Abstract: Current research on rock freeze-thaw damage mainly focuses on uniform freeze-thaw tests. However, the situation of unidirectional freeze-thaw action is widely present in cold region engineering, and there is a lack of sufficient understanding of the evolution of mechanical properties and damage models under unidirectional freeze-thaw conditions. Therefore, this study selected sandstone as the research object and conducted unidirectional freeze-thaw cycle tests and uniaxial compression tests. The elastic modulus, uniaxial compressive strength, stress-strain curves, and failure modes under uniaxial compression were analyzed for sandstone samples parallel and perpendicular to the freeze-thaw direction after undergoing freeze-thaw cycles. The results indicate that, following unidirectional freeze-thaw action, the compressive strength of sandstone parallel to the freeze-thaw direction is greater than that perpendicular to it, while the elastic modulus parallel to the freeze-thaw direction is smaller than that in the perpendicular direction. Both the peak stress and strain in the parallel direction are higher than those in the perpendicular direction. In uniaxial compression tests, the failure mode of sandstone parallel to the freeze-thaw direction remains consistent with that of samples that have not undergone freeze-thaw action, exhibiting X-shaped shear failure, whereas the failure mode perpendicular to the freeze-thaw direction manifests as splitting along the loading direction. Under unidirectional freeze-thaw action, the mechanical properties of sandstone transition from isotropy to anisotropy. Based on the aforementioned experimental observations, an anisotropic coefficient for unidirectional freeze-thaw was introduced, and a damage model for sandstone under unidirectional freeze-thaw conditions was established. The model was subsequently validated using experimental data.

Key words: sandstone, unidirectional freeze-thaw, mechanical characteristics evolution, anisotropy, damage model