Analysis of mesoscopic damage evolution in freeze-thawed sandstone under dynamic disturbance

To investigate the damage evolution law of rock masses in cold regions under different disturbances, red sandstone was subjected to freeze-thaw cycles and dynamic disturbance tests. CT images were processed using techniques such as the black top-hat algorithm and three-dimensional visualization to reconstruct models for quantitative analysis of pore and crack development characteristics, revealing the cross-scale driving mechanisms of rock mass damage under freeze-thaw and dynamic disturbances. The experimental results indicate that in the early stages of freeze-thaw cycles, dynamic disturbance plays a dominant role in crack propagation. The porosity, fractal dimension, and pore connectivity of the sandstone initially increase and then decrease with increasing disturbance intensity, reaching peak values of 19.81%, 2.64, and 95.56%, respectively. In the later stages of freeze-thaw cycles, the deterioration of freeze-thaw damage exacerbates the effect of disturbance damage, leading to continuous growth in porosity and pore connectivity. The freeze-thaw sandstone reaches the threshold of microstructural evolution at a disturbance intensity of 0.05 MPa. Below this threshold, dynamic disturbance promotes the development of microcracks in a "shallow and broad" transverse pattern. Beyond the critical threshold, crack propagation shifts to a "deep and narrow" longitudinal dominant path. Additionally, freeze-thaw action can regulate the degree of freedom for crack extension. The cumulative damage from freeze-thaw weakens the spatial structural constraints within the rock mass, promoting the formation of multi-directional interconnected crack networks and pores. The findings provide a theoretical basis for engineering construction in cold regions and the prevention and control of dynamic disturbance disasters.