缓倾斜煤层开采下伏煤岩裂隙动态演化规律

Dynamic Evolution Law of Coal-rock Fissures under Gently Inclined Coal Seam Mining

保护层开采可以有效地预防煤与瓦斯突出,研究保护层开采过程中的应力演化、围岩变形特征和裂隙演化可为开采被保护层提供理论保障。选取青东煤矿7煤作为上保护层,8煤作为下伏煤层。通过FLAC^(3D)、UDEC建立伏岩应力模型,采用盒分形维数的方法对工作面开挖后煤体裂隙发育程度进行定量分析,并结合现场试验研究上保护层开采对被保护层影响。结果表明:工作面回采后,采空区应力得到充分释放,围岩出现膨胀位移,在充分卸压区域最大垂直位移15.26 mm;对比盒分形维数数据,随着巷道开挖,裂隙发育复杂程度逐渐增加,各阶段煤层开挖顶板裂隙发育优于底板。顶底板分形维数由1.99增加到2.37,增长率达到19%,底板分形维数从1.92变化到2.24,增长16.6%;通过试验,上保护层开采有助于瓦斯卸压通道的形成,使得卸压区内瓦斯压力降低了65.4%,煤层透气性系数增大76倍。

Protective layer mining can effectively prevent coal and gas outburst. Studying the stress evolution and the fracture evolution of surrounding rock deformation characteristic box in the process of protective layer mining can provide theoretical guarantee for the mining of protected layer. 7 coal seam of Qingdong coal mine is selected as the upper protective layer, and 8 coal seam is selected as the underlying coal seam. The rock stress model was established by FLAC^(3D)and UDEC, and the box fractal dimension method was used to quantitatively analyze the development degree of coal fracture after working face excavation. Combined with field test, the influence of upper protective layer mining on protected layer was studied. The results show that after the mining of the working face, the stress in the goaf is fully released, and the surrounding rock has an expansion displacement, with the maximum vertical displacement of 15.26 mm in the fully depressurized area. Compared with box fractal dimension data, the complexity of fracture development increases gradually with roadway excavation, and the fracture development of roof is better than that of floor in each stage of coal seam excavation. The fractal dimension of roof and floor increased from 1.99 to 2.37, and the growth rate was 19%. The fractal dimension of floor changed from 1.92 to 2.24, and the growth rate was 16.6%. Through the test,the upper protective layer mining is helpful to the formation of gas pressure relief channel, which reduces the gas pressure in the pressure relief area by 65.4% and increases the permeability coefficient of coal seam by 76 times.