d = pile diameter 



f = unit local friction sleeve resistance 

 s 



A 1 = pile-soil contact area over f depth interval 

 L = total embedded pile length 



CPT Cone Pressure, q c 



pile end bearing = q D 



Icl + 1c2 



q c j = Average q c over a distance of y (diameter), when y is any value 

 (y d) below the pile tip (path a-b-c). Sum q c values in both the 

 downward (path a-b) and upward (path b-c) directions. Use 

 actual q c values along path a-b and the minimum path rule along 

 path b-c. Compute q j for y-values from 0. 7d to 4.0d and use 

 the minimum q c j value obtained. 



q c 2 = Average q over a distance of 8d above the pile tip (path c-e). 



Use the minimum path rule as for path b-c in the q c j computations. 

 Ignore any minor "x" peak depressions if in sand, but include in 

 minimum path if in clay. 



Figure 29. Dutch procedure for predicting pile tip capacity 

 (from Schmertmann, 1978). 



The correction factors K and K can be found in Figure 31. Other 



s c 

 procedures are also available and are reported by Schmertmann (1978). 



One method involves estimating s and then reducing it by multiplying by 

 the factor given in Figure 30. Another incorporates effective stress by 

 including overburden pressure but still relies on an empirically derived 

 factor. The method presented herein has been demonstrated by Schmert- 

 mann and has given good results; therefore it is recommended. Negative 

 side friction caused by downloading on the pile by the soil is usually 

 taken as two-thirds of the positive friction values. 



48 



