Development law of fractures in overlying strata of lower seam of contiguous seams in upward mining
In upward mining,the overlying rock movement may damage the overall integrity of the overlying coal seam and make it unminable.Based on the engineering background of the impact of the mining of the 9#coal seam on the overlying 5#coal seam in a certain mine.Theoretical analysis,numerical simulation,and similar material simulation are used to study the damage of the overlying rock strata,the development law of rock fractures,and the behavior law of the working face's rock pressure after coal mining in close range coal seams.The results are as follows,after the 9#coal seam is mined,the three zone discrimination method obtained an average height of 9 m for the collapse zone and 36 m for the water conducting fracture zone;the ratio analysis method K is 19.99,which is greater than 7.5 for medium hard rock layers;the necessary layer spacing for safe mining of the overlying 5#coal seam using the surrounding rock balance method is 45 m,which is much smaller than the 60 m spacing between the 5#coal seam and the 9#coal seam.Numerical simulation shows that the overlying 5#coal seam of the 9#coal face are located in the plastic area formed after the mining of the lower coal seam,and there will be no stress concentration phenomenon in the area where protective coal pillars are left.Similar simulations indicate that after mining the 9#coal seam,the maximum subsidence of the 5#coal seam is 10mm,and the height of the model collapse zone is basically around 15 cm,which is consistent with the development laws of mining pressure and overlying rock movement.The relevant research results demonstrate the feasibility of mining the overlying 5#coal seam after mining the 9#coal seam.
contiguous coal seamsupward miningtheoretical analysissimulation studyfracture law of overlying strata
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