Precise Evaluation of Gas Expansion Energy Within Coal Bodies in Coal-and-Gas Outbursts: Innovation in Calculation Model and Experimental Methods

Coal-and-gas outbursts represent a significant hazard in coal mining, with gas expansion energy (GEE) in coal seams being a primary energy source. Accurate GEE assessment is vital for outburst prediction and mitigation, thereby enhancing mining safety. Traditional calculation models have struggled with limited understanding of outburst mechanisms and experimental constraints, leading to broad GEE estimates with considerable discrepancies. Addressing this gap, this study introduces an experiment-driven, highly practical calculation model, along with innovative experimental methods to measure accurately key determinants of GEE: fracture porosity, CH₄ desorption amount, and gas pressure in coal seams. For the first time, this study employed remade and raw coal columns as media to simulate accurately the real conditions of tectonic and raw coal seams for exploring the coupling effects of stress and gas pressure on GEE. This study calculated the GEE as stress increases from 5 to 50 MPa and gas pressure decreases from 2 to 0.5 MPa. The results indicate that, for two remade coal columns, the GEE decreased from 1870 to 62 kJ/t and from 2039 to 356 kJ/t while for the raw coal column, the GEE dropped from 130 to 6 kJ/t.