A novel constitutive model of the anisotropic sand accounting for the fabric evolution

The mechanical behavior of the sand is affected by anisotropy. This paper presents a novel constitutive model for anisotropic sand that accounts for fabric evolution. In this proposed model, a novel hardening parameter and a new state variable are introduced to capture the effects of the evolving anisotropic fabric. A universal fabric tensor evolution law, independent of specific fabric tensors, is proposed based on the characteristics of the unified hardening model and the findings from discrete element simulations. Additionally, a dilatancy anisotropy compression line (DACL) is defined to compute the state variable, ensuring the uniqueness of the critical state line (CSL). The proposed model has been validated through a large number of monotonic shear datasets obtained from experiments and DEM simulations, while parameters in this proposed model are physically meaningful and easy to be determined. Analysis of fabric evolution under different loading paths indicates that the undrained triaxial compression test is the most effective for reaching the critical state, providing a useful reference for the critical state soil mechanics.