Mechanical behavior of deep sandstone under high stress-seepage coupling

The mechanical behavior evolution characteristics of sandstone are important to the application and practice of rock engineering. Therefore, a new method and concept of deep rock mechanics testing are proposed to reveal the mechanical behavior evolution mechanism of deep roadway surrounding rock after excavation with a depth over 1000 m. High stress-seepage coupling experiments of deep sandstone under various confining pressures are conducted using GCTS. Stress - strain and permeability curves are obtained. The three-stage mechanical behavior of deep sandstone is better characterized. A platform and secondary compaction phenomena are observed. With the confining pressure increasing, the platform length gradually decreases, even disappears. In the stade I, the rigid effect of deep sandstone is remarkable. In the stage II, radial deformation of deep sandstone dominates. The transient strain of confining pressure compliance is defined, which shows three-stage evolution characteristics. In the stage III, the radial deformation is greater than the axial deformation in the pre-peak stage, but the opposite trend is observed in the post-peak stage. It is found that the dynamic permeability can be more accurately characterized by the radial strain. The relations between the permeability and stress-strain curves in various stages are revealed.