Abstract Knowledge of the mechanical behavior and permeability evolution of tectonically deformed coal (TDC) is the foundation for the successful design of enhanced gas drainage. However, our understanding of the effect of progressive damage on the fluid flow in TDC is limited due to its unique structure and low visibility. We report measurements of the deformation, strength and permeability evolution during triaxial compression of soft coal samples made by TDC. According to the experimental results, the soft coal can generate an obvious nonlinear-elastic deformation before the yield strength, leading to the formation of unique features of the fracture volume evolution of soft coal. The closure of the existing microcracks in soft coal continues until the reversal of the total volume when the confining pressure is greater than or equal to 8 MPa. The fracture compressibility constants of the three soft coal samples were 4.71E-2 MPa−1, 4.63 E−2 MPa−1 and 4.89 E−2 MPa−1, which are much smaller than the literature values reported for other intact coals, which range from 6.21E−2 MPa-1 to 2.71E−1 MPa−1, indicating that the stress sensitivity of TDC is weaker than that of the intact coal. During the progressive deformation of soft coal, the permeability only reverses when the stress state exceeds the fracture damage stress. The study's achievements show that the simplification of the pre-failure behavior as a perfectly elastic mode is not applicable to the soft coal and would lead to mistakes in further permeability calculations. Further work should be extended to develop a more appropriate constitutive model and a permeability model to describe the pre-failure non-linear (elastic) deformation and the corresponding permeability evolution of soft coal.

中文翻译：

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淮南煤田构造变形煤损伤渗透与变形关系试验研究

摘要 了解构造变形煤 (TDC) 的力学行为和渗透率演化是强化瓦斯抽采成功设计的基础。然而，由于其独特的结构和低能见度，我们对渐进损伤对 TDC 中流体流动的影响的理解是有限的。我们报告了 TDC 制作的软煤样品在三轴压缩过程中变形、强度和渗透率演变的测量结果。根据实验结果，软煤在屈服强度之前会产生明显的非线性弹性变形，导致形成独特的软煤裂缝体积演化特征。当围压大于或等于 8 MPa 时，软煤中现有微裂缝的闭合一直持续到总体积反转。三个软煤样品的断裂压缩系数分别为 4.71E-2 MPa-1、4.63 E-2 MPa-1 和 4.89 E-2 MPa-1，远小于文献报道的其他完整煤样的值。范围从 6.21E-2 MPa-1 到 2.71E-1 MPa-1，表明 TDC 的应力敏感性弱于完整煤的应力敏感性。在软煤逐渐变形过程中，只有当应力状态超过裂缝破坏应力时，渗透率才会发生逆转。研究成果表明，将破坏前行为简化为完全弹性模式不适用于软煤，并且会导致进一步渗透率计算的错误。