瓦斯压力非线性增长诱发煤巷围岩变形失稳机制与防控原理

With regard to the gas of coal body with the features of high dispersion, adsorption/desorption and nonlinear flow, the gas pressure is sensitive to external disturbance. At present, for the mechanism of gas disaster, the research focuses primarily on dynamic disaster, such as coal and gas outburst, but it is rare on the instability mechanism of surrounding rock induced by nonlinear growth of gas pressure and its principle of prevention and control. In this project, the microstructure change in coal body and temporal and spatial evolution of plastic zone induced by nonlinear growth of gas pressure and fluid-solid coupling, was used as the main object of research. On the one hand, the experiment is used to study on the deterioration law for microstructure of coal body and mechanical strength with nonlinear growth of gas pressure under fluid-solid coupling. On the other hand, the fluid-solid coupled mechanical model was established through theoretical and numerical analysis, the analytic expression on the radius of plastic zone is obtained in consideration of gas pressure. Moreover, taking the plastic zone theory as the bridge, the influence mechanism of the key factors of deformation and instability of surrounding rock on plastic zone was analyzed, and the spatial geometric distribution and boundary expansion of plastic zone under the action of gas was investigated, so as to clarify the scientific connotation of unstable cracking in plastic zone, to reveal the deformation and unstable mechanism of surrounding rock induced by nonlinear growth of gas pressure in coal roadway, and then to construct the instability criterion for unstable cracking of plastic zone in surrounding rock. And finally, the principle of differential coupling control of pressure relief and increase stability was put forward.

瓦斯在煤层中具有高度离散性、吸附/解吸与非线性流动等特征，其瓦斯压力受外扰动很敏感，目前针对瓦斯致灾机制的研究主要侧重于煤与瓦斯突出等动力灾害领域，而对瓦斯压力非线性增长诱发围岩变形失稳机制及防控方法的研究相对滞后。本项目以瓦斯压力非线性增长与流-固耦合效应诱发煤体细观结构异变及围岩塑性区时空演化规律为主要研究内容，通过试验研究流-固耦合作用下的煤体细观结构异变及其力学强度参数随瓦斯压力非线性增长的劣化规律；采用理论与数值分析建立流-固耦合力学模型，给出考虑瓦斯压力的煤巷围岩塑性区半径解析表达式，并以塑性区理论为桥梁，分析煤巷围岩变形失稳关键因子对塑性区的影响机制，研究瓦斯压力对塑性区空间几何分布形态及边界扩展的影响规律，明确塑性区非稳态扩展的科学内涵，揭示瓦斯压力非线性增长诱发煤巷围岩变形失稳的力学本质，构建高瓦斯煤巷围岩塑性区非稳态扩展失稳判据，提出增稳卸压差异化时空耦合控制原理。

本项目以高瓦斯煤巷为工程背景，通过理论分析、实验室试验、数值模拟与现场工程应用等方法，基于弹塑性理论，考虑瓦斯压力参量，利用莫尔-库仑强度准则，导出了瓦斯煤巷围岩塑性区边界隐性方程，分析了侧压系数、瓦斯压力、内聚力、内摩擦角、支护强度与巷道半径对围岩塑性区分布形态特征的影响，开展了岩体宏-细观变形破坏特征试验，获得了各种加卸载模式下岩体宏-细观变形破坏特征及强度弱化规律，探讨了塑性区几何分布形态与巷道冒顶之间的内在联系，揭示了锚杆锚固机理，最后提出了巷道围岩控制原理和具有针对性的巷道围岩控制技术。取得了以下创新性成果或发现：煤巷围岩塑性区主要存在圆形、椭圆形、圆角矩形和蝶形四种分布形态，侧压系数、瓦斯压力、内聚力与内摩擦角共同决定塑性区的分布形态及其范围，而支护强度与巷道半径不会改变塑性区的分布形态，仅仅影响塑性区范围。圆形和椭圆形塑性区对瓦斯压力、内聚力与内摩擦角的敏感程度较弱，而蝶形塑性区对瓦斯压力、内聚力与内摩擦角非常敏感，主要表现为4个蝶叶随瓦斯压力的减小或内聚力与内摩擦角的增大而快速退化，蝶叶尺寸越大，蝶叶的退化速度越快；巷道围岩的损伤程度与破坏形态不仅与最终破坏时的应力状态有关，还与围岩之前的受力状态以及应力水平密切相关，加载历史会对其本身产生一定程度的损伤和一定量的塑性变形；锚杆支护对巷道顶板围岩应力场和塑性区的作用不明显，不能有效控制巷道顶板围岩的塑性破坏，但对抑制层状软弱顶板岩层之间的离层与滑动等非连续性变形效果非常显著，而对非层状巷道顶板围岩的弹塑性变形等连续性变形控制作用非常有限。基于以上研究成果，提出了以巷道围岩塑性区的分布形态为切入点，通过改变围岩松散结构和力学性能，提高围岩自身承载能力和抵抗外力破坏的能力，影响塑性区扩展速率、分布形态与范围，进而增强巷道围岩整体性和稳定性的支护理念和方法，取得了明显的社会经济效益，推动了巷道支护理论与技术的发展。