Development characteristics and prediction model of the water-conducting fractured zone in typical mining-induced structural overburden in the mountainous areas of Southwestern China

Abstract

In mining areas of the mountainous regions of Southwestern China, the overlying strata above goafs are mostly thick bedrock with well-developed structural planes. With large-scale exploitation of mineral resources, extensive water- conducting fractured zones (WCFZs) may develop in the overlying strata, frequently inducing water inrush and high-position collapse-sliding hazards. Rapidly estimating the height of the WCFZ (HWCFZ) is therefore critical for the prevention of water hazards and collapse-sliding disasters. In this study, mining- induced structural overburden was taken as the research object. Based on the instability criterion of the three-hinged arch structure, the influences of mining thickness, strata thickness, joint spacing, broken expansion coefficient, and damage factor on the HWCFZ were analyzed. A simplified fitted prediction model constrained by the three-hinged arch mechanism was established. Using the calculation results of the three-hinged arch mechanical discrimination model as benchmark values, fitting error analysis was conducted through 27 orthogonal tests, and the prediction model was applied to engineering cases in typical mining areas. The results show that, within the parameter ranges considered in this study, the HWCFZ is approximately linearly and positively correlated with mining thickness, and negatively correlated with strata thickness, joint spacing, and broken expansion coefficient in an inverse-function form, characterized by a rapid decrease at the early stage and subsequent stabilization. In the high-damage range, the HWCFZ shows an accelerated nonlinear increase with increasing damage factor. The sensitivity ranking of the factors affecting the HWCFZ is mining thickness, strata thickness, broken expansion coefficient, joint spacing, and damage factor. The simplified fitted prediction model has a mean absolute error of 3.26 m and a coefficient of determination R2 of 0.96, indicating that the model exhibits good internal consistency with the theoretical three-hinged-arch discrimination model. When applied to the Faer Coal Mine in Shuicheng, Guizhou, and the Zengziyan Bauxite Mine in Nanchuan, Chongqing, the calculated results are close to those obtained from theoretical formulas, numerical simulations, and centrifuge model tests. The results provide a reference for calculating the HWCFZ induced by ore-seam mining under similar geological conditions.