Extended UH Model: Three-Dimensional Unified Hardening Model for Anisotropic Clays

Extended UH model is a three-dimensional elastoplastic constitutive model that builds on a modification of the UH model with a unified hardening parameter, to account for the effect of anisotropy and the influence of $K_0$ consolidation on the stress-strain-strength behavior of clays. The combined effects of anisotropy and stress magnitude are considered through the minimum value of angles ($\alpha$) made by the spatially mobilized planes (SMPs) and soil depositional plane. The original transformed stress tensor is revised by incorporating the anisotropic peak stress ratio $M_{\alpha }$, which is defined as a function of $\alpha$, with the stress tensor ${\sigma }_{ij}$. The comparison with test results on San Francisco Bay Mud demonstrates the capability of the proposed anisotropic criterion. The UH model is extended to account for the combined effects of inherent anisotropy and $K_0$ conditions on the stress-strain-strength response of anisotropic clays by incorporating the revised transformed stress tensor $\widetilde{{\sigma }_{ij}}$, the potential strength ratio $M_f$, the characteristic stress ratio $M$, and the state stress ratio ${\tilde{\eta }}_a$. A series of undrained triaxial tests on isotropically and anisotropically consolidated specimens with different overconsolidation ratios (OCRs) are successfully predicted using the proposed extended UH model. New parameters for anisotropic soils can be determined conveniently from the conventional triaxial compression tests on vertical and horizontal specimens.