Experimental study on instability destruction of slab-failure brittle rock under influences of loading rates

Excavation of deep brittle rock often leads to slab failure, and may further to flake spalling, rock explosion and other engineering disasters, which is a serious threat to the safety of construction of deeply buried tunnels. In deep rock mass engineering, the rate of stress redistribution after excavation varies due to the factors such as tectonic stress, excavation conditions and engineering disturbances. In order to investigate the effects of loading rates on the destabilization damage of slab-failure surrounding rock, the unilateral limit uniaxial compression tests are conducted using brittle rock processed into slab-failure specimens, and the macroscopic rupture, strength characteristics, acoustic emission (AE) characteristics and energy mechanism of the specimens are comprehensively investigated under different loading rates. The results show that: (1) The specimens exhibit large pieces of spalling, overall instability and separation under low loading rates. The specimens did not separate in large pieces under high loading rates, but there are small pieces of power ejection. The compressive strength of the specimens increases with the increase of the loading rates. (2) The increase of low frequency and high amplitude signals and the change of b-value indicate that the specimens have a sudden failure instability propagation, and the large- and small-scale fractures are alternately generated during this process. (3) At the steady loading stage, the high loading rates make the AE activity of the specimens more intense, while the opposite is true at the near destabilization damage stages, and the low-frequency signal and large-scale fracture events account for a greater proportion under low loading rates. The difference in the speed of stress re-distribution due to different excavation schemes and construction methods in engineering is the cause of further damage in different modes after the occurrence of slab failure in the surrounding rock.