Abstract: In cold region tunnels, the moisture migration during the frost heave always aggravates freeze-thaw induced damage of the surrounding rock. Therefore, it is of great importance to consider the moisture migration effect on the collapse and landslide mechanisms of rocks due to freezing and thawing weathering. In this paper, the moisture migration was introduced into Helmholtz free energy as an intrinsic variable based on internal state variables theory. A general thermo-hydro-mechanical coupled constitutive model was proposed under the thermodynamic framework. The effects of temperature and moisture migration on the damage threshold, isotropic hardening saturation and isotropic hardening rate of the rock after freezing and thawing were described. The degradation of mechanical properties of rock after freezing and thawing was simulated. This model was given as an incremental form, which was convenient for the numerical modelling under complex stress loading conditions. The parameters used in the constitutive model had clear physical meanings. Finally, the simulation stress-strain curves of the constitutive model were compared with the results of triaxial compression test of the rock specimens after freeze-thaw cycles. It was proved that the proposed constitutive model could well describe the mechanical behaviors of rock after freeze-thaw cycles.

Key words: freeze-thaw cycles, thermodynamics, internal state variables, water migration, constitutive model