Study on determination of development height of mining-induced fissure zone in deep outburst coal seam

The use of high-level directional long borehole gas extraction technology instead of high-level extraction roadway to extract mining pressure relief gas can greatly reduce the amount of rock roadway excavation. And it can effectively relieve the tension situation of mine mining replacement. Moreover, it can achieve remarkable gas control effect. But the high-level directional long borehole gas extraction technology often has problems in practical application. Due to inaccurate determination of the development height range of the upper "three zones" of mining overburden, the directional long borehole layout horizon is too high or too low. The application effect is poor. In order to solve this problem, taking the VI₁₅-15050 working face of No. 8 Coal Mine of Henan Pingdingshan Tian'an Coal Mining Co., Ltd. as the research background, the development height of mining-induced fissure zone in the coal seam of the working face is determined by using empirical formula method and numerical simulation experiment method. The maximum development height of the caving zone is 13.2 m, and the maximum development height of the fissure zone is 48 m. The kilometer directional drilling rig is used to construct high-level directional long borehole in the VI₁₅-15050 working face, and the fissure zone development height is verified. The results show that the lithology of overburden is relatively broken at 20 m from the roof of the coal seam, and the high concentration gas area in the fissure zone is more than 23 m from the roof. When the VI₁₅-15050 working face is pushed to 105 m, the high-level directional long borehole and the fissure zone in the goaf have been fully communicated. The gas in the upper corner and return air flow of the VI₁₅-15050 working face is kept at 0.47%. The maximum gas extraction volume fraction of a single hole of the high-level directional long borehole is 13.2%. The daily net gas extraction volume is kept at 3-4 m³/min, and the air distribution volume is calculated as 2500 m³/min. The gas extraction volume of high-level directional long boreholes can reach 25.5%-34.0% of the air exhaust gas volume. During this period, there is no gas overrun, and the high-level directional long boreholes arranged in the current layer can successfully control the gas in the upper corner and return air flow. The correctness of the development height of the fissure zone obtained by the two methods is verified.