Estimating clay undrained shear strength using CPTu results

Abstract

Estimation of the undrained shear strength su of clays using piezocone penetration test (CPTu) results has been based mainly on the cone factor Nk. In this study a new CPTu-based method for estimating su is proposed and evaluated. It is aimed at reducing uncertainties in the estimation of su and enhancing the application of CPTu results. To develop the method, a selected site on a marine clay deposit was subjected to an extensive experimental testing programme. The proposed method defines a direct correlation between su and the cone resistance qt, involving the initial in situ pore pressure but excluding the need for overburden pressure calculation and therefore the need for undisturbed soil sampling. To verify the proposed method, additional test sites and example sites from the literature that encompass a variety of soil conditions are selected and examined. Values of su obtained from the proposed method are in good agreement with measured values of su for all the selected verification cases.