真三轴条件下含瓦斯煤岩损伤与渗流耦合机理研究

Gas-bearing coal-rock kept in a state of threedimentional unequal compressive stresses under the influence of geological structure and mechanical turbulence. Developing research on the coupling mechanical of gas-bearing coal-rock damage and seepage under the condition of true triaxial is essential in the reason of the damage of coal-rock and gas seepage mutual influence under the influence of mining. Firstly, an analysis on the microstructure and morphological characteristics of fracture before and after the stress started from the microscopic angle. Then we developed experimental study on seepage properties of gas-bearing coal-rock under the condition of different bedding structures in true triaxial, established the qualitative and quantitative relations between characteristics of permeation and the maximum principal stress, the intermediate principal stress, the minimum principal stress, the effective stress, the gas pressure and the different bedding structures, and mainly studied the influence mechanism of the intermediate principal stress and the different bedding structures on characteristics of permeation with gas-bearing coal-rock. Secondly, the dynamical evolution model on permeability of gas-bearing coal-rock in the process of plastic deformation under different loads and the coupling model of coal-rock damage and seepage were established, then we got the dynamical evolution characteristics on permeability of gas-bearing coal-rock and the mechanical about growth and extended of fractures by combing numerical simulation, at the same time verify the correctness of the mathematical model. Finally, We verified reliability and correctness of the experimental study and the numerical simulation results. The research results have important theoretical significance and practical value in optimizing the gas drainage parameters, improving the gas drainage rate, preventing and controlling the coal and gas outburst, and reducing the“greenhouse effect”caused by gas emission.

含瓦斯煤岩受地质构造及力学扰动的影响，所处的应力环境为三向不等压状态，采动影响下煤岩损伤与瓦斯渗流是相互影响的，因此开展真三轴条件下含瓦斯煤岩损伤与渗流耦合机理研究迫在眉睫。项目从微观角度分析煤体裂隙微观结构及受力前后形态特性；利用真三轴不同层理构造条件下含瓦斯煤渗透特性的实验研究，建立渗透特性与最大主应力、中间主应力、最小主应力、有效应力、瓦斯压力、不同层理构造之间的定性与定量关系，重点考察中间主应力和不同层理构造对含瓦斯煤渗透特性的影响机制；建立不同载荷塑性变形过程含瓦斯煤渗透率动态演化模型及煤岩损伤与渗流耦合模型；结合数值模拟得到含瓦斯煤渗透率动态演化特性和裂隙发育扩展机制，并验证构建数学模型的正确性；通过现场考察验证实验研究和数值模拟结果的可靠性。项目研究成果对优化瓦斯抽采布置参数、提高瓦斯抽采率、防治煤与瓦斯突出、减少因瓦斯排放引起的“温室效应”具有重要的理论意义和实际价值。

我国煤层赋存以“三高一低”(高应力、高瓦斯压力、高瓦斯含量及低渗透性)为主要特征，煤储层构造复杂，煤层存在许多强烈变形，受载煤体的三向应力受到煤层赋存情况、煤层倾角等地质条件，以及构造运动等力学扰动的影响而有明显差别，所处的应力条件一般为三向不等压状态。另外，瓦斯抽采、煤层开挖等采动行为也会使应力重新分布导致局部应力集中，其应力环境同样为三向不等压状态，即真三轴应力状态(最大主应力σ1＞中间主应力σ2＞最小主应力σ3)。与此同时，由于我国成煤历史过程的不均匀性、煤体本身构造、孔隙裂隙发育和变形程度的不同，很大程度上影响着煤体强度和力学变形特征，致使煤层不同层理方向上裂隙扩展特征和渗透率演化有明显差别。因此，开展真三轴条件下不同层理构造（垂直、平行和斜交层理）受载煤体渗流特性的研究迫在眉睫。项目采用理论分析、实验研究、模拟研究和现场应用相结合的研究方法，从细观微观角度分析煤体受载前后裂隙微观结构及不同层理煤样受力前后形态特性的差异，开展真三轴载荷含层理煤体的渗透率实验研究，构建真三轴条件下渗流特性与最大主应力、中间主应力、最小主应力、有效应力、不同层理构造之间的定性与定量关系，建立考虑Klinkenberg效应、瓦斯压力压缩变形、吸附膨胀和有效应力影响的真三轴载荷煤体渗透率动态演化模型及煤岩损伤与渗流耦合模型，并进行煤岩损伤与渗流特性的数值模拟及现场应用，研究成果不仅对优化瓦斯抽采设计、防治煤与瓦斯突出、减少因瓦斯排放引起的“温室效应”具有重要的实际价值，而且对煤矿的安全高效生产具有重要的现实意义。