Study on the Mechanical Properties and Interaction Mechanism of Fractured Rock Subjected to Freeze–Thaw Cycles

This study investigates the mechanical behavior of fractured sandstone under various factors, including freeze–thaw cycles, fracture dip angle, roughness, grouting material, and confining pressure. Freeze–thaw and triaxial compression tests were conducted to analyze the effects of individual factors and their interactions on the mechanical properties of sandstone. The results indicate the following: (1) Under independent factor conditions, freeze–thaw cycles generate frost heave forces through the water–ice phase transition, leading to the expansion of microcracks and deterioration of the pore structure, which results in a weakening effect. Grouting material enhances the bonding strength and supporting capacity of the rock sample, roughness improves the anchoring effect of the grout, fracture dip angle improves stress transmission efficiency, and confining pressure increases rock sample density and restricts deformation, all of which exhibit strengthening effects. (2) Interaction analysis revealed three types of interaction mechanisms for the peak stress and elastic modulus of the rock samples: interaction enhancement mechanism, where peak stress or elastic modulus significantly increases when the related factors are at high levels, demonstrating a synergistic strengthening effect; interaction inhibition mechanism, where factors at high levels suppress each other’s strengthening or weakening effects; and interaction reversal mechanism, where the influence trend of certain factors reverses under different conditions. Specifically, the interaction enhancement mechanism for peak stress is observed in the interactions between grouting material and roughness, grouting material and confining pressure, and fracture dip angle and roughness. The interaction inhibition mechanism occurs between grouting material and freeze–thaw cycles and confining pressure and freeze–thaw cycles. For elastic modulus, the interaction enhancement mechanism is observed in the interactions between fracture dip angle and confining pressure, grouting material and roughness, and confining pressure and roughness; the interaction reversal mechanism appears in the interaction between freeze–thaw cycles and fracture dip angle.