Mechanisms of rock burst in hard and thick upper strata and rock-burst controlling technology

Rock burst frequently occurs during coal mining at the Huafeng Coal Mine because of the high-strength, thick conglomerate strata above the coal seam. Given this situation, theoretical analysis, physical simulation, and field measurement methods were applied to study the mechanism of rock burst of hard and thick upper strata in this paper. The results show that rock burst in the mine is caused by a combination of movement, special breaking laws of thick conglomerate, and special breaking-induced stress fields. The combined structure of the upper hard thick conglomerate and the lower soft red layer can provide favorable conditions for the occurrence of bed separation. Accordingly, technical evaluation of bed separation grouting as a means of controlling rock burst under such conditions of hard and thick upper strata was proposed. The engineering application of bed separation grouting was shown to effectively control the movement of thick conglomerate and reduce the accumulation of stress. The range of underground microseismic event energy decreased by 40-60 %, which greatly reduced the frequency and intensity of rock burst. The occurrence of strong rock burst in particular was greatly curtailed. Meanwhile, the velocity and degree of surface subsidence decreased notably and surface cracks were effectively controlled. These achievements provide references for controlling rock burst under conditions of hard and thick upper strata.