Assessing Water and Sand Inrushes Hazard Reductions due to Backfill Mining by Combining GIS and Entropy Methods

Backfill coal mining, an environmentally friendly practice, is widely used to mitigate the hazards of water and sand inrushes (WSIs) and surface subsidence. In this study, a quantitative analysis for assessing the hazard reduction of WSIs due to backfilling was established that combines a modified analytic hierarchy process (AHP) with a geographic information system (GIS) and entropy. The analytical and quantitative model consists of four criteria and eight factors for the hazard assessment target layer. The weight of each index is comprehensively determined based on the modified AHP and entropy. Then, a hazard zone map that is color-coded is overlay analyzed based on GIS to comparatively evaluate the degrees of hazard from WSI due to longwall caving and paste backfill. The Taiping coal mine was used as a case study to validate the accuracy of the evaluation model. The results indicate that paste backfilling can effectively reduce the influence of the overburden failure height on WSI hazards. The highest hazard index of backfill mining was significantly reduced, and high-hazard and very high-hazard zones of longwall caving were transformed into low-hazard or even no-hazard zones. The evaluation results are in good agreement with actual engineering practices and offer an effective reference for practical engineering projects and prevention and control measures for safe mining under loose sand aquifers.