Evolution Law And Application Of Pressure Relief Gas Storage And Transportation Area In Coal Seam Group With Repeated Mining

China is rich in coal resources,and most coal fields contain multiple recoverable or partially recoverable coal seams.The overburden fracture evolution,morphological characteristics of unloading gas storage and transportation area and gas extraction system arrangement are more complicated after mining coal seam clusters compared with single seam mining,which is still one of the important directions of gas management in China’s mines.In this paper,we analyze the evolution of overburden fissures under mining coal seam group conditions from theoretical,physically similar simulation experiments and numerical simulations,and clarify the formation and evolution characteristics of unloading gas storage and transportation zones,and apply the research results to mine sites.The paper analyzes the overburden fracture evolution law and stress change characteristics after mining the coal seam group by using physical similar simulation experiments and FLAC3D numerical simulation.The initial incoming pressure step is 40m,the average cycle incoming pressure step is 18.3m,the collapse zone height is 12m,and the fissure zone height is 58m after single upper seam mining;the initial incoming pressure step is 37m,the average cycle incoming pressure step is 14.1m,the collapse zone height is 14m,and the fissure zone height is 85.5m after repeated mining of the coal seam group.The stresses in the central part of the mining area are decompressed and gradually recovered with the overburden compaction stresses;the double decompression mining of the coal seam group leads to further reduction of the stresses in the coal and rock bodies above and below the mining area and further increase of the stresses in the coal and rock bodies around the mining area.After repeated mining of the coal seam group,the shape and characteristic parameters of the unloading gas storage and transportation area change,and it is considered that the single coal seam is trapezoidal along the coal seam direction or tendency profile after back mining,and the longitudinal profile is "O" fissure circle;after repeated mining of the coal seam group,the trapezoidal fissure area is superimposed on each other,and the longitudinal profile is "O"fissure circle.O"-shaped fissure circle in the longitudinal section increases the amount of overburden sinking.The fracture network is well developed after coal seam group mining,and the collapse angle and width of storage and transportation area are larger than those of single seam mining;the rate of unloading gas storage and transportation area after coal seam group mining is 1.3 times of that of single seam mining;the broken fractures are well developed after coal seam group mining,and the penetration degree increases,so the ability of unloading gas to float upward is enhanced,and the gas extraction system can be arranged to higher levels to get better extraction effect.Based on the actual recovery situation of the working face,the unloading gas extraction method is determined.By monitoring the gas extraction situation in the working face of the upper and lower coal seam group separately and analyzing the effect of three-dimensional gas extraction in the working face,the results of the thesis and the rationality of the optimized extraction system arrangement are further verified,which ensure the safe mining of the working face and provide a reference for the unloading gas extraction in similar mines of the coal seam group and are of great significance for the realization of accurate gas extraction.