The technical problems of high in situ stress, high gas pressure, high gas content, and low coal seam permeability are widespread in deep soft coal seam excavation, which leads to frequent occurrences of dynamic phenomena, such as coal cannons and blowout holes. Based on the high-pressure hydraulic fracturing technology and process, this study puts forward a new technology of gas drainage in deep and soft coal seams by fracturing the overlying key strata to cut off the stress transmission path among coal and rock strata. According to the theories of key layer and masonry beams, the distribution locations of the main and subkey strata are determined, and based on uniaxial compression and Brazilian splitting experiments, the mechanical parameters of key stratum were tested. Combined with the results of numerical simulation and field test, initial pressure and fracturing radius of hydraulic fracturing technology for overlying key strata were determined, the stress relief effect and permeability variation law of coal seam after hydraulic fracturing in the main and subkey strata were analyzed, and then technical schemes for simultaneous fracturing of the key layer were designed. Field application results showed that the stress concentration phenomenon in soft coal seam excavation had been alleviated, and the stress relief effect of coal seam and the permeability were increased obviously. The volume and concentration of gas drainage were increased by 10 and 11%, respectively, the gas amount by 1.22 times; the frequency of dynamic phenomena such as coal cannons decreased by 95%, the gas concentration in return air flow by 20% during mining processes. This paper provided an innovative technical idea and process for gas control in deep and soft coal seam excavation, which could effectively solve the common and difficult problems about frequent occurrences of excessive gas concentration and dynamic phenomena.

中文翻译：

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深软煤层上覆关键层水力压裂卸压增透

深部松软煤层开挖普遍存在高地应力、高瓦斯压力、高瓦斯含量、低煤层渗透率等技术难题，导致煤炮、爆孔等动力现象时有发生。本研究在高压水力压裂技术工艺基础上，提出通过压裂上覆关键层，切断煤岩层间应力传递路径的深层松软煤层瓦斯抽放新技术。根据关键层和砌体梁理论，确定了主次关键层的分布位置，并基于单轴压缩和巴西劈裂试验，测试了关键层的力学参数。结合数值模拟和现场试验的结果，确定了上覆关键层水力压裂技术的初始压力和压裂半径，分析了主次关键层水力压裂后煤层的应力释放效果和渗透率变化规律，提出了关键层同步压裂的技术方案被设计。现场应用结果表明，松软煤层开挖应力集中现象得到缓解，煤层应力消除效果明显提高，渗透率明显提高。瓦斯抽放量和浓度分别提高10%和11%，瓦斯量增加1.22倍；采煤过程中煤炮等动力现象频率降低95%，回风气体浓度降低20%。