T - (II) V5 (8) 



n h 

 where T = relative stiffness (m) 



E = Young's modulus for the pile (Pa) 

 I = polar moment of inertia of the pile (nr) 

 n, = coefficient of horizontal subgrade modulus (Pa/m) 



Piles with embedded lengths larger than 4T act as if they were embedded 

 to an infinite depth (Davisson and Gill, 1963). 



The desirability of small deflection takes on increased significance 

 when repetitive loading is present. This will be discussed more in the 

 section on repetitive loading. 



Pile Axial Capacity 



Pull out Capacity in Clay . A semi -empirical procedure (Vi jayvergiya 

 and Focht, 1972) was used to predict the pullout capacity of the piles 

 for cohesive soils (A, B, C). The method of analysis expresses pile 

 fricitonal resistance as a function of mean vertical effective stress and 

 mean undrained shear strength: 



«i = x B. + 2s m > A s (9) 



where Q = side friciton on pile (n) 



X = dimensionless friction coefficient 



a = mean vertical effective stress over pile length (Pa) 

 m 



2 

 A = lateral area of embedded pile (m ) 



s = mean undrained shear strength over length of pile (Pa) 



The friction coefficient was based on available data from load tests at a 

 number of different locations. Comparison of predicted friction pile 

 resistance to observations showed good agreemait (Vijayvergiya and Focht, 

 1972). 



Pullout Capacity in Sand . For category D soil (sands) a simplified 

 empirical procedure was followed. Pullout resistance was taken as a 

 function of mean vertical effective stress, a : 



53 



