Prediction of the Height of Water-Conductive Fractured Zone under Continuous Extraction and Partial Backfill Mining Method—A Case Study

Abstract

Longwall backfill mining effectively mitigates the height of water-conductive fractured zone (HWCFZ), preventing it from reaching the overlying aquifer and thus preserving the groundwater. However, it has the disadvantages of insufficient filling time and space as well as the mutual constraints between filling and mining. A novel continuous extraction and partial backfill (CEPB) water-preserving mining method was therefore proposed. The analytic hierarchy process (AHP) method was employed to identify the factors affecting the HWCFZ of CEPB, and five main factors, namely, the hard-rock lithology ratio, mining height and depth, and the width of the Wongawilli and protective block, were determined based on the weight distribution. UDEC software was used to establish a numerical model to simulate the HWCFZ under five factors. By using a multiple linear regression analysis of the numerical simulation results, a model for predicting the HWCFZ was established. It was applied in a colliery of the Yu-Shen mining area, and the HWCFZ was 57.7 m, 9% higher than that of borehole television logging of 53.1 m from the field measurement, indicating its rationality. Subsequently, the model was generalized and applied to the whole mining area, and the thematic map of the HWCFZ and the protective zone thickness of CEPB and longwall caving mining were obtained. The criterion for water-preserving mining based on the equivalent permeability coefficient of the protective zone is then proposed, which can provide guidance for the mining parameters optimization of the CEPB.