Ren Qihan, Cao Jianjun
State Key Laboratory of Coal Mine Disaster Prevention and Control, Chongqing, 400037, China.
China Coal Technology and Engineering Group Chongqing Research Institute, Chongqing, 400037, China.
Sci Rep. 2024 Oct 19;14(1):24551. doi: 10.1038/s41598-024-76612-6.
Coal (Rock) pillar retaining in the mining of protective layer would cause gas dynamic disaster in the protected layer. Based on the gas geological conditions of the two-layer coal seam in Jinhe Coal Mine of Yaojie Mining District, the stress evolution law of coal seam in the rock pillar affected area was studied by theoretical analysis and numerical simulation, and the crack development law of coal seam in different loading stages under conventional triaxial loading was studied by CT scanning technology. With the analysis of the stress evolution and crack development of coal in rock pillar affected area, the gas extraction effect under different stress states and the gas desorption law after pressure relief antireflection were studied on site. The results showed that the stress of coal in the rock pillar affected area is in the approximate elastic stage of the conventional triaxial stress-strain curve, and the cracks of coal are mainly closed at this stage. Meanwhile, the increase of stress leaded to the decrease of coal permeability and the poor gas extraction effect. CT scanning tests under conventional triaxial loading were carried out in the laboratory, and three-dimensional visual models of coal sample cracks were constructed at different loading stages. When loading to the linear elastic stage, the crack volume and surface area were reduced by 74% and 71% compared with the ones in initial state. At the same time, the expression between stress σ and crack density T was further established. After comprehensive control measures such as intensive drilling discharge, presplitting blasting and coal water injection were taken to the coal in rock pillar affected area, the crack density T could reach the crack development level of the conventional triaxial loading softening stage, realizing the crack development of the coal under low stress. The enclosed gas in front of the coal could desorption flow during the roadway driving. And the predict index value K also decreased from 0.57 mL/(g·min) to 0.17 mL/(g·min) continuously. The safety of coal roadway in rock pillar affected area was realized, and the accuracy of numerical simulation and laboratory test results was verified, which had certain reference significance for coal roadway excavation under this similar conditions.
保护层开采中煤（岩）柱留设会引发被保护层瓦斯动力灾害。基于窑街矿区金河煤矿两层煤层的瓦斯地质条件，通过理论分析和数值模拟研究了岩柱影响区域煤层的应力演化规律，采用CT扫描技术研究了常规三轴加载下不同加载阶段煤层的裂隙发育规律。通过分析岩柱影响区域煤体的应力演化和裂隙发育情况，现场研究了不同应力状态下的瓦斯抽采效果及卸压增透后的瓦斯解吸规律。结果表明，岩柱影响区域煤体应力处于常规三轴应力 - 应变曲线的近似弹性阶段，此时煤体裂隙主要处于闭合状态。同时，应力增加导致煤体渗透率降低，瓦斯抽采效果不佳。在实验室进行常规三轴加载下的CT扫描试验，构建了不同加载阶段煤样裂隙的三维可视化模型。加载至线弹性阶段时，裂隙体积和表面积与初始状态相比分别减小了74%和71%。同时，进一步建立了应力σ与裂隙密度T之间的表达式。对岩柱影响区域煤体采取密集钻孔卸压、预裂爆破和煤体注水等综合防治措施后，裂隙密度T可达到常规三轴加载软化阶段的裂隙发育水平，实现煤体在低应力下的裂隙发育。巷道掘进过程中，煤体前方的封闭瓦斯能够解吸流动。且预测指标值K也从0.57 mL/(g·min)持续降至0.17 mL/(g·min)。实现了岩柱影响区域煤巷的安全，并验证了数值模拟和实验室试验结果的准确性，对类似条件下的煤巷掘进具有一定的参考意义。
