A new risk zoning method for water inrush from separated layers at coal mines: a case study, Cuimu coal mine, China

Water inrush from separated layers (WISL) is a new type of hydraulic hazard, which causes severe damage in coal mines. In this study, a new risk zoning method, which considers the theory of subjectivity, objectivity, and variable weight, is proposed for WISL during mining. First, the formation mechanism of separated layers (SLs) and evolution conditions of WISL were systematically investigated based on the engineering geological conditions. Then, Cuimu coal mine, located in Ordos basin, China, was taken as the study case, and eight primary factors were selected for overburden conditions, mining-induced disturbance, and water abundance of aquifer. Subsequently, on the basis of analytic hierarchy process (AHP), entropy weight method (EWM), and variable-weight method (VWM), a mathematical model is proposed for risk zoning for WISL in Cuimu coal mine. Finally, the new method was compared with the previous method to verify its validity in assessing the risk of WISL; then, some protection methods are proposed to effectively control WISL in coal mines. As a result, the study area is divided into five parts: high danger zone (HDZ), middle danger zone (MDZ), low danger zone (LDZ), middle zone (MZ), and safe zone (SZ). According to the collected field data in working faces, it is verified that the proposed zoning method (AHP-EWM-VWM) is more accurate than the conventional method for risk evaluation of WISL; constructing drain holes, limiting mining height as well as velocity, and monitoring the water table of primary aquifer are effective methods for predicting and preventing WISL in coal mines. This study is considerably beneficial to avoid the damage caused by WISL during mining.