Quantifying fracture roughness effects on coal mine spontaneous combustion through a coupled thermos hydro mechanical...

Accurately predicting and preventing spontaneous coal seam combustion is crucial for mining projects. However, quantitatively assessing the influence of fracture roughness in gas seepage analysis remains highly challenging. To address this issue, we present a novel predictive model for engineering-scale combustion forecasting, which incorporates an interdisciplinary fracture roughness parameter and integrates fracture roughness, heat conduction, chemical reactions, gas pressure, coal-rock stress and deformation, and adsorption-desorption mechanisms to achieve a comprehensive multi-factor coupling in coal seam gas migration. Introducing this parameter provides a more precise representation of gas permeability, heat transfer, and coal seam deformation, thereby enhancing risk assessment accuracy. After rigorous validation, the model was applied to evaluate spontaneous combustion tendencies in the 9th, 14th, and 15th coal seams and their adjacent strata at the Luling Coal Mine in China. Results indicate that the proposed fracture roughness parameter (η) accurately characterizes fracture irregularities, substantially influencing gas flow behaviour and hence spontaneous combustion potential. When η increased from 0.5 to 0.8, the gas proportion in the return airway rose by 7.3%, while coal seam permeability decreased by 51.7%. Under equivalent ventilation durations, higher fracture roughness elevated return airway gas concentrations by up to 16.7%. All these mechanisms were thoroughly and quantitatively evaluated. This study introduces a new quantitative framework for predicting and mitigating coal mine spontaneous combustion, underscoring the pivotal role of fracture roughness in hazard assessment.