The damage and degradation of coal-measure sandstone in cold-region open-pit mines due to freeze–thaw effects has become one of the significant factors inducing instability in the rock mass of open-pit mine slopes. This study conducts experiments on the physical and mechanical properties of saturated coal-measure sandstone under varying freeze–thaw cycle counts and freezing temperatures, revealing the intrinsic mechanisms of damage and degradation in saturated coal-measure sandstone due to freeze–thaw effects. The experimental results indicate that, with an increase in the number of freeze–thaw cycles and a decrease in the freezing temperature, the elastic modulus and peak compressive strength of the specimens exhibit an exponential decrease. In contrast, the peak strain shows an exponential increase. However, compared to the freezing temperature, the increase in the freeze–thaw cycle frequency leads to a more significant change in the mechanical parameters of the specimens, indicating that the frequency of freeze–thaw cycles has a more pronounced effect on the deformation resistance of saturated coal-measure sandstone than the freezing temperature. The failure mode of coal-measure sandstone specimens under uniaxial compressive loading primarily exhibits shear failure; however, as the number of freeze–thaw cycles increases and the freezing temperature decreases, the specimens begin to exhibit tensile failure modes, which gradually develop into a combined tensile and shear failure mode. Based on the experimental data, two sets of surface equations were fitted to characterize the relationship between the mechanical properties (peak compressive strength, elastic modulus) of the specimens and the experimental parameters (number of freeze–thaw cycles, freezing temperature). The research findings can provide references and insights for engineering disasters caused by the degradation of coal-bearing sandstone in cold-region open-pit mines.

The stability of open-pit mines under low-temperature conditions is critical for safe and efficient coal extraction. However, the mechanisms of rock damage and fracture under combined temperature and stress effects remain unclear, particularly regarding the evolution of mechanical properties under repeated freeze–thaw cycles and varying peripheral pressures. This study investigates the damage and rupture behavior of coal-bearing sandstone in cold-region open-pit mines through experimental testing and theoretical modeling. The research was conducted in three stages: (1) freeze–thaw and peripheral pressure experiments to evaluate mechanical property evolution; (2) acoustic emission monitoring to analyze internal fracture initiation, propagation, and coalescence under temperature–stress coupling; (3) development of a local deterioration model to quantify post-damage strength decay considering low-temperature erosion and freeze–thaw effects. Results show that increasing freeze–thaw cycles leads to a transition from brittle to ductile behavior, while higher peripheral pressures significantly enhance ductility. Mechanical parameters are highly sensitive to peripheral pressure but largely independent of freeze–thaw cycle count. Acoustic emission signals respond strongly to temperature, and temperature–stress coupling governs the three-stage evolution of fracture germination, extension, and penetration. The local deterioration model effectively captures post-peak residual strength and damage evolution. These findings indicate that in regions with higher microcrack density, fault propagation is driven by rapid coalescence under stress concentration, whereas in lower-density regions, it is dominated by gradual fracture growth and temperature-induced expansion. The results provide theoretical guidance for stability assessment and support design in open-pit coal mines in cold environments.

To investigate the mechanical properties of concrete-foamed cement composite specimens (C-FCCS), uniaxial compression tests were conducted on composite specimens with varying proportions and strengths of foamed cement. The analysis focused on the peak compressive strength, peak strain, macroscopic failure morphology, and acoustic emission (AE) characteristics of C-FCCS. The experimental results indicate that the peak compressive strength of C-FCCS exhibits a negative correlation with the proportion of foamed cement and a positive correlation with the proportion of concrete. At foamed cement proportions of 10% and 20%, the peak compressive strength of C-FCCS is predominantly governed by concrete, with AE energy concentrated primarily during the initial loading phase and near the peak stress. In contrast, at foamed cement proportions ranging from 30 to 50%, the peak compressive strength is dominated by foamed cement, with AE energy concentrated around the peak stress. The peak strain of C-FCCS shows a trend of initially increasing and then decreasing with the increase in height ratio (Height ratio = Foamed cement height/C-FCCS height). Under different height ratios, the peak strain of C-FCCS is approximately 175.61–558.13% of that of pure concrete specimens. Furthermore, variations in the strength of foamed cement have a minimal impact on the peak compressive strength of C-FCCS but significantly affect the peak strain. The peak compressive strength of C-FCCS is about 77.67–83.87% of that of pure concrete specimens, while the peak strain ranges from 128.46 to 361.38%. Lastly, the macroscopic failure of C-FCCS is primarily characterized by tensile failure, with shear failure commonly observed at the edges and corner interfaces of C-FCCS.