Experimental study on unloading mechanical characteristics of sandstone considering water-mechanical coupling and different stress paths

In order to study the unloading mechanical properties of rock under different seepage pressures, this paper selects the sandstone as the research object, conducts triaxial unloading tests under different seepage pressures and different stress paths, and compares the results with conventional triaxial tests. The rock strength characteristics under different stress paths are compared, and the effect of seepage pressure on the rock deformation and strength parameters is further analyzed. The test results show that the increase of seepage pressure will weaken the rock strength, the peak strength of rock decreases with the increase of seepage pressure, and the axial deformation increases with the increase of seepage pressure. Aiming at two different unloading stress paths, under the condition of constant axial pressure and unloading confining pressure, the cohesion of rock keeps decreasing and the internal friction angle increases; under the condition of increasing axial pressure and unloading confining pressure, the cohesion of rock keeps increasing and the internal friction angle decreases.