Hypoplastic constitutive model with critical state for granular materials

This paper presents a hypoplastic constitutive model for the three-dimensional nonlinear stress-strain and dilatant volume change behavior of granular materials. The model is based on nonlinear tensorial functions and is developed without recourse to the concepts of elasto-plasticity theory such as yield surface, plastic potential, flow and hardening rules and decomposition of deformation into elastic and plastic parts. The material constants in the model can be identified with triaxial compression tests. The effect of void ratio and stress level on the behavior of granular materials is accounted for by integrating the critical state into the constitutive equation. It is shown that the model is applicable to both initial and fully developed plastic deformation of granular materials, and many well established concepts in soil mechanics, which are otherwise entirely independent, can be unified with the constitutive model. Simulations of various elementary tests, including oedometer, triaxial and simple shear tests, show that the model is capable of capturing the salient behavior of granular materials under monotonic as well as cyclic loading.