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Roof water inrush when conducting longwall mining is a complex global issue. Here, we study the theoretical prediction method and factor of roof water inrush. First, according to the geological conditions of the Cuimu coal mine, China, physical experiments were conducted to investigate the overburden movement and roof inrush evolution under longwall mining. Second, numerical simulations using FLAC software were performed to analyze the water-resisting key strata's stress distribution and failure status during mining. Based on the stress intensity factor (SIF) theory in fracture mechanics, a time-dependent risk coefficient is proposed to represent the mechanics criterion of the roof inrush under longwall mining. Furthermore, the influences of the hanging length, overlying load, thickness, and lithology of the water-resisting key stratum on roof water inrush are theoretically analyzed. Finally, using in situ measured data of the Cuimu coal mine, the limit advance distance when inrush occurs is theoretically calculated based on the proposed risk coefficient. The results show that the Jurassic soft stratum acts as the water-resisting key stratum. Before inrush, the fractured water-resisting key stratum is intact where compression is concentrated, and thus, it still has water-resisting properties. The fracture initiation threshold of the water-resisting key stratum under compression–shear stress represents the mechanical criterion of roof water inrush under longwall mining. The hanging length of the water-resisting key stratum has a more significant effect on strata cracking than the overlying load applied to the water-resisting key stratum. The thickness of the water-resisting key stratum is critical for preventing cracking of the water-resisting key stratum. The water-resisting key stratum with a higher viscosity of a rock tends to crack quicker, and the initial elastic modulus affects the ultimate status of the water-resisting key stratum. The agreement between the predicted and experimental values confirms that the SIF-based prediction method is useful for predicting roof inrush under longwall mining. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]