of this book contains information relating to the promotion of the stability of the soil1 and it is not here intended to refer to the most approved methods of construction1 but only to name some points requiring attention4 ,a barge or ordinary ship canal is usually placed at a shallow depth in the ground and meanders through a district1 avoiding deep cuttings and heavy embankments1 such an undertaking as the ,suez1 or the ,panama1 ship canals being altogether exceptional undertakings2 and also the ,manchester ,ship ,canal4 ,some of the most treacherous soils are named in ,chapter ,,ii41 but probably the worst earth in which a canal can be made is peat-bog land2 the method of procedure is then different to that required in making a railway or a road1 and in such soil the construction of a canal should be avoided1 as it necessitates most experienced and skilful treatment and extensive drainage1 which causes subsidence2 difficult maintenance to preserve the channel and retain the water of navigation1 control the drainage waters1 and keep unimpaired the towing-path1 which must be firmly covered throughout4 ,fine sand is also an unfavourable soil as it so readily becomes a quicksand1 but almost all other earths usually met with can be so protected that failure should be an improbable contingency1 except when the cuttings are of extraordinary depth1 as on the ,panama ,canal2 the chief danger being when there is considerable diversity1 irregularity1 fissuring1 looseness1 and upheaval of the soil1 for varieties of almost every surface earth may be encountered1 each with its own characteristics and behaviour when dry or water-charged1 and requiring great attention1 especially at the joints1 and not a few separate treatment1 not only of the soil but of the same earth in a cutting and in an embankment4 ,it sometimes happens that there is not enough clayey earth to form a canal bank1 but if the whole of the excavation1 except the mere surface earth1 is used there is sufficient1 and that it must be employed for reasons of economical construction4 ,in such a case the clayey earth should be deposited upon the water side1 and the gravelly or sandy soil on the land side and as a towing-path covering1 great care being exercised that no stratification of the earth takes place1 or it may separate1 and water seams be created4 ,the bottom and slopes of a canal embankment must be covered with an impervious layer1 puddle or concrete being most frequently used for the bottom1 and puddle or a coating of well rammed vegetable soil sown closely with grass seeds for the slopes1 or stone pitching in a wide canal liable to wash3 also in loose or doubtful soil4 ,in canal cuttings when the water is drawn off the counter-thrust against the slopes is removed1 and unless this is maintained the earth1 if in a delicate or loosened condition1 may slip1 as a flow may be caused of previously dammed up waters4 ,prior to any works being commenced upon a canal embankment it is advisable to strengthen it for a distance of not less than about #fj feet in length on each side of a proposed railway bridge or other structure1 particularly when it will be subject to vibration4 ,water will soon find a weak place in any earthwork and1 certainly1 when an engineer can maintain heavy earthworks in treacherous soils in canal construction1 where part of one slope is submerged in an embankment and the other dry1 and in a cutting part wet and part dry1 he should be able to do so in any analogous situation1 making due provision for vibration1 the chief disturbing agency canals are not subject to1 but which is so potent in its effect upon railway earthwork4 ,canal and reservoir embankments are so similar as regards the stability of earthwork that they are here considered under one head4 ,the object of a canal1 reservoir1 or river embankment is in a desired position to hold water without leakage1 subsidence1 or deterioration of the earth1 or other works connected with the general construction4 ,in dock1 canal1 or any earthworks made for the purpose of containing or expelling water1 it is obvious the position is entirely dissimilar to that of railway works3 for whereas a slip or a subsidence in an embankment upon railway work may be of slight moment and give comparatively little trouble or anxiety1 any movement in earthwork constructed for the purposes named is of grave importance1 as it may mean the destruction of the work1 loss of life and property1 not only upon the site but also in the surrounding district4 ,no leakage or marked weeping of such an embankment should be disregarded1 as unless arrested it will gradually deteriorate the earth until the equilibrium becomes so affected that the embankment fails4 ,as a rule1 upon railway works1 serious slips1 except in very unstable soil1 such as drift earth1 or those quickly decomposed by atmospheric influences1 seldom occur1 vide ,chapter ,,ii41 until a year or two has elapsed1 the process of disintegration from water being necessarily slower in its action1 the material having an opportunity to return to its normal condition1 and the surface being more equally exposed4 ,in earthwork for hydraulic purposes1 although not subject to frequent and sudden vibration1 the slopes being unequally exposed and part generally either permanently or temporarily submerged or alternately wet and dry1 and the top and land side unsubmerged and fully open to the action of the weather1 percolation cannot be equal and regular upon its surfaces1 and slips and subsidences therefore usually occur within a short time1 varying from a few weeks to a few months2 and after about a year or a cycle of seasons they are not frequent1 unless the inherent design and construction of an embankment is faulty1 permitting leakage through the submerged slope or bottom1 pools of water to collect upon the top1 and the bank to become fissured and unequally wet or dry4 ,especial care should be exercised to ensure a complete and impermeable connection with the earth upon which it is placed4 ,in embankments to contain or expel water time should always be allowed for an embankment to consolidate before the admission of the water1 but in the case of a cutting the presence of the navigation water as soon after construction as practicable may be an advantage1 depending upon the nature of the earth in each case2 as it may protect the submerged portions of the slopes from the deteriorating effects of being in a constantly changing degree of dryness and wetness1 and shield them from the sun and drying winds4 ,except under peculiar circumstances the unstable places will be known in a few months1 and provided a canal is properly constructed1 it will not cause much trouble after six months or a year from earthwork movement if the embankments and cuttings receive ordinary attention1 as the navigation water will quickly indicate the unconsolidated places4 ,in clay1 clay marls1 clay loams1 and where loamy soil is intermixed with permeable and water-bearing strata1 movement of the earth in canals will speedily occur unless proper precautions have been taken in the construction1 as they are seldom homogeneous4 ,earthworks to contain or expel water should be made proof against even improbable deterioration and accident1 and in proportion as the soil is less solid and firm it should be consolidated by ramming or other means1 or be covered and protected to prevent it cracking1 and only firm and binding material should be used in canal embankments or those holding or expelling water in order to prevent slips and subsidences4 ,chapter ,,ii4 treats of some conditions under which slips and subsidences may be expected4 ,no precaution should be omitted that will render the work solid and uniform1 and nothing should be left to chance4 ,the location is of great importance1 for the earth may vary in stability within a very short distance1 not only in character but as regards the superimposition of the strata4 ,upheaved and distorted beds should be avoided1 and all loose and fissured earths1 especially rock or other soils having more or less vertical seams3 for all embankments constructed upon fissured soils are sure to cause anxiety and trouble1 and will always be liable to become in a dangerous state from an excessive rainfall4 ,impermeable horizontally deposited earth of considerable thickness is that to be desired1 or firm ground that cannot slide upon another stratum or be affected by any artificially brought addition to the percolating waters consequent upon the construction of waterworks4 ,having carefully selected a site1 which for waterworks purposes must almost invariably be upon high ground and may have to be upon the top cap soil of a hill and be peculiarly exposed1 the next step to guard against a slip or a subsidence is to prepare the foundations so that no leakage or trickling of water can undermine or gradually deteriorate the seat of the embankment2 and1 therefore1 a thorough connection between the deposited embankment and the ground must be established and the whole be prevented from movement4 ,the selection of the best available earth is one requiring careful consideration1 and it may be necessary to experiment to test the capability of the soil to be made watertight by compression or other comparatively inexpensive means4 ,in some cases none may be obtainable2 if so1 the only course to pursue may be to consolidate the earth as much as possible1 and protect it with an impermeable homogeneous and durable covering1 and one that experience has shown can be trusted to equally resist percolation4 ,the whole practice of stable earth dam construction is comprised in the employment of homogeneous1 fine1 and tenacious earth uniformly deposited in thin layers1 gently watered sufficiently to aid ramming and consolidation1 rolled1 pressed1 or trodden down by the passage of carts1 men1 or animals1 and in its due surface protection4 ,heavy rolling is to be preferred1 for it is more effective than ramming1 as may be judged by the greater compression2 the thickness of the layers and the weight being so regulated that it compresses the earth to its state of maximum solidity1 and does not pulverize it1 as the compression is more uniform1 and irregularly compact masses are not created1 which not only destroy uniformity of condition of the mass1 but cause seams and veins and destroy homogeneity4 ,after rolling1 the compressed layer should be gently watered1 as the weight of the roller will have made the top crust drier than the lower portion1 unless it has been made into too moist a state4 ,the thickness of the layers should not exceed1 when the soil is to be heavy steam-rolled1 about #f inches in earth1 and #d inches in clay soils2 they may be compressed to about four-fifths to two-thirds of their normal thickness1 the degree of compression to ensure maximum solidity indicating the openness of the original earth4 ,in sand1 the layers when simply wetted and rammed with an ordinary rammer1 should be about #d to #e inches in thickness1 and ordinary earth about #b inches4 ,the volume of the sand will be reduced from #aj to #ae per cent4 ,simple ramming of sand will only reduce it about #f to about #i per cent41 and water about #d to #f per cent41 making the total compression as before stated1 the quantity of water used being some #bj per cent4 of the volume of the sand4 ,embankments of moderate height have been made of sand when no other earth was available1 except clay loamy soil in comparatively small quantities1 the surface of the embankment being worked by thin bars1 and the loam being incorporated with the sand and made to fill its interstices1 surface protection being thus afforded1 and all the usual means to promote consolidation being adopted4 ,wet earth well mixed with a grout of quicklime has also been used to make a firm embankment of little height4 ,clay is not a good material to use unless it is incorporated with a considerable percentage of sand to prevent fissures and to lessen expansion4 ,many prefer the sand to be in the proportion of about two-thirds of the mass1 only one-third being clay2 the soil being then a loam1 and cannot be classed as a clay4 ,there is much diversity of opinion as to the relative value of a central puddle wall or protection of the slope and toe4 ,such a wall is placed in the centre1 not only to give support to an earth embankment and prevent any through leakage1 but also to keep the puddle in a uniformly moist condition1 and therefore to prevent it fissuring and cracking from exposure to the sun or air4 ,in an embankment erected upon an earth foundation it may be advantageous and warrant the expense1 but when the embankment of earth is placed upon rock it should not be erected1 for it is impossible to make a watertight joint between rock and clay puddle1 and should it be placed in a rock trench leakage will not be prevented by it1 and water will accumulate when it does not at once pass through the seat of an embankment until the surface of its base becomes softened1 and the whole mass almost worthless either as a means of support or of prevention of through percolation2 and1 moreover1 there is the danger that the clay will draw away from the sides of the rock4 ,what is wanted is1 as it were1 to insert as far as the top of an embankment an artificial rock having a thorough connection with the foundation1 consequently a ,portland cement concrete wall should be adopted in such a case and not one consisting of clay puddle4 ,two great advantages of a ,portland cement concrete central support over that of a clay puddle wall are that it does not settle and the weight is evenly distributed1 whereas a puddle wall in subsiding may draw away from the earth of the embankment and cause cavities and cracks and consequent leakage4 ,the chief consideration is to produce an embankment having impermeability1 solidity1 and homogeneity1 and a thorough connection at the foundations2 and as the central puddle wall system rarely does so1 and usually only under circumstances which would probably hardly warrant the expense of its adoption1 it is in a state of obsolescence2 and should central wall support be necessary1 which may not infrequently be the case1 ,portland cement concrete is being adopted in its place1 a solid and durable material being used instead of one varying in shape and size1 according to its state of dryness or wetness1 liable to fissure1 and incapable of being permanently and firmly joined to any material4 ,this system may be described as one of arresting the percolation of water in the interior of an embankment2 but the great aim is to prevent any percolation into the mass1 as when once a passage is made the water will escape along the line of least resistance1 and a fissure become a cavity1 a cavity a breach4 ,the protection of the slope and toe has for its object the prevention of any percolation into the mass1 and it may effect all that is requisite1 but its efficiency and completeness much depends upon the preparation and deposition of the layers during the construction of an embankment1 and also the time that can be allowed for consolidation1 so as to prevent any cracking or fissuring of the face covering from settlement of the embankment4 ,it is obvious in the case of a reservoir embankment or a slope alternately submerged and unsubmerged1 that an exposed clay puddle covering cannot be used1 as heat or the sun's rays will cause it to crack1 although if constantly wet it would succeed4 ,a puddled clay covering with a broken stone bed placed upon it to receive dry or mortar-set stone pitching has been frequently adopted2 a simple cement concrete facing about #f to #ab inches in thickness1 depending upon the depth of the water and the nature of the soil1 or in conjunction with an asphalt coating of ordinary thickness4 ,in the two latter cases care must be taken that they do not separate from the embankment either from the force of pent-up water1 frost1 or shrinking of the earth embankment4 ,as any perforation of the surface must be prevented1 in certain districts the covering should be capable of resisting the attacks of rodents and crustacea1 and1 therefore1 a stone pitched or concrete covered slope is necessary1 or the puddle towards the surface must be well incorporated with small stones or ashes or other tough material4 ,in ,european countries the effects of the burrowing of rats may be insignificant1 but in warmer climates1 as1 for instance1 on the coast of ,coromandel and in some parts of ,bengal1 where rats may measure as much as #b feet in length1 their attacks are not to be disregarded with impunity4 ,the causes of failure of water-containing embankments afford an indication of the direction in which especial care should be exercised in their construction4 ,assuming a reservoir embankment to be of the necessary form and bulk1 and to be properly constructed1 the principal causes of failure are as follows3-- #a4 ,leakage along the line of a culvert or pipe passing through the lower portion of an embankment4 #b4 ,leakage under the seat of an embankment4 #c4 ,water overflowing the top and eroding the land slope and so destroying the equilibrium4 #d4 ,bursting of springs over the site4 ,vide ,chapter ,,xii4 on 8boils0 in loose soils4 ,with regard to the first1 the most frequent cause of the failure of a water enclosure embankment2 the culvert or outlet passages have been rendered unnecessary by conducting the waters in a tunnel passage under the seat of the embankment and without interfering with it2 but this method is expensive4 ,one of the causes of failure is the weight of the embankment owing to unequal settlement producing a breach in a culvert1 the probable result of insecure foundations or want of a firm concrete base to the culvert to evenly distribute the weight2 or it being placed upon clay puddle1 which should never be done2 or the embankment being constructed without due care4 ,all culverts should be sufficiently large for a man to easily pass through and should be equally watertight within and without1 for a leakage from the culvert to the bank is equally dangerous1 and means should be provided so that it can be closed in short lengths4 ,reports on the temporary failures of reservoir embankments almost invariably state1 failure occurred from water penetrating between the puddle and the culvert1 from water percolating between the rock foundation and the central puddle wall1 or the embankment gave way as water issued through interstices in it caused by settlement of the masonry outlet passage4 ,careless construction has often been shown by inspection to be the reason of so many embankments yielding along the line of the culvert2 but when the latter is properly designed and built it seldom causes a temporary failure of a well-made reservoir embankment4 ,respecting the second cause of failure1 it generally proceeds from want of care in thoroughly binding an embankment to the solid ground and protecting the toe2 by 8boils0 in the foundations2 or by a porous earth seam1 such as fine sand1 existing under the stratum upon which the embankment is erected becoming a quicksand on flowing water reaching it4 ,in connection with the third1 it may be said that it is not a frequent cause of failure1 as provision is almost always made to prevent it1 but it may occur in a reservoir embankment from extraordinary circumstances1 or in a much less degree from sufficiently high waves being generated upon a lake or impounding reservoir that the top of the bank may be loosened1 and the water dash over it and erode the land slope1 and convert it into a kind of tail-race2 tarpaulins have been temporarily laid upon the surface on an emergency to protect a soft place1 also sand bags and planking to prevent an overflow4 ,in an embankment erected for such a purpose the top width is more severely strained1 consequent upon the greater exposure1 than in a reservoir embankment1 and the height must be sufficient to prevent water passing over it4 ,with reference to the fourth cause of failure1 8boils0 in loose soil and the bursting of springs are referred to in ,chapter ,,xii4 ,when a reservoir is emptied the weight of the water on its bottom is removed1 but the load from the embankment is the same1 and should the ground be soft the embankment may subside towards the reservoir and the bed be uplifted2 hence it may be advisable not to draw off the water unless the bottom is weighted or movement prevented4 ,due regard of the different causes of failure herein enumerated and care in construction1 will reduce to a minimum the probability of a slip or a subsidence in an earth embankment erected to contain or expel water4 ,the temporary or permanent diversion of rivers or streams being so often necessary in public works1 a few paragraphs are here devoted to it so far as regards earthslips and subsidences4 ,if it be possible when the soil is very porous and incapable of retaining water1 it is advisable not to divert a river4 ,some of the most vulnerable places in a newly-formed river-bank are3 ,the ends that join it to the old bank or to the land1 to which it should be thoroughly connected4 ,the toe of the slope and seat1 which should be tied into the bed of the river or be well protected by making the slope flat towards the base4 ,any abrupt bends or angles should always be avoided as they increase erosive action4 ,the wind and water line which requires especial protection4 ,provided these points are remembered and the usual precautions taken in forming a river-bank to make it thoroughly sound and homogeneous1 a slip or subsidence of serious moment is improbable4 ,in order to protect the sandy bed of a river and to prevent the banks slipping and subsiding1 it may be necessary to guard against scour of the bed and consequently of the toe of the banks4 ,stone thrown in will settle and compress the bed by weighting and consolidation4 ,by periodical depositions the sand becomes more protected and the quantity of stone required is reduced1 but especial care should be taken to preserve the normal bed1 to offer no obstruction1 and not to cause whirlpools or to interfere with the current except to direct and train it1 or the erosive action so created will cause movement4 ,stones simply cast in and allowed to sink and find a permanent bed until the regular surface of the bottom of a river is so reached1 have been proved in many instances to be a sure protection in sandy soils provided eddies do not exist4 ,the preservation of the slopes is particularly referred to in ,chapter ,,vii4 ,,chapter ,,xi4 ,,notes ,,upon ,,the ,,failure ,,of ,,dock ,,and ,,other ,,walls ,,from ,a ,,forward ,,movement ,,of ,,the ,,earth ,,filling ,,or ,,backing4--,,consideration ,,of ,,the ,,causes ,,of ,,such ,,action ,,and ,,some ,,preventive ,,and ,,remedial ,,measures4 ,the most serious consequences often result from slips or 8boils0 of sand or loose soil during the construction of docks1 and from the sliding forward or subsidence of quay walls1 as in addition to the great expense of restoring the damaged wall must be considered the loss of receipts caused either by delay in opening the docks or from interference with the traffic4 ,in this chapter no attempt is made to lay down rules and to declare that if they are followed failures from pressure1 subsidence1 or a slip of earth1 can be obviated by careful attention to them4 ,many of the most renowned engineers and contractors throughout the world1 whose scientific attainments and practical knowledge are universally and deferentially acknowledged by those competent to form a judgment1 have had anything but pleasant experiences in the construction of docks and similar works4 ,the two banes of dockworks may be said to be3-- #a4 ,defective foundations4 #b4 8,boils10 or the rushing up of loose soil and water in the foundations4 ,to say that a failure of a dock-wall cannot but be the result of defective engineering is a statement which it would be difficult to substantiate4 ,to disturb the earth below the required depth of the foundations at intervals over the area of such works in treacherous soils in order to ascertain its character would simply be to offer a general invitation to it to commence movement1 vide p4 #bjh4 ,it would be worthy to rank with the erudite report of a local committee formed to declare the best means of preventing floods in a district1 which1 after deep consideration reported3 8,that the committee were of opinion the floods would be permanently removed provided the engineer diverts all rivers1 streams1 watercourses1 and ditches1 to the next valley1 and closes the up-stream hole in the hill1 or causes the water to be discharged elsewhere1 and reduces the rainfall within the limits required from time to time by the inhabitants of the district40 ,inasmuch as it is impracticable to ascertain the exact character and condition of any earth over a large area in such a location as that usually occupied by a dock1 and to be certain that no unstable seams exist1 and as the forces of nature are infinitely more powerful than those of man1 it cannot be said that a failure is absolutely impossible4 ,all that can be done is to render improbable any slip or subsidence by the employment of every known means to promote stability justified by the importance of the work and with a due regard to economy4 ,dock-works are peculiarly liable to slips and subsidences because of their position necessarily being near to the sea1 an estuary1 river1 or lake1 and therefore in usually treacherous superficial soil of an insecure1 water-charged character4 ,the foundations are also at but comparatively little depth below the lowest water-level1 and although they are not subject to the frequent vibration railway cuttings and embankments have to withstand1 they are jarred by blows from vessels and falls of heavy goods1 vibration from cranes and machinery1 and also are liable to be suddenly and unevenly surcharged4 ,the earth backing may also become quickly water-charged1 and a force caused by the tide varying in height has to be considered in earth embankments for docks or reclamation purposes1 particularly in sandy or loose soil1 namely1 that of the foundations being 8blown0 up by the upward pressure of the tidal or permanent head of water above the level of the bottom of the foundation2 thus inside an enclosure embankment1 or cofferdam1 a depth of water of #cj feet would give an upward pressure of1 say1 #jhe ton per square foot1 and when the excavation has extended to a depth of #cj feet an insistent natural weight of a column of sand #a foot square upon the foundation has been removed by the excavation equal to #afe ton1 vide ,chapter ,v4 ,thus the upward and relieved pressure #jhe #afe equals #bej tons per square foot1 #jhe ton of which constantly varies4 ,it is obvious that in very permeable soils1 such as sand1 the hydrostatic pressure will be most felt1 and should the range of tide be considerable the strain upon the earth will change and an active disturbing force be constantly present4 ,this varying disturbing agent must be seriously considered in all dockwork or excavation near the sea or a tidal river1 and also approximate to water1 for there will always be danger of the water percolating1 and when the foundations are not sufficiently deep of their being undermined4 ,the weight and depth must therefore be sufficient to balance or exceed any upward pressure of the water in the soil due to its head level4 ,the bottom of the foundation will almost invariably be below the depth at which water is usually found in the locality1 and it should not be forgotten that sooner or later the earth upon which dock-walls rest is nearly certain to become wet and perhaps saturated1 and that when saturated any additional water must flow away4 ,in sandy or loose soils this may become dangerous4 ,care must also be taken in loose soil that it is not loaded by any temporary works so as to force the earth in any direction1 or a slip will occur and any trenches may become filled1 and every effort should be made to cause equal loading and pressure and to prevent unequal settlement4 ,the selection of the site of a dock is generally confined within narrow limits such as railway connection1 roads1 location of the want of dock accommodation1 currents1 the proper position of the entrances1 c41 c42 nevertheless the nature of the soil should be considered1 for upon a tidal river a few hundred feet one way or other may cause the works to be upon various kinds of earth each more or less treacherous1 and when intermixed perhaps more unstable4 ,even upon one side of a comparatively narrow river the earth may be in a much more stable condition than upon the other2 and when an old watercourse or a dry ditch passes across the site of a dock it must not be disregarded1 as failures and damage have occurred because the same section of a wall was continued throughout4 ,it is then necessary to adopt a system of construction suitable for softer or less stable ground1 and especially so if the wall has to be built upon a firm stratum overlying sand1 as a diminution in the thickness of the bed may cause a settlement and the wall to be pushed forward2 for there is always danger in sandy soils1 unless the superimposed layer is of considerable thickness1 that the latter may be pierced and the whole site be in jeopardy from a flow of the sand4 ,it may be that a dock must be built at a particular place1 although the ground may be full of springs1 the beds inclined1 or a level stratum overlies an inclined bed of rock or softer earth incapable of standing at any but a flat slope1 the whole being an unstable mass1 for the deposits may extend to such considerable depths that to go below them is impracticable2 however1 uniform weighting and consolidation by the deposition of firm soils having insoluble particles will generally make it firmer1 and by compression and admixture will ultimately cause the ground to be more solid4 ,it should be loaded as long as possible1 and the material be deposited beyond the site so as to prevent the outside and less consolidated earth slipping upon the works1 and as it will be disturbed by the loaded portion having subsided it may require slight support upon the lower portion of the slope4 ,when the settlement over the base and the slopes to the original bed is equal and regular and care is taken that the soft soil cannot run1 by a due protection of its surface it can be built upon4 ,the rise of the mud in front and for some distance from the wall is generally from about one-third to one-half of its subsidence when loaded4 ,the rate of sinking and uplifting of the soil should be noticed1 and whether it is equable and the depth to which settlement extends is the same over a considerable area and practically ceases at a certain depth4 ,where a dry dock had to be made upon soft fine sand1 ,portland cement concrete has been successfully used to cover the whole site4 ,in such soils1 to avoid the danger of the bottom being blown up when a dock is empty1 and has not the counterbalancing weight of a ship1 arrangements should be made so that sufficient water is let in to counteract the uplifting force4 ,if it can be avoided it is advisable not to erect a graving dock upon very porous earth1 as the expense of an impervious lining1 whether of ,portland cement concrete or clay puddle1 and of keeping it dry will be considerable2 and when unequal settlement takes place a run of the soil may occur and a slip of earth cause it to become fissured and separated1 especially in an estuary or bay with headlands1 as natural springs may make the sand a quicksand4 ,much depends upon the head1 if the water comes from the adjoining hills it may be so great as to prevent any but a strongly constructed dock1 acting as a watertight box1 being successful4 ,the bearing power of the soil will also be practically the same whether the foundations are a few feet or at a considerable depth1 as the head will be sufficient to make the springs issue1 and therefore disturb the earth4 ,the drainage of the site requires to be carefully deliberated1 and no rules can be laid down1 but the flow of all surface water and springs should be controlled4 ,the chief aim should be rather to prevent water reaching the site than to allow it to be present and then pump it away1 hence it is well to have the deepest sump and all water-raising apparatus1 if possible1 outside the area of the works of art and in the direction of the land or river flow4 ,the first operation in draining the site is to construct the necessary surface drains around it and also the sinking of a sump1 cylinder1 or wells where required1 which to be effectual must be some few feet deeper than the lowest level of the works of construction2 but the depth should be no more than is absolutely requisite1 as the greater the lift of a pump the less the efficiency2 care being taken that the bottom of the sump is sufficiently low that water gravitates to it1 and that the pumping apparatus is at such a height that it cannot be 8drowned40 ,when the soil is of so loose a character that pumping will cause it to 8run10 the bottom can be closed and holes made in the ring and water pumped in through them1 and in addition coarse gravel or broken stone can be inserted to act as a filter4 ,the act of drainage may cause soil that has been full of springs to be entirely free from them1 and cannot but always tend to consolidation1 if only because of settlement and the interstices or fissures being less occupied by water or being reduced in size4 ,in loose soils1 especially at the commencement of pumping operations1 it is advisable that it be not very rapid1 as a quick change of condition may cause the ground to be disturbed too much1 whereas slow pumping may clear the water as effectually and enable the soil to settle to its new state4 ,the location of the sump should be at or about the lowest level of the ground well away from any wall or the dock area1 and on the line of the greatest flow of the land waters or natural watercourse1 thus1 dealing with them before they reach the site of the works4 ,in loose and almost all earth the foundations should be covered up quickly so as to preserve the natural condition of the soil4 ,it is also important to offer every possible support to the earth to prevent initial movement1 and slight assistance may afford the required strength4 ,unless there are cogent reasons to the contrary1 the excavation for dock-walls is better executed in trenches1 the frames of which being struck as the work progresses can be used again2 the wall can thus be supported by the earth on either side1 and no lateral thrust is brought upon the wall until it has set1 and therefore the danger of bringing1 perhaps1 the greatest strain upon it when in an imperfectly solid condition is obviated1 the back and top of the wall being protected from the weather1 and any movement or slip of the earth prevented2 hence a wall should act as quickly as practicable as a monolithic mass1 and the material forming it be thoroughly bonded and set in ,portland cement or the best hydraulic lime mortar1 or be wholly of strong ,portland cement concrete4 ,the trench system of constructing dock-walls1 covered ways1 and all work below ground is the safest to adopt1 and in loose soils or clay that expands and is quickly affected by atmospheric influences1 and where there are buildings or the ground is weighted1 the erection of side walls in trenches1 and then the completion of the invert or arch is often the only way in which the work can be executed4 ,even should the formation be rocky1 and the beds be inclined towards the site1 the short #ae to #bj feet in length trench system is the best to adopt2 and it may be advisable or necessary to work day and night in order that the ground may be left exposed for the least possible time and as machine mixed ,portland cement concrete walls can be erected much quicker than masonry or brickwork1 in such situations it is the best material to use4 ,the excavation for the walls should be confined within the smallest limits1 but no under-cutting should be allowed in the excavation trenches1 or the portion undercut may strain the upper part and cause it to slip and subside4 ,in ,chapter ,,viii4 soft soil or weak ground is referred to1 and as in dockworks this so frequently occurs1 the necessity of making every reasonable provision against undue settlement is apparent4 ,in such foundations the weight upon them should be as equable as possible1 for any excess of load will cause subsidence at that place1 and a large bearing area is required which may not be easy to obtain1 except by increasing the area at the back1 as the face must be nearly straight1 or only slightly curved1 to enable vessels to get alongside1 but the wall should not be the heavier in front as it will aid an overturning movement4 ,any dredging operations should be effected at such a distance that the stability of a wall cannot be impaired1 or a slip of earth may occur1 as the bared soil may commence to 8blow0 or run consequent upon the dredging having relieved the ground of weight and1 perhaps1 removed an impervious covering4 ,a row of sheet piles inserted before dredging is commenced1 if well supported in front1 may be sufficient to prevent movement4 ,in dockwork1 the margin allowed to resist lateral strain being considerable1 walls seldom fail by being fractured from excess of lateral pressure2 but either by vertical or lateral pressure causing subsidence or the whole of a wall to slide forward upon the foundations2 and not from defective form1 workmanship1 or materials2 but from a compressive strain upon the face of a wall caused by a force tending to overturn it2 and1 as a rule1 when a wall inclines towards the face very little more pressure will upset it4 ,generally the foundations are sufficiently firm to support the insistent load1 and the chief cause of failure or undue movement is principally the result of slipping forward and the want of adhesion of the soil and frictional resistance of the wall upon it4 ,how can this forward movement of the earth be prevented8 ,before proceeding to name some means that can be employed it is advisable to remember the cardinal principles of the construction of dock-walls to resist lateral thrust1 because a structure may be so designed as to induce a movement or a slip of earth4 ,they may be briefly stated to be as follows3-- #a4 ,that the maximum weight is not required in the front of a dock-wall but at the back1 in order that the centre of gravity may be as far distant from the face as the exigencies of sound construction will allow4 #b4 ,that the centre of gravity should be as low as possible consistent with the due strength of the upper portions of a wall so as to increase the resistance to an overturning movement4 #c4 ,to have an equal load upon the ground1 and to guard against any extra strain upon the foundations near the face of a wall consequent upon the lateral thrust1 which has a tendency to cause a wall to overturn4 #d4 ,particularly to provide against any forward movement either by having deep foundations1 protective works at the base of a wall1 or by other means4 ,,note4--,it is obvious1 in order to counteract a sliding movement1 that the foundations should be at right angles to the face batter at the base1 and not be horizontal4 ,these inclining inward foundations1 however1 can only conveniently extend for a portion of the width in very thick walls1 but throughout in those of less thickness4 ,when no support is possible in the front of a wall1 such as an extra depth of foundations1 an invert1 or a firm connection between the lower portion of opposite dock-walls1 c41 it is advisable to counterfort the wall4 #e4 ,that the wall should be as symmetrical in form as possible1 particularly upon a soft foundation1 in order to ensure equal loading and settlement1 and that it subsides without a forward movement or tilting4 #f4 ,that it should be homogeneous1 especially when the strata dip toward it1 sufficient provision being made to prevent any lodgment of water at the back4 #g4 ,that it must have the usual margin of stability above the sufficient weight and mass to resist the calculated lateral thrust of the earth and that caused by it being surcharged by buildings1 goods1 cranes1 or machinery1 which may cause unequal and sudden loading and strain2 and to withstand in sidelong ground the additional lateral thrust caused by the inclination of the strata4 #h4 ,that the face be sufficiently perpendicular to allow ships to lay close alongside1 and that it be of the required hardness to resist the rubbing of vessels1 and especially of barges4 #i4 ,that1 when a wall is constructed of different materials1 a complete union is effected of all the parts1 and anything tending to make it of varying strength1 unless exceptionally required1 should be avoided2 such as the junction of lime concrete with ,portland cement concrete1 or the employment of the hardest and strongest bricks or stones and their connection by means of a weak mortar4 #aj4 ,that the resultant of the vertical and lateral pressure of the wall1 whether surcharged or not1 falls well within the middle third of the wall at its base4 ,if not1 the foundations will be unequally strained4 #aa4 ,that any mooring posts or bollards1 gate or sluice chamber machinery be so placed and secured that they cause no serious additional strain upon a dock-wall4 #ab4 ,in soils that expand1 such as the clays1 dry backing should be provided of absorbent and even material capable of compression sufficiently to relieve a wall of severe pressure from the expansion of the earth4 #ac4 ,that selected material be used for the backing1 and that it be raised in layers inclining in a direction opposite to that of the wall1 care being taken that it cannot become water-charged4 ,having briefly referred to a few of the chief principles of construction of dock-walls1 the connection between them and slips and subsidence in earthwork has to be considered4 ,it is seldom a dock-wall fails from insufficient mass or incorrect design4 ,the chief element of danger being imperfect foundations causing a forward movement of the wall1 which may either result in a bulge or a complete advance of the whole section for a considerable distance1 and usually when this forward motion commences it extends for a long length1 and has an apex1 and is not only of a disastrous character1 but also difficult to quickly and permanently restore to a state of stability4 ,the wall may be most carefully designed1 and be amply sufficient to resist lateral thrust due to the pressure of the earth and any load upon the quay1 and nevertheless1 although as a wall it is perfect and unimpaired1 the whole mass from want of sufficient depth of the foundations or hold in the ground frequently slides forward3 and there are few extensive docks that have been constructed in any but the firmest earth that have been free from such a mishap4 ,in order to limit the extent of a sliding movement1 it might be said1 reduce the lengths of the wall and make the unsupported from the front length as short as possible1 and in doubtful earth it may be advisable to abandon all long straight walls and adopt the system of short jetties1 with ample width at their heads for unloading and loading operations1 for a vessel to lay alongside1 for store-house room1 and a double line of rails and the necessary free action of machinery2 so as to avoid the expense of slips pushing forward the wall3 but to do this may almost ruin the commercial prospects of a dock1 for naturally owners and captains of ships will send their vessels where the greatest facilities are offered and the impediments to movement the least4 ,local considerations in each case alone can determine the shortest required clear length4 ,however1 in designing jetties to dock-walls it is advisable to so construct them that they may act also as face counterforts to a wall1 and be located at any apparently weak place so as to give support where it is needed4 ,the chief danger is from variation of the earth in the foundations and the existence of thin seams of an unstable character1 or fissures in rocky soil allowing percolation of water1 most difficult1 if not bordering upon the impossible1 to discover unless by trial pits and borings over the whole area of the site of a dock1 which would be a most unwise proceeding1 as has been previously named in this chapter4 ,the marvellous labours of geologists and others have enabled an accurate opinion to be formed of the locality and the depth at which water and certain minerals are to be found and also to indicate the earths in which fissures and seams are frequent2 but it must ever be impossible for man to absolutely state that no unstable seams or veins exist over a considerable area of ground1 more especially in the superficial beds upon which a dock-wall has to be constructed1 although the probability of their presence may be determined with some degree of precision4 ,the importance of a complete examination of the ground of the site and neighbourhood is imperative1 and particularly of any cuttings and embankments in the locality4 ,in ,chapter ,,ii4 many conditions of earth are referred to in which slips and movement are probable1 but that now under consideration is usually caused by a wall resting upon seams or weak veins of unstable soil2 therefore1 there is danger when a comparatively thin seam of soft slimy earth interposes between the hard bed upon which the foundations may rest and one below the vein2 for1 but a little additional moisture may sufficiently lubricate the surface to enable the firm bed to slide upon it1 the frictional resistance being thereby so reduced that movement results4 ,similarly1 in the case of a seam of gravel overlying clay1 the firm gravel bed may slide upon the clay3 the foundations should then be carried down to the clay4 ,piles at the base driven into the gravel will be of little use2 in fact1 for permanent work1 they are now almost abandoned except for jetties1 cills1 aprons1 dolphins1 c41 for uniformity of support is very difficult to obtain in pilework and cannot be proved to exist2 but piles may be useful to help to sustain a structure until it has taken its permanent bearing and is in possession of its full strength4 ,for purposes of permanent support they are somewhat unreliable1 for failures have happened because of their weakness1 and walls have consequently been overturned2 their chief use is as auxiliary temporary aids to lateral stability1 such as confining concrete or lessening the percolation of water4 ,however1 the earth may be in such a condition that it cannot retain them in position when they are strained1 then they are useless for lateral support4 ,their resistance to horizontal strain varies much with the nature of the soil and not necessarily according to its cohesive power2 for instance1 experiments have shown sand to afford the greatest horizontal resistance2 clay1 less2 and in loose ashes the power is further reduced4 ,when a clay stratum is thin and overlies gravel or sand1 provided the necessary precautions are taken that the sand does not 8boil10 it is better to have the foundations upon the underlying gravel or sand1 as the layer of clay may bulge and slide upon the gravel and thrust out the wall4 ,should a stratum of clay be superimposed upon another of similar character1 it will always be in a damp state conducive to lateral instability1 as there will be two sliding surfaces1 and the upper may be forced forward and carry the wall with it1 and should a seam of sand be interposed it may become 8quick0 and flow away4 ,in such cases the foundations should extend to a safe depth in the lower clay stratum or be below the unstable seam1 and when the depth of silt or unstable soil overlying a firm bed1 as rock1 is considerable1 the well system can be adopted1 provided the bottom is levelled4 ,as seams1 weak veins1 and fissures are so frequently met with the examples might be continued almost ad infinitum4 ,to ascertain whether they exist and their location is one of the primary precautions to be observed1 as dock-walls usually fail from bulging or slipping forward1 causing fracture or overturning4 ,additional weight or increase of the thickness of a wall may not suffice to arrest movement of the base or forward motion of the earth4 ,to place the foundations at a greater depth may be impracticable1 although it may be the best method of restoration2 it then becomes necessary to insert an invert or strut between the walls in a narrow dock1 or in a large dock to attempt to remove the unstable seam in front of the wall and prevent movement of the vein by a curtain-wall1 additional weight1 or other means of consolidation2 or by removing the solid backing1 draining the back1 and the erection of a timber platform instead of the earth1 so that it reposes at its natural slope without creating a thrust upon the wall2 or by having packed rubble filling instead of ordinary solid backing so as to remove or lighten the lateral pressure upon it1 by draining the ground at the back2 or by counterforts from the foundation to the ground level1 at the front of the wall1 especial care being taken to prevent their parting from the main wall4 ,the arched wall system is sometimes adopted for docks1 but as it requires a longer time to construct1 and is obviously more liable to be damaged from settlement and by pressure of the earth and the failure of joints and weak places1 solid walls of ,portland cement concrete with a hard face are more to be desired2 as in such situations a monolithic and equally resisting mass is required1 weight and mass being of importance4 ,the relative bulk of materials for a certain expenditure should be considered1 as it may happen that greatly increased weight and mass may be obtained for no extra expense by the employment of a certain substance4 ,combinations of brickwork and masonry and concrete are being abandoned in favour of one homogeneous material throughout1 and no yet known aggregate fulfils this condition for such work as ,portland cement concrete1 owing to the difficulty of making secure and perfect joints1 although hard brick facing may be necessary to protect the face from wear by the rubbing of vessels4 ,by a judicious adoption of material for a dock-wall in order to give it weight and mass1 and sufficiently deep foundations1 neither counterforts nor other special means of protection against failure may be required1 and slips and movements of the earth may be prevented4 ,in the case of a stratum of soft soil of considerable depth overlying a firm foundation1 dock and quay-walls upon arches1 not exceeding about #cj feet span1 have been successfully erected upon wells sunk in or to the solid ground1 when by reason of the cost it was impracticable to carry a solid wall to the firm ground2 and no slipping1 sliding forward1 or subsidence has occurred4 ,to prevent movement of the earth at the back of a wall pushing or fracturing it and being the cause of a slip1 it may be well to briefly state a few points to which attention should be especially directed4 ,in adopting two systems of design of a wall1 it is advisable that the change of form be gradual and not made abruptly1 or cracks may occur from unequal settlement or load upon the foundations1 and also when a concrete bed is used under a wall a lime concrete layer cannot be firmly joined to one composed of more solid and unyielding material1 such as ,portland cement concrete4 ,similar walls erected upon different soils are not equally strained1 as one earth may scarcely change from the effects of air and water1 and another may vary daily according to the weather4 ,to counteract any overturning tendency1 a wall should have a large bearing area under the face portion1 all projections and heavy copings should be avoided1 or anything that increases the load near the face at the top4 ,weight and width of base and considerable depth of foundations are most important1 for well designed walls when placed upon stable ground have been pushed forward simply from an insufficiently deep hold in the ground2 and the load upon the earth must be within its safe bearing power4 ,a wall should be designed so that its centre of gravity is as far from the face as practicable1 and when it is constructed of stone or brick it is necessary that the joints be as strong as possible1 and be capable of resisting varying strains4 ,should lime mortar be used it is probable it will be partly washed out1 and ,portland cement mortar should always be preferred upon the face1 or water may percolate into the wall and even pass through it to the earth and cause slips and subsidences4 ,counterforts erected upon the outer face of retaining walls are much to be preferred to any placed at the back1 for support at the face is what is required3 in the latter case there is always a chance of their becoming separated from the main wall1 although when so located at the back they are considered to lessen the lateral pressure of the earth by dividing it1 but any reduction caused by friction of the soil against the sides may vary so greatly1 according to the condition and subsidence of the earth1 that it is prudent to disregard it1 and it is well to remember that the pressure may become intensified or uneven upon the main wall by deflection and concentration caused by the counterforts1 the result being the creation of weak and unduly strained places2 it may therefore be better to uniformly increase the thickness of the wall4 ,counterforts of triangular shape on plan have been adopted in order to lessen the lateral thrust by directing it to the sides of the triangles1 their bases being against the wall4 ,it is doubtful whether the thrust of the earth so acts under the usual varying conditions of work4 ,the necessity of mooring vessels alongside a dock or quay-wall prevents the adoption of face counterforts except to a very limited extent2 however1 although the form of a ship permits of only a slight batter for the upper half1 the lower portion may be inclined for a few feet from the bottom4 ,as the adoption of a batter on the face increases the area of the base of a wall and its frictional surface upon the ground1 and tends to lessen overturning movement and undue strain upon the face1 a dock1 quay1 or retaining wall having a batter is to be preferred to one with a vertical face2 in fact1 it acts as a triangular front counterfort1 with the great advantage of being an inherent part of a wall4 ,in foundations of a sandy or silty character1 a dock or quay-wall having wells in the cross section to within a few feet of its base filled with rammed light dry material1 the width of the bottom nearly approaching that of the depth of water1 has been adopted in preference to a solid wall of less thickness1 as affording a wider base1 greater resistance to overturning1 and a reduction of the weight upon the foundations4 ,a slip of the earth backing is frequently caused from insufficient drainage and a consequent accumulation of water behind a wall1 producing such pressure that the friction of the weight of the wall upon the foundations is impaired and the support in front insufficient to resist a forward movement1 therefore the back drainage should receive due attention4 ,when a dock-wall has been thrust forward by the earth it may be a serious movement1 likely to increase and culminate in the destruction of the wall1 or be merely a slight lateral settlement4 ,such slips are usually of considerable length1 and have an apex where the greatest forward motion has occurred4 ,the chief remedies consist in securing the foundations1 supporting the face1 lightening or removing the pressure of the backing1 draining the backwaters and preventing their reaching the wall4 ,provided a wall is intact and not damaged1 but solidly and horizontally pushed forward1 it need not be taken down1 but if vertical subsidence has taken place1 or a settlement1 at the face only1 it is generally of serious importance1 and it may be necessary to remove and replace it4 ,when a wall bulges slightly from the pressure of the earth at the back and then ceases to move1 the ground behind may have become in a state of permanent equilibrium1 and the lateral thrust1 which before movement was too great1 may be so reduced that in the altered position it may remain stable1 provided the void is filled with light porous backing1 and the drainage of the earth receives due attention4 ,counterforts of piles reaching to the level of the ground in front of the face have been adopted to arrest and prevent a forward movement1 but when the ground is much disturbed and in a loose state1 it is unadvisable to drive piles because of vibration which may induce further motion4 ,instead of timber pile counterforts1 trenches might be cut at intervals along the toe and be filled with quick-setting cement concrete1 the filling to follow the excavation as closely as possible1 and no unsupported earth to be allowed to remain4 ,as improper backing often induces a slip and subsidence of the earth and the failure of a wall1 it is of importance that it should be carefully executed1 for many well-designed walls have failed or bulged from being badly and hurriedly backed with unsuitable and soft retentive material in a deteriorated condition1 the result being movement of the earth4 ,care should be taken that the material of which the backing is composed will always maintain the slope of repose upon which the calculations have been based that determined the dimensions of the wall2 therefore1 it should always have an angle of repose which is not much affected by moisture4 ,it is important to remember that according to the nature of the backing so will be the pressure upon a wall1 depending principally upon the coefficient of friction of the earth upon similar earth1 its cohesion1 its friction upon the surface of the back of a wall1 the inclination of the layers1 the general character of the soil and the effect of moisture upon it2 and no vegetable1 decayed1 or 8made0 earth should be used for such a purpose1 nor material which gives a varying thrust according to the state of dampness or dryness1 and the lightest dry1 firm1 and stable earth should be preferred4 ,when rubble backing is adopted and is carefully packed1 the lateral thrust may be greatly reduced1 as in some degree1 instead of backing a dry wall may be considered to have been built at the back of the face wall4 ,clean ashes are an excellent material for filling damp places in a wall1 because they not only absorb moisture1 but are light1 and stand permanently at a slope of about #a to #a ,,to #a to #a1 but they can seldom be obtained in sufficient quantity to be used in considerable masses2 also broken bricks and burnt ballast1 although heavier1 make good backing4 ,earth that is much affected by air or water1 or that expands1 contracts1 or fissures1 such as clay1 is not good for filling1 and dry masonry retaining walls should not be hacked with earth but with rubble1 or in countries with a heavy rainfall the wall will most probably be forced forward4 ,care should be taken to have plenty of weep-holes in a wall so as to obviate any accumulation of water1 and it is well if the back has a rough face in order to increase friction and prevent cavities in the backing down which water may percolate4 ,during construction a few weep-holes in a dock or quay-wall should always be provided1 until the water is to be let in to a dock1 when it is best to fill them with strong ,portland cement concrete as water would proceed along them from the face and accumulate at the back of a wall2 the permanent drainage being affected by other means4 ,in pulling down walls that have been built with offsets at the back it will usually be noticed that the filling does not rest upon them1 but that hollows occur as the earth subsides2 for this reason1 a straight batter at the back is to be preferred4 ,no support from the weight of the earth1 which is supposed to be upon them1 should be relied upon1 although it may temporarily exist4 ,the filling should be commenced at the wall1 and the layers be so deposited that their slope approximates to that of being at right angles to the surface of the slope of the ground rather than parallel to it4 ,when thought desirable and the natural ground is solid1 it can be benched1 and the backing be damped and rammed4 ,the backing of a wall may consist not only of an inverted triangular piece of earth1 but extend for some distance to the rear1 and may have a top surface at a considerable height above it2 the wall will then have to sustain a severe thrust4 ,the angle of repose of the earth should be ascertained and the filling be thoroughly drained1 or it may be disintegrated by moisture1 the whole mass gradually become unstable1 and finally push the wall forward with great force4 ,,chapter ,,xii4 ,,notes ,,upon ,,slips ,,of ,,earth1 ,,subsidences ,,and ,,movement ,,in ,,foundations ,,caused ,,by 8,,boils0 ,,or ,,an ,,upward ,,rush ,,of ,,water ,,in ,,loose ,,earths4--,,consideration ,,of ,,some ,,precautionary ,,and ,,remedial ,,operations4 ,with regard to 8boils0 in sandy soils and the general drainage of the site of dockworks1 operations should be commenced as long as possible before the works of construction1 so as to lessen the probability of the occurrence of slips1 subsidences1 and movement of earthwork4 ,in order to reduce infiltration1 it is well to make a trench round the area of any ground that has to be excavated1 which may embrace the whole site4 ,a system of drains and conduits should be established within it1 and at the lowest level a sump at a convenient position1 and to a depth a few feet below that of the work2 it can then be made the chief pumping station of the dock2 but all drawing away or flow of the earth must be prevented3 and to obviate erosion of the drains1 they may require to be rough lined with an impervious covering such as clay4 ,the sump should consist of an iron cylinder with proper provision against a run of soil4 ,in all loose earths the pumping station should be some distance from buildings or roads so as to avoid any settlement4 ,when a choice of sites exists and the position of a dock is not absolutely fixed1 it may be possible to have the foundations of the whole work in one kind of earth2 if otherwise1 one portion may be stable and another unstable1 always treacherous1 and liable to slip and subside4 ,in any case settlement is not likely to be equal1 and therefore a foundation which is well able to sustain an evenly distributed load may yield from unequal strain and excess of lateral thrust4 ,consequent upon the situation of docks1 the superficial beds upon which they have to be erected frequently vary in stability and reliability2 and the location being altered in any direction may result most seriously2 the earth upon one side of a comparatively narrow river being stable in character and on the opposite bank most treacherous4 ,difficulties often arise in foundations1 especially in sandy soils1 from making borings and trial pits too near the important parts of the work2 they should be made as reasonably far away as is convenient4 ,in boring1 a sand flow may occur1 when it may be necessary to fill the bore-hole and sustain the soil by a covering1 or by consolidating the sand by means of ,portland cement1 and then1 perhaps1 reliable operations may be continued4 ,borings should be considered as unreliable if merely superficial2 in any case of importance they should only be trusted for the place where they are made1 and not as indicating the nature or condition of the soil over a considerable area4 ,when pits cannot be sunk1 it is desirable that in a suspectedly treacherous site the bore-holes should be at every #bjj or #cjj feet4 ,excavating pits1 using test-bars1 and driving piles are some of the methods of determining the character of foundations1 but care should be taken to ascertain in boring that boulders1 or thin strata of hard gravel1 are not mistaken for solid rock4 ,in sand1 mud1 or soft clay they can be made by means of an iron pipe and the water-jet system4 ,experience has proved that boring with an auger is not so reliable as boring with a tube1 such as is used for artesian wells4 ,in the case of augers1 when boulders are encountered1 further boring is usually arrested in that place and another bore-hole has to be commenced4 ,trial pits1 where practicable1 should be preferred to boring1 and they should be sunk to a depth considerably below the lowest level of the intended foundations1 and then they may do for sump holes for pumping operations4 ,in testing ground by borings1 several should be made1 as one hole might encounter a boulder or some hard soil1 such as indurated clay1 and the latter may adhere to the auger and arrest its progress2 the specimens then brought up1 being crushed and pressed together1 will appear to be firmer than the actual condition of the ground4 ,having briefly referred to the preliminary drainage1 and some methods of ascertaining the nature of the ground1 the former to lessen1 and the latter to aid discovery of the character of any probable upward lushes of soil3 8boils0 in foundations are more specifically considered4 ,it may be said that they generally proceed from an impervious top stratum being pierced1 thereby tapping the water in a pervious bed which may be imposed upon another impervious layer2 for the upper bed being excavated removes the weight upon the lower strata and induces a flow of the previously confined water4 ,the source of disturbance may be either from surface-water in the top soil or from deep underground springs1 depending in great measure upon the extent of the catchment area and head-water level of the district1 as its quantity and uplifting pressure will be principally governed by them4 ,when the soil is in a delicate state of equilibrium it only requires a slight deteriorating alteration of the normal condition to initiate a movement4 ,the disturbance of the ground may be merely superficial1 nevertheless its effect may be sufficient to start a 8boil10 although the chief cause potently exists at some considerable depth and distance4 8,boils0 produced by simply surface-water require one system of treatment2 if from underground waters1 another remedy is necessary4 ,every effort should be made to know the reason1 trace the origin1 and to ascertain the power of the disturbing forces4 ,it may be possible to determine them1 although generally it can only be done by deductive reasoning and logical inference4 ,in any event immediate action is invaluable when a 8boil0 appears4 ,weighting the ground around a 8boil0 with an impervious mass of clay1 and the insertion of a stand-pipe will indicate the level to which the water will rise1 varying according to the seasons1 and will give an approximate idea of the head supply and pressure2 care being taken that the pipe does not become obstructed and that the water has a free flow4 ,it may also be ascertained by the insertion of pipe-rods to different depths1 and by noticing the effects1 such as the rapidity1 the quantity and the character of the discharge4 ,there may be an appreciable difference in the height to which the water rises in various stand-pipes2 if so1 its flow is obstructed or the source is not identical4 ,an examination of the colour and nature of the suspended matter in the water and a comparison of it with the strata may show its source1 but it is not always reliable unless the same colour is maintained for the lowest depths4 ,a perusal of ,chapter ,,ii4 will indicate some situations in which 8boils0 may be expected4 ,the conditions under which they may appear are so numerous that it may be stated they generally occur in any situation when a layer of loose soil has a superimposed bed of more or less impervious boil upon it which is perforated by the excavation for a dock or other work2 and especially should a water-bearing stratum1 such as chalk1 underlie a sand stratum2 also when a water-bearing stratum is superimposed upon sand which lies upon an impervious bed such as clay1 as water will percolate to the sand2 and when sand overlies a water-charged stratum2 or at the outcrop of chalk hills near the site2 or where sand is below an impervious layer of clay and the latter is tapped4 ,the 8boils10 of course1 become more serious as the head of water increases1 and also when the strata dip towards the site4 ,an impervious bed may be of such thickness1 that when the lowest foundation is excavated there may be no fear of water from any underground source being forced up through it2 however1 unless the thickness of the upper layer is known to be nearly uniform over the site of a dock1 which is seldom the case1 the water pressure1 aided by the weight of the structure1 may separate or loosen the soil at a weak place1 and then a 8boil0 will be the result4 ,the thickness of the crust required1 which may be anything from about #ae feet upward1 may be approximately ascertained by weighting the earth considerably above the load it will permanently have to sustain1 and by watching the subsidence and general effect4 ,great care should be taken not to perforate the firm stratum1 as danger will at once ensue should loose soil1 such as sand1 be tapped1 for cavities will then be produced causing subsidence1 probable fracture of the firm stratum1 8boils10 and slips of serious extent4 ,when a heavy structure has to be built upon such a soil1 and it is impossible because of the expense to place the foundations except upon this superficial bed1 experiments in the direction indicated should always be made1 and any other means of proof that circumstances may allow other than by perforation of the stratum3 in any case every effort should be made to reliably ascertain that the firm stratum is of uniform depth and character4 ,the discharge channel of any underground waters likely to disturb the foundations should be discovered1 and when there are adjacent hills1 by tracing their dampest part the probable direction of the surface flow may become known4 ,inquiry should be made to find out whether any borings have been made over the site in order to determine if the 8boils0 have been artificially created or are natural blow-wells1 in which the water rises over the top and can1 perhaps1 be led away by gravitation4 ,it is advisable to fill every bore-hole with ,portland cement mortar before any excavation is commenced1 or they will burst out when the surrounding ground is disturbed4 ,bags containing shot have been used to help to close a hole1 but a preferable method is to insert a pipe down the bore1 it having been previously cleared of all dirt2 and to fill it with neat ,portland cement mortar1 the tube being raised as the hole is filled4 ,such a method1 although successful with small holes1 is useless in the case of 8blows0 of the ordinary size4 ,a permanent shaft or cylinder is then necessary4 ,with regard to the treatment of 8boils0 in foundations1 when in the possession of the information hereinbefore named it may indicate a remedy either for 8boils0 in which the cause of disturbance is at a considerable depth and the head and fall of water moderately large1 or when the agitation is merely superficial1 which may result from the range of the tidal waters or the want of surface drainage4 ,when a 8boil0 is of the first order1 it is useless attempting to simply stop it by force and prevent the issue of water1 as such a method of procedure would result in merely diverting the disturbance1 and in addition leave a weak place in the foundations2 however1 if many 8boils0 appear1 and the disintegrating agency of the water is removed either by conducting or diverting the flow from the site1 they can then be filled1 and it should be simultaneously effected1 or any mere exudation in the whole of the 8boils0 may become increased in one or two to a flow sufficient to cause a slip or instability1 and any concentration of the discharge may produce movement of the ground4 ,small springs or 8boils0 have been sufficiently arrested by depositing clay over them1 excavating it1 and putting in the foundations very promptly and before the 8boil0 burst out again2 such treatment1 however1 may lead to the backing of a wall becoming saturated and the water being dammed up3 on the other hand1 the 8boil0 may be sealed and the water flow away in the original underground channels2 also when a 8boil0 is tapped it may induce an increased flow of the underground waters1 for they will find the course of least resistance2 and should they reach a fine sand stratum will filter through and set it in motion1 provided the head is sufficient to overcome friction2 and the support rendered to any overlying stratum will therefore be destroyed4 ,in the event of there being only one 8boil10 but that of important extent1 perhaps the best way to proceed is to place clay upon the surface for a few feet around it1 the weight of which should not be less than the normal pressure of the earth removed by excavation1 vide ,chapter ,v43 and by the insertion of a cylinder1 with a properly designed bottom1 to prevent the issue of soil to a level some feet below the lowest intended excavation upon the site1 or to the depth at which the greatest flow of water is obtained2 care being taken that no run of sand or soil is allowed and that the water is not charged with earth1 either by a thick gravel layer until the sand ceases to pass through it1 or by other means1 remembering that the motive power of running sand is that of the pressure of water4 ,the flow should be gently led away1 if necessary1 to a sump1 and discharged by pumping1 thus draining the works4 ,the sump should always be lined1 not only to prevent any flow upon or into the surface causing saturation1 but so as to control and regulate the water some feet below the lowest level of the foundations1 the great point being to draw downwards the water from the earth and then to carry it away4 ,an iron or wooden cylinder sump is to be preferred to one constructed of sheet piles or timber-lined1 as the soil may be so loose that any shaking or vibration should not be allowed1 and a close joint is not easy to attain in timber pile work4 ,it is well to deposit some clay puddle for a little distance round the sump after sinking it in order to weight the soil and steady the cylinder4 ,when a discharging outlet has been made it should be maintained in perfect condition1 or a slip or subsidence may occur from leakage or diversion of the flow4 ,it may also happen that no discharge is necessary1 for if the 8boil0 is only1 as it were1 of local extent and caused by a weak vein in otherwise stable soil1 the water may rise to the head level and there remain2 the equilibrium being restored which had been destroyed by reason of the upper strata of an impervious character being excavated4 ,the removal of the normal pressure upon the loose soil to some extent1 liberates the water1 and the head ceasing to be balanced by it1 the earth cannot do otherwise than allow water to upraise it4 ,a calculation of the weight of the earth removed may give an indication within which will be the probable head level of the supply1 and usually it is much below a head of water that would equal the normal pressure of the soil4 ,supposing the weight of the earth to be twice that of water1 when #aj feet of soil is excavated before a 8boil0 began1 its removal would approximately be equivalent to a #bj feet head of water4 ,the great point is to confine a 8boil0 within a certain space1 and there to treat it and so prevent the appearance of others and interruption to the prosecution of the works4 ,all agitation of the surface of sand1 especially when a 8boil0 appears1 must be prevented1 as inducing a disturbed and more porous condition4 ,when the seat of a 8boil0 must be built over1 the well system of foundations can be used as not only affording reliable support1 but also preventing a 8boil0 extending1 and allowing the flow of water to be discharged1 care being taken that complete connection is made with a wall constructed upon any other principle4 ,if 8boils0 appear over a considerable area1 it is evident that the disturbance is general1 and may either be because the site or the foundations of the works are below the level at which water is usually found in the district1 or be produced by the rise and fall of tidal waters4 ,when by the former1 drains are required a few feet below the general water-bearing level1 and they should intercept the percolation of the land waters and conduct them from the site of the works1 or so gently localize them that they can be treated as before described4 ,the land waters are the most troublesome because their volume1 time of appearance1 and duration of flow will vary1 whereas the range of the tidal waters is known1 and therefore the effects may be ascertained with some approach to accuracy4 ,it may be impossible to erect walls in very loose soils without encircling the site with sheet piles to prevent a run of sand1 to lessen 8blows0 and to reduce the disturbance1 as placing them upon an impervious stratum maybe prohibitory because of the expense3 but the adoption of the well system of foundations down to a firm stratum1 or at a sufficient depth to be stable1 and the building walls thereon may cause the temporary pile support to be unnecessary and prevent a slip or subsidence4 ,quick erection and the least exposure or disturbance of earth are essentials in such cases4 ,by the use of ,portland cement concrete1 foundations can now be cheaply obtained with the ground in a wet condition1 which in the days when it was considered only suitable for secondary works1 would have required the employment of expensive methods of construction4 ,it may be unwise to arrest the upward flow of the tidal waters in loose soil except by intercepting1 lessening1 or preventing it by shore protection1 for the upward pressure of the head of water may 8blow0 up the earth and cause disturbance2 on the other hand1 should the 8boils0 be merely superficial and the head very little1 a thick watertight covering of ,portland cement concrete1 when accompanied by the necessary drainage operations1 may suffice2 the surface water blows being covered1 and the pressure of the water being overbalanced by the superimposed weight4 ,all works to prevent 8boils0 or to drain waters from the site should1 if possible1 be executed prior to the excavation1 as the effect of draining can then be observed and whether any 8boils0 arise from land waters or from a tidal flow1 and the earth will have had some time in which to subside and become consolidated4 ,a month's test will afford some criterion in a variable climate and when changes of weather are frequent2 but should a long period of drought prevail it may be no indication of the state in which the earth would be in a wet season1 or under ordinary meteorological influences2 and further1 the land waters may take a considerable time in flowing to the shore1 depending upon the catchment area1 character of the soil1 position of the beds1 whether the district is drained or not1 and many other local conditions4 ,when the soil is firm clay1 the locality of any leakage or water seam in it will usually be indicated by surface exudation over the water-charged vein2 also in nearly all compact earth1 particularly if of a clayey or loamy nature1 and therefore the seat of disturbance may not have to be discovered as in looser or sandy soils4 ,should a water-bearing fissure occur in rock and it be necessary to stop it1 there being no danger of diverting the flow to another place upon the site of the works1 it can be done by means of neat ,portland cement mortar pressed down and kept in place by timber strips1 weights or other means until it has set2 the face of the fissure should be made as clean as possible1 and the water-bearing seam be filled and weighted directly a leak appears1 or the flow may become much increased and accelerated and a current of water be induced which may become of serious extent4 ,to avoid slips and movement of the ground when it is necessary that a water-charged bed of sand be excavated to enable a structure to be built upon a firm impervious stratum below it1 sheet piles can be used or corrugated iron sheets1 strutted at intervals1 so as to prevent a run and slip of sand2 and the space between them can be excavated1 a ,portland cement concrete foundation being inserted upon the firm soil1 the wall being erected in lengths1 and the piles or case being practically three-sided so as to leave no unsupported surface of sand1 care being taken to prevent any run between the front and the back of the last built length of wall and the earth1 so that each length is erected in a contained area4 ,,index4 ,a4 ,absorption1 broken earth1 #gj ----1 chalk1 #bi ----1 sand1 #cd ,alignment of public works1 vide location1 #i-ab1 #adf ,alluvial deposits1 safe load upon1 #hh-hi ----1 soil1 slope1 #ajj ----1 protection of the banks of rivers1 #abf ,angular particles in earth1 #cf ,approaches to culverts1 #hd1 #he ,arched system1 dock-walls1 #baj1 #baa ,argillaceous rocks1 slopes1 #bd ,ashes1 slope1 #ajj ,atmospheric pressure1 influence of1 #ag ,b4 ,backing1 dock-walls1 #bad1 #bae ,ballast1 upon soft soil1 #hb1 #aea ,basalt1 #ah ,beach1 artificial slope1 #ahj ----1 natural slope1 #ajj1 #aja ,benching ground1 #afj1 #afb ,blue clay1 #ch1 #hi ,bog-land1 safe load upon1 #hh ----1 sustaining power1 #aeb ----1 treatment of1 #adi-aea 8,boils0 in foundations1 ascertaining character of1 #bah1 #bai1 #bbd ----1 disturbance of soil1 #bah1 #bbj1 #bba ----1 origin and source1 #bah1 #bai1 #bbc1 #bbd ----1 treatment of1 #baf1 #bah-bbe 8,boils0 in foundations1 well system of foundations for1 #bbc ,borings1 effect of1 #bag1 #bbj ,boulders1 #bb ,breakwaters and piers1 foundations of1 #aha1 #ahb ,brown clay1 #ac1 #db1 #dc ,bulging of ground1 #adg1 #adh ----1 of walls1 #bjg1 #bac ,burning1 slipped earth1 #fb1 #fc ,c4 ,canal and similar earthworks4 ----1 admittance of navigation water1 #aij ----1 clay and loamy soils1 #aij ----1 concrete wall1 #aic ----1 consolidation1 #aij-aib ----1 drawing off water1 #ahh1 #aif ----1 failure of1 #h1 #aid-aif ----1 leakage in1 #ahi ----1 peat and bog1 #ahg ----1 precautions1 #aij1 #aic ----1 preparation of foundations1 #aia ----1 protection of surfaces1 #ahh1 #aib-aid ----1 puddle wall1 when objectionable1 #aib ----1 sand1 #ahg ----1 selection of earth1 #aia1 #aib ----1 ---- location1 #adf1 #aij ----1 time of occurrence of slips1 #aij ,catchwater drains1 #gf1 #gg ,causes of slips and subsidences in earth4 ----1 principal1 #h ,causes of slips and subsidences in earth1 universality1 #a ----1 variety of1 #a ----1 water1 the chief cause1 #h ,causes of slips in cuttings and embankments1 enumeration thereof1 #b-h ,chalk1 absorption of1 #bi ----1 affinity for water1 #bh ----1 angle of friction of water in1 #bh1 #bi ----1 characteristics of1 #cj ----1 classification for earthwork purposes1 #ca1 #cb ----1 cohesion of1 #ca ----1 cuttings in1 #cc ----1 difficulty of draining1 #bi ----1 discharge of water in1 #bi-cj ----1 faults1 crevices and pot-holes1 #bh ----1 flints in1 #bh ----1 magnitude of many slips in1 #cb ----1 mutability of1 #bi ----1 non-water bearing1 #cj-ca ----1 pressure on1 effects of1 #cc ----1 safe load upon1 argillaceous1 #hi ----1 ---- white1 #hi ----1 separation1 danger of1 #bh ----1 slopes1 #bg1 #ajj ----1 treacherous condition1 #ca ----1 ---- soil1 #ac ----1 treatment of springs in1 #bi ----1 tunnel entrances in1 #cb1 #cc ----1 use as drains in other soils1 #bh ----1 varieties of1 #bf1 #bg ----1 veins and seams in1 #bi ----1 water-bearing level in1 #cj ,classification of earths1 #bc1 #cf1 #df ,clay1 beds of1 #da1 #db ----1 characteristics of1 #cg1 #ch1 #dj-dc ----1 classification of1 #df ----1 condition of stability1 #ci ----1 contraction of1 #ch1 #ci ----1 expansion of1 #cg1 #ch ----1 fissures and cracks in1 #ch1 #ci ----1 humid1 #da ----1 load upon1 blue1 #hi ----1 ---- damp1 #hi ----1 ---- diluvial1 #hi ----1 ---- intermixed beds1 #hi ,clay1 load upon1 muddy1 #hh ----1 ---- solid1 #hi ----1 ---- upheaved beds1 #hi ----1 ---- wet1 #hh ----1 ---- yellow1 #hi ----1 mud mistaken for solid clay1 #db1 #dc ----1 notes upon1 blue1 #ch1 #ci ----1 ---- boulder #ac1 #db1 #dc ----1 ---- brown1 #ac1 #db1 #dc ----1 ---- gault1 #dc ----1 ---- lias1 #ac1 #ci ----1 ---- marl1 #de1 #df ----1 ---- mica in1 #dc ----1 ---- red1 #dc ----1 ---- rock1 #bb ----1 ---- sandy1 #ci-da ----1 ---- slate1 #ah ----1 over-draining it1 #ci ----1 protecting the surface of1 #dj ----1 slopes1 #ad1 #df-di1 #ajj1 #ajh ----1 testing character of1 #dj1 #da ----1 time of slip in1 #dc ----1 underground excavation in1 #di ----1 weakness in1 #dc1 #dd ,cohesion of earths1 general consideration1 #ad1 #aje1 #ajf ----1 values1 #ajf ,concrete blocks1 slopes of1 #aja ,condition of earth1 worst1 #af ,configuration of ground1 influence of1 #ah ,consolidation1 soft soil1 #adh1 #adi1 #aec1 #aed ,continuous surface1 value of1 #hg ,counterforts1 earth1 #eg1 #eh1 #fa1 #aba ----1 in slopes1 #aai-abb ,covering1 nature of1 #abb1 #abc ----1 slope1 #abb ,crumbling of the surface1 #b ,crystalline rocks1 #ba ,culverts1 approaches to1 #hd1 #he ----1 design of1 #he ----1 failures of1 #aie ----1 form1 #hc1 #hd ----1 general considerations1 #hc1 #hd ----1 influence on slips and subsidences in earthwork1 #hc ----1 special systems1 #he1 #hf ,cuttings1 causes of slips in1 #b-e ----1 side1 #aeg ----1 slips in1 require separate consideration1 #b ----1 vibration in1 #acf-ada ,d4 ,deposition of embankments4 ----1 effect of1 #afa ----1 failure of1 #afg ----1 form of tip head1 #afh ----1 general1 #aef1 #aeg1 #aei ----1 height of tip1 #afc1 #afd1 #afe1 #aff1 #afg ----1 junction of high embankments1 #afd1 #afe ----1 long lead1 #afc ----1 method of1 on soft soils1 c41 #aed1 #aee ----1 precautions in the1 #aeg1 #aeh1 #afa1 #afb ----1 preparation of ground1 #aei1 #afj ----1 from side-cutting1 #aeg1 #aeh ----1 side tipping1 #afg1 #afh ----1 specifications1 impracticable1 #aef1 #aeg ----1 steam navvy and the1 #afi1 #agj ----1 systems of1 #aei1 #afa-afd1 #aff-afi ----1 weather influence1 #afg ,depth1 influence of1 in cuttings1 #hg ----1 ---- embankments1 #hg ----1 ---- foundations1 #hi1 #ij ,diluvial soil1 safe load upon1 #hi ,diversion of land waters1 #ae ----1 ---- rivers1 streams c41 #aif1 #aig4 ,vide ,,river4 ,dock earthworks4 ----1 ascertaining nature of soil1 #aih1 #aii1 #bjh-baj1 #bag1 #bah ----1 8,boils0 in foundations1 #baf4 ,vide 8,,boils40 ----1 causes of slips and subsidences in1 #c-h ----1 difficulties of construction1 #aih-bjj ----1 ditches and watercourses1 #bja ----1 drainage of site and pumping of water1 #bjb1 #bjc1 #baf1 #bbd ----1 execution of1 #bjc1 #bjd ----1 foundation1 #bja ----1 liability to slip1 #aii-bja1bjd1 #bje ----1 location of1 #bjj-bjb1 #baf1 #bag ----1 pressure of water in1 #aii1 #bjj ,dock-walls4 ----1 arched system1 #baj1 #baa ----1 back drainage1 #bac1 #bae ,dock-walls1 backing1 #bad1 #bae ----1 bulging1 #bjg1 #bac ----1 construction of1 #bje-bjg1 #baa-bac ----1 counterforts to1 #bab ----1 jetties as face counterforts1 #bjg1 #bjh ----1 material1 #bjc1 #baj ----1 piles1 use of in1 #bji ----1 ,portland cement concrete wall1 #bbc ----1 prevention of movement in1 #bjg-bab ----1 repairing a slipped wall1 #bac1 #bad ----1 sliding forward of1 #bjg1 #bjh1 #bac ----1 well system of1 #bbc ,drainage1 ballasting1 #hb ----1 catchwater drains and ditches1 #gf1 #gg ----1 chalk1 #bi ----1 clay1 #gc-ge ----1 controlling discharge1 #gd ----1 counterforts and trench drains1 #gg-hj ----1 culverts1 #hc-he ----1 equable1 necessary1 #aej ----1 field drains1 interception of1 #gg ----1 filling of trench drains1 #gh1 #gi ----1 formation1 #ha1 #hb ----1 mixed soils1 #gb ----1 number and depth of drains1 #ge ----1 object of1 #fe1 #gb1 #gc1 #ha ----1 overflowing earthworks1 #gd1 #ge ----1 peat1 #gg1 #adi1 #aej ----1 sand1 #gg1 #hj1 #ha ----1 seat of an embankment1 #hb1 #hc1 #he1 #hf ----1 slope drains1 #gg-hj1 #aaa1 #aab ----1 soft soils1 #gc1 #adi1 #aej ----1 spoil banks1 #hj ----1 springs1 #ge1 #gf1 #hj1 #ha ----1 systems required1 #gb-gg1 #hj1 #ha ----1 well system1 #ha ,drifts of snow1 protection against1 #aca-acd ,drift soil1 treacherous1 #ac1 #ah ----1 ---- upon sidelong ground1 #adc-ade ,e4 ,earths1 preservation when loaded1 #hh ----1 maximum safe load upon1 #hg-ia ----1 table of weights of1 #ib ----1 treacherous1 #ac ----1 universality of slips in1 #b ,effect of a slip1 cuttings1 #ej ----1 embankments1 #ej ----1 influence of depth of cutting and height of embankment1 #ej1 #ea ,embankments1 ballast upon1 #aea ----1 causes of slips and subsidences1 #b1 #e-h ----1 condition of earth1 #ig ----1 consolidation of soft soil1 #adh-aea1 #aec-aee ----1 consolidation by time1 #ag ----1 deposition of1 #aef-aei1 #afa-i ----1 deposition1 from side cutting1 #aeg1 #aeh ----1 depositing upon soft soil1 #aed1 #aee1 #afh1 #afi ----1 deterioration of excavated earth1 #ic1 #id ----1 drainage of the seat of1 #afj1 #afa ----1 failure of1 #afg ----1 fascine mattress bed1 #aee ----1 forming1 #aeh ----1 height1 safe1 #ia1 #ib ----1 ---- of tip1 #afd-afg ----1 high1 #ie ----1 homogeneousness1 #aeh ----1 junction of1 precautions1 #afd1 #afe ----1 long lead1 #afc ----1 precautions in deposition1 #aeg-aei1 #afa-afc ----1 preparation of ground1 #aei-afa ----1 safe maximum heights of1 #id-if ----1 safe load upon1 #hh1 #ic1 #id ----1 sidelong ground1 #adb1 #adc1 #ade ----1 side tipping1 #afg1 #afh ,embankments4 ----1 soft soil1 #adg-adi ----1 specifications1 impracticable1 #aef1 #aeg ----1 steam navvy1 influence of1 #afi1 #agj ----1 systems of deposition1 #aei1 #afa-afi ,embankments1 tip head1 form of1 #afh ----1 vibration1 effects of1 #acf-ada ----1 weather influence during deposition1 #afg ,estuary or shore embankments4 ----1 closure of1 #agg ----1 deposition of1 #agf-agg ----1 design1 #aga-agc ----1 effect of erection1 #agc1 #agi1 #ahj ----1 excavation for1 #agf1 #agg1 #ahg ----1 height1 #agi ----1 material1 #ahg ----1 pressures1 calculations showing changes of #ahb-ahg ----1 protection of slope1 #agd-ahj ----1 shore deposit protection1 #agf1 #agg ----1 site1 #aga ----1 slope1 form of1 #agd1 #ahj ----1 trestle work1 and on sea-shore1 #ahj ----1 viaducts and1 #agb1 #agc1 #ahj ,f4 ,fascine covering of slopes1 #abh1 #abi1 #agh1 #agi ,field drains1 interception of1 #gg ,fissures in slopes1 #abg1 #abh ,flint1 beds in chalk1 #bh ,flood-waters1 protection against1 #eg ,foot of slope1 general considerations1 #aae ----1 protection and preservation1 #aae-aca ,formation1 special form of1 #aei ,formation width1 ballast1 #aea ----1 influence of1 #acd1 #ace ----1 junction of embankments1 #acf ----1 lateral settlement1 #ace ----1 severe climates1 #acd1 #ace ----1 sidelong ground1 #adc ----1 temperate climates1 #ace ----1 value of width1 #acd1 #ace ----1 wet cuttings1 #acd 8,forming0 embankments1 #aeh ,friable rock1 slopes1 #bd ----1 chalk1 slopes1 #bg ,friction of earths1 effects of water on1 #ajc ----1 general considerations1 #aja-ajc1 #aje1 #ajf ,friction of earths1 necessity of relying upon1 #aje1 #ajf ----1 relation to slope1 #ajb ----1 table of slopes calculated from coefficient of friction1 #ajd ,g4 ,glacial deposits1 treacherous1 #ah ,gneiss1 slopes1 #bc ,granite1 slopes1 #bc ,grass1 covering slope with1 #abb-abd ,gravel1 angularity and roundness of particles1 #cf ----1 ascertaining character of1 #cf ----1 boulder1 and gravel and sand1 safe load upon1 #hi ----1 capability of subsidence1 #ce ----1 classification for earthwork purposes1 #cf ----1 compact1 safe load upon1 #hi ----1 counterforts1 #aai ----1 interstices in1 #ce ----1 slopes1 #cg1 #ajj1 #aja1 #ajf1 #ajg ,ground1 configuration of1 #ah ,groynes1 protecting slopes by1 #agd-agf ,h4 ,height1 of embankments1 #ia-ig ----1 influence of length on safe1 #ie ----1 influence of nature and condition of earth1 #ig ----1 limit of1 in embankments1 #ia-if ----1 table of approximate safe maximum heights for different earths1 #id-if ----1 usual limitations1 #id1 #ie ,i4 ,igneous rocks1 slopes1 #bc ,impairing elements1 variableness of1 #a ,inclined beds1 danger in rock1 #bj1 #ba1 #bf ,instability1 earth's crust1 #a ,irrigation earthworks1 special causes of slips and subsidences1 #ahg4 ,vide ,,estuary ,,embankments4 ,j4 ,jetties1 as counterforts to dock walls1 #bjg1 #bjh ----1 foundations of1 #aha1 #ahb ,junction1 of high embankments1 #acf1 #afd1 #afe ,l4 ,land drains1 cause of slips1 #ae ,land waters1 diversion of1 #ae ,lateral settlement1 in embankments1 #ace1 #acf ,lead1 effect of long1 #afc ,lengths1 short excavated lengths1 when necessary1 #cc1 #adc1 #bjc1 #bjd1 #bbe ,limestone1 #ah1 #bd1 #be ,load on earth1 continuous surface1 #hg ----1 detached portions1 #hg ----1 experiments to ascertain safe1 #hg1 #hh ----1 influence of area1 #hg ----1 influence of normal load1 #ij1 #ia ----1 safe1 #hg-ij ,loamy soils1 slopes1 #cg ----1 safe load1 #hi ,location of earthworks1 configuration of ground1 #aj1 #ab1 #adf ----1 drift soil1 #i1 #aa1 #adf ----1 obstructing drainage1 etc41 by embankment1 #i-aa ----1 river near to1 #aj ----1 river and stream diversions1 #aj ----1 road1 near to1 #aj ----1 road approaches1 #aa ----1 stations1 position of1 #aj ----1 trestles or solid embankment1 #ab ----1 tunnels or cuttings1 #aa ----1 valley or hill-side line1 #aa ----1 valley1 stable side of1 #aj ----1 valley1 sunny or wooded side1 #aa ----1 wetter side of a hill1 #ab ,loose chalk1 #bg ,loose rock1 #bd ,m4 ,maintenance1 soft ground1 #aea ,marly chalk1 slopes1 #bg ,marly soils1 characteristics of1 #dd-df ----1 difficulty of draining1 #df ----1 safe load upon1 #hi ----1 slopes1 #ajj ,marsh earth1 slope1 #ajj ,marsh land1 safe load upon1 #hh ,metalling1 slope1 #aja ,mica-schist1 hardness of1 etc41 #bd ----1 quantity of quartz in it1 #bd ,mixtures of earth1 troublesome1 #bj ,moraine1 treacherous soil1 #ah ,morass1 safe load upon1 #hh ,mud1 consolidated1 slope1 #ajj ,mutability1 of the created elements1 #a ,n4 ,normal load1 influence of1 #hi-ia ,normal pressure1 consideration of1 #ia ,number of drains1 #ge ,o4 ,object of1 drainage1 #gb1 #gc1 #gd1 #ha ,obstruction1 of drainage by embankment1 #i1 #aj1 #aa ,open trestle work versus embankments1 #ahj ,overflow1 drainage by1 #ge ,p4 ,peat moss1 safe load upon1 #hh ,peat soil1 consolidation of1 #aec1 #aed ----1 drainage of1 #adi-aea ----1 nature of1 #aeb1 #aec ----1 necessary test1 #aea1 #aeb ----1 sustaining power of1 #aea1 #aeb ,peat turf1 slope1 #ajj ,percolation of water1 overflow and requisite pumping1 #fi1 #gj ----1 chalk1 #gj1 #ga ----1 clay soils1 #gj ----1 cuttings and embankments1 #fe-fg ----1 effect of1 #ff-fi ----1 excavated earth1 #gj ,percolation of water1 fissures1 #fi-ga ----1 loamy soils1 #gj-gb ----1 marly clays1 #gj ,percolation of water1 maximum1 #ff1 #fh ----1 principles of1 #fg-gb ----1 regulation of1 #fe1 #ff ----1 sand1 #ga ----1 top soil1 #gj ,piers1 foundations of1 #aha1 #ahb ,pitching1 on unequally consolidated soil1 #aca ----1 precautions respecting1 #acj-aca ----1 protection of slope by1 #abi1 #acj ----1 when necessary1 #abi1 #acj ,porphyry1 slope1 #bc ,pressure1 normal1 on earth1 #ia ,probability of a slip1 #ac-ah ,protective works1 burning the slipped earth1 #fb1 #fc ----1 cover shed and catch trenches1 #ei1 #fj ----1 different methods necessary1 #eb-fj ----1 earth counterforts1 #eg1 #eh1 #fa1 #aba ----1 enumeration of1 #ec-ee ----1 exceptional1 #ee1 #eg1 #eh ----1 flexible v4 rigid drains1 #ef ----1 flood waters1 #eg ----1 general principles1 #ee-eh ----1 object of1 #eb ----1 salifiable earth1 #ei ----1 slopes1 general considerations1 #aae-aag ----1 trickling of surface soil1 #eh ----1 turf and plant1 #abb-abd ----1 weighting the foot of1 #aai ----1 when drainage alone required1 #ef ----1 when required1 #eb ----1 where to commence drainage operations1 #ef ,q4 ,quartz1 slope1 #bc ,quicksand1 safe load upon1 #hh ,r4 ,rainfall1 influence of1 #ae1 #af ,rammed earth counterforts1 #fa1 #aba ----1 thickness of layers1 #abj ,reclamation embankments4 ,vide ,,estuary ,,embankments4 ----1 special causes of slips in1 #h ,removal of slipped earth1 general considerations and treatment1 #fj-fd ,repairing slope1 #aba ,reservoir embankments1 #ahg1 etc4 ,vide ,,canals4 ,retaining walls1 desirability1 #aag1 #aah1 #adf ----1 draining back of1 #aag ----1 failure of1 when probable1 #aah ----1 form1 #aah1 #aai ----1 protection to slope1 #aae-aai ,river banks4 ,vide ,,canals1 #ahg1 and ----1 ----1 ,,estuary ,,embankments4 ----1 protected v4 unprotected slopes1 #dh1 #di ----1 slopes of1 #dh ----1 tree protection of1 #abf1 #abg ,river diversions1 #aif1 #aig ,road metalling1 slope1 #aja ,rock1 ascertaining character of1 #ah-ba ----1 character1 etc41 #ah-bb ----1 classification for earthwork purposes1 #bc ----1 crystalline1 #ba ----1 examination of1 #ai ----1 general consideration1 #ah-bf ----1 inclined beds1 #bj1 #ba1 #bf ----1 mica schist1 #bd ----1 nature of some1 #ba1 #bb ----1 safe load upon1 #ij1 #ia ----1 sandstone1 #ij ----1 schistose1 #bd ----1 slopes1 friable1 #bd ----1 ----1 loose1 #bd ----1 ----1 sedimentary1 #bc ----1 stratified1 #ah-bj ----1 treacherous condition of1 #h1 #i ----1 unevenness of surface1 #ah1 #ai ----1 unstratified1 #ah ----1 variation of character1 #ah1 #ai ----1 water levels in1 #bd ,rubble mound1 safe load upon1 #ia ----1 slope1 #aja ,s4 ,salifiable earth1 #ei ,sandstone1 #ai1 #bb1 #be ,sandstone1 slope1 #bc1 #bd ----1 in tropical climates1 #be ,sand1 absorption of water1 #cd ,sand1 angularity v4 roundness of particles1 #cf ----1 capability of subsidence1 #ce ----1 compact1 safe load upon1 #hi ----1 delicate state of some1 #cd ----1 drainage of1 #cd ----1 drawing away of1 #cc ----1 excavating in short lengths1 #cc1 #adc1 #bjc1 #bjd ----1 firm1 safe load upon1 #hi ----1 interstices in1 #ce ----1 light sand1 protection of1 #abc-abe ----1 loose sand1 safe load upon1 #hi ----1 mutability of condition1 #cd ----1 sand 8boils0 in foundations1 ,vide 8,,boils40 ----1 silty1 safe load upon1 #hi ----1 slopes of repose1 #cf1 #cg1 #ajj1 #ajf1 #ajg ----1 soft sand rock1 #ij ----1 springs in1 #cc ----1 superficial beds of1 #hi ----1 when likely to slip1 #cd ,sandy clay1 #ci1 #dj ,schistose rock1 #bd ,seat of embankment1 drainage1 #afj ,setting out1 with reference to earthwork1 #i-ab ,settlement1 lateral1 of an embankment1 #ace ----1 provision against in slopes1 #abe1 #abf ,shales1 characteristics of1 #bj1 #ba1 #dd ----1 iron pyrites in1 #dd ----1 safe load upon1 #hi ----1 slopes1 #ba1 #ajj ,shore embankments4 ,vide ,,estuary ,,embankments4 ,sidelong ground1 cuttings and embankments upon1 #adb-adf ----1 depositing embankments upon1 #ade1 #adf ----1 excavating in short lengths1 #cc1 #adc1 #bjc1 #bjd1 #bbe ----1 object of precautionary works1 #adb-ade ----1 precautions1 #adb-adf ----1 when inclined rock1 #adf ----1 when especially treacherous1 #add-adf ----1 varying the slope1 #adf ,silt1 safe load upon1 #hh ----1 slope1 #ajj ----1 treacherous1 #ah ,slake1 safe load upon1 #hh ,slate rock1 #ba ,slipped earth1 treatment and removal of1 #fj-fd ,slips in canals1 special causes1 #h1 #ahg ---- time of occurrence1 #aij1 etc4 ---- docks of occurrence1 #ahg ---- drainage works1 #ahg ---- irrigation works1 #ahg ---- reclamation works1 #ahg ---- waterworks1 #ahg ,slips in cuttings1 causes of1 #b1 #c1 #d1 #e1 #h ----1 embankments1 causes of1 #e-h ,slips1 immediate action necessary1 #fa ,slopes1 bare1 when can be left1 #abe ----1 cess upon1 #aaa1 #aac1 #aad ----1 counterfort at foot of1 #aai-abb ----1 curved1 #aji-aaa ----1 disturbance of1 #aaa1 #aab ----1 fascine covering1 #abh1 #abi ----1 fissures in1 treatment of1 #abg-abh ----1 flat1 should not be too1 #ih ----1 form of1 #ajg-ajh1 #aaj1 #aaa ----1 general considerations1 #ih-ii1 #aje-aaj ----1 nature of covering1 #abb-aca ----1 object of protection1 #aai1 #abb ----1 permanent1 of earth1 #ih-aja1 #ajf-aji1 #adf ----1 precautions concerning tree protection1 #abf1 #abg ----1 protection and preservation1 general considerations and different systems1 #aae-aca ----1 protection against burrowing animals and crustacea1 #abg ----1 protection of light sand1 #abc-abe ----1 protective coverings1 #abb-abi ----1 provision against settlement1 #abe1 #abf ----1 range of slopes in different earths1 #ajj1 #aja ----1 repairing1 #fa-fd1 #aba1 #abb ----1 sand veins in1 #abj ----1 steepest1 #aab1 #aac ,slopes1 stone pitching upon1 #abi-aca ----1 terraced1 #aaa ----1 time to trim1 #abe ----1 trees and shrubs upon1 protection by1 #abf1 #abg ----1 trench drains in1 #gg1 #gh1 #aaa1 #aab1 #aba ----1 trimmed as excavated1 #aaa ----1 turfing1 grass and plant protection1 #abb-abg ----1 varying the form of1 #aji1 #aaj1 #aaa ----1 walls1 #aag-aai ,snow-drifts1 prevention of1 protection against1 #aca-acd ,soft soil1 consolidation of1 #aec1 #aed ----1 depositing embankments upon1 #aed1 #aee ----1 drainage1 #gc1 #adi-aea ----1 embankments upon1 #adg-adi ----1 equable drainage necessary1 #aej ----1 influence of ballast on formation1 #aea ----1 sustaining power of1 #aea1 #aeb ----1 testing1 #adh1 #adi1 #aeb ,springs in chalk1 treatment of1 #bi ,subsidence1 capability of sand1 #ce ---- in soft ground1 #aea ,subsidences in embankments1 causes of1 #e-h ,t4 ,time of occurrence1 slips1 #ac-ag ----1 usual1 #ae-ag ----1 submerged and unsubmerged work1 #ag1 #ahi ,trap rock1 slopes1 #bc ,treacherous earths1 #ac1 #bjd1 #bag ,tree protection1 general1 #af1 #abf ----1 precautions concerning1 #abf1 #abg ----1 slopes1 #abf1 #abg ,trickling of surface soil1 #eh ,trimming slopes1 #aaa1 #abe ,tunnels1 entrances of1 in chalk1 #cb ,turfing slopes1 #abb-abf ,u4 ,universality of slips1 #a1 #b ,unstable soils1 #ac1 #bjd1 #bag ,upheaval of ground1 #adg1 #adh ,v4 ,variableness of1 impairing elements1 #a ,variety of causes of slips and subsidences1 #a ,viaduct1 versus embankment1 #aga-agc1 #agi1 #ahj ,vibration1 in cuttings and embankments1 #acf1 #acg ----1 deteriorating influence of1 #acf-ada ----1 effect on earths1 #acf1 #acg ----1 influence of1 #h1 #i ----1 lateral pressure and1 #acg ----1 test of effects1 #ada ,w4 ,water1 the chief cause of deterioration of earth1 #h ,water-bearing level1 #ad1 #bd ,waterwork earthworks1 special causes of slips and subsidences in1 #h1 #ahg4 ,vide ,,canals1 etc4 ,water pressure in cuttings1 #ad ,weights of different earths1 #ib ,widening works1 consideration respecting slopes1 #aab-aad ----1 steepening the slopes1 #aab-aad ,y4 ,yellow-clay1 #dc1 #hi ,,london3 ,,printed ,,by ,,william ,,clowes ,,and ,,sons1 ,,limited1 ,,stamford ,,street ,,and ,,charing ,,cross4 ---------------------------------------- -------------------------------- ,crown #hvo41 cloth1 price #ds4 #f;d4 ,,notes ,,on ,,concrete ,,and ,,works ,,in ,,concrete4 ,,by ,,john ,,newman1 ,assoc4 ,m4 ,inst4 ,c4,e4 ,,reviews ,,of ,,the ,,press4 ,,engineering--#aath ,november1 #ahhg4 8,an epitome of the best practice which may be relied upon not to mislead40 8,the successful construction of works in concrete is a difficult matter to explain in books40 8,all the points which open the way to bad work are carefully pointed out by our author with a pertinacious insistence which demonstrates his clear appreciation of their value40 ,,iron--#bast ,october1 #ahhg4 8,as numerous examples are cited of the use of concrete in public works1 and details supplied1 the book will greatly assist engineers engaged upon such works40 ,,the ,,builder--#bdth ,september1 #ahhg4 8,a very practical little book1 carefully compiled1 and one which all writers of specifications for concrete work would do well to peruse40 8,the book contains reliable information for all engaged upon public works40 8,a perusal of ,mr4 ,newman's valuable little handbook will point out the importance of a more careful investigation of the subject than is usually supposed to be necessary40 ,,american ,,press4 ,,building--#aith ,november1 #ahhg4 8,to accomplish so much in so limited a space1 the subject-matter has been confined to chapters40 8,we take pleasure in saying that this is the most admirable and complete handbook on concretes for engineers of which we have knowledge40 ,,london3 ,e4 ,f4 ,n4 ,,spon1 #abe1 ,,strand4 ---------------------------------------- -------------------------------- ,,transcriber',s ,,notes #a4 ,changed 8the sinking a sump0 to 8the sinking of a sump0 on p4 #bjb4 #b4 ,silently corrected typographical errors4 #c4 ,retained anachronistic and non-standard spellings as printed4 #d4 ,enclosed italics font in underscores4