Experimental study on progressive failure process and permeability characteristics of red sandstone under seepage pressure

Rock masses in underground spaces often experience in-situ stress field and seepage field coupling which gives them complex mechanical behavioural and permeability characteristics. In this study, a High Pressure Triaxial Automated System for Rock (HPTAS) is employed in triaxial compression testing of red sandstone under different seepage pressures, and the variation laws of strength, deformation, axial strain stiffness and permeability during rock failure are analysed. The results show that with changes in the seepage pressure, there are also changes in the rocks strength and ability to resist deformation, and the stress threshold decreases with an increase in the seepage pressure. In addition, seepage pressure does not affect the strain stiffness trend, but it affects the value. Throughout the process of stress and strain, the permeability curve firstly decreases and then increases rapidly before finally stabilizing, and the peak value of the permeability curve lags behind that of the stress-strain curve. According to the law of permeability evolution during the pre-peak progressive failure process, a piecewise functional relationship model between permeability and stress is established in this study, and theoretical values agree well with experimental results. These experimental results can be used as a reference for monitoring and controlling rock stability during geological engineering when a seepage-stress coupling action is applied.