Study on failure test and precursor of granite affected by loading rate

In order to study the fracture response mechanism of each stage in the process of instability and failure of the surrounding rock of the deep hard rock roadway affected by the loading rate effect, five tests with different loading rates are carried out on the granite, and the variation law of the fracture evolution characteristics, mechanical parameters and acoustic emission parameters of granite specimens at each stress stage under variable loading rate is analyzed, and the early warning information of granite instability failure precursors is obtained based on the variation law of the Γ of the acoustic emission amplitude concentration curve. The results show that the larger the loading rate, the shorter the time required for the specimen to fail and the more severe the failure. When the loading rate exceeds 0.1 kN/s, the growth rate of both of them slows down, the increase of peak strength decreases from 26.00% to 6.50%, and the increase of elastic modulus decreases from 35.60% to 12%, showing a good negative correlation between peak strain and loading rate. The AE activity showes an obvious phased increase, the AE ringing count showes an exponential increase, and the AE energy signal gradually changes from “solitary seismic type” to “group seismic type”. The b value of AE generally showes a “W” pattern with the loading time, and the b value of AE decreased with the increase of the loading rate when the specimen is damaged, from 0.47 （0.02 kN/s） to 0.30 （0.50 kN/s）, which indicates that the larger the loading rate, the larger the rupture scale of the specimen and the more complete the damage of the specimen became. The distribution characteristics of RA-AF scatter data in each stress stage show that the larger the loading rate, the better the internal shear crack development of the specimen. The amplitude concentration curve Γ the abrupt change point of slope between the oscillating rising stage and the abrupt rising stage is defined as the critical damage factor of granite specimens under variable loading rate, which can be used as early warning information before rock instability and failure.