Prediction of water-inrush risk areas in process of mining under the unconsolidated and confined aquifer: a case study from the Qidong coal mine in China

The unconsolidated Cenozoic formation is well developed in the Qidong coal mine. Water-inrushes from the bottom unconsolidated Cenozoic aquifer, which is the confined aquifer, have happened several times during mining in the north mining area of the Qidong coal mine. To predict the water-inrush risk areas in the south mining area of the Qidong coal mine where some working faces have just begun to mine, the engineering analogy method is used on basis of the Fisher’s discriminant model from the actual mining situation in the north mining area. Six main influence factors including the effective thickness, the specific yield, and the load transfer coefficient of the aquifer, the effective thickness of the protective bedrock layer, the fractal dimensional value of bedrock faults and the distance between the key hard stratum and the primary mineable coal seam are selected as discriminant indexes, and their corresponding data in the north mining area of the Qidong coal mine are served as training samples. On this basis, the Fisher’s discriminant model for water-inrush is established and water-inrush risk areas including the safety, the medium risk and the risk areas of no. 6₁, 8₂ and 9 primary mineable coal seams in the south mining area of the Qidong coal mine are predicted by the model. The model’s accuracy is 90.4 %, the scatter diagram of training samples shows obviously classified effect and the field verification indicates that the predicted type is consistent with the actual type. Results show that the discriminant model is well applied in the engineering analogy method and the water-inrush risk areas predicted by the discriminant model contribute to the subsequent mining in the south mining area in the Qidong coal mine.