IQ A STATISTICAL ACCOUNT OF THE 



jDroportion ; because the abutments must have approach- 

 ed each other, so as to occupy the position now open, 

 through the land or side arches. 



No persons engaged in such difficult works, should 

 risque any project to save expence of foundations, for 

 piers or abutments. But on the other hand, coffer dams 

 should be avoided, if any other means can, with common 

 prudence, be adopted. Their expence is enormous, 

 and their success not alwaj'^s to be ensured. The great 

 proportion of the expenditures in the Schuylkill bridge, 

 has been incurred by the inevitable necessity for coffer 

 dams. The labour applied, and the difficulties encoun- 

 tered and overcome, will appear to the best informed 

 engineers, uncommon and singularly arduous, as will 

 appear by the short account of them subjoined to the 

 present statement. Every effiDrt was made to avoid 

 the necessity of these dams, but on duly weighing all 

 the projects suggested, none could be adopted with any 

 prospect of safety. The irregularity of the bottom, 

 and depth of water, at once ^^'ere found to forbid the 

 use of Battei'deaus. Floats were thought of, com- 

 posed of a platform of logs, on which masomy should 

 be formed. These were to be built on, with logs 

 at the sides, and others crossing the whole, bolted 

 like wharves; filled in with masonry, and raised on as 

 they sunk, till having lodged on the bottom, they should 

 compose the foundation for masonry, from low ^vater 

 mark. But no horizontal, or solid position could be 

 obtained for them. All the objections to batte?'deaiis 

 lay against them. A flood too, might have carried them 

 off in an unfinished state. This was proved, when a 

 few of the belts of the. coffer dam (light and buoyant. 



