Estimating clay undrained shear strength using CPTu results

Estimation of the undrained shear strength s_u of clays using piezocone penetration test (CPTu) results has been based mainly on the cone factor N_k. In this study a new CPTu-based method for estimating s_u is proposed and evaluated. It is aimed at reducing uncertainties in the estimation of s_u 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 s_u and the cone resistance q_t, 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 s_u obtained from the proposed method are in good agreement with measured values of s_u for all the selected verification cases.