A geomechanical method for predicting the height of a water-flowing fractured zone in a layered overburden of longwall coal mining

Mine water inrushes result in serious casualties and property losses, and mining-induced water-flowing fractures are important channels for mine water inrushes. The prediction of the height of the water-flowing fractured zone (HWFFZ) is conducive to avoiding such disasters to a certain extent. In this study, the HWFFZ in layered overburden strata was systematically investigated by means of similar simulations, theoretical analyses and engineering verification. The following results were obtained. Fractures occur in overburden strata because the tensile stress exceeds the tensile strength, while fractures penetrate the overburden strata because the compressive stress exceeds the compressive strength. Whether a fracture penetrates the overburden strata can be expressed by the fracture penetration criterion (FPC) value and the compressive-tensile ratio (i.e., the ratio of the compressive stress to the tensile stress). If the FPC value is greater than the compressive-tensile ratio, the fracture penetrates the overburden strata. For both the 31401 mining face of the Bulianta Coal Mine and the 7130 coal mining panel of the Qidong Coal Mine, the FPC values of the water inrush regions are larger than those of the normal regions, and the compressive-tensile ratios of the water inrush regions are smaller than those of the normal regions.