Macro-meso physical and mechanical deterioration properties and damage prediction model of rock under Freeze–thaw cycles

Red sandstone is selected for freeze–thaw cycles, nuclear magnetic resonance, and triaxial compression tests to study the changes in macro-meso physical and mechanical properties under freeze–thaw cycles. Based on the expansion characteristics of meso structure, the porosity and fractal dimension are introduced to determine initial and freeze–thaw damage variables. During loading process, considering the dynamic evolution process from non-damage to damage, the load damage variable is determined. Based on the impact of reducing the effective bearing area on each damage, the total damage variable and constitutive prediction model of rock under freeze–thaw cycles are established. The results show that with the increase of freeze–thaw cycles, the meso structure undergoes penetration and expansion, and the porosity increases by nearly 30% when freeze–thaw cycles reaches 60 times. From a macro perspective, it shows that the decreases of compressive strength and deformation resistance. With the increase of confining pressures, the pores are compacted, and the lateral deformation is limited. At the same time, the bonding force between particles is strengthened, so the damage is suppressed. Macroscopically, it shows that the resistance to failure is enhanced. Under freeze–thaw cycles and confining pressure, the predicted mechanical parameters have a small deviation from test obtained mechanical parameters, generally not exceeding 5%. So the prediction model can describe the entire process of deformation and failure of rock under freeze–thaw and load, and can effectively reduce mechanical parameters data required to determine model parameters, making model more adaptable, so as to provide a new idea for the theoretical research of rock mechanics in cold regions.