In the process of Hydraulic jet cavity completion (HJCC), the elastic energy and gas expansion energy endowed in the coal around cavity can be instantly released under the strong disturbance of the water jet and cause dynamic disasters. Currently, the influence mechanisms of external disturbance and gas desorption on the cavity instability are unclear, and the technical methods to ensure cavity stability cannot be obtained. In this paper, a cavity instability model under water jet impact loading was derived, which considered both the dynamic stress field and the gas pressure field of the coal, and the control method was given by studying the influence mechanisms of the jet (or coal seam) parameters on the energy leading to instability. The results show that the jet pressure and ground stress affect the elastic energy by determining the effective stress distribution within the energy release zone. The initial gas pressure affects the gas expansion energy by determining the ratio of free to adsorbed gas pressure for the same desorption time. Besides, the jet pressure determines the dominant energy of cavity instability. Finally, the guidelines for “Pressurization by step” were proposed to ensure cavity stability. The results can ensure the safety of HJCC’s operation.

中文翻译：

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水射流冲击载荷作用下空腔周围煤体失稳的建模及控制方法


在水射流腔完井 （HJCC） 过程中，在水射流的强烈扰动下，腔周围煤体中赋予的弹性能和气体膨胀能可以瞬间释放，并引起动态灾害。目前，外界扰动和气体解吸对型腔不稳定性的影响机制尚不清楚，无法获得保证型腔稳定的技术方法。本文推导了水射流冲击载荷作用下的空腔失稳模型，该模型同时考虑了煤的动应力场和瓦斯压力场，并通过研究射流（或煤层）参数对导致失稳的能量的影响机制，给出了控制方法。结果表明，射流压力和地应力通过确定能量释放区内的有效应力分布来影响弹性能。初始气体压力通过确定相同解吸时间内自由气体压力与吸附气体压力的比率来影响气体膨胀能。此外，射流压力决定了腔体不稳定的主导能量。最后，提出了“Pressurization by step”的指导方针，以确保腔体的稳定性。结果可以确保 HJCC 的运行安全。