1841.1 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



171 



found that much of the information we may furnish is not to be found 

 in anv other publication. 



The heads under which our observations will be given, are — 



1st. Heat. 



2nd. Steam. 



3rd. Investigation of the reciprocal proportions of marine engines. 



4th. Investigation of the requisite strength of the parts of ditto. 



5th. Boilers. 



Gth. Practical details. 



Critical and illustrative annotations by Mr. Farey, Dr. Lardner and 

 others, will he appended, which, for the sake of distinction, will be 

 marked with Iheir respective initials. 



Beth. 



WESTMINSTER BRIDGE. 



In the preceding volumes of our Journal we gave several notices of 

 the repairs and improvements in progress at Westminster Bridge, and 

 have now great pleasure in fulfilling our promise of continuing them. 



The second coffer dam has been closed within the last five months, 

 and a more successful result from work of this description we have 

 never witnessed ; indeed it appears to be one of the greatest triumphs 

 of hydraulic engineering, to find a dam, (erected in a tidal river with 

 a rise and fall of Is feet of water, and exposed to every trial that one 

 of the severest winters on record could subject it to,) so completely 

 resist the efforts of its most insidious adversary, that after the wear 

 and tear of five months, there is scarcely sufficient water from leakage 

 to supply the ordinary demand of the works, and this too, on ground 

 that was declared unsuited for the purpose, by the engineer who con- 

 structed the bridge, and by all who succeeded him up to the time when 

 the present works were commenced, if we may judge from the way 

 in which they carried on the repairs, ard from the schemes for restor- 

 ing it as exhibited in their reports. 



The present dam encloses the IG feet and 15 feet piers. Of the 

 former we have only to observe, that the foundations were found 

 similar to those in the first dam, the caisson resting on abed of gravel, 

 underneath which was the blue clay ; they have since been secured in 

 the manner already described in a former notice (vol. ii. p. 203j, and 

 the masons are proceeding with the new facing, of Bramley-fall stone, 

 above the lowest low water mark, and also with the extension of the 

 pier on the upper side, whereby the roadway may at any future time be 

 widened 12 feet, without again having recourse to the expensive pre- 

 paration of coffre dams. 



The 15 feet pier is the one memorable in-the history of the bridge, 

 as having, by its sinking, delayed the opening to the public for three 

 years, and given an apology to the party opposed to Labelye, (the 

 engineer), to assail him with every slander that malice could invent, 

 and by tampering with the commisioners, to nearly prevent the com- 

 pletion of the bridge according to his original design. How severely 

 this treatment affected Labelye, we may see from a work published by 

 him afterwards, in which he repels their attacks with great spirit, and 

 with a bitterness that must have arisen from feeling himself deeply 

 injured. We will here give a few extracts from this work, detailing 

 the extent of damage done to the bridge by the accident, and the 

 means he adopted to remedy it. 



"On the 14th November 1746, the bridge and the roads and streets 

 on both sides were completely finished, and the whole was performed 

 in seven years nine months and sixteen days. The commissioners in- 

 tended soon after to have opened the bridge for the service of the 

 public, but were prevented by an accident entirely unforeseen, and not 

 easily accounted for. In the months of May and June, 1747, the wes- 

 tern fifteen foot pier was perceived to settle, very gently at first, but 

 so much faster towards the end of July, that it was thought ab- 

 solutely necessary to take off the balustrades, &c., by the continuation 

 of the settling, the adjoining arches lost their semicircular figure, and 

 considerable openings in the joints showed them in danger, some of 

 their stones both in itieir fronts and soffits were split and broken, and 

 one of them actually fell out of the least arch into the river." 



The first steps taken weie to carry up the two external piers of the 

 two arches that were damaged quite solid, in rubble stone and mortar, to 

 the level of the top of the arches, and to load them sufficiently, in 

 order to preserve the other arches and piers of the bridge ; centers 

 were then put up to carry the two arches, and they commenced loading 

 the damaged pier. The account of the last proceeding Labelye thus 

 describes; "the whole weight of load placed on the said pier was so far 

 magnified by writers of daily news and monthly magazines, as to be 

 called 12,000 tons, while it never did exceed 700 tons, which was about 

 a third of what I intended to load it with." What prevented this, was 

 the influence of the party opposed to him, who persuaded the com- 



missioners that further loading would be dangerous, and prevailed on 

 them to give him orders to unload the pier, and take down the damaged 

 arches." "This order," says he, "was the first and only one I ever 

 received from the commissioners contrary to my judgment or opinion, 

 and which I obeyed, but I oion nut wil/wiil some concern." 



We may here remark that the execution of this order, (as will be 

 seen in the latter part of our notice,) has allowed the pier to remain in 

 an unstable condition ever since, and had it not been for the successful 

 repair lately effected, must finally have occasioned the destruction of a 

 portion of the bridge. 



His next proceeding was to inclose the foundation with 12 in. piles, 

 and to rebuild the arches ; "the dove-tailed piles were driven all round, 

 close to the bed of timber on which the pier is built, and so deep as 

 to reach about 15 feet under it all round, and afterwards were all sawn 

 off" low enough below low water mark, as never to be any obstruction to 

 the navigation of any boat or vessel. Then the two damaged arches 

 were rebuilt the very same in appearance, but with uuicli less material 

 in the inside." 



After the preceding extracts, an account of the state in which 

 the pier was found when the water was excluded from the dam, and 

 of the works executed since then to secure its stability, cannot fail to 

 be interesting to our readers. 



On the removal of the ground about the pier, the joints of the dove- 

 tailed piling, described above, were found any thing but close, and to 

 make the matter worse, several of the piles had broken in the driving. 

 As no dependence could be placed in this work, new sheet piling, of the 

 same description as that used for the IG feet pier, was driven all round, 

 enclosing the foundation, thus at once preventing the escape of the 

 finest particles of sand from under the pier. The old piles were after- 

 wards sawn off at a low level, in preference to drawing them, as it was 

 thought their removal might disturb the ground. 



During the progress of driving the piles, considerable movement 

 took place in the adjoining arches, showing evident symptoms of further 

 sinking in the pier, and to prevent any injurious eHect upon the ma- 

 sonry, strong shoring of whole timbers was fixed from the coffre dam 

 to the sofiit of the 64 feet arch, a precaution that has been attended 

 with considerable advantage, as the arch stones have remained nearly 

 uninjured, although several of the mortar joints were broken. 



On the removal of the ground within the sheet piling, the project- 

 ing part of the timber bottom of the caisson was found to be broken 

 and separated from that part underneath the pier, this had arisen from 

 the space intended for the caisson not having been dredged sufticiently 

 large to receive it, so that it was resting on the slope of the excava- 

 tion, the centre part being hollow, until the weight of the masonry- 

 broke away the sides and allowed the pier to settle on the loose sand 

 and gravel which had run in ; the level of the blue clay being nearer 

 the surface at this pier than the adjoining one, the excavation was 

 principally in that material, and its intense stiffness will account for 

 the dislocation that took place in the timber work. 



The critical position of this part of the work recjuired much cau- 

 tion, and in applying a remedy to so uncommon a case, we are glad to 

 bear testimony to the most perfect success 6f the plan adopted; we 

 have no doubt that this pier is now as trustworthy as any of the others 

 that have been taken in hand. 



The whole of the disturbed foundation timbers were removed, as 

 also all the loose and muddy ground to the solid clay — the depth in 

 some parts being as much as two feet, — under the foundations a body 

 of concrete was filled in, level with the underside of the caisson, and 

 to increase the bearing of the pier, timbers were laid parallel to the 

 sides of the caisson, crossed by others placed IS inches apart, and in- 

 serted to the length of 2 feet G inches under the masonry, — -to insure 

 their perfect bearing each timber was cut wedge form, and driven tight 

 into the space it was intended to occupy. This operation was con- 

 tinued all round the pier, thus increasing its bearing surface about 

 three feet on each side. 



Fioni that level a mass of brickwork was built, backed with con- 

 crete to receive the stone work of the pier, which in this case is to 

 form a projecting footing of masonry, and the space within the sheet 

 piling is to be finished with a capping similar to the other piers. 



The masons are now employed Ujion this part of the work, aud in 

 extending the pier for widening the roadway, and if we may judge 

 from the number of men employed, aud vast store of materials pro- 

 vided, no very long time will elapse before the use of that magnificent 

 temporary work, the dam, may be dispensed with. 



We are happy in having had this opportunity of removing the un- 

 certainty and error that has hitherto prevailed about the settling of 

 this jiier,— it has always been attributed to the ballast-men lifting 

 gravel too near the foundations, and the late Mr. Telford and others in 

 their plans for securing the piers, had only one object in view, that of 

 preventing any farther scour from the river — in the present instance 



