Polytechnic Association Proceedings. ggx 



upward force only, and in some less frequent cases the same founda- 

 tions may be subjected alternately to an immense weight resting 

 upon it, and to a corresponding force operating in a diametrically 

 opposite direction. 



In the case where the natural bottom is rock, resistance to the 

 downward pressure is already provided for, and the upward force 

 can also be readily resisted by the simple expedient of iron or 

 copper bolts, inserted in holes drilled into the rock, and then 

 secured by the method known as fox-wedging, or by forming the 

 lower end of the bar into a "lewis," and when the place is free 

 from dampness further security is sometimes given by pouring into 

 the interstices melted lead, for which sulphur or cement is occa- 

 sionally substituted. 



The propriety, however, of placing two different metals together 

 is very doubtful, except for temporary purposes, when the galvanic 

 action may be disregarded. 



Bars or rods so employed are termed holding-down bolts, and are 

 not properly within the subject of foundations, though intimately 

 connected with it, as can be readily seen. 



The cases to which I more particulai'ly wish to call attention are 

 those of foundation piles having to resist an upward strain in direc- 

 tion nearly corresponding with the longitudinal axis of the pile. 



Experiments upon piles in this relation are very meagerly 

 recorded in the books, and as such experiments are always expen- 

 sive, and their results very valuable when accurately recorded, it 

 seems to be the duty of every engineer possessing such records to 

 place them where they will be permanently recorded, and can be 

 made available, especially by the profession. 



The experiments which I am about to describe specially, were 

 made in 1851 at the United States Navy Yard, Pensacola, Florida, 

 and were ordered by Commodore Joseph Smith, Chief of the 

 Bureau of Yards and Docks (now Rear Admiral Joseph Smith), to 

 enable the Department to determine how much lifting force each of 

 the wooden piles, to which were secured the timber bottom of the 

 floating dry dock basin, was capable of resisting. 



A copy of the order of Commodore Smith to the commandant 

 of the navy yard, is as follows: 



iCopy.} 



Bureau of Yards and Docks, ) 

 S th May, IS51. $ 



CAPTAiy — You will please call upon the engineer of the yard for a report stating 

 the average depth to which the foundation piles in the floating dock basin hare 



