A Comparison of Mechanical Properties and Failure Processes of Saturated and Unsaturated Slate from Sichuan-Tibet Plateau Area, China

Water content significantly affects the physical and mechanical properties of rock and can cause rock mass to become unstable. This, in turn, can cause geologic disasters such as water inrush and surrounding rock deformation. Uniaxial compression experiments on slate samples drilled from the surrounding rock of a tunnel in the Chinese Sichuan-Tibet Plateau area were performed coupled with acoustic emission (AE) monitoring. The changes in mechanical properties and failure processes of unsaturated and saturated slates were investigated comparatively through test results. Phenomena of a slight drop of σ1 in the compaction and elasticity stage were observed, and it is due to the sliding of slate along the layered surface. According to the results, the average compressive strength of saturated slates was reduced by 24.3% compared to the unsaturated slates. The spatiotemporal evolution characteristics of AE indicated that the deformation and fracturing of unsaturated slates happened concentratedly and violently in the accelerated crack growth stage, while that of saturated slates occurred with low energy and uniform distribution spatially and temporally in the whole process. Moreover, water content reduced the brittleness index of unsaturated slate by 17.1%. For both conditions, the abundance of AE activity before failure shifted from a high level to a low level and lasted until failure. This can be used as a preliminary failure prediction of slates.