Study on key water isolated layer of Fengfeng Formation affected to pressurized mining in seam of low group

In order to evaluate a water inrush danger of seam under high water head pressure of Ordovician karst water and to seek mining technical pan of the seam i n the low group,there were 10 hydrogeological holes driled in Xiegou Mine and a study was conducted on the rock core identification,simple hydrogeological observation,w ater pumping tests,water chemical analysis and other test. The study showed that the crack development of the top stratum in Fengfeng Formation of Xiegou Mine was poo r. During the drilling and exploration process,there was no high increasing abnormal conditions occurred in the drilling consumable liquid. The unit water inrush volume fro m Fengfeng Formation was 10 ~ 105 times lower than the unit water inrush volume from the combined water bearing layer of Majiagou Formation and Fengfeng Formation. The chemical compositions of the underground water from the two formations were different and could showed that the aquifer in Fengfeng Formation would be less watery and could have good water resistance capacity. The stratum thickness of Fengfeng Formation with a thickness of 30 meters would be considered as a water insulation laye r. A pressurized mining in No. 13 seam of the minefield would have a water inrush cofficient less than0. 1 MPa / m and a pressurized mining could be conducted theoretically.