Polytechnic Association Proceedings. gg| 



could not be equally distributed, and some portions of the founda- 

 tion had to sustain a weight of three or four tons per square foot. 



The material as developed by the excavation, preliminary borings, 

 and subsequent examinations to a depth of sixty feet below the 

 foundation, was a silicious sand mixed with comminuted particles 

 of mica and a little vegetable loam, and was generally encountered 

 in the form of quicksand. 



The material into which the foundation piles were driven was 

 nearly uniform in character, which furnished an excellent opportu- 

 nity of comparing the experiments made at different times, with 

 hammers of different weights and falls. 



It may be interesting to state, that the whole number of bearing 

 piles driven for the foundation was 6,539 and 1,744 sheeting piles, 

 acting in part as supporting piles, which gives nearly 1.7 piles per 

 square yard, or, excluding the sheet piles, 1.4 per square yard. 



These piles were chiefly of spruce timber, from twenty-five to 

 fort}^ feet long, and averaged thirty-two feet driven length. They 

 were from twelve to eighteen inches diameter at the head, and 

 never less than seven inches at the foot. They were banded with 

 iron, and occasionally shod, but shoeing produced no increase of 

 penetration. 



The average number of blows given to each pile was seventy- 

 three. The average distance moved by the first five blows was 

 eight inches at each blow, by the middle five blows, three inches at 

 each blow, and by the last five blows from two inches to no move- 

 ment at each blow, 



TVhen from any cause the piles went more than an inch at each 

 of th« last five blows, another was driven in the center of the quad- 

 rangle, and it was found that this so compacted the material, that 

 the adjacent piles were immovaljle under the effect of almost any 

 number of blows, of a ton ram, falling thirty feet. 



In other words, all of the piles were driven " home," or equiva- 

 lent to such home driving. The Nasmj'th hammer, it is true, 

 produced a deeper penetration of perhaps ten per cent, but under 

 its persuasive powers, the strongest and toughest timbers yielded. 



A record was kept of the distance moved by each blow, on every 

 pile used in the structure, and the weight and fall of the hammer. 



The piling machines were unusually well made, so as to reduce 

 the friction of the hammer in its fall, and facilitate the operations. 

 The leaders were generally thirty-five feet long, though there was 

 one of fifty-seven feet. The hammers were generally of a ton weight 



