Computations of Cone Penetration Resistance in Undrained Clay Incorporating a Full-Strain-Range Non-Linear Model

Cone penetration test (CPT) and cavity expansion are widely used to investigate and interpret in-situ soil properties. Current research typically treats clay as an elastic-perfectly plastic material and ignores the nonlinear stress-strain behavior of clays. This study proposes a small-strain elastoplastic model to characterize the nonlinear degradation of small-strain stiffness before yielding and subsequent nonlinear plastic hardening. Large deformation finite element analysis employing the Arbitrary Lagrangian-Eulerian technique is performed to simulate cone penetration in undrained clay, aiming to validate the applicability of the presented constitutive model against centrifuge tests. Numerical analyses reveal that both full-strain-range nonlinearity and small-strain elasticity significantly influence cone tip resistance. Specifically, the cone factor increases with the small-strain shear modulus and the threshold shear strain but decreases with the soil failure ratio. Compared to results based on the elastic-perfectly plastic assumption, incorporating soil nonlinear behavior reduces the cone factor and alters the effect of in-situ stress ratio on the cone factor. A semi-analytical solution of cavity expansion is derived based on the small-strain model, providing a closed-form formula to evaluate the bearing capacity factor of spherical cavity expansion. A novel parallel relationship is identified between the cone factor and the spherical cavity-bearing capacity factor. A corresponding evaluation method for the cone factors is established, and its validity is confirmed through comparative analysis with field tests. This study highlights the significant influence of accounting for the nonlinear stiffness of clay across its full strain range.