Deformation and seepage characteristics of water-saturated shale under true triaxial stress

True triaxial loading-unloading tests of natural and water-saturated shale were conducted using a multifunctional true triaxial fluid-structure coupling experimental system, and the deformation and seepage characteristics of the samples during loading were analyzed. Compared with the natural sample, the stress-strain curve of the water-saturated sample was not smooth, its swing was more obvious, and its volume expansion also appeared in each stage of loading. Both water-saturated and constant water pressures changed the deformation characteristics of the sample and led to a decrease in its ductility. The water flow in the initial and failure stages was higher. When the yield limit was exceeded, the stress-state parameter of the natural sample began to increase rapidly, the water flux above the sample increased owing to the nonlinear expansion of cracks, and the total water flow rate increased rapidly. The stress-time curve of the water-saturated sample showed a wavy change before failure, resulting in no noticeable change in the stress state at the yield point. The repeated changes in expansion and compression caused the change in water flux above the sample to lag behind the yield point. The total water flow began to increase rapidly after the specimen failed.