CHAP. VI. 



WATERLOO BRIDGE. 



181 



and in much larger and more substantial pieces of 

 masonry than had previously been practised. 4th. The 

 adoption of elliptical stone arches of an unusual width, 

 though afterwards greatly surpassed by the same engi- 

 neer in his New London Bridge. 



Mr. Kennie invariably took the greatest pains in 

 securing the most solid foundations possible for all his 

 structures, and especially of his river works, laying them 

 far below the scour of the river, at a depth beyond all 

 probable reach of injury from that cause. The practice 

 adopted in founding the piers of the early bridges across 

 the Thames, was to dredge the bottom to a level surface, 

 and build the foundations on the bed of the river, pro- 

 tecting them outside by rubble, by starlings, or by 

 sheet-piling. Mr. Dodds had proposed to follow the 

 method employed by Labelye at Westminster Bridge, of 

 founding the piers by means of caissons ; but Mr. Rennie 

 insisted on the total insufficiency of this plan, and that 

 the most effectual method was by means of coffer-dams. 

 This would no doubt be more costly in the first in- 

 stance, but vastly more secure ; and he foresaw that the 

 inevitable removal of the piers of Old London Bridge, 

 by increasing the current of the river, would severely 

 test the foundations of all the bridges higher up the 

 stream which proved to be the case. Having already 

 extensively employed coffer-dams in getting in the 

 foundations of the London and East India Dock walls, 

 he had no doubt as to their success in this case; and 

 they were adopted accordingly. 1 



1 The coffer-dams in which the 

 foundations of the abutments were 

 built, were formed by driving two 

 rows of piles 13 by G inches each, 

 with a counter or abutting pile at 

 every 12 feet, 12 by 12, driven in the 

 form of an ellipsis, and strongly ce- 

 mented together, at low-water and 

 high-water levels, by double hori- 

 zontal walings or bracks, having a 

 space of about 8 inches clear between 



them for the intermediate or half 

 piles. The whole were driven close 

 together from 15 to 20 feet deep into 

 the ground, well caulked, so as to be 

 water-tight, and all connected firmly 

 together by strong wrought iron bars 

 and bolts, besides shores and inter- 

 mediate braces. The spaces between 

 the two rows of piles were then 

 rammed close with well-tempered 

 clay, so that they formed, as it were, 



