Progressive Asymmetry Damage Behavior and Macro–Micro-Scale Coupled Constitutive Modeling of Sandstone with Intersecting Fractures Under Freeze–Thaw Cycles and Loading

To investigate the progressive asymmetry damage characteristics of intersecting fracture rock under the coupled effect of freeze–thaw cycles and loading, nuclear magnetic resonance tests were conducted on intact, single fracture, and intersecting fracture sandstone under freeze–thaw cycles. Uniaxial and triaxial compression tests were conducted to investigate the mechanical behavior and failure characteristics of fractured rock, while the effects of freeze–thaw cycles on pore structure evolution, microscopic damage, and mechanical degradation were further evaluated. The results showed that the intersecting fracture rock was more sensitive to microscopic damage caused by freeze–thaw cycles. As external loading was applied, the initiation stress and peak stress of the intersecting fracture rock were the lowest of the three rock types, and the failure mode changed from shear failure to tensile failure. Based on damage localization theory and fracture mechanics, the expansion of macro-fissures in the rock were found to be equivalent to the growth process of crack clusters at the tip, and a progressive damage constitutive model considering the coupled effect of freeze–thaw cycles and loading was developed. This model was able to reproduce the main characteristics of the mechanical response and damage evolution of intersecting fracture rock. It provides a potential reference for understanding the mechanical behavior engineering rock in cold regions.