Interpretation of cone resistance and pore-water pressure in clay with a modified spherical cavity expansion solution

Abstract

A theoretical approach to interpreting the cone penetration resistance and the pore-water pressure measured on the face of the cone during piezocone tests of clays is proposed. The mechanism for the penetration of the piezocone is assumed to be spherical cavity expansion in modified Cam clay critical-state soil. Using large strain theory, the spherical cavity expansion problem is reduced to solving a system of first-order ordinary differential equations for effective stresses in the plastic zone. By taking the normal and shear stresses acting on the cone face to be the ultimate cavity expansion pressure and the effective friction at the cone–soil interface, respectively, the cone resistance was evaluated at force equilibrium. The pore-water pressures induced by cone penetration include components caused by changes in normal and shear stresses, for which the normal term can be predicted by integrating the radial equilibrium equation in terms of total stress. As it is based on an exact constitutive relationship, the present method takes more factors (such as the effects of interface shear and the traditional overconsolidation ratio) into account than other methods of tackling this problem. Comparisons between the predicted and measured values of cone resistance and pore-water pressure at different well-documented sites are in good agreement for most relatively homogeneous low- and medium-sensitivity clay sites.