Thermodynamic constitutive model for rheological behavior of sand

Based on the non-equilibrium thermodynamics, a granular entropy s_g and a granular temperature T_g are introduced to describe the collisions, sliding, rolling of sand particles. The elastic relaxation caused by granular temperature variation is used to reflect the irreversible deformation of sand. The thermodynamic governing equations are derived to predict the macroscopic mechanical behavior of sand. Confined compression and isotropic compression tests are investigated using the proposed method. The results indicate that the proposed model can well describe sand relaxation and creep behavior. The granular entropy is excited and increases until a steady value in loading process, and the granular entropy gradually decays until to zero in the rheological process after loading. The elastic relaxation caused by granular temperature leads to the rheological behavior, and the rheology eventually stops at a steady value when the granular entropy decays to zero.