Abstract: The structure and thickness of the floor aquifuge are important influencing factors for the safety mining above confined aquifer. Due to Ordovician strata missing in the certain areas of Henan Province, coalmines are often serious threatened by the floor Cambrian limestone Karst water inrush. The hydrogeological structure characteristics in the upper member with the thickness of at least 25 m of Cambrian limestone in Malingshan coalmine is detected in this paper, and then, the water-resisting-isolating capability of the upper Cambrian limestone is assessed. Subsequently, based on the GIS platform, the method of risk assessment for floor water inrush by using the relative impermeability of upper member of Cambrian limestone is studied. By adopting the research result, 13.4 million tons of coal resources in Malingshan coalmine are liberated and 4 million tons of coal resources are safety extracted and then, the shaft station at -350 m elevation is successful tunneled with the depth of 55.5 m and the length of 320 m into the upper member of Cambrian limestone. Owing to considering the existence of the relative aquifuge section locating in the upper member of Cambrian limestone, the result, which more tally with actual situation, has been successful applied in Malingshan coalmine for its coal mining practice above confined water with high pressure.

Key words: coal mining above confined water with high pressure, upper member of Cambrian limestone, relative aquifuge, water inrush assessment, mining above aquifer