860 Transactions of the American Institute 



mass of the earth into which they are driven. Where the earth 

 is liable to subsequent disturbance, piles so used are always value- 

 less. 



It is particular]}'^ necessary to caution the young engineer of the 

 danger of using piles, either for compacting the earth or as mere 

 columns of support. 



Trustworthy foundations, as reliable as those on rock or hard 

 earth, may be obtained by the means of piles, if they are properly 

 driven, and in places where they are not liable to decay or lose 

 their support by scour. 



When each pile in the foundation is driven to the same point of 

 resistance, they will each bear the same load. The force of the 

 blow of the ram, the resistance which the pile meets, and the 

 weight which it will bear, are of course all equal. So that if piles 

 of different sizes are driven into different kinds of soil, until they 

 cease to move, by the same ram falling the same distance, they will 

 all bear the same load. 



I recently read a paper before the Franklin Institute, in which 

 I discussed this subject at considerable length, and from which I 

 extract as follows: 



"The formula which is generally used to determine the support- 

 ing power of wooden piles, is either that of Weisbach or Saunders. 

 In the common range of practice, the results of these two formulfe 

 do not widely differ, but the latter says that his result gives the 

 •'safe load," while the former says that "for duration and security 

 such piles are only loaded with from one-tenth to one-hundredth of 

 their strength." 



The formula which I have to submit to your consideration is as 

 follows: 



P=80. (W-f .228Vf— 1.) 



Where P represents the extreme supporting power of the pile in 

 tons; w, the weight of the ram in tons, and f the fall of the ram 

 in feet. 



This formula was derived from a number of experiments, made 

 upon piles driven for the foundation and coffer-dams of the United 

 States Dry Dock at Brooklyn. 



The gentlemen present are doubtless all familiar with the char- 

 acteristics of that work, and it will only be necessary to state that 

 the structure weighed fifty thousand tons, which had to be sup- 

 ported on an area of forty-four thousand square feet; but the weight 



