Mechanical Properties and Acoustic Emission Characteristics of the Bedrock of a Hydropower Station under Cyclic Triaxial Loading

The bedrock of hydropower stations is susceptible to irreversible failure due to dynamic unloading and loading related to earthquakes, rock bursts or blasting. To ensure operational safety, the damage evolution process of bedrock under cyclic loading must be investigated. Hence, this study investigates the mechanical properties and acoustic emission (AE) characteristics of the bedrock from different positions of the Badantoru hydropower station under different confining pressures. First, the relationship between the dynamic elastic modulus and residual strain is analyzed, and then the brittleness and damage of the rocks are quantitatively characterized. Subsequently, the failure process and crack development of the rocks are revealed from the obtained AE characteristics. The results show that as the applied confining pressure increases, the peak differential stress and fatigue life of the rock specimens increase; whereas, the shear failure angle decreases. Under the same confining pressure, the rocks with a greater number of internal joints and pores (Dam Site I) have a lower bearing capacity under cyclic loading, a greater brittleness after strain softening, and a smaller shear failure angle. With increasing plastic strain, all of the specimens exhibit cyclic softening, and an obvious four-stage fatigue damage evolution can be observed.