Polytechnic Association Proceedings. 895 



The last blows produced a penetration of from two to five inches, 

 averaging about three and three-quarter inches. 



The weight of the piles were estimated by Colonel Mason, to be 

 nine hundred and sixty pounds each. According to the formula 

 adopted by him and given below, in which 



W=weight of the ram in pounds. 

 W= weight of the pile in pounds. 



h=height in inches ram fell last blow. 



d=depth in inches of penetration from last blow. 

 I^=retarding force of the pile. 



"W h 

 Formula: R = W H 1 , 



W + W d 

 which gives, after substituting the figures, the value of R=118,175 

 pounds for the above average weights and measurement. 



These piles had actually been loaded with 28,575 pounds for a 

 number of years, when I left the work, without the slightest indi- 

 cation of settlement; this should be the case, inasmuch as they 

 are only loaded to one-quarter of that weight, which the force of 

 resistance is capable of holding in equilibrio, according to the 

 above formula. 



Many cases have come under my observation in whicb," after a 

 pile had been driven and remained undisturbed for a longer or 

 shorter period, another blow was struck with the invariable result 

 of less motion than was to have been expected if this blow had 

 immediately succeeded the others; and there is reason to believe 

 that the vertical force necessary to withdraw a pile becomes mate- 

 rially greater the longer a pile remains driven and undisturbed. 



Respecting experiments, I cannot do. better here than repeat the 

 exact language of my lamented friend, Mr. Warren Q. Dow, Civil 

 Engineer of the Government at Pensacola Navy Yard, who said, 

 after the experiments at that station: 



" In experiments made to determine the comparative settlement 

 of piles, note should be made of the time which passes between 

 the successive blows of thfe hammer. 



" The results of a few experiments on these piles show that piles 

 which six-tenths of an inch per blow of a 4,087 pound hammer, 

 falling ten feet one day, were found to settle one-eighth, one-half, 

 six-tenths inch by three similar and successive blows applied the 

 following day — the three blows being given in a minute." 



This increase of resistance or "setting" of piles by a delay after 

 driving, corresponds to my own experience respecting piles in all 



