In response to the challenges posed by long-term cyclic loading and unloading in underground rock engineering, this study systematically investigates the macro- and meso-mechanical response mechanisms of fractured rock masses under cyclic loading conditions. We performed graded cyclic loading–unloading tests on parallel double-fractured sandstone samples with varying spatial distribution configurations. These tests were integrated with digital image correlation (DIC) technology, fractal dimension analysis, and discrete element method (DEM) numerical simulations to analyze the mechanical properties, deformation characteristics, crack propagation features, and meso-fracture mechanisms of the fractured rock masses. The findings indicate that the diverse spatial distribution characteristics of the double fractures exert a significant influence on the loading–unloading processes, surface deformation fields, and fracture states of the rock. Cyclic loading leads to an increase in the fractal dimension of the fractured samples, resulting in more intricate and chaotic crack propagation patterns. Furthermore, DEM simulations reveal the impact of fracture spatial configurations on the force chain distribution within the rock bridges. The equivalent stress nephogram effectively represents the stress field distribution. This offers valuable insights for predicting meso-fracture trends in rocks. This paper comprehensively integrates both experimental and numerical simulation methodologies to deliver a thorough analysis of the complex mechanical behavior of fractured rock masses under cyclic loading conditions, with direct relevance to engineering applications such as mine excavation and slope stabilization.

Engineering structures, including rock slopes and embankments, are vulnerable to wetting–drying cycles caused by tidal shifts and rainfall, which exacerbate mechanical degradation in hole-fissured sandstone. This study investigated the effects of 0, 10, and 20 wetting–drying cycles on sandstone samples using uniaxial compression tests combined with digital image correlation (DIC), computed tomography (CT), and scanning electron microscopy (SEM). The results revealed that wetting–drying cycles progressively reduced peak strength and the elastic modulus while increasing macroscopic crack quantity and width. Internal crack networks simplified, transitioning from tensile-dominated to combined tensile–shear and shear failure modes. An energy analysis showed diminished energy storage capacity—both the total energy density at peak stress and elastic strain energy density declined with increasing cycle numbers, whereas dissipated energy density decreased initially before rising. SEM observations indicated that wetting–drying cycles enhanced the surface roughness of the sandstone, characterized by a scaly texture, thereby compromising its structural integrity. This study provides a theoretical basis for stability and safety assessments of protective engineering systems.

To explore the mechanical evolution and damage mechanisms of rock in cold regions under freeze–thaw cycles, this study selected white sandstone from mining areas in western China as the research object. Uniaxial compression tests were performed after different numbers of freeze–thaw cycles. Digital Image Correlation (DIC) was employed to analyze the deformation evolution and crack propagation characteristics, and the damage mechanisms were interpreted from the perspective of energy evolution. The results show that with an increasing number of freeze–thaw cycles, the peak stress and elastic modulus of the white sandstone decrease significantly, with the most substantial reduction occurring between the 15th and 30th cycles. The stress–strain curves exhibit a prolonged compaction stage and increased peak strain, indicating that freeze–thaw action exacerbates the accumulation of internal damage in the rock. DIC analysis reveals that freeze–thaw action causes rock deformation to concentrate at the specimen edges at an earlier stage, accelerates crack propagation, and leads to a gradual transition in failure mode from tensile failure to tensile-shear composite failure, with the degree of failure becoming more severe. Energy evolution analysis indicates that freeze–thaw cycles reduce the total input energy and the elastic strain energy at peak stress, while the proportion of dissipated energy increases, suggesting that freeze–thaw damage results in greater energy consumption through irreversible deformation. Finally, based on the Lemaitre strain equivalence hypothesis and the Weibull distribution, a damage constitutive model considering the coupled effects of freeze–thaw and mechanical loading was established by introducing correction factors, and its validity was verified.