Study on the destabilization and deformation breakage characteristics of the mine roof under repetitive mining of close coal seam group

Poor stability of the quarry roof is particularly prominent in close coal seam group mining. To address this challenge, the stability of the quarry roof under repeated mining disturbance was investigated using a combination of indoor tests, similar simulations and numerical simulations. The study obtained that: under the influence of two repeated mining disturbances, the 17# coal roof fissures are especially developed, and the rock seam strength is lower and the deformation is increased. Compared with the single seam mining roof, the direct roof of the close coal seam group is more easily destroyed under the same roof pressure; the thickness of 16# coal seam is small, the basic roof breaks regularly with the forward advance of the working face, forming a stable “The roof will go through the process” of “stability-destabilization-restabilization”; while the thickness of 17# coal seam is larger, the broken rock of the roof cannot be hinged due to the large rotation angle. During the mining process, the overlying rock above the 17101 mining face will form a “cantilever beam” structure due to the direct collapse of the basic top rock. This formation leads to a significant stress concentration on the coal wall and top plate in front of the working face of the lower coal seam. The repeated mining of the lower coal seam causes the overlying rock to act as a bedding layer, moderating the mine pressure. Consequently, the mining of the upper coal seam results in a reduction of cyclic pressure steps during the repeated mining of the lower coal seam.