An improved risk zoning method of bed-separation water inrush in underground coal mines: a case study in Ningxia, China.

Bed-separation water inrush (BSWI) is a new type of coal mine disaster that has caused serious damage. The shortcomings of previous studies on this topic are as follows: 1) most studies focused on the BSWI mechanism, evolution, and control methods, and there is a lack of research on BSWI risk assessment methods and 2) previous risk assessment studies ignored the factors of the water yield property. First, based on the proposed BSWI engineering geological model, three first-order factors are proposed: 1) separation space between layers, 2) water production characteristics, and 3) water resistance effect. Then, eight secondary factors are determined: 1) production thickness (MT), 2) hard rock thickness (HRT), 3) improved lithology index (ILCI), 4) core recovery (CR), 5) aquifer depth (AD), 6) drilling fluid consumption (DFC), 7) protective layer thickness (PLT), and 8) self-healing potential index (SPI). Subsequently, the corresponding weights are calculated, and the multifactor superposition method is used to draw the BSWI risk map. The area is divided into three risk grades: low, medium, and high. The results are validated by observations of BSWI accidents and bed-separation water exploration and discharge boreholes in the study area. The proposed method can be used to effectively prevent BSWI disasters in other coal mines with similar geological conditions.