MODEL FOR THE DEFORMATION OF SAND DURING ROTATION OF PRINCIPAL STRESS DIRECTIONS

Abstract

This paper presents an elastoplastic constitutive model for the deformation of sand during loadings involving rotation of principal stress directions. The model employs a plastic potential formulation that allows for the dependency of flow on the stress increment direction and a stressdilatancy relation that incorporates the effects of the non-coaxiality of the principal stress and principal plastic strain increment directions. The continuous plastic deformation of sand during principal stress rotation at constant shear stress level is allowed for in the model by using a very small elastic region in the stress space. In the deviatoric stress space, an associated flow is employed to model the dependency of yielding on the stress increment direction. Hardening behaviour is modelled using discrete surfaces of equal plastic hardening modulus which are allowed to move with the stress point during loading. To model cyclic effects, the plastic hardening modulus is allowed to stiffen during loading depending on the amount of accumulated normalized plastic shear work. The model is used to simulate the deformation of hollow cylindrical sand specimens subjected to rotation of principal stress direction.