Study on the Coupled Mechanism of Seepage-Stress-Damage and Damage Constitutive Model of Rock after Freezing and Thawing

Tunnel engineering in the cold region often experiences the coupling of the stress field and seepage field, which has complex mechanical behavior and permeability characteristics. This study takes sandstone as the research object and uses the multifunctional RLW-2000 rock triaxial instrument to perform triaxial compression tests on sandstone with different freeze-thaw cycles under seepage pressure and confining pressure. The development law of rock mass cracks under different load combinations is analyzed, and the correlation characteristics between permeability and crack state of freeze-thaw sandstone in the process of seepage-stress-damage are studied. The results show that the permeability decreases gradually due to the compaction of pores and microcracks in the rock at the beginning of loading. As the crack radial strain increases, the internal cracks in the rock begin to grow steadily, and the permeability increases slowly. As the load continues to increase, the accelerated crack propagation leads to a rapid increase in permeability. In addition, under certain freeze-thaw cycles, the initial permeability of sandstone decreases with the increase of confining pressure. Under a certain confining pressure, the initial permeability of sandstone increases with the number of freeze-thaw cycles. Finally, based on the test results, theoretical methods are used to study the characteristics of rock damage under different freeze-thaw cycles, the correlation between the damage variable and, the crack radial deformation is established. The relationship between the permeability and the damage variable is deduced, which reveals the permeability evolution mechanism of freeze-thaw sandstone. These test results can provide a reference for rock stability monitoring under the coupled action of permeability and stress in geological engineering.