288 Wisconsin Academy of Sciences, Arts, and Letters. 



The Brooklyn caisson of the East river bridge rests for the 

 most part on a bed of boulders and hard-pan at a depth of AA\ 

 feet below mean high tide and the top of the caisson at 20 feet. 



The depth of water is from 12 to 16 feet in front of the tower ; 

 the river drift was perhaps 12 to 14 feet deep. This leaves us but 

 SO feet from mean high tide to a good foundation, if properly 

 treated. 



This Brooklyn caisson cost something over $300,000 ; a coffer- 

 dam would have cost less than $100,000 ; the excavation would 

 have cost less also than the masonry ; so that it is very evident 

 that there would have been a considerable saving in cost. The 

 weight resting upon the bottom is about 5^- tons per square foot, 

 and is considered entirely safe. The settling at the water line 

 has upon close observation barely exceeded one inch at any point. 



The consideration of these two extraordinary structures has 

 brought us to the subject of foundations in water. Many of the 

 plans mentioned in a preceding part of this paper are applicable 

 to piers and abutments in water. The solid and hollow screw 

 pile and iron cylinder can be applied with success. A very com- 

 mon plan for piers consists of a sufficient number of bearing piles 

 surrounded by timber cribs and the space filled with loose stone 

 to support the piles against lateral motion. The crib is not per- 

 mitted to rest upon the bottom but is supported some distance above 

 so that the stone may roll out and assume a position which will 

 give a broad base to the filling. 



A very excellent plan for building piers and permanent wharves 

 has been extensively applied by the U. S. Bog. Corps, where the 

 bottom was of substantial material : A scaffold is erected upon 

 piles driven by a floating pile driver, upon this the exact location 

 of each pier is determined. Loose stone or bowlders are removed 

 from the site and a sufficient number of bearing piles are driven 

 and sawed off perfectly level close to the bottom. See plan of saw. 

 The bottom course of the pier of 4, 6 or 8 feet square and 2 feet 

 or over in thickness is composed of one stone, this stone is 

 lewised at the corners and supported by chains to which are at- 

 tached large screws. which pass through timbers on the staging. 

 The first stone being placedain the slings it is lowered to the level 



