GO 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[Fee. 



l)p of no iisP, ;i3 it would be pushed o\it; the most elVectual preventive, 

 or remedy, is wattling and IjhsIi drains. Wlien time will allow, it is 

 belter to make tlie enibankments in layers, and between each layer of 

 earth putting in a course of brushwood, clippings of hedges, or wat- 

 tlings. When embankments are obliged to he poured out hastily, 

 allow thein to take their natural slope, and if it slips let it remain, for 

 however much it may he attempted to reduce it to its former shape, 

 it will still again slip and regain its position. A good practice to 

 provide against slips is to forma slight abutment of earth, a short dis- 

 tance from the toe of the slope, so that it should stay the slip if it 

 takes place ; this plan is more particularly available when the work is 

 obliged to be erected on a natural slope — for instance, on the side of a 

 hill. The Professor, then, for the information of the younger students, 

 explained, by diagrams, the nature of slopes, and the meaning of the 

 expression "two feet to one," &c., and concluded by recommending 

 that, in forming slopes, the engineer should run some risk of slips, in 

 order to save the great expense of removing more earth than is actually 

 necessary — the cost of repairing these slips being but little in com- 

 parison. He likened the work to an insurance on life — the risk to be 

 run being calculated upon by precedents. The principle is to get the 

 greatest extent of work finished at the least possible expense, and 

 many of the great slips that have taken place might have been pre- 

 vented, or speedily cured, had the plans he laid down been better fol- 

 lowed. 



Lecture G. Wednesday, the 29th Dec. 184 1.— Professor Vignoles 

 stated that, before continuing the subject of earthworks, he wished to 

 set right an erroneous impression with the public, in consequence of 

 an expression he made use of at his last lecture ; he had then recom- 

 mended that "the engineer should run some risk of slips, in order to 

 save the great expense of removing more earth than was actually 

 necessary — the cost of repairing those slips being but trifling in com" 

 parison." He need not say that he so ex|)ressed himself, but it vv^is 

 alwavs on the supposition that no risk was to be run where there was 

 the remotest probability of danger. He mentioned this because of the 

 circumstance of the slip on the Great Western Railway, which was 

 atteniled with such fatal results, and liappening only a few hours after 

 he had niaile that statement. From all that had been stated, it appeared 

 that the slip itself was but very inconsiderable; the cutting where it 

 took |)lace was .')7 feet deep, the slope two to one, and the width 

 of the road 'lU feet; the slip took ])lace about half way up the bank. 

 A number of smaller slips had occurred, and tiles were used for drain- 

 ing instead of bushes, c&c, to cure them — still the mode of curing 

 them was the same as he advocated — by drainage. As he had before 

 stated, the slip itself was very inconsiderable, but, by having nothing 

 to check it, the earth fell vipon the rails. A doubt seemed to exist 

 whether the concussion produced in the air by the passing of the 

 former train had not brought it down, for the accident happened in 

 the interval between the passing of the two trains — the lirst one 

 having proceeded uninjured, wdiilst the latter was attended with such 

 fatal consequences. If the precaution had been taken, when it was 

 first observed that a slip was likely to occur, to put up a fence of 

 hurdles to check its advance to the rails, doubtless the accident would 

 not have happened. The manner of the slip showed that it was 

 caused solely bv the infiltration of water, probably a considerable way 

 back from the edge of the cutting, or, perhaps the water had found 

 its way in by the ditch along the top ; the water which had thus got 

 info the soil having expanded during the frost, the sudden change of 

 the weather brought down the earth. The Professor then, by means 

 of a diagram, explained the nature of the cuttuig, from which it 

 appeared that the "top lift" was deposited in spoil bank ; at tbe top 

 of the cutting a drain had also been cut, but he was of opinion that 

 such drains were injurious, when the soil was at all precarious. The 

 spoil bank was not the occasion of the slip, since it did not take plate 

 at the top, but bulged out in the middle. Although this slip was very 

 small, from the latal effects which attended it, it was the more 

 necessary to guard against the recurrence of the like ; there were but 

 a few feet of earth on the rails, yet the effect was the same as if so 

 many planks had been placed upon them. The Croydon slip arose 

 from' the same cause, but, though so much larger, no accident occurred. 

 In the late accident there were but thirty or forty waggon loads of 

 earth, and all was right again in a few hours, while in the Croydon 

 slip 3,000 or 1,001) cubic yards of earth fell ; the soil in both instances 

 consisted of the London clay, with pot-holes of sand. It was clear 

 that the accident was not to be set down as one of cutting, similar 

 slips having taken place upon cuttings not more than twelve or four- 

 teen feet deep. He must impress upon the nnnds of the students 

 that it was not the length or depth of the cutting which regulated the 

 slopes, but the soil and practicability of drainage ; unfortunately it was 

 impossible to know exactly how these matters might stand, experience 

 alone could teach them. He had dwelt long upon this subject, but he 



wished it to be understood that it was well-judged economy he advo- 

 cated, not such as would, in the least degree, tend to produce such 

 fatal eflc'cts as in the case previously alluded to. 



The balancing of the line was equally necessary for railroads as for 

 canals or common roads; it should be the engineer's aim that the quantity 

 of earth from the cuttings should be as near as possible sutlicient for the 

 embankments; compared with former times, the mode of transit was 

 so much facilitated, that where some years back it was necessary that 

 the balance line should be limited to the hill to be cut through, and the 

 valley to be filled up, now the line might extend two or three miles. 

 It was essential in balancing that the engineer shoidd be aware of the 

 different degrees of compressibility of the matter; it was known of 

 sand that it would occupy the same cubic contents in the embank- 

 ment as it did in the hill, and one yard or 100 vards of gravel would 

 be still the same, but in clays it was very different, they occupying 

 less space in the embankment than they did in the hill, in their original 

 position ; 100 yards of clay would nOt make 100 yards of embankment, 

 the average amount of compressibility being not less than 10 per 

 cent., or even, upon occasions, as much as 15 per cent. He had known 

 occasions when 100 yards cut from a hill had only made 85 yards of 

 embankment, but, upon an average, it would require 110 yards of clay 

 to make 100 yards of embankment. Rock cuttings, on the contrary, 

 expanded, because the solid rock could never again be restored to the 

 same degree of density ; tlie difference would vary much, according 

 to tlie size of the fragments, but where the pieces were large, 100 

 yards would make 120 yards of embankments.* Chalk, again, would 

 be rather upon the excess, though much depended upon its quality. In 

 rock cuttings you might make them nearly perpendicular, but in chalk 

 much discussion'i' has arisen as to what was the proper slope, some 

 engineers having even recommended that it should overhang the road, 

 but he contended that it should slope, to carry off the water; he had 

 found a slope of one quarter to one generally sullicient. Rock chalk 

 would stand perpendicular, while several of the softer descriptions 

 would require a slope of one-half to one, or even two to one. 



The Proi'essor then proceeded to speak of the correct mode of com- 

 puting the quantity of earth in a cutting or embankment, and made a 

 section of a hill half a mile long, to be cut down, the true cubic con- 

 tents of a portion of which was 332,000 cubic yards, computed 

 according to the prismoidal formula; but the ordinary method by 

 which contractors would calculate the contents of the hill, by mean 

 heights, would only show 310,000 cubic yards — that is to say, there 

 would be a difi'erence of 22,000 cubic yards against the contractor, the 

 consequence of which had beer, that the person contracting to cut 

 down such a hill, at so much per yard, wouUI lose, from his bad method 

 of calculation, above .t' 1,000. Another methotl was also in use — 

 calculating by the mean area; which system, instead of 332,000 cubic 

 yards, would show 37(5,000 cubic yards, being an excess in favour of 

 the contractor of 14,000 cubic yards. Many contractors had realised 

 large fortunes by mean areas, and sustained serious losses by mean 

 heights. Having thus shewn the erroneous methods of calculation in 

 use, he then, at some length, explained the prismoidal formula, 

 accompanying his instructions with many diagrams, without which any 

 attempt at explanation on our part would be useless. The learned 

 Professor concluded his lecture by strongly recommending a close 

 study of mathematics to the junior (all) students, as the greatest assist- 

 ant to the labours of the civil engineer. 



F.mbi-Wilimenls of imiAin.— We have heard it stated, and wc believe on 

 "110(1 grounds, thai a great and strikuig improvement is about to be made in 

 the appearance of Piccadilly, conscqiicnl upon the removal of the ranger's 

 house in the Green Park, which will be demolished early in the spring. Tliis 

 tasteful suggestion, we have heard, was made by the Premier, and is to con- 

 sist of a noble terrace ami pnbhe walk, from the gate into the Palace-gardens 

 at Hyde Park corner, to the jimctiou of the houses at the lower end of llie 

 basin. The form ot the ground on this line is particularly favourable to jiic-^ 

 tiuesfjue elfect in laying out and planting, and to arcli'tectural beauty of 

 design in the esplanade. Fountains and statues, too, are likely to he inlro- 

 diieed, to add to the grandeur of the plan, give cncour.agement to the arts, 

 and comhine the whole with the palatial residence of llie Sovereign, by 

 carrying it, perhaps, further on hereaft r, along the line opposite to (iros- 

 venor-place. The magnificent ec|uestriau statue of Wellinglon, now casting 

 by Wyalt, «dl surmount the areh facing Apslcy house ; and wes ee no reason 

 why it should not he b.alanced at the other termination by a statue of 8ir 

 Robert Peel, together with his name to the work, the idea of which, as we 

 liave mentioned, is understood to have emanated from him. At all events it 

 will be a splendid embellishment of this principal street in entering the 

 caiptal from the west. — Literary Gazette. 



» These remarks strongly corroborate tho.se of .an American engineer, 

 inserled in the .K)Urnal of December last.— Fn. C. E. & A. Journai,. 



I .See the evidence on the Brighton Railway before the House of Lords. 



