Study on the macro-micro mechanical behavior of freeze-thaw fissured sandstone under uniaxial compression

Long-term freeze-thaw cycles in cold-region rock masses degrade their mechanical properties, significantly impacting engineering safety. This study investigates fissured sandstone using uniaxial compression test and discrete element numerical simulations to analyze the effects of freeze-thaw cycles, fissure dip, and water contents on mechanical parameters, acoustic emission characteristics, and cracks propagation. The macro-micro damage mechanisms of fissured sandstone subjected to freeze-thaw cycles are elucidated. The results indicate that the peak strength and apparent stiffness of fissured sandstone after freeze-thaw cycles reduce, with the degree of reduction decreasing the greater the fissure dip. Acoustic emission signals correlate with the cracks propagation process, and freeze-thaw cycles diminish the intensity of these signals during sandstone failure. Increasing fissure dip suppresses wing cracks development, enhances secondary cracks formation, and intensifies shear effects during failure. The failure mode of freeze-thaw fissured sandstone transitions progressively from tensile failure to tensile-shear failure, ultimately culminating in X-shaped conjugate shear failure as the fissure dip approaches 90°. In addition, the quantitative analysis using the Gray Relational Analysis identifies fissure dip as the primary factor affecting the mechanical properties of freeze-thaw fissured sandstone, followed by water content and the number of freeze-thaw cycles (within 20 cycles).