Anisotropic elasto-plastic coupling model for soils incorporating fabric evolution

Abstract

For many solids, irreversible deformation is often accompanied by changes in the internal structure, impacting the reversible responses, a phenomenon termed elasto-plastic coupling. This coupling has been observed experimentally in various geomaterials, including clayey and sandy soils, as well as hard and soft rocks. Fabric anisotropy, which characterizes the internal structure, is a distinct feature of soils and significantly influences both reversible and irreversible behaviors. In this study, we adopted a coupling formulation based on the framework of anisotropic critical state theory (ACST) to describe the anisotropic elasto–plastic coupling response of soils. The formulation incorporates a deviatoric fabric tensor F, which consistently quantifies the internal structure of soils in both reversible and irreversible range, into a hyperelastic formulation and a plastic model, respectively. A novel evolution rule of F, defined based on the current stress ratio and plastic strain, is proposed, where the direction gradually aligns with the loading direction and the norm achieves different asymptotic values depending on the applied loading paths. This allows for the representation of evolved anisotropy effects on elasticity, dilatancy and strength simultaneously, providing a natural description of elasto-plastic coupling. Within this coupling framework, any anisotropic model within ACST can serve as the plastic platform for developing the elasto–plastic coupling models with anisotropic hyperelasticity. Herein, a bounding surface plastic model is utilized for illustration. The proposed model’s performance is demonstrated by especially comparing simulated results to test data on evolving elastic stiffness ratios and overall elastoplastic responses under varying monotonic and cyclic loading conditions.