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浅埋厚层状顶板大采高工作面末采水力压裂顶板来压调控研究

Study on roof weighting control at the end mining in large mining height working face with thick and hard roof by hydraulic fracturing

  • 摘要: 以张家峁煤矿厚层状顶板5217工作面末采为研究背景, 通过物理模拟试验、数值模拟和理论计算, 确定了顶板水力压裂进行顶板结构及来压调控的合理层位, 分析了压裂前后支架阻力、采场应力分布和煤壁位移, 揭示了顶板垮落规律和来压规律, 建立了不同层位弱化顶板结构模型, 给出了支架阻力计算公式, 提出了低、中、高3种弱化层位判据。研究结果表明: 低层位弱化后平均周期来压步距缩短14.5%, 来压时支架最大阻力降低14.1%; 中层位弱化后平均周期来压步距缩短47.3%, 来压时支架最大阻力降低21.6%; 高层位弱化后平均周期来压步距增大11.8%, 来压时支架最大阻力升高24%。采用“水力压裂+支架阻力监测”相结合的数值模拟方法弱化中层位, 平均周期来压步距缩短60%, 来压时支架最大阻力降低13.2%; 弱化后工作面前方平均垂直应力始终较弱化前低21%, 主回撤通道右侧煤体平均垂直应力始终高于弱化前33%, 工作面煤壁水平位移较弱化前减小52.2%。根据不同层位弱化结果, 建立了中层位弱化的“高位短砌体梁”结构模型以及高层位弱化的“低位台阶岩梁”结构模型, 计算得出控制顶板稳定支架需要提供的阻力分别为15 450 kN和9 437 kN。实测得出顶板中层位水力压裂后, 周期来压步距为6.38 m, 来压时最大支架阻力为9 463 kN, 较未压裂减小了46%和26%, 科学合理的压裂层位及结构调控保障了工作面安全回撤。研究成果可为顶板水力压裂层位确定及结构调控实践提供理论参考。

     

    Abstract: Taking the end mining of 5217 working face with thick layered roof in Zhangjiamao Coal Mine as the research background. Through physical simulation experiment, numerical simulation and theoretical calculation, the reasonable layer of roof structure and pressure control by roof hydraulic fracturing is determined. The support resistance, stope stress distribution and coal wall displacement before and after fracturing are analyzed, and the roof caving law and weighting law are revealed. The weakening roof structure models of different layers are established, and the calculation formula of support resistance is given. Three weakening horizon criteria of low, medium and high are proposed. The results show that the average periodic weighting step is shortened by 14.5% after the low-level weakening, and the maximum resistance of the support is reduced by 14.1%. After the middle position is weakened, the average periodic weighting step is shortened by 47.3%, and the maximum resistance of the support is reduced by 21.6%. After the high-level weakening, the average periodic weighting step increases by 11.8%, and the maximum resistance of the support increases by 24%. The numerical simulation method of 'hydraulic fracturing + support resistance monitoring' is used to weaken the middle position. The average periodic weighting step is shortened by 60%, and the maximum resistance of support is reduced by 13.2%. After weakening, the average vertical stress in front of the working face is always 21% lower than that before weakening, the average vertical stress on the right side of the main withdrawal channel is always 33% higher than that before weakening, and the horizontal displacement of the coal wall of the working face is 52.2% lower than that before weakening. The ''high short masonry beam'' structural model with middle-level weakening and the ''step rock beam'' structural model with high-level weakening are established. The resistance required to control the roof stability support is 15 450 kN and 9 437 kN. After hydraulic fracturing in the middle layer of the roof, the periodic weighting step is 6.38 m, and the maximum support resistance is 9 463 kN, which is 46% and 26% lower than without fracturing. Scientific and reasonable fracturing horizon and structure control ensure the safe withdrawal of working face. This study can provide theoretical basis and reference for the determination of roof hydraulic fracturing layer and the practice of structural regulation.

     

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