Surrounding rock effect on coal burst under unloading condition: a numerical study

In the coal burst induced by excavation, the burst body is not a closed system because the surrounding rock (the roof and the floor) can work on it. In order to investigate the surrounding rock effect on coal burst caused by unloading, the discretized virtual internal bond is employed to comprehensively simulate the burst process of the rock-coal-rock (RCR) body. The simulation results suggest that there exists a critical in situ stress, which is about 0.7 times of the uniaxial compression strength of RCR. When the in situ stress exceeds this critical value, the unloading can induce the RCR burst. There also exists a critical surrounding rock stiffness, which is about 8.0 times of the coal stiffness. When the surrounding rock stiffness is smaller than this critical value, it has significant impact on the coal burst while when it exceeds the critical value, it has almost no effect on unloading burst. The characteristic surrounding rock size, over which the surrounding rock has no effect on the burst, is about 4.0 times of the coal seam. Besides these, some quantitative regularities of acoustic emission during coal burst have been obtained. These findings are helpful to improve the understanding on coal burst. They provide valuable references for the prediction of coal burst.