DEFECTIVE PILE-HEADS. 



397 



P = supporting power of piles in tons. 



w = weight of ram. 



h = fall of ram. 



I = length of pile. 



s = sectional area of pile. 



x = set of pile at last blow. 



e = modulus of elasticity. 



m = weight of pile. 



Defective Pile-heads. When the head of a pile becomes 

 broken up, broomed, or cushioned by the repeated blows of the 

 monkey, the value of the blow is partly lost through the extreme 

 degree of elastic resistance at the pile-head, even though the 

 brooming may not extend to a greater depth than one inch. 

 The following results of experiments 1 show the comparative 

 influence of the solidity or looseness of the pile-head on the 

 effect of the blow. 



A green Norway pile was placed in position, and, when 

 dropped through 10 feet of water, it penetrated the silt at the 

 bottom of the river for a depth of 10 feet ; the monkey was then 

 set to work. 



The 3rd foot of penetration required 

 4th 

 5th 

 10th 



5 blows. 

 15 

 20 

 73 



12th 153 



14th 684 



The head was then adzed off. 



The 15th foot of penetration required 275 



18th 825 



The head was then sawn off. 



The 19th foot of penetration required 213 



22nd 378 



Total number of blows 5228 



A similar pile that had not been adzed or sawn during the 

 driving required 9923 blows to descend to the same depth as the 

 first pile. The weight of the ram was 2800 Ibs., the fall 3 feet, 

 and worked at the rate of 65 blows per minute. The friction 

 caused by the working of the fibres upon each other under the 

 blows of the ram was sufficient to ignite and burn the interior 

 of the head of the pile from side to side. 



Water-jet in Pile-driving. At the Calais Harbour works, 



1 Transactions of American Society of Civil Engineer*, Nov. 1883, p. 441. 



