This study first investigates the effect of subzero temperatures on the mechanical behavior of frozen sandstone through triaxial compression tests conducted at temperatures of \(-\) 15 °C, \(-\) 10 °C, \(-\) 5 °C, and 10 °C, and confining pressures of 0 MPa, 5 MPa, 10 MPa, and 15 MPa. The strength, stiffness, deformation characteristics, and failure modes of the sandstone are analyzed in detail. Frozen sandstone is conceptualized as a quasi-brittle composite material, consisting of a sandstone skeleton, mesocracks, and ice-filled micropores. Based on the experimental results, a novel multiscale model is developed to describe its mechanical response. The model uses a two-step Mori-Tanaka homogenization approach to relate microstructural changes to the elastic properties of the homogenized medium. A pore ice activity factor is introduced to capture the nonlinear increase in stiffness of ice-filled micropores and the enhanced damage resistance at the ice–sandstone interface as temperatures decrease. The model also incorporates the frictional sliding and propagation of mesocracks at the ice–sandstone and mineral interfaces, accounting for dissipation processes under loading. The proposed multiscale constitutive model is validated through comparison with experimental data, demonstrating its ability to accurately predict the strength, stiffness, and deformation characteristics of frozen sandstone under varying subzero temperatures and confining pressures. The results emphasize the critical role of ice-pore interactions and mesocrack behavior in the mechanical performance of frozen sandstone.
