A Chcqyter on Foundations. 285 



Major Sanders of the Engineer Corps and Mr. McAlpin, Civ. 

 ^Engr., have had perhaps the best opportunities of investigating 

 this class of foundations and supplying reliable practical formulas. 

 Major Sanders has experimented and successfullj constructed at 

 Eort Delaware and Reedy Island on the Delaware river, on the 

 most treacherous alluvium, upon which a permanent extensive 

 building has perhaps ever been erected. Borings were made at 

 these places to a depth of about 50 feet and nothing but a liquid 

 impalpable sea of mud was found. Piles were driven from forty 

 to ninety feet deep with the greatest ease. Trial piles were driven 

 and loaded with great weights and the effect of these weights was 

 observed and recorded during a series of years ; from these obser- 

 vations a formula was deduced which became a basis of the con- 

 struction of the foundation of Fort Delaware and similar 

 structures. 



Mr. McAlpin, eminent in his profession, had charge of the con- 

 struction of the United States dry dock in the Brooklyn navy 

 yard, and had to contend with a treacherous bed of quick sand 

 and springs, where the difficulties encountered " are almost inde- 

 scribable and the engineers were at times almost driven to 

 despair. 



The results of the labors of the aforementioned engineers were 

 almost identical and the application of their formulae, will, in 

 doubtful cases, be liable to err on the side of safety. 



At Fort Delaware, the possibility of reaching a bottom support 

 for piling was out of the question, on account of the expense. 

 The alternative was to consolidate and compact the super strata 

 in such a manner as to support the weight of the design by driv- 

 ing as many piles as the ground would admit of; the piling was 

 substantially capped, the spaces filled with betonand covered with 

 a strong timber floor, upon which the Fort now stands, without 

 any failure. Had there been a hard substratum at a reasonable 

 depth, the piles would in that case be only so many columns sap- 

 porting the superstructure. 



Major Sanders' formula is as follows : 



Divide the fall of the ram in inches by the motion of the pile 

 at the last blow in inches ; multiply the quotient by one-eighth of 



