Failure and deformation characteristics of shale under true triaxial stress loading and unloading under water retention and seepage

A multifunctional true triaxial fluid-structure coupling system was used to conduct water retention and seepage tests of shale under true triaxial loading and unloading stress paths. The stress-strain evolution law of shale specimens under different experimental conditions was obtained, and the corresponding deformation and strength law was analyzed. The evolution law and failure characteristics of cracks in shale were obtained by CT scanning images before and after the experiment. The results show that under the condition of water retention, the volumetric strain of shale specimen increases first, then decreases and finally continues to increase with the increase of deviational stress, indicating that the volumetric change has experienced a process of compaction-expansion-compacting. The partial stress-maximum horizontal strain curve of the sample increases first and then decreases, while the deformation of the sample in the direction of intermediate principal stress shows the characte...