Non-linear creep damage model of sandstone under freeze-thaw cycle

Abstract

To study rock damage characteristics under long-term freeze-thaw cycles and loads, rock freeze-thaw and creep damage factors were defined based on nuclear magnetic resonance porosity and volume strain, respectively. The damage factor is introduced into the basic rheological element, and the non-linear creep damage constitutive model and freeze-thaw rock equation are established to describe non-linear creep characteristics under a constant load. Simultaneously, the creep test of freeze-thaw rock under step loading is performed. Based on the test data, the applicability and accuracy of the creep damage freeze-thaw rock model are analyzed and verified. The results show that freeze-thaw cycles result in continuous rock pore structure damage and deterioration, and nuclear magnetic resonance porosity enhancement. The constant load induces increasing rock plastic deformation, volume, and creep aging damage. As the loading stress increases, the instantaneous rock elastic parameters increase, and the rheological elastic and viscosity parameters decrease. Furthermore, the damage degradation of freeze-thaw cycles weakens the rock viscoplasticity, resulting in a rapid decrease in the viscosity parameter with an increase in freeze-thaw cycles. Generally, the continuous damage of the rock is degraded, and the long-term strength decreases continuously.