Mechanism of rock burst in steep and extremely thick coal seam using horizontal section top-coal caving

Rock burst dynamic disaster of steep and extremely thick coal seam is special and more and more prominent in China. In order to reveal the mechanism of rock burst under this condition,the structure and mechanical model of o- verburden is established,and the laws of overburden movement,energy release and stress distribution of surroundings were analyzed. Also,the resistance monitoring data of hydraulic support was applied to analyze the loading and dynam- ic distribution law on the working face,and the activities of micro-seismicity in space indicating the strata movement and energy release were studied. The results show that in the horizontal section top-coal caving of steep and extremely thick coal seam,the broken step of roof in dip direction is nonlinearly increasing with the increase of dip angle. When the dip angle is greater than 60°,the broken step increases sharply,and the broken block of lower hard stratum can form a balanced structure temporarily along the dip direction. With subsection mining and top coal caving,the balanced structure can be destabilized by three types:broken and rotation,broken block falling,structural extrusion and subduc- tion under the action of roof and floor clamping,leading to dynamic load on the top coal of working face and asymmet- ric distribution of mining stress along working face. The coal mass close to the roof side is under a closed clamping state,the stress concentration is high,at the same time the coal body in this zone is subjected to strong shear stress, and is in the elastic-plastic boundary zone under the mining face,which is prone to unstable,while that close to the floor side is under an open clamping state,the coal body is easy to destroy and release pressure and energy and nor- mally in a plastic state. The over strata breaking step of the steep and extremely thick coal seam using horizontal sec- tion top coal caving is comparably larger with a strong break instantly energy release. The rock burst mechanism of strata clamping and shocking in the horizontal section top coal caving of steep and extremely thick coal seam is put for- ward. The monitoring results of hydraulic support show that the maximum dynamic load coefficient reaches to 3. 25 at the middle to head,which indicates that the overlying rock blocks form a suspended structure,and the micro-seismic monitoring of mine seismicity results show from the middle of the working face to the side near the roof,the bottom coal is easy to accumulate elastic deformation energy,the side to the floor is easy to release energy,and the movement of the roof is easy to form dynamic load disturbance. The research results were verified by the site monitoring.