Overburden structure evolution and pressure law of second mining in close-range coal seam group

The mining layout of the lower coal seam under the condition of close seam is greatly influenced by the remaining coal pillars in the upper coal seam.Thus the stress concentration and the sharp rock pressure appear frequently which seriously threaten the normal production of the mine.The roof structure characteristics, movement law and roof pressure distribution law of the lower working face were studied by numerical simulation, theoretical analysis and field measurement in this paper.The results show that the mining of the lower extra-thick seam leads to the development of the direct roof to higher and farther, and covers the direct roof and the main roof range of the upper seam after mining, forming the typical overburden structure of the stope with super-large mining space, which is "super-long distance and super-large damage height".Mining of the upper seam plays a certain pressure relief protection to the lower seam.As a result, the peak value and influence range of the advanced abutment pressure in the lower coal seam face are reduced, but the caving and compaction of the upper roof and the remaining coal pillars cause the local dynamic pressure manifestation in the lower coal seam, which has a negative impact on the mining of the working face.The research results provide a scientific basis for improving resource recovery rate and ensuring production safety.