Dynamic cracking properties and generating conditions of coal under rapid gas release

Abstract Rapid gas release (RGR) is a key link in the outburst process, and its damage effect on coal induces and promotes outbursts. To study the cracking damage behavior and generating conditions of coal during the RGR process, gas release tests were performed on coal with the initial damage and gas release velocity as variables, and the damage factor and crack evolution of the coal samples during the test were obtained. The results revealed that the dynamic effect of the RGR led to the instantaneous generation of type I cracks with propagation velocities ranging from 145 to 198 m/s, and the initiation and development of cracks were jointly controlled by the initial crack length, residual strength, and gas release velocity. In the tests, when microcracks and macrocracks were generated by the RGR, the corresponding pressure change rate thresholds were 3.35 and 7.75 MPa/s, respectively, and the corresponding initial damage thresholds were the yield point and peak point of the coal samples. On the basis of fracture dynamics and crack generation conditions obtained from tests, a new criterion model and a new risk coefficient suitable for coal damage caused by the RGR were constructed, which provides theoretical support for outburst risk prediction from the perspective of fracture mechanics.