Synergistic and Participation Mechanisms of Effective Stress and Temperature on Coal Mechanical Behavior and Permeability Characteristics

The coal deformation, damage, and gas migration under a coupled temperature and effective stress environment are pivotal for coal seam mining and gas extraction. A permeability model that integrates the effects of temperature, effective stress, and damage is established in this study. A series of thermal-hydro-mechanical (THM) coupling experiments are conducted to investigate the mechanical behaviors, permeability evolution, and damage evolution based on acoustic emission. The roles of effective stress and temperature in jointly influencing the mechanical behavior and permeability characteristics of coal are thoroughly analyzed, with a focus on the extent of their respective contributions. The results indicate that during cyclic loading, the elastic modulus initially increases and then decreases, while the AE ring count exhibits a cyclic pattern of first rising and then falling. The cumulative ring count follows a “ladder-like” growth trend. Moreover, the elastic modulus and peak strength progressively decline under growing temperature, whereas the maximum AE ring count and cumulative ring count increase. In the volumetric compaction stage, permeability decreases with axial strain, and higher temperatures result in a smaller reduction in permeability. Permeability increases during the dilation stage, with a more pronounced increasing trend observed at higher temperatures. The accuracy of the proposed permeability model has been thoroughly confirmed. Furthermore, the contribution of effective stress on gas seepage is significantly greater compared to temperature for the same burial depth increment. Finally, the mechanisms by which stress and temperature influence permeability are discussed in detail.