4'i 



THE CIVIL ENGirJEER AND ARCHITECT'S JOURNAL. 



[Fkbruart, 



stutp of slavery, tliiit which encliains the very heart's hest feehngs, and 

 renders them beings (if tliat degraded and subservient charaottr to 

 Iheir fehow men, lliat they begin tii doubt wliether tlidse who thus 

 goad tliem be not somelliiiig below the sphere of that mortal whom the 

 God and Fatlier of all has endowed with the faculty of reason,) to 

 drag on a wretched existence in the service of their country, without 

 one cheering consohuion, not even that which long and faithful service 

 ought to secure to every good servant — comfort and peace of mind in 

 liis declining years ? There is One who will exact from us submission 

 to his laws; nut only that we should render him perfect love and 

 obedience, but that our fellow men should receive at our hands ample 

 justice, and kind and charitable consideration in every relation of 

 life. 



ZOPTORUS. 



Jamianj 1, 1813. 



ON SLIPS IN CUTTINGS AND EMDANKMENTS. 



(From the Mhmtes of the Instilulion of Civil Engineeis.J 



(Conlimtedfrom pngc 27.) 



Mr. Cowi'Eit said, that he should he inclined to attribute the slips to the 

 expansion of the clay, from the action of water. He had recently examined 

 the retaining walls, on the London and Birnungham Railway, in the cutting 

 near the fusion Square station, and liad found they were, in several places, 

 forced forwards, apparently by some action behind them. This action was 

 irregular, for its effects appeared indiscriminately at the top, at the bottom, 

 and in the middle of tbe retaiinng walls, which were built of brick, generally 

 aliout 5 feet 6 inches thick at the bottom, and 2 feet 6 inches at the top, 

 with a curved face. Wherever the wall had been removed, for the purpose 

 of rebuilding it, the face of tbe clay behind appeared to stand quite straight, 

 without any fissure. He was therefore induced to think that water descended 

 to various depths, according to the degree of perracahility of tbe clay, and as 

 far as its action extended, expansion took place. If the whole mass had ex- 

 panded, from having been exposed to the action of air, before the face was 

 covered with brickwork, the entire wall would have been moved forward, 

 which was not the case. 



General Pasley said, that from bis observation of tbe usual character of 

 slips, he was induced to think, that the slopes were generally too steep ; 2 to 

 1 had been considered sufficient for almost all kinds of earth, although Sir 

 Henry Parnell, in his Treatise on Uoads, said, " When it is necessary to make 

 a deep cutting through a lidl, the slopes of the banks should never be less, 

 except in passing through stone, than 2 feet horizontal to 1 foot perpendi- 

 cular; for altliough several kinds of earth will stand at steeper inclinations, 

 a slope of 2 to 1 is necessary, for admitting the sun ami wind to reach the 

 road." The same authority stated, *' in the Loudon and plastic clay forma- 

 tions, it will not be safe to make the slopes of embankments or cuttings, that 

 exceed 4 feet in height, with a steeper slope than 3 feet horizontal to 1 foot 

 perpendicular. In cuttings in cbaik, and chalk marl, the slopes will stand at 

 1 to 1. In sandstone, if it be solid, hard, and uniform, the slopes will stand 

 at i to 1, or nearly perfiendicular." " There are many instances of slips in 

 sandstone and marl strata alternating (when tlie line of road is parallel to the 

 line of the licaring of the strata), where the slopes are as mrryh as 4 to 1." 



General Pasley had arrived at the conclusion, that 3 or 4 to 1 ought to be 

 given, in order to insure good work ; he bad, therefore, aulhni\zed the rail- 

 way companies to take possession of land, to increase tbe inclinalkm of their 

 slopes. It was remarkalile that the slips rarely occurred during, or imme- 

 diately after, the formation of the cuttings ; it would appear Ihereforr pro- 

 balrle, that the moveme'ni was caused by the comliined action of the air upon 

 the surface, and that of water, whi.h had percolated through the upper strata 

 and acting liehind it, forced the earth forwards in the line of least resistance. 

 He believed, that a series of gravel counterforts, with a revetment at the 

 foot, was the most eft'ectrral method of irreventing slips. On the South 

 Western Railway, hard chalk had lieen used «ith good efToct, instead of 

 gravel, for that purpose. The perfect drainage both of the surface of the 

 ground, on either side of tlie cuttings, and of tire slopes themselves, was of 

 the ntnrost importance. On the Eastern Counties Railway, shafts had lieen 

 sunk at infervals in the sinews, and tilled up with dryrublile; fronr their 

 bottom's, iron pipes proceeded to the face of the cutting (tig. 6) ; these had 

 proved effective in drainirrg away the water. With regard to einhankments, 

 be was of opinion, that it more altentnin was paid to lorming them only in 

 propitious weather, placjiig the material in thinner layers, in a concave form, 

 and draining them well, as the work proceeded, the result would be more 

 satisfactory, and less expensive, not only in the first cost, hut in suhsequently 

 avoniin.: sbps. He Ihoughr, that in situations of difficuUy, advantage woulil 

 arise from the employment of wooden stages, like those which had been used 

 by Mr. Jolin 13rarrhwaiie at the Colihester embariknrent ; the trcffic of the 

 railway wa> there carrieil on. over the wooden viariiret, untrl the srrhsidence 

 of the earth had ceased, when the timber work was either cut off, or drawn 

 out, as tbe corrtractur fuuod least expensive. 



Mr. Bruff remarked, that the timber viaduct at the Colchester embank- 

 ment, was only adopted in consequence of the extreme subsidence of the 

 material, which had assumed a slope of 6 to 1 ; he had seen tbe same mate- 

 rial, which was plastic clay, stand well at a slope of 2 to 1. If an embank- 

 ment was formed with that material in a wet state, it would inevitably spread 

 at the foot. The cuttings of the Eastern Counties Railway had remained 

 open for 2 J years, but owing to the nature of the soil, the water would not 

 drain from them. 



Eastern Counties Railway. 



Mr. Prirprs corroborated the statement, relative to the use of the timber 

 viaduct on the Eastern Counties Railway ; it was only an expedient to enable 

 the railway to be opened, at an earlier period than it couhl otherwise have 

 been, in corrsequence of the subsdence of the embankment, which however 

 now stood very well. He approved of the formation of embankments, by 

 depositing the material in thin layers, and by several lifts ; the embankment 

 was by that means rendered sounder and less liable to slip. Dry shafts and 

 gravel counterforts had prevented many slips, but be thouglrt that sutficient 

 time had not elapsed since their adoption, to enable an unqualified approval 

 of them to be given. The pipes which bad been inserted into tbe clay slopes, 

 did not appear at present to draw away much water. 



Mr. Bhaithwaitf, said, it should be remembered, that the soil at Brent- 

 wood Hill, was very different from that on the Croydon Railway. The 

 Brentwood sand was so full of water, that when it was opened it appeared 

 semifluid, like a quicksand ; the gravel counterforts, which had been effectual 

 in stopping the movement of the London clay, would have hut little effect in 

 sand of such a quality as he had described. 



He had seen much of the Loudon clay in sinking wells, and it was note 

 rious to well-sinkers, that even in the absence of moisture, if the London 

 chiy was left exposed to the air for a few hours, expansion took place, and 

 the surface of the cutting began to fall away : by this expansion the walls of 

 wells were frequently fractured, unless allowance was made for it. 



He could not agree with Mr. Cowper, as to the cause he had assigned for 

 the partial action upon the walls of the Euston Square cutting. TheLoirdon 

 clay was impervious to water, therefore it could not arrive at the different 

 parts of the wall, unless tbe line of junction between that clay and rbe per- 

 vious superstrata, was very irregular in its course, as compared with the incli- 

 nation of the railway. 



General Paslky coincided in the opinion, of the difficuUy of working a 

 material like the Brentwood sand, which was mixed with silt and qrricksand. 

 and demanded more than ordinary care ; he thought that such ground should 

 not be worked upon at all in wet seasons. He believed, that in nrany cases, 

 slips had occurred irr consequence of the too great proximity of side cuttings, 

 by which the ground between them and the foot of the embankment, was 

 too much weakened. He had in some cases recommended, that the side 

 cuttings should be filled up in order to consolidate the embankment. 

 Croydon Railway. 



Mr. Gregory believed, that the expansion of the clay was in some degree 

 (hut not entirely), the cause of slips. 'Jhe blue clay was impervious to 

 water; the yellow clay permitted the water to traverse it freely, by the 

 natural joints and fissures in it, and also by those which were formed by the 

 drying action of the air upon its surface. When the face of the bed of the 

 blue clay was softened by the action of water, and its surface became lubri- 

 cated, there was not any longer sufficient friction between the strata, to re- 

 tain the weight of the superposed yellow clay, the mass of which, on the 

 slightest impetus being given by expansion, travelled forward down the in- 

 clined strata, which in the ease of the New Cross cutting, was towards the 

 railway. 



lie had tried the insertion of pipes into the sides of cuttings, and almost 

 ever'y other kind of diaiuage, without effect, and he was of opinion, that the 

 general saturation of the mass, was tbe cause of the slip in the New Cross 

 cutting. 



Mr. Hoof said, he had executed the greatest portion of the works on the 

 Croydon Railway ; bis experience induced him lo agree with Mr. Gregory in 

 the statements contained in the paper, and in the reasons he Irad assigned 

 for the causes of the New Cross slip. 



Loudon and Birmingham Railway. 



Mr. DocKRAY doubted the advantage of the benches in tbe face of the 

 slopes ; he thought, that they not only caught and absorbed all the rain, but 

 also a great portion of the water, from the drains of the upper part of tbe 

 cuttings ; a well-drained slope, at a regular angle from the top to the bot- 

 tom, would, in bis opinion, act better. 



He bad observed, that the slips on the London and Birmingham Railway 

 generally commenced, either in the line of the fence difcb, or in that of a 

 catch. water drain, or at some natural or artificial obstruction, which pre- 

 vented the free passage of the water, over tbe surface of ihe slope, into the 

 liallast drains. He considered it of great importance that the surface water 

 should be carried off as rapidly as possible, and that it should not be per. 

 milled to lodge on the slopes, or in the drains; from whence it could only 

 escape, either by evaporation, or by absorption into the ground : it wai to 

 the gradual operation of this latter cause, that he attributed most of the slips 

 in clay cuttings. 



In repairing such slips Mr. Robert Stephenson had used a plan, (fig. 1,) 

 which had hitherto proved very successful. He regarded tbe slip aimply a 



