Study On Destressing Effects After Mining Protective Seams Of The Deep Thick Coal Seam With Large Obliquity And High Burst Liability

During the past few years, Huafeng coal mine of Xinwen Mining Group has become one of the most dangerous rockburst mines in China. The mining depth has exceeded 1000m. The seam belongs to high burst liability item with three tough conditions including hard roof, hard coal seam and hard floor. It is very effective to decline the fatalness of the rockburst after using methods of caving mining and extracting lower protective seam in shallow, but rockbursts turn to be much more serious when mining depth exceeds 900m.On the background of Huafeng coal mine, the destressing effects of mining upper and lower protective seams are researched with the methods of similar material simulation experiment and numerical simulation analysis, to make sure whether it is available to mine in the deep level. The theory of"three decline one increase destressing principles"which includes roof and floor structural protective principle, gangue pressure relief protective principle, moving protective principle along with stope progress and the side direction stress recovery principle are put forward through analyzing the results of physical simulation, numerical simulation and microseismic monitoring. According to roof and floor structural protective principle, the design idea is brought forward that the lower tunnel of seam 4 is arranged in the structural destressing region of seam 6.Through monitoring the stress change of the protected seam in the process of mining the protective seam and after it reaches a stable state, the rule of the stress change is analyzed, the lower reasonable destressing angle of the lower protective seam is computed and the lower tunnel's reasonable position of the protected seam is fixed. According to gangue pressure relief protective principle, computation models of the critical depth leading to rockburst are built in the condition of mining upper protective seam solely and mining both the upper and lower protective seams. Despite mining the lower protective seam, the upper tunnel of the protected seam is still in a highly concentrative stress area which is prior to rockburst, and the result is contrary when the upper protective seam is mined, the stress in the upper tunnel of the protected falls obviously, which is proved both by the physical simulation and numerical simulation that the upper protective seam destresses obviously, so it is feasible and effective to extract the upper protective seam. The reasonable position of the upper protective seam workface is chosen by comparing the destressing effects of the twice simulation experiments of mining upper protective seam. According to moving protective principle along with stope progress, the viewpoint that an ultimate stress restoration distance existing between the protective and protected seams along strike direction is put forward. The experiment testifies that the"rebound"phenomenon occurs on the earth's surface before rockburst with high energy happens in mine. The research of destressing effects of mining the protective seams has been effectively applied to mining practice and provides the theory guidance for the mining design of the deep workface which is very important for preventing and controlling rockburst in project practice.