A 3D non-orthogonal elastoplastic constitutive model for transversely isotropic soil

The significant influence of transverse isotropy on mechanical behaviours of soil has long been recognised, but it is still difficult to capture well under 3D stress conditions. In this study, a method of establishing 3D non-orthogonal elastoplastic (NOEP) constitutive models for transversely isotropic soil (TI-soil) is proposed. The effect of transverse isotropy is considered by extending the characteristic stress with the fabric tensor of TI-soil. The extended characteristic stress can be used to treat the mechanical behaviour of TI-soil from the perspective of isotropic soil. Therefore, a unified strength criterion for TI-soil is developed in the same form as the Drucker–Prager criterion. In order to reflect the non-orthogonality of the plastic flow direction with respect to the yield surface, the non-orthogonal plastic flow rule is adopted, which obviates the tedious work of constructing the plastic potential function or the dilatancy relation. Based on the yield function and hardening parameter expressed in the extended characteristic stress space, specific formulations of the NOEP model for TI-soil can be derived. Comparisons between model predictions and test results show that the developed model can well reflect the effects of transverse isotropy and intermediate principal stress on the strength and deformation behaviour of TI-soil