Evaluation of Water Richness in Coal Seam Roofs Based on Combined Subjective–Objective Weighting and a Matter-Element Extension Model

The roof aquifer of the Jurassic coal seam is the primary source of water inrush in the Nalinhe Mining Area. It poses a severe threat to safe mining operations. Accurate prediction of its water richness is crucial for production safety. This study focuses on the Nalinhe No. 2 Coal Mine. Seven key controlling factors were selected as evaluation indicators, including aquifer thickness, burial depth, core recovery rate, the thickness ratio of brittle to plastic rock, fault scale density, fault fractal dimension, and the density of fault endpoints and intersections. A hybrid weighting strategy was applied in this study. This strategy integrates the Analytic Hierarchy Process (AHP) and the Entropy Weight Method (EWM) to assign scientific weights to the evaluation indices. A water richness evaluation model was subsequently developed based on matter-element extension theory. The model calculates the comprehensive correlation degree for each grid node and determines the corresponding water richness level. Zoning results were validated with unit inflow data from pumping test boreholes, mine inflow observations, and ground transient electromagnetic survey findings. The predicted water richness zones closely matched the measured hydrogeological data. These results demonstrate the scientific rigor and reliability of the matter-element extension model. The proposed model provides a novel approach for assessing water richness in coal seam roof aquifers.