New method for estimation of soil shear strength parameters using results of piezocone

Soil shear strength parameters, c and φ, can be determined by the use of laboratory tests and in situ testing data. In this study, a new method is presented for c and φ prediction using all quantities, qc, u2 and fs from CPTu considering bearing capacity mechanism of failure at cone tip and direct shear failure along penetrometer sleeve. One of the advantages of this method is the improvement of accuracy in the case of erroneous data by using all three outputs of CPTu. Laboratory test results, two sets of non-linear equations by the proposed approach, and existing correlations of c and φ parameters were compared to data compiled from four other sources. In previous investigations, cohesive parameters are not considered in bearing capacity equation and they cause the failure loads to be transferred to the second part of the basic bearing capacity equation which is a function of the internal friction angel. It was observed that the internal friction angles which are obtained by current methods are relatively higher than the measured values. Furthermore, the comparison of predicted and measured c and φ values indicates appropriate consistency and less scattered for the proposed method in comparison to other approaches.