Influences of Water Content on Acousto-Mechanical Properties and Failure Behaviors of Triaxially Compressed Shale

Due to the extreme water sensitivity of shale, the excavation of shale underground engineering is prone to major disaster accidents such as roof falls and collapses. However, current investigations have failed to fully explain the mechanisms by which water content affects shale damage behaviors. In this study, the acousto-mechanical properties and failure behaviors of laminated shale under different confining pressures σ₃ are investigated with the aid of AE monitoring for three different water content states. The results show that the shale strength decreases with the increase of the water content, but it increases as the confining pressure σ₃ increases. For the shale, the change in the wetting angle and the distance between the centroids of the two adjacent particles inside the bedding plane is more prominent than the surrounding shale matrix, and the swelling pressure is generated among the clay minerals, which are the two main mechanisms for the bedding-participating failure and the shale softening after immersion. Moreover, with the increase of the water content and σ₃, the damage mode of shale specimens gradually changes from tension damage to shear damage. Controlled by bedding, shale failure shows significant suddenness without clear acoustical precursors. This study provides experimental and theoretical bases for the stability analysis of shale underground engineering.