Study on microscopic failure mechanism and numerical simulation of sandstone under different saturated pressure

X-ray diffraction and SEM scanning are conducted to examine the alterations in sandstone under different saturation conditions to reveal the water-rock softening effect on sandstone from the Qilicun tunnels in China under varying saturation pressures. The mechanisms underpinning the strength softening of sandstone are analyzed using uniaxial compression tests. The experimental results demonstrated that after immersion in water, the internal cementing material within the sandstone dissolves, and the mineral particles fragment or disintegrate, increasing porosity. In the presence of water, the macroscopic compressive strength of sandstone exhibits a declining trend. Concurrently, as the saturation pressure escalates, the compressive strength diminishes by approximately 10%, the elastic modulus decreases by about 30%, and Poisson's ratio incrementally falls by about 25%. The sandstone's failure is characterized by both axial multiple splitting surface failure and shear failure surface. Finally, a strain-softening numerical model is employed to simulate the failure behaviors of sandstone under various saturation pressures. The findings indicated that the sandstone sample exhibits plastic failure characteristics under high saturation pressure.