Coalbeds are subject to diverse load conditions stemming from hydraulic fracturing, mining activities, and geological tectonic forces. Understanding how coalbed permeability evolves under various stress conditions—such as effective stress, peak stress, axial deviatoric stress, and stress cycling—is crucial for optimizing coalbed methane flow dynamics. In this study, coal sample permeability evolution was assessed using the steady-state method under various loading paths. The study revealed insights into the impact of irreversible deformation induced by different axial deviatoric stresses on coal permeability. Our results indicate that confining pressure has a greater impact on axial permeability than axial stress does. Initial stress cycles involving confining pressure notably reduce coal permeability, an effect that is less pronounced in subsequent cycles. Different levels of axial deviatoric stress have varied consequences for coal fractures. Specifically, high axial deviatoric stress conditions promote fracture propagation, thereby enhancing coal seam permeability. Conversely, under low axial deviatoric stress, the cyclical application of axial and confining pressures results in coal compaction and fracture closure, leading to a decrease in permeability after unloading. To visualize microcrack development and propagation in coal under differing axial deviatoric stress conditions, we integrated the discrete element method with the Mohr–Coulomb model in a particle flow program. The findings from our triaxial seepage experiments corroborate well with this computational model, providing a robust validation and deeper insight into the observed permeability changes.

煤层要承受来自水力压裂、采矿活动和地质构造力的各种载荷条件。了解煤层渗透率在各种应力​​条件（例如有效应力、峰值应力、轴向偏应力和应力循环）下如何演变对于优化煤层气流动动力学至关重要。在本研究中，使用稳态方法评估了不同加载路径下煤样渗透率的演变。该研究揭示了不同轴向偏应力引起的不可逆变形对煤渗透率的影响。我们的结果表明，围压对轴向渗透率的影响比轴向应力更大。涉及围压的初始应力循环显着降低煤的渗透性，这种影响在后续循环中不太明显。不同水平的轴向偏应力对煤体破裂产生不同的影响。具体而言，高轴向偏应力条件促进裂缝扩展，从而提高煤层渗透性。相反，在低轴向偏应力下，轴向压力和围压的循环施加导致煤体压实和裂缝闭合，导致卸载后渗透率下降。为了可视化不同轴向偏应力条件下煤中微裂纹的发展和扩展，我们将离散元方法与粒子流程序中的莫尔-库仑模型相结合。我们的三轴渗流实验的结果很好地证实了该计算模型，为观察到的渗透率变化提供了可靠的验证和更深入的了解。