Dai Jiahui, Liu Chao, Li Minghui, Song Zhenlong
State Key Laboratory of Coal Mine Disaster Dynamics and Control, Chongqing University, Chongqing 400030, People's Republic of China.
College of Resources and Environmental Science, Chongqing University, Chongqing 400030, People's Republic of China.
R Soc Open Sci. 2019 Feb 13;6(2):181438. doi: 10.1098/rsos.181438. eCollection 2019 Feb.
stress is generally an anisotropic/true triaxial stress ( > > ). Bedding weakens the continuity and integrity of coal. It is critical to understand the mechanical behaviour and gas migration of coal under true triaxial stress conditions. We performed experiments of cubic coal samples to investigate the permeability evolution and mechanical behaviour of coal under true triaxial stress conditions by using newly developed true triaxial geophysical apparatus. We analysed the effect of principal stresses on deformation and permeability characteristics of coal containing bedding planes. The results show that volumetric strain, stress states and bedding directions determine the permeability comprehensively. The variable quantity of strain was the largest in the direction normal to the bedding plane. The expansion or compression degree was characterized by the difference between the major and minor principal strain ( - ). Essentially, this represents the difficulty degree with regard to coal being compressed at the initial stress state and the deformation degree in and direction. The variation of ( - ) was consistent with that of permeability. Under an identical true triaxial stress condition, permeability was smaller when larger stress was applied in the direction normal to the bedding plane. Additionally, stress level in the direction parallel to the bedding planes and the directions between stresses in the direction parallel to the bedding planes and the flow direction also affect the permeability and strain. By solving lateral expansion coefficient, coal also exhibited anisotropic properties.
应力通常是各向异性/真三轴应力（ > > ）。层理会削弱煤的连续性和完整性。了解真三轴应力条件下煤的力学行为和瓦斯运移至关重要。我们通过使用新开发的真三轴地球物理仪器，对立方煤样进行实验，以研究真三轴应力条件下煤的渗透率演化和力学行为。我们分析了主应力对含层面煤的变形和渗透率特性的影响。结果表明，体积应变、应力状态和层理方向综合决定渗透率。垂直于层面方向的应变变量最大。膨胀或压缩程度由主应变差（ - ）表征。本质上，这代表了煤在初始应力状态下被压缩的难易程度以及 和 方向的变形程度。（ - ）的变化与渗透率的变化一致。在相同的真三轴应力条件下，当在垂直于层面的方向施加更大应力时，渗透率较小。此外，平行于层面方向的应力水平以及平行于层面方向的应力与流动方向之间的方向也会影响渗透率和应变。通过求解横向膨胀系数，煤也表现出各向异性特性。
