Drained Soil Shear Strength Parameters from CPT and CPTu Data in Coastal Deposits by an Analytical Approach

Due to a few limitations through laboratory testing, CPTu has been realized as a multipurpose apparatus with an acceptable performance especially in coastal deposits. Traditional methods for obtaining shear strength parameters using CPT data, estimate conservative values for ϕ (internal friction angle) in granular soils and S_u (undrained soil shear strength) in cohesive soils. In this study by combining bearing capacity theorem and direct shear modes at CPTu tip and sleeve and considering the pore water pressure at the shoulder of Piezocone (u₂), a set of equations is derived. Hence by input of CPTu data including q_t, f_s and u₂ at a certain depth, soil shear strength parameters i.e. C (cohesion) and ϕ can be calculated simultaneously. Via establishing a data bank, consisting of 38 sets of CPT and CPTu boreholes from marine deposits at various coastal regions, measured soil shear strength parameters are compared with traditional and proposed approach estimations. Although the calculated C and ϕ by proposed method are relatively closed to the measured results and covering all sorts of soils, they can satisfy CPTu measured shear strength collaborating to each other. Moreover, a soil classification chart and a graphical solution with utilizing the proposed method are provided.