关键层结构对保护层卸压开采效应影响分析

Analysis of the Effect of Key Strata Structure on Relief-Pressure Mining in Protective Seam

由于保护层卸压开采,导致覆岩结构的运动,致使上覆煤层变形,产生卸压效应,改变被卸压煤层的透气特性,为卸压瓦斯抽采创造有利条件.采用RFPA2D-Flow数值模拟软件,分析了上覆煤岩层采动裂隙演化、卸压煤层采动应力及位移分布、瓦斯参数变化等规律,结果表明:1)下保护层开采引起的上覆煤岩层采动裂隙集中分布在采场两端部,并呈竖向偏采空区方向发育,离层裂隙发育至被卸压煤层上方;2)开切眼和停采线附近区域顶板裂隙明显发育,卸压开采导致上覆煤层产生膨胀变形,透气性明显增加;3)由于被卸压煤层和保护层之间关键层结构的力学效应,使被卸压煤层透气系数增加幅度不显著,导致抽采孔瓦斯压力降低速度放缓.无关键层结构时,采动影响区内抽采孔瓦斯压力降低较快.

Relief-pressure mining of the protective seam can cause the movement of overlying strata, lead to relief-pressure effect by deformation of the upper coal seam, change the permeation properties of protected seam, and create favorable conditions for gas drainage in pressure releasing area. In this paper, by adopting numerical simulation software of RFPA2D-Flow, we analyzed the regularities of mining-induced fractures evolution, stress and displacements distribution, and gas parameters change, et al, in the upper protected seams. The results shows that the mining-induced fractures of overlying seams caused by protective seam mining centralize in two ends of the stope, with vertical growth deviate to the goaf, the separated fractures develop to the upperside of protected seam, and the fractures in the roof develop mainly near the open-off cut and stopping line. Meanwhile, the relief-pressure mining causes the expansion deformations in the upper coal seam to be generated, and the permeability increases obviously. Furthermore, because of mechanical effect of the key strata between the protective and protected seam, the permeability coefficient of protected seam increases indistinctively, and the gas pressures in the drilling holes decrease slowly. But, the gas pressures decrease rapidly in the infection zone of coal mining, if there＇s no key strata structure.