ELASTIC-VISCOPLASTIC MODEL FOR LARGE DEFORMATION OF SOILS

An elastic-viscoplastic model for large deformation of metals (Rubin 1987b) has been generalized to include the major features of cap-type models for geological materials. Specifically, the effects of shear-enhanced compaction and dilation are conveniently modeled using kinematics that naturally separate plastic distortion from plastic dilatation (volume change). The constitutive equation for stress is hyperelastic in the sense that the stress is a function of elastic deformation and is equal to a derivative of the Helmholtz free energy. Although the theory is formulated without the explicit use of a yield function, the flow rule for plastic deformation rate can best be described as nonassociated. In this regard, special attention is focused on satisfying a physically plausible thermodynamic restriction on the constitutive equations, which ensures that the rate of plastic dissipation is nonnegative. Specific constitutive equations are proposed, and the material constants are determined by matching experimental data for Yuma clayey sand. © ASCE.