Risk assessment of water inrush to coal seams from underlying aquifer by an innovative combination of the TFN-AHP and TOPSIS techniques

Abstract

Coal seam exploitation in many coal mines of North China coalfields is threatened by water hazards from underlying aquifers. Resolving the potential risk zonation of water inrush to prevent and control flood water disasters is important and challenging work. To effectively assess the risk of water inrush from the Ordovician aquifer to the exploitation of the No. 11 coal seam in the Zhaizhen coal mine, Xinwen coalfield, China, this paper proposes a water inrush risk index (WIRI) model based on a combination of the triangular fuzzy number (TFN), analytic hierarchy process (AHP), and Technique for Order Performance by Similarity to Ideal Solution (TOPSIS) methods. The WIRI model integrates seven factors, namely, the water abundance of the Ordovician limestone aquifer, water pressure of the Ordovician limestone aquifer, aquifuge thickness, brittle rock percentage within the aquifuge, fault intensity index, fault endpoint and intersection density, and height of the mine-damaged zone, and was established using the TOPSIS method based on the initial decision data and the factor weights determined by the TFN-AHP method. The potential water inrush risk zonation was finally determined by the WIRI method. There are two zones in the study area: the safe area, and the dangerous area which was further classified into two subzones including the moderately dangerous area and the extremely dangerous area, providing guidance for engineers to predict and control floor water inrush. The predictions were validated by limited water inrush cases and safe mining samples. The results predicted by the WIRI method conform to the actual results, while the predictions by the T method do not agree well with the observation: with the T method, the three water inrush samples were judged to be safe. These results indicate that the proposed method can effectively predict water inrush risk and can be extended to other mines threatened by an underlying aquifer.