损伤和剪胀效应对裂隙煤体渗透率演化规律的影响研究

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FLAC3D软件进行二次开发，建立了基于双重孔隙模型的TOUGH2(CH4)-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。

Influences of damage and shear dilation on permeability evolution of fractured coal

Gas permeability is a significant parameter influencing gas extraction and coal-gas outburst prediction in coal seams. To investigate the effects of coal damage and shear deformation on fracture permeability, a damage variable is introduced to reflect the failure state of coal damage. A constitutive model is established with the increment of volumetric strain. The evolution model of fracture permeability influenced by shear and compression is obtained, and Hurst coefficient is applied to represent the roughness of fracture surface. Based on the dual permeability media of matrix pore and fracture, a gas-solid coupling software named TOUGH2(CH4)-FLAC is built by the secondary development of the codes of TOUGH2 and a DLL file for FLAC3D. A case study is performed to investigate the influences of damage and shear dilation on gas flow in the process of uniaxial compression using the proposed model. Numerical results show that the accumulation and coalescence of damaged elements largely control the failure of coal, and the damage zone is the main factor resulting in the failure of coal. The location of permeability change is highly related to the damage zone. The fracture permeability can be increased by two orders of magnitude in most of damage zones. The variety of fracture permeability in the shear damage zone increases drastically with the increase of shear dilation. The proposed method provides a theoretical basis for the development of gas control.