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THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



[July, 



of a cutting, not deeper than the eighth of an ordinary railway tunnel. 

 The sevenil part3 of a tunnel derive support from each other, which 

 is not the case with ordin;iry retaining walls, whose efficiency depends 

 whollv upon the resistance which their own mass or weight and ex« 

 tent of base, enable them to offijr to the pressure of the body to be 

 retained. If to two opposite retaining walls, be giren sulBcient means 

 of assisting one another, they may be at once reduced to one-third of 

 the bulk they require without such assistance and would then be as 

 safe as the sides of a constructed tunnel, the strength of which is only 

 limited by the power of the setting material employed in the work, to 

 resist compression. 



Before proceeding to the consideration of the means of enablir.g 

 opposite retaining walls to assist each other, it may be worth while to 

 consider, whether retaining walls are generally constructed in such a 

 manner, as best to adapt their components to the duly to be performed. 

 No one would place a buttress intended to resist the thrust of an arch, 

 within the springing walls, or under the arch whose thrust is to be re- 

 sisted ; yet in tlie construction of retaining walls the counterfort is 

 placed on that side which receives the pressure, where its utility is 

 very questionable, except to keep the retaining wall from falling back 

 against its load, which, from the transverse section too generally given 

 to such walls, they would be apt to do, if they were not so propped 

 up by their counterforts. Wharf and quay walls, and the revetment 

 walls of military works, may require a fair face, unbroken by projec- 

 tions in front, but this is not the case with retaining walls for roads 

 and railways, where a long line of projecting buttresses would be un- 

 objectionable, the counterforts becoming buttresses and merely chang- 

 ing places with the wall. On account of the common practice of bat- 

 tering the faces of retaining walls in curved lines and of radiating the 

 beds of the brickwork composing them from the centre of curvature 

 in every part, the back of the wall must contain more setting material 

 than the face, with the same quantity of solid brick ; that is, if the 

 work be bonded through. Hence the back of the wall will be more 

 liable to compression and settlement than the face. Counterforts 

 must be built in the same courses, and consequently must have still 

 thicker beds of compressible mortar than the wall, or the bond between 

 the wall and its counterfort must be dropped and the counterfort thus 

 become utterly inefficient. Perceiving the fallacy of the back coun- 

 terforts, as an aid to the retaining wall to resist pressure from behind, 

 the author designed a retaining wall a few years ago, with greater 

 substance in itself than the usual practice would require, but without 

 back counterforts. The wall was substantially of brickwork, with 

 concrete coffered in the heart, to give mass and weight without the 

 expense of solid brickwork; the concrete being in layers of 30 inches 

 thick, separated from one another by two thorough courses of brick- 

 work in every twelve courses in height. The wall was battered in 

 face upon a curved line and had radiating courses of brickwork ; but 

 the arrangement spoken of, gave the means of making the longer line 

 of the back of the wall with bricks instead of mortar, by inserting 

 within the height of each coffer at the back, an additional course of 

 brickwork ; anti the whole construction was well tied together, both 

 longitudinally and transversely, with hoop-iron laid between the 

 thorough courses of brickwork. 



The retaining walls, in the cutting upon the line of the extension of 

 the London and Birmingham Railway, from Camden Town to Euston 

 Square, are designed according to the common practice ; they are 

 built wholly of brickwork in radiating courses and with counterforts 

 following their own contour. In this case the centre of gravity of the 

 wall falls wholly behind its base ; and the counterforts, not commenc- 

 ing until the wall has reached one-third its height, render it still more 

 dependent for support upon the ground it is intended to retain. It is 

 well known that these extensive walls, though furnished with all the 

 collateral works necessary to protect them from exposure to undue 

 influences and although set nearly one-fourth of their height in the 

 ground, have failed to a considerable extent. A system of strutting 

 with cast-iron beams, across from the opposite walls, to make each 

 aid the other, has been applied to meet the exigency (figs. 1 and 2) ; 

 but this is limited to the upper parts of the walls and the author 

 thinks it may yet be found, that the toes of the walls will require to 

 be strutted apart, or otherwise fortified. 



Abutting struts from opposite walls, occurring at intervals only, 

 leave the intermediate portions of the walls exposed to pressure from 

 behind without support, unless these intermediate portions are so dis- 

 posed, as to communicate the pressure upon them to the struts. Hence 

 a common retaining wall, abutted at inteivals, would require these 

 intervals to be more or less distant, in proportion to the strength of 

 the wall between them. Instead, therefore, of a continuous wall on 

 each side of the cutting, the author suggests (figs. 3, 4, 5, and tj), that 

 buttress walls should be placed at intervals, opposite to one another, 

 and strutted apart at their toes by an inverted arch, and above, at a 



height sufEcient for whatever trafiBc the cutting is to accommodate, by 

 a built beam of brickwork, in vertical courses, supported on an arch, 

 and prevented from rising under the pressure by an invert upon it. 

 This built beam will then be, as it were, a piece of walling turned 

 down on its vertical transverse section, and will resist any pressure 

 brought upon it through the buttress walls, to the full extent of the 

 power of such a wall built vertically, to bear any weight laid upon its 

 summit ; the pressure would be applied, in the line of tlie greatest 

 power of resist;ince, and there would be no tendency to yield, except 

 to a crushing force. Let such transverse buttress walls, so strutted 

 apart, with the road between them, lie the springing walls of longi- 

 tudinal counter-arched retaining walls, which, being built vertically 

 and in horizontal courses, but arched in plan, against the ground to be 

 retained, will carry all the force exerted against them to their spring- 

 ing walls and the springing walls or buttresses will communicate, 

 through the struts, the power of resistance of each side to the other 

 and thus insure the security of both. This arrangement may be car- 

 ried to any extent in height, by repeating the abutting beam or strut 

 at such intervals as the thrust to be resisted and the strength of the 

 buttress-springiiig-walls may require. 



It will be admitted, that whatever insecurity there may be in the 

 sloped sides of a cutting, becomes greater, as the depth is increased, 

 the inclination being the same ; so that a slope of 40 feet in vertical 

 height is not deemed so trustworthy as a similar slope in the same 

 place of 20 feet in height and, indeed, to give the same degree of 

 security, as the height increases, the inclination of the slope must be 

 increased. Consequently, the expense of a cutting with slopes, in- 

 creases even in a greater degree than the mere additional depth would 

 require, and if it can be shown, that a cutting 05 deep, in the London 

 clay, or other similar soil, may be made and its sides retained by effi- 

 cient permanent constructions, at less cost per yard forward than the 

 same cutting would require, with the slopes at which such soils can 

 be trusted to stand, — it will be admitted, tliat greater advantage 

 would be obtained by the use of such constructions, where the depth 

 is greater; especially where such treacherous soils occur, as those 

 through which the cuttings at New Cross and Forest Hill have been 

 made. 



It will not be exaggerating the case against sloped sides in clay 

 cuttings, to assume, that they cannot be trusted at less than IJ to 1, 

 even up to 20 feet in vertical height, nor beyond 40 feet at 2 to 1 ; 

 nor will it be extravagant to state the slopes for a cutting 65 feet 

 deep, at Si to 1. Many instances, besides those of the Croydon Rail- 

 way cuttings, give conclusive evidence that the London clay and the 

 superposed strata which occur in connexion with it, will not stand at 

 less than 3 to 1 when the vertical height much exceeds 65 feel; 

 whilst the uncertainty connected with ' silty clays' and 'soapy earths,' 

 exposed to the alternate action of air and water and of heat and cold, 

 renders even slopes of that degree of inclination, a subject of constant 

 anxiety and expense. If then, safe and (so to speak) imperishabltt 

 constructions, can be applied to retain the sides of a cutting in any 

 soil that cannot be trusted at a less inclination than 24 to 1, at lea's 

 cost and in no greater time, than the excavation with such slopes 

 could be made, — taking no account of subsequent cost for slips, or for 

 the dry shafts and bushed drains, in some cases, or the gravel revet- 

 ments and buttresses in others, — there can be no question, but that 

 such constructions vpould be better than slopes. 



It would be for every engineer to decide upon the substance re- 

 quired under the circumstances of any particular case ; that assumed 

 in the accompanying diagrams (figs. 3, 4, 5, and 6) is submitted as, in 

 the judgment of the author, sufficient in ordinary cases of clay cuttings, 

 if executed with materials and workmanship of fair average qualitr, 

 and such constructions may be applied in any such case, where the 

 depth exceeds 40 feet, and the slopes would require an inclination of 

 more than 2 to 1, at less expense than that of forming slopes to the 

 full depth. Of course, shoring to retain the ground, while the con- 

 structions are in progress, would form an important item in any such 

 arrangement; but as the amount of earthwork in forming slopes, and 

 the cost of contingencies connected with them when made, must in- 

 crease, at least as much as the difficulty of temporarily retaining th« 

 ground increases, the proposed arrangement would not be deprived of 

 its presumed advantage, as it regards economy, on this account. 



The diagams (figs. 3 and 5) represent a cutting 65 feet deep to the 

 level of the rails. It is assumed, that the ground at the top may stand 

 for the first 15 feet at less than 2 to 1, and that it may, therefore, be 

 cheaper to run out to that depth with slopes, leaving 50 feet from th« 

 rails, or about 52 feet in all, to be retained. As the bricklayer may 

 follow up the excavator with bay after bay, his woik lying mostly on 

 the side and out of the way of the excavator, the latter would run out 

 the spoil without interruption, his work being benched onwards and 

 shored as he proceeded. As every compartment, with its buttresses 



