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煤层瓦斯渗透率是影响瓦斯抽采和动力灾害防治的重要参数。为了研究煤体损伤和剪胀变形对渗透率的影响,首先引入损伤变量反映煤体损伤破坏状态,建立了基于体应变增量的煤体损伤本构模型。并采用Hurst指数表征裂隙表面粗糙度,基于裂隙表面的分形特征,建立了裂隙渗透率在压缩和剪切作用下的演化模型。通过对TOUGH2和FLAC~(3D)软件进行二次开发,建立了基于双重孔隙模型的TOUGH2(CH_4)-FLAC气-固耦合数值分析工具。采用本软件对煤样单轴压缩过程进行模拟分析,结果表明:煤体的破坏是损伤单元累积和贯通的结果,最终形成贯通煤体的损伤带是造成煤体失稳破坏的主因;围岩内的渗透率增加区域与损伤区位置基本一致,其中裂隙系统的渗透率增加幅度最大可达2个数量级;剪切破坏区的裂隙发生剪胀变形,引起裂隙渗透率大幅增加。建立的理论模型与数值计算工具为制定瓦斯治理措施提供了理论指导。
Gas permeability of coal seam is an important parameter that affects gas drainage and power disaster prevention. In order to study the influence of coal damage and dilatancy deformation on permeability, the damage variable is first introduced to reflect the damage status of coal body, and a constitutive model of coal damage based on body strain increment is established. The Hurst index is used to characterize the surface roughness of fractures. Based on the fractal characteristics of the fracture surface, an evolution model of fracture permeability under compressive and shear conditions is established. Through TOUGH2 and FLAC 3D software, the TOUGH2 (CH_4) -FLAC gas-solid coupling numerical analysis tool based on double porosity model was established. The software was used to simulate the uniaxial compression of coal sample. The results show that the destruction of coal is the result of accumulation and penetration of the damaged unit, and finally the formation of the damage belt through the coal is the main cause of the instability of coal. The permeability increase rate within the fracture zone is basically the same as that of the damage zone. The permeability of the fracture system increases up to 2 orders of magnitude. The fracture of the shear failure zone dilates and deformation leads to a significant increase of fracture permeability. The established theoretical models and numerical calculation tools provide theoretical guidance for the development of gas control measures.