Structural characteristics of the overburden and water yield property of weathered bedrock aquifer in a representative medium-deep coal seam

Background  The weathered bedrock aquifer represents a major water-filled aquifer encountered during coal mining in the Jurassic coalfield in northern Shaanxi Province. Therefore, evaluating the water yield property of the weathered bedrock aquifer is the key to the prevention and control of water hazards in coal seam roofs.

Methods  This study investigated panel 12 of the Caojiatan Coal Mine, Shaanxi Province. Analysis of the stratigraphic and lithological structure types of the overburden of coal seam 2⁻² identified the weathered bedrock as the primary overlying water-bearing aquifer of the coal seam. Using net-to-gross (NTG) ratio, sandstone thickness, weathering influence index, burial depth of weathered bedrock, specific yield, permeability coefficient, rock quality designation (RQD), and apparent resistivity as evaluation indicators and based on the coupling of analytic hierarchy process (AHP), coefficient of variation (CV), and grey relational analysis (GRA), this study constructed a comprehensive AHP-CV-GRA evaluation model for the water yield property of the weathered bedrock aquifer. By calculating the weights and performing spatial overlay analysis for these indicators, this study predicted the zoning of the water yield property of the weathered bedrock aquifer.

Results and Conclusions  The water yield property of coal seam 2⁻² can be categorized into three types: strong, moderate, and weak. The detection results of the anomaly areas of water yield property obtained using the transient electromagnetic method demonstrated that most of zones with strong water yield property in the study area corresponded to the low-resistance anomaly areas near the bottom boundary of the weathered bedrock. To further validate the evaluation results obtained using the AHP-CV-GRA model more accurately, the underground drainage volumes of mining face 122104 were adopted for validation. The results indicated that zones with large drainage volume featured strong water yield property, revealing a good agreement between the evaluation results and the actual conditions. Therefore, the proposed AHP-CV-GRA method enables the scientifically robust elevation of the water yield property of aquifers.