Study on the Physico-Mechanical Properties and Damage Mechanisms of Weakly Cemented Sandstone under Freeze-Thaw...

Weakly cemented sandstone is a critical rock type in cold-region engineering. It is characterized by a loose fabric and well-developed pores, which makes it highly sensitive to freeze-thaw disturbance. In this study, weakly cemented sandstone from Gansu Province, China, was investigated. Freeze-thaw cycling tests were performed. Uniaxial compression, ultrasonic P-wave measurements, nuclear magnetic resonance (NMR), and fractal theory were combined to clarify the evolution mechanism of freeze-thaw damage. The results show a typical three-stage deterioration in physical and mechanical properties. The uniaxial compressive strength (UCS) and elastic modulus (E) decreased by 59.09 and 66.37%, respectively. The failure pattern shifted from a single dominant crack to cooperative failure with multiple cracks. Porosity increased from 12.86 to 22.21%. The proportion of micropores first increased and then decreased, whereas macropores became dominant, indicating an evolutionary trend of micropore activation, mesopore expansion, and macropore predominance. The pore fractal dimension decreased, indicating that pore growth was accompanied by enhanced connectivity and structural simplification. Pearson correlation analysis further demonstrated strong coupling between pore structure parameters and mass, P-wave velocity, UCS, E, and fracture patterns. These findings comprehensively clarified the multiscale damage evolution mechanism of weakly cemented sandstone under freeze-thaw cycles and revealed a sequential damage development path characterized by pore expansion, structural simplification, mechanical degradation, and increasing complexity of fracture patterns. This study provides scientific insights and experimental support for stability evaluation of rock masses in cold region engineering.