Paleokarst crust of Ordovician limestone and its utilization in evaluating water inrushes in coalmines of North China

Detailed analysis of exploratory borehole data suggests presence of a paleokarst crust at the top of Middle Ordovician Fengfeng Formation in North China. Because of its mechanical strength and low permeability to water, the paleokarst crust can function as an additional water-resisting layer in evaluating water inrush risks in mining the Carboniferous-Permian coal seams in the area. The paleokarst crust is characterized by heterogeneity and may not be ubiquitous. This paper takes Sihe Mine of Shanxi Province as an example to study the geotechnical and hydrogeological characteristics of the paleokarst crust. Incorporation of this additional hydrological barrier into water inrush risk assessment led to more minable coal seams in the coalmine.