Evaluation of water inrush from underlying aquifers by using a modified water-inrush coefficient model and water-inrush index model: a case study in Feicheng coalfield, China

Water inrush from underlying aquifers seriously threatens mining of Permo-Carboniferous coal seams in many North China coalfields. To evaluate the risk of water inrush from underlying aquifers, a modified water-inrush coefficient method-using the water inrush coefficient (T) and geological structure index (G)-and a water-inrush index model (WII model) were proposed. The T_G model improved the traditional water-inrush coefficient method by quantifying the degree of geological structure development, considering three main controlling factors: G, aquifer water pressure (P) and aquitard thickness (M). The WII model was constructed to assess the risk of floor water inrush by the entropy weight method, which integrated six factors: G, P, M, the depth at which ground pressure creates a broken-rock zone (C-p), aquifer water yield property (Y), and percentage of brittle rock within the aquitard (B). Results from the engineering practice data analysis validated the T_G and WII models as operational tools to evaluate the risk of water inrush from an underlying aquifer. The comparative analysis of the predictions by these two models shows that the prediction accuracy of the WII model is 13% higher than that of the T_G model, and approximately 21% of the two model predictions are not in agreement. A more reasonable prediction was obtained with application of the T_G and WII models to Feicheng coalfield in Shandong Province to evaluate water inrush risk from the underlying aquifer, and the prediction offers guidance on different preventive measures against water hazards in the underlying Ordovician limestone in the different zones.