Yinghu Li

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1. Introduction In the process of multi-coal seam mining, after the upper coal seam is mined, a large amount of coal pillars are often left behind [1]. When the lower coal seam mining face advances into the influence range of the mining area, the roof structure collapses again, and the thick and hard suspended roof breaks and fails under the additional stress of the residual coal pillar [2].

3.5. Adsorption Characteristics of Dynamic Leaching of Gangue Figure 11a and Figure 12a show that the pH of the dewatering solution of the muddy siltstone and medium-grained coarse sandstone changed rapidly and eventually stabilized after dewatering with mine water of different pH values. The pH values of the dewatering solution of the muddy siltstone were stabilized at 6.25, 6.5, 8.2, and 8.5 after dewatering with mine water with pH values ranging from 4 to 10.