The failure of rock in cold regions due to repeated freeze–thaw (F-T) cycles and periodic load-induced fatigue damage presents a significant challenge. This study investigates the evolution of the multi-scale structure of fractured granite under combined freeze–thaw (F-T) cycles and periodic loading and develops a constitutive damage model. The results indicate that after F-T cycles, network cracks develop around pre-existing cracks, accompanied by block-like spalling. After applying the fatigue load, the nuclear magnetic resonance (NMR) T₂ spectrum shifts to the right, significantly increasing the amplitude of the third peak. The freeze–thaw process induces a “liquid–solid” phase transition, weakening the original pore structure of the rocks and leading to meso-damage accumulation. The pores in fractured granite progressively enlarge and interconnect, reducing the rock’s load-bearing capacity and fatigue resistance. The combined effects of F-T cycles and periodic loading induce particle movement and alter fracture modes within the rock, subsequently affecting its macro-damage characteristics. The theoretical curves of the constitutive model align with the experimental data. The findings can serve as a theoretical reference for preventing and controlling engineering disasters in fractured rock masses in cold regions.

Joints and fractures lead to different failure mechanisms in rock masses under different environments. The mechanical properties and failure mechanisms of rocks with fissures are key problems in rock mass engineering. Parallel double-fracture quasi-sandstone specimens with different dip angles were prepared and subjected to triaxial compression tests after a single freeze-thaw cycle. Pore development, crack propagation, damage evolution, and failure characteristics were analysed. Combined with the strength distribution theory of microelements and the static elastic modulus theory, a damage constitutive model of double-fracture quasi-sandstone under freeze-thaw cycles and loads was established. This study explored the pore development, fracture propagation, damage evolution, and failure characteristics of fractured sandstone after thawing. The results showed that the compression wave velocity of the thawed specimens decreased, the nuclear magnetic resonance (NMR) T₂ curve shifted to the right, and the frost heave force promoted the development of the internal porosity in the specimens. With an increase in the crack dip angle, peak stress, expansion stress, cohesion and internal friction angle, the specimen showed a ‘U’ shaped change trend, compression cracks, and rock bridge penetration rate after failure decreased, and mixed failure of tension and shear gradually changed into shear failure. When the dip angles were 30° and 60°, the double fractured quasi-sandstone had larger total damage and more obvious brittle failure characteristics.

The artificial frozen wall crossing the water-rich sand layer is prone to failure during thawing. To study the loading fracture characteristics and damage evolution of single-fissured sandstone after thawing, quasi-sandstones with prefabricated single fissure at different angles were prepared using the sandstone of the Luohe Formation as the original rock to conduct freeze–thaw tests with various temperature differences, and triaxial compression tests were performed on the samples. Based on the distribution theory of rock micro-element strength and static elastic modulus, a damage constitutive model of single-fissured quasi-sandstone under freezing–thawing and confining pressure was established. The results show that with the decrease in freezing temperature, the amount of flake spalling on the sample surface increases, and the frost-heaving cracks of quasi-sandstone become more numerous and longer, which makes the single-fissured quasi-sandstone tend to have a more complex tensile–shear hybrid failure than a shear failure. Moreover, with the increase in fissure angle, the absolute value of the freezing temperature required to produce frost-heaving cracks increases. An S-shaped damage evolution curve corresponds to each stage of triaxial compression of single-fissured quasi-sandstone. With the decrease in freezing temperature, the strength of rock after thawing decreases, and the brittleness characteristics strengthen.

Rockbursts are common dynamic phenomena in coal mining and have become a prominent topic in the mining industry. This study examines the isolated island coal face in an extra-thick, fully mechanized top-coal caving operation in deep burial conditions, using it as a representative case. A comprehensive pressure relief strategy was employed at the coal face, incorporating directional roof blasting and loose roof blasting techniques. These techniques facilitated the pre-cracking and fracturing of the hard roof, addressing the issue of excessive suspended roof areas and high rock pressure affecting the roadway. Furthermore, a multi-source monitoring and evaluation method was developed to assess the effectiveness of the pressure relief measures. This method was based on the evolution of the rock loosening zone, stress distribution, displacement, and microseismic events. The study demonstrates that this approach can accurately evaluate the conditions at the coal mining face, providing valuable data to inform decision-making and enabling timely implementation of prevention and control measures.

Research on the damage and fracture mechanism of freeze-thaw (F-T) rocks under loading is a key scientific endeavor derived from numerous safety concerns in cold region rock mass engineering. This study analyzed the relationship between the entire triaxial compression process of the red sandstone and acoustic emission parameters. Based on the nonlinear growth characteristics of cumulative event counts of acoustic emission, a predictive method was proposed for determining the crack initiation strength, damage strength, and failure strength of F-T sandstone. The results demonstrated that this method exhibited good consistency with the crack volume strain approach and accurately and conveniently predicted sample failure strength. The fitted curve of the equation closely aligned with experimental data. These findings offer insights into the classification of damage and fracture mechanisms in F-T sandstone and provide valuable groundwork for research on rock failure prediction and forecasting methods employing acoustic emission monitoring.