Risk Assessment Of Water Inrush From Ordovician Limestone In Hebi No.9 Coal Mine Based On GIS And FLAC^3D

Hebi No.9 Coal Mine is located in the northernmost end of Hebi Mining Area,Henan Province.It belongs to Hebi Coal and Electricity Company.It mainly mines ?1 coal of Shanxi Formation of Permian,and is close to the concentrated drainage zone of Xiaonanhai Spring karst water system in Anyang.The Carboniferous Taiyuan Formation limestone and Ordovician limestone in coal seam floor are well developed with strong water-rich,abundant karst water supply and complex hydrogeological conditions.The mining production is threatened by water inrush from confined water of coal seam floor limestone.Historically,24 water inrushes with the Ordovician karst water as the source of water occurred,with the maximum water inrush volume of 4090 m3/h,causing huge losses.Mining in No.9 Coal Mine has entered the third and fourth levels,with the coal seam elevation ranging from-540 to-800m.The water pressure acting on the coal seam floor is currently 6.7 MPa,and the lowest mining position in the future will be 9.3 MPa Water inrush risk is very high.It is necessary to qualitatively and quantitatively evaluate the danger of water inrush from confined water in the third and fourth horizontal coal seams of the No.9 Coal Mine.It is also necessary to divide the water inrush danger zoneBased on the comprehensive analysis of NO.9 mineral exploration,drilling,geological and hydrogeological data,combined with the typical cases of water inrush from Ordovician limestone floor,the paper analyzes the cause of the water inrush from the confined limestone floor and determines the influence of ?1 coal seam.The five main controlling factors of water include water pressure of Ordovician limestone aquifer,water-rich of Ordovician lime,the thickness of the effective aquifer,the fractal dimension of the faults and the distribution of faults and folds.The weights of each main control factor were determined by fuzzy analytic hierarchy process(FAHP)and principal component analysis(PCA).The weights of each main control factor were 0.24,0.151,0.282,0.13,and 0.197,respectively.With the powerful data processing and spatial analysis functions of ArcGIS,the thematic maps and normalized maps of the five main factors of water inrush are drawn.The normalized maps are superimposed and added to obtain the danger map of water inrush from the coal floor.The discontinuous point grading method is used to determine the subarea threshold,and the water inrush risk of the third and fourth coal seams level of NO.9 mine is divided into five areas:dangerous area,relative dangerous area,transition area,relative safe area and safe area,then the risk of floor water inrush was evaluatedThe evaluation results show that the dangerous area,the relative dangerous area and the transition area account for more than half of the total area of the third and fourth level The relative dangerous area and the dangerous area are located in the north of mining area 33,32 and the south of mining area 34.These areas are the key areas to prevent floor water inrush.Under the condition of less water inrush data in the early stage,the risk of water inrush can be evaluated objectively.