-. 1.0 



0.5 1.0 1.5 2.0 2.5 3.0 3.5 



Undrained Shear Strength, s (kips/ft ) 



Figure 30. Correlations of clay adhesion- 

 pile ratio with undrained shear 

 strength (Schmertmann, 1978). 



The factor of safety recommended by Schmertmann for piles designed 

 from electrical friction cones is 2.25. This factor is applicable to 

 tip bearing and side friction and should result in a factor of safety of 

 at least 2.0 to the yield point. 



Methods are also available for analyzing tapered piles, friction 

 with no friction sleeve data, capacity variations due to pile shape, and 

 insertion method. The reader is referred to Schmertmann (1978) for 

 these details. 



Bearing Capacity 



Bearing capacity can be estimated by the Terzaghi bearing capacity 

 equation or by graphs that convert cone pressure directly to bearing 

 capacity. Schmertmann recommends using the Terzaghi equation, which is 

 valid for footing embedment to D/B SI. 5 (depth to width or diameter 

 ratio). 



B M 



" Y 2\ 



where: 



DN 



cN 



(6) 



q c 

 q = unit bearing capacity 

 y = unit weight of soil 

 B = footing width or diameter 

 D = footing depth 

 c = soil cohesion 



N , N , N = bearing capacity factors 

 Y q c 



N and N are estimated as 

 Y q 



0.8 N *0.8N « q„ 

 Y q c 



in kgf/cm 



(7) 



0-1.5 B 



49 



