A comprehensive study on fracture behavior and its impact on gas emissions in high-temperature coal seams under coupled thermo-hydro-mechanical condition

Temperature changes in high-temperature mining operations strongly affect gas desorption, migration, and outburst behavior in coal seams. Under these conditions, gas desorbs more quickly from the coal matrix and spreads rapidly through fracture networks, which increases gas emissions. At the same time, changes in fracture roughness, caused by temperature, gas pressure, adsorption–desorption processes, and stress, further influence outburst patterns. To capture these interactions, we propose a thermo-hydro-mechanical model based on porous media theory that treats fracture roughness as a factor linked to permeability. By integrating permeability and gas flow as functions of effective stress and porosity, this model offers a clear way to study how fracture roughness affects gas outbursts under multiple combined factors. Validation and numerical simulations show that the proposed roughness parameter accurately describes changes in fracture structure. These changes then strongly affect permeability, pressure, and desorption intensity. Higher temperatures boost gas activity and promote desorption and migration. However, extremely high temperatures can cause fractures to close, which lowers permeability. These findings provide important support for ventilation design and safety assessments in high-temperature mining.