Acoustic emission precursors of static and dynamic instability for coarse-grained hard rock

To investigate the acoustic emission (AE) precursors of coarse-grained hard rock instability, an experimental study on the rockburst and slabbing process of granite was carried out using a true triaxial test system. The evolution of the AE signals was monitored and analyzed in terms of the AE hit rate, fractal dimension of the AE hit number, AE count rate, b-value, dominant frequency and microcrack type. The test results show that after rock slabbing occurs, the AE precursors that can be used to predict the final dynamic instability (rockburst) are as follows: indicators such as the AE hit rate and AE count rate suddenly increase and then suddenly decrease; the AE hit rate exhibits a "quiet period"; during the "quiet period", a small number of high-amplitude and low-frequency hits occur, and the signals corresponding to shear fracture continue to increase. The AE precursors for the final static instability (spalling) are as follows: both the AE hit rate and the b-value continuously decrease, and intermittent sudden increases appear in the high-frequency hits or the AE count rate.