I I I I M I I I I I II I I I I I I I 



Begemann tip 



//. 



' » »■*=« ■ 



For K s for wood use — 



J 1.2 5 K s steel 

 I I I I I I 1 I I I I I I 



J I L 



J L 



l.o 



f s (kgf/cm 2 ) 



(b) For clay. 



1.0 2.0 



K s (sand) 



(a) For sand. 



Figure 31. Correction factors to be applied in 

 Equation 5 (Nottingham, 1975) (from 

 Schmertmann, 1978). 



where q is the average cone pressure from the soil surface to a depth 

 of 1.5 footing widths (kgf/cm 2 ). 



A factor of safety of 2 to 3 is then applied to obtain the allow- 

 able bearing pressure. This procedure will result in error if the cone 

 pressure is being significantly affected by pore pressure effects. 



Clay bearing capacity is more directly related to the cone 

 pressure. For shallow footing, the cone pressure for 1.5 footing widths 

 below the footing can be averaged to obtain the ultimate footing 

 pressure. The allowable footing pressure is obtained by applying a 

 factor of safety of 2 to 3. 



Settlement 



Settlement of footings on sand and clays can be estimated using CPT 

 data. The results for sand are quite adequate for the static loading 

 conditions for which the procedures apply. For clays, more uncertainty 

 exists, and the results give more of a qualitative indication of settle- 

 ment rather than a quantitative estimation. The procedures involved in 

 making settlement estimates are too involved to present here. The 

 reader is referred to Schmertmann (1978) for details regarding these 

 procedures. 



50 



