Precursor discrimination and mechanism of rock burst in the island workface with hard roof

Taking 8939 workface in Xinzhouyao coal mine as the research engineering background, elastic plate theory is used to analyze the elastic energy released during the breaking of hard roof, and using FLAC^3D numerical simulation software to divide the high stress area of panel, according to the fractal theory the internal relation of time distribution and spatial distribution of microseismic event and rock burst was analyzed. The research results show that before the hard roof was broken, the coal body in front of the panel had been slowly loaded by exposed suspending roof because of rotation and subsidence. Because the process was slow, the stress and energy were transferred to the deep coal and rock mass. Therefore, the rock burst is not easy to occur. When the roof fractures, great amount of bending strain energy releases instantly, inducing strong pulse effect to the coal body around a working face. If the pulse energy is higher than the critical value of rock burst, then rock burst is more likely to occur. And before the occurrence of rock burst, coal-rock mass is in unsteady state, will actively exchange energy with the outside world, at this moment the microseismic events are in the active phase. When microseismic energy exceeds a certain value or the fractal dimension of microseismic events is lower than a critical value, rock burst is easy to occur.