Multi-criteria decision analysis of gas enrichment risk and land degradation in goaf areas

Gas enrichment in goaf areas significantly threatens mine safety and surface environmental stability, particularly under top-cutting and pressure-relief mining methods. This study proposes a comprehensive multi-criteria decision-making framework that configures the Analytic Hierarchy Process (AHP) and the Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) to evaluate a coupled gas enrichment-land degradation risk in goaf areas under top-cutting and pressure-relief mining. Five main criteria, geological conditions, mining parameters, ventilation characteristics, gas emission rates, and ecological vulnerability, were assessed through expert judgment and field data. AHP was used to derive criterion weights, with fault density (11.5%) and coal seam gas content (10.2%) identified as key sub-factors. TOPSIS analysis ranked six goaf zones, identifying G5 as the lowest-risk (C_i = 0.815) and G4 and G6 as the highest-risk areas. Sensitivity analysis confirmed the model's stability under varied weighting scenarios. The findings reveal a strong link between subsurface gas behavior and surface degradation indicators such as subsidence and vegetation loss. Beyond the generic use of MCDA for multi-factor integration, the study (i) develops a criteria hierarchy that explicitly combines geological, mining, ventilation, and gas-emission drivers with ecological vulnerability indicators, (ii) tailors AHP-derived weights to top-cutting and pressure-relief goaf conditions using a large expert panel, and (iii) quantitatively links the composite risk index to observed land subsidence and vegetation loss to reveal the coupled mechanism between subsurface gas behavior and surface degradation. This model supports early risk detection and informed decision-making, offering practical value for gas control strategies and ecological restoration in mining regions.