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THE CIVIL ENGINEER AND ARCHITECTS JOURNAL 



[Feb. 



ney, fwnnly-two feet square, where the natural soil wag a shifting 

 quicksLiml ; concrete was put in in layers, until the bed was eight feet 

 thick ; on tliis was jilaced a layer of flag-stones, five feet square ; eight 

 days after the work was completed, the whole sunk eighteen inches, 

 without the least deviation from the perpendicular. Other modes 

 liad been adopted, amongst which was f lie following: — A number of 

 tiniber balks were laid across, and concrete placed in the spaces be- 

 tween ; then filled up with bricks; timbers were laid in a cross direc- 

 tion, and the fiat stones placed upon them. In this instance the wood 

 was laid where no change of atmosphere could affect it. The nature 

 and use of a coffer-dam was then explained, and the Professor, at some 

 length, showed tlie danger of incautiously drawing the piles; the va- 

 cuity occasioned by their withdrawal being filled up by the surround- 

 ing matter, greatly injured the stability of the foundation. In making 

 one of the London bridges, a great disfigurement had occurred in con- 

 sequence of the incautious withdrawal of the piles, one side of the 

 pier having sunk one foot. The modern plan to prevent such acci- 

 dents was to have a double coiler-dam — the piles of the inner one 

 being cut oft', and the outer piles might be withdrawn without danger. 

 In laying foundations, lie supposed there was a hiyer of soft ground, of 

 moderate depth, with a hard substrata; piles must be driven through 

 the soft soil into the bard bed ; a very slight depth would be suflicient, 

 but still, in most cases, t.heet piling would be necessary. 



The Professor said that he was lately indebted to an officer of the 

 Bengal Engineers for an account of a very ingenious method, almost 

 universally practised in laying the foundations of bridges and temples 

 in India. It would not answer here, labour being so dear ; but there, 

 where wood was very scarce, building materials in great plenty, and 

 labour very cheap, it was the simplest and most effective that could 

 be imagined. From the explanation, it appeared that the system was 

 the same as piling, but, instead of using wood, small wells of brickwork 

 were substituted. Take, for instance, the pier of a bridge ; a small 

 well of brickwork was constructed — say, six feet deep, seven feet in 

 diameter, with a hole through it, three and a half feet in diameter ;" 

 this is placed on the sandy bed where the foundation is to be made ; 

 a workman gets into it, and undermines the well from the inside, the 

 earth being drawn up in buckets, additional layers are added to the 

 top of the weU until a sound bottom was reached ; and the singularity 

 was, that there was not one or two of these little wells, but hundreds, 

 and, in certain cases, to a depth of fifty-five feet ; arches were then 

 thrown across, and the superstructure raised. Wheu the foundation 

 was in the bed of a river, the excavation went on by the workmen 

 diving through the water to the bottom of the well, anil working there 

 until obliged to come to the surface for air; for instance, through ten 

 feet of water in the river and to the extent of forty feet of water in 

 the well — one of the most extraordinary instances of perseverance 

 upon record. English engineers bad somewhat abridged the labour 

 by substituting an oblong square of fifteen feet by four feet, "vith two 

 elliptical holes for the workmen, so that, instead of three v^clls of six 

 feet, they get one of fifteen feet — the principle being precisely the 

 same. 



In France a number of bridges had been built where the water was 

 not rapid, upon a very simple foundation; a framework of timber 

 being made, furnished with short piles at the corner, and laid in the 

 bed of the river, and the superstructure raised upon it by means of a 

 wooden diving-bell. The pier perdue was another way, but could only 

 be used in still water ; a quantity of stones were thrown in until a 

 foundation was obtained ; where there was any current this foundation 

 was sure to give way, as in Plymouth Breakwater and Kingston Har- 

 bour. He then alluded to the case of one of the London docks, where 

 the wall, being made with too great a curve, from the want of pile 

 sheeting, the soil gave way— the engineer adding fresh matter until 

 the toe of the wall actually appeared (to the astonishment of all) above 

 the surface on the other side. He then gave examples of several ori- 

 ginal methods of preparing for the formation of foundations in Italy 

 and Ireland by means of baskets of stones, &c. 



CONCRETE. 



The Professor next explained tlie nature of concrete, and gave 

 directions for its formation — viz., one part of lime, twice that quantity 

 of sand, and twice as much broken stone, or gravel, as there was sand. 



The goodness of the concrete depended upon the quality of the 

 lime. In making concrete, it must be borne in mind that the materials 

 were far more bulky separate than when mixed ; for instance, to make 

 a cubic yard of concrete, which contained twenty-seven cubic feet, it 

 would be necessary to liave thirty-four cubic feet of materials, besides 

 the water. The three ingredients should be mixed dry, and the water 

 added ; iu slaking, the concrete will expand about one-thirtieth in 

 bulk. 



The great expense of cofler-dauis, and of piers generully, had lately 



. led to a very peculiar construction of bridges by piling only, as, for 

 instance, in iron bridges, no masonry being used. The Professor 

 stated, that he had built seven or eight bridges upon that system ; 

 the piles were driven in and the iron work erected upon the wood. It 

 had been tried to substitute cast-iron for piles instead of wood, but 

 they had not succeeded, the iron being very liable to break. He also 

 alluded to a beautiful arrangement for fixing branches to piles by means 

 of a sliding collar, but which it is impossible to explain without dia- 

 grams. A French work, above 2U0 years old, was produced, with 

 some very curious engravings of the modes then in use for securing 

 foundations, and which proved that we are using the same means at 

 present, and that many of our so-called new processes were in use at 

 that time. He then concluded by stating, that, at his next lecture, he 

 should bring forward some more general rules respecting foundations, 

 and after that proceed to .consider the best method of securing slopes 

 of earth, now so generally in use. 



Lecture 3. Wednesday, Sth Dec, 1S41. — Mr. Vignoles explained 

 that at his former lectures he had applied the term "concrete" too 

 generally, and would now explain the difference between " beloii " and 

 " concrete." Beton was formed of the usual quantity of sand and 

 gravel, broken stones, &c., but, instead of using the ordinaty stone 

 lime, hydraulic lime was applied. He then stated that beton is used 

 exclusively under water, concrete only where water does not get in ; 

 beton never sets until it is under water, while concrete will not set 

 except it is dry. The lime used for beton must be first slaked, while 

 for concrete it slakes in the process of mixing. Beton sets best when 

 let down gently in cases, and concrete when scattered from an emi- 

 nence. Beton takes months to become hard, while concrete hardens 

 in a few minutes. The both are in purport essentially the same — to 

 form an artificial stone or rock — the one for works under water, and 

 the other for those on land. He then alluded to the knowledge of the 

 ancients of beton and concrete, and read extracts from the works of 

 sundry authors, from Josephus to the present time, proving that asser- 

 tion. The use of piles was also very ancient, the foundation of a brick 

 pyramid in Egypt having been constructed on that principle. After 

 impressing upon the minds of the students the great importance of a 

 good foundation, and the efficacy of concrete for attaining that end, he 

 concluded, by stating that his next lecture would be again on the sub- 

 ject of foundations, and after that he would proceed to lecture upon 

 slopes of earth, and explain the causes of the late accidents upon the 

 different railways, pointing out where the errors of judgment had 

 occurred. 



Lecture 4. Wednesday, 15th Dec. 1841. — Mr. Vignoles commenced 

 by explaining the mode in which piles were driven in, and produced 

 a model of a pile-driving machine (from the museum of the cohege), 

 by means of which he showed the meihod in which steam power was 

 applied to that machine for expediting the work — stating, however, 

 that, far from that application being a novelty, he had used it himself 

 twelve or fourteen years ago. 



ROCK FOUNDATIONS. 



Having treated in his former lectures upon foundations in natural 

 soils, or various kinds of artificial bases, he would now notice such as 

 were of the composite order, being partly on rock, and partly requiring 

 artificial means to render them sufficiently sound for the required pur- 

 pose. It often happens that, in making a bridge, there may be rock 

 on both sides of the river, and the first pier may rest upon rock, while 

 the second and third may have an insecure foundation, in consequence 

 of a " pot-hole " (as it is called) of sand unexpectedly being discovered 

 in the very spot where these piers are to be erected ; the only plan 

 to get over this difficulty is to cut the edge of the hole in steps ; 

 sheet-pile it a short space from the wall of the hole, and fill up the 

 intervening space between the piling and the hole with beton, or some 

 other substance, and thus form a continuation of the rock itself. Diffi- 

 culties also present themselves in solid rock foundations ; for instance, 

 in such an erection as that at the Devil's Bridge ; the ravine over 

 which the bridge is to be thrown may have been formed by the run- 

 ning of water — the strata, accordingly, runs with the usual inclination 

 on both sides. If foundations for the piers of the bridge were not 

 sunk deep enough into the rock, the press of the water filtering 

 through the fissures of the strata have such force that, notwithstanding 

 the resistance of the arch, he had known instances of the pier being 

 actually pushed outwards. The only method of avoiding this was to 

 sink the pier so low into the rocks, and, by means of steps, secure it 

 so firmly, that the force of the water must break the pier — not force it 

 outwards — before it could destroy the bridge. The Professor, before 

 going into the question of rock foundations, begged to state, that, iu 

 these lectures, he only laid down the general principles of foundations ; 

 he could not go into the details of the business, and the circumstances 

 of stoue foundatious were so varied, that it was only by a life of labour 



