Interpretation of Undrained Hollow Cylinder Shear on Natural Shanghai Soft Clay Using Three-Dimensional Constitutive Model

The mechanical response of natural clays can exhibit significant directional dependence due to loading history and layered soil structure. We report an experimental investigation of the stress–strain-strength response of undisturbed Shanghai clay subjected to undrained hollow cylinder shear that covers a wide range of principal stress rotation angles and intermediate principal stress ratios. The three-dimensional rotational hardening model proposed by Huang et al. ( 2011) is used to interpret experimental observations. Test data indicate that the undrained strength first decreases and then increases as the major principal stress direction rotates away from the soil deposition direction. This nonmonotonic trend primarily results from different shear-induced pore pressure responses and cannot be explained by loading history-induced anisotropy. These findings suggest the presence of mechanical anisotropy of the tested natural clays that is related to the laminated soil structure. The measured undrained strength, on the other hand, monotonically decreases as the intermediate principal stress ratio increases. This variation is mainly due to the dependence of strength parameters on shear modes. We present a simple approach to include anisotropy related to the laminated soil structure into the constitutive model. The comparison between measured and simulated results validates the new proposition.