204 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[June 



during its progress, proceeds, at tlio rcipiest of the Commissioners, to 

 answer tlie difl'erent objections tliat had been urged against liis mode of 

 construction. He puts tliem in the form of " Objection" and " An- 

 swer." Tlie experience of 100 years has now tested tlie accuracy of 

 his replies, and in only two instances luis it proved liim in error. We 

 will give these here, as tliey are intimately connected with the present 

 works. 



3rd Objection. — "Why could not the foundations of the piers liave 

 been laid by the help of coU'er dams, suc^l as are called by tlie French 

 Battardaux ?" 



Answer. — After explaining tlie construction of coffer dams, he 

 states — " Tho first inconveniency attending this manner is, that if the 

 enclosure be not strong enough, or not sufficiently propped or braced 

 in the inside, it will not be able to support the pressure of the external 

 water (especially if the water be agitated by stormy winds), which, by 

 breaking and bursting in, often destroys many lives, and entirely de- 

 feats the intentions of tlie [irojectois that have not taken the necessary 

 precautions, of which I could give a great many instances, some of 

 which I liave been an eye-witness to. But if this metliod had no other 

 inconveniency, it could easily liave been remedied in the execution of 

 the intended bridge, — England, and London especially, abounding with 

 excellent artificers of all kinds. But what would have rendered it 

 entirely useless or ineffectual, is tlic nature of the bed under the river 

 Thames, wliich at the place where the bridge is, is everywhere a gravel, 

 covered over on the Surrey side with a soft loomy sand, all which 

 woidd suffer the water to ooze up (notwithstanding the sides of the 

 battardeau, or coffer dam, should be perfectly tight) so fast, especially 

 the gravel, as to put it out of the power of any engine or engines to 

 drain tlie battardeau or coffer dam. Indeed, where the ground under 

 the foundation is a stiif clay, or an earth of a suflicieiit consistency to 

 hold water, battardeau x or cotter dams have been used w itli success, though 

 attended with an immense expense and trouble, and what I would have 

 used if I had not foreseen that in tliis place it would have been in vain 

 to attempt to come at the bottom, and raucli more so to reach several 

 feet under the bed of the liver by any sucli means. Those that have 

 seen (or have been concerned in) buildiiics erected in water when 

 the ground is a gravel, or a loose clay, or a sand, well know the insepara- 

 ble difficulties that would have arisen if such coffer dams had been 

 attempted on the Thames over against the Woolstaple, where, besides 

 the agitation of the water, occasioned by the winds, the height of the 

 water is perpetually increasing or decreasing from six feet to about 

 twenty-three feet perpendicular height above the surface of the bed, 

 which two circumstances alone would make it difficult and very ex- 

 pensive to provide proper materials, and construct a coffer dam suffi- 

 ciently strong to resist such unequal pressures so as to kceji out the 

 ambient water." 



" As to the oozing in of the water through the pores and interstices 

 of the gravel, loose clay, or sand, it may easily be shown, that if all the 

 interstices in the bottom of the foundation of one of the piers taken to- 

 gether amount only to a hole of six inches square (which is a supposi- 

 tion much under the truth) ; and, supposing the tide or head of water 

 above the foundations, as it is at a mean or an average between the 

 highest and lowest, about 15 feet perpendicular, it would give 770 

 tons per hour, which is more than 70 men could pump out, even sup- 

 posing them to act always with the same strength as they do at first, 

 and to work day and night without ceasing, and more than 150 men 

 or 30 horses could do working as tlicy commonly do." 



7th Objection. — " Notwithstanding all the precautions that have 

 been taken to render the foiuidations of the piers as firm and solid as 

 if they were built upon dry ground, they will always be in danger of 

 the water gulling underneath and carrying away the ground from under 

 the planked gratings on which the piers stand." 



Answer. — He enters into an explanation of the elTect of running 

 water on the beds of rivers, and into calculations respecting the con- 

 sequences in case London Bridge siiould be removed, and con- 

 cludes with, " I rather suspect (with regard to the river Thames and 

 Westminster Bridge) the reverse of the objection will happen ; viz., 

 that the piers will in time be more and more buried in the ground by 

 the silting of the river which must accumulate in a long course of years, 

 for in all tide rivere (at least in those that have no extraordinary 

 declivity towards the sea), we find their beds continually rising, and 

 in the Thames in particular, it is well known that the bed of the river 

 (especially above London Bridge) is several inches higher than it was 

 one hundred years ago, which 1 conceive to be occasioned by the tide 

 of ebb having so long a time to deposit its settlement, and every tide 

 of flood preventing in a great measure part of that settlement from 

 being carried down to the sea." 



It is needless to ofFer any remarks on these opinions of Mr. 

 Labelye. He appears to have acted with the greatest consideration 

 while engaged in this arduous undertaking, and if we bear in mind that 



an engineer at that time had very little from the experience of 

 others to guide him, and that this was unquestionably the greatest and 

 most difficult work that had ever been attempted in this country, we 

 must feel more inclined to admit the genius of its author and to give 

 him praise for the amazing skill and ingenuity displayed in its construc- 

 tion, than to cavil at any errors he may have committed. 



We now pass over a period of seventy years, during which there is 

 nothing worthy of notice. The proposed removal of one of the piers of 

 old London Bridge appears to have been the first thing to call the at- 

 tention of the Commissioners of Westminster Bridge to the security 

 of its foundations, for we find that in May, 18'23, tlie late Mr. 

 Telford was called on by them for his opinion as to the probable 

 effect which might be occasioned by such removal. In his report, he 

 mentions that the platforms upon wliich the piers rest, which were de- 

 scribed by Mr. Labelye to have been placed none less than five feet nor 

 more than fourteen below the bed of the river,are now found torange be- 

 tween thieeand seven ; and if LoudonBridgebe wholly removed, the con- 

 sequences will most likely be fatal toWestminster Bridge ; he then recom- 

 mends certain works to be done for its safety. These works proceeded 

 under his direction during the remainder of his life ; they consisted of 

 piling round some of the piers and protecting them with masonry by 

 means of a diving-bell, rebuilding some of tlie cutwaters and octagons, 

 &c. 



In August, 1835, notwithstanding wliat had been done by Mr. 

 Telford, we find, when Mr. Cubitt was called on to report how far 

 the proposed embankment for the New Houses of Parliament would 

 aflect the stability of the foundations of the bridge, he states that the 

 foundations were still far from being in a secure state — and in June, 

 183G, he reports " on the present state and best manner of rendering 

 secure the foundations of this bridge." 



He points out three modes of securing them : — 

 1st. Depositing heavy rubble stone round them. 

 '2d. Surrounding each of the piers with sheet piling of oak or cast- 

 iron, coming up above low water, securing them to the piers and filling 

 the space with stones and cement. 



3d. Paving the whole space under the arches, anddrivingsheet piling 

 on each side of the bridge the whole way across the river. 



This last plan he estimates at not less than 1'20,00()/. and not more 

 thau 150,000/., and to completely restore the superstructure besides, 

 in all from 160,000/. to 200,000/. 



In February, 1837, Mr. Walker reported on the same subject. His 

 instructions with reference to the present bridge, he states, were — 



" That I survey Westminster Bridge, and report my opinion on the 

 state of its foundations, and what I deem necessary to be done to put 

 the existing bridge in a state of permanent security, with an estimate 

 of such repair." 

 His opinion is — 



1st. That the best mode of securing the piers of Westminster Bridge 

 is by coffer-dams, then pumping out the water, and piling roimd the 

 piers. 



'2d. That the expense of this for all the piere will be . . £70,000 

 3d. That renewing the ends and spandrils of all the piers 



in the way already begun, will cost 21,000 



4th. That the present parapet ought to be taken oft', 

 and a lower one substituted, and that the inclination of tlie 

 road may and ought to be improved ; the cost of these will be 1 2,000 



Total cost .... £103,000 



Shortly after tliis Messrs. Walker and Barges prepared plans and a 

 specification for the repairs of the bridge, and the Commissioners ac- 

 cepted Mr. William Ciibitt's tender in May, 1838. 



The specification is formed into two divisions : — 



The first contains the coffer dams and securing the foundations of 

 eleven piers, deepening the bod of the river, at the bridge, after the piers 

 are secured ; putting in a new coinice and a new parapet for its whole 

 extent, lowering the carriage road and footpath upon the bridge, raising 

 the approaches at each end, and repairing the footpaths witli new stone. 



The second embraces the repairs to the masonry of the superstruc- 

 ture ; such as restoring the injured faces of the stones of tlie arches and 

 piers, rebuilding such of the cutwaters and octagon piers sis may be 

 ordered, and also repairing and rebuilding the spandril walls of the 

 arches. 



Mr. Cubitt immediately commenced operations, and in eight months 

 completed the cotter dam round the 13 and 14 feet piers on the West- 

 minster side ; and notwithstanding all that had been said about the 

 impossibility of keeping the water out, and that it would require 150 

 men to pump constantly in a dam round one pier only, it appears that 

 one man, working two or three liouis during the day, is sufficient in this 

 dam round two piers. 



When the mud wliich had accumulated during the execution of the 



