Risk Assessment Of Ordovician Limestone Water Under High Pressure Mining In Hemei No.8 Mine

Hemei No.8 Mine is located in the buried depth and deep buried zone of Xujiagou spring karst water system in the south of Hebi Mining Area.The main coal is Permian Shanxi FormationⅡ₁ coal.Carboniferous and Ordovician limestone karst developed in the coal seam floor in the area,with rich water and abundant replenishment.The mining production is seriously threatened by the limestone confined water in the seam floor.There have been many limestone water accidents since the construction of the No.8 mine,which has caused huge losses,especially the current No.8 mine production has entered the third level（-400～-800m）mining and the water pressure on the coal seam floor has increased sharply.The mine’s safety in production is facing tremendous pressure.Therefore,according to the existing mine production information,objectively evaluating the risk of floor water inrush by subareas has become an urgent problem at the current stage.Aiming at the problem of water inrush from the coal seam floor of Hemei No.8 Mine,based on detailed knowledge of existing mine geology,hydrogeology and historical water inrush data,combined with previous experience in water control,through the combination of theoretical analysis and FLAC^3D numerical simulation,analysis and research are conducted from many aspects such as geological structure,aquifer,aquiclude,etc.Identify five factors that have a greater impact on floor Ordovician limestone water inrush,including:fault fractal dimension,distribution of fault endpoints and intersections,effective aquiclude thickness,water pressure and richness of aquifer.At the same time,the fuzzy analytic hierarchy process coupled with coefficient of variation method（FAHP-CV）was used to calculate the weight,and the weight values of each influencing factor were respectively 0.1528,0.1599,0.2998,0.2409 and0.1465.Finally,with the help of Arc GIS software,using the vulnerability index method and the water inrush coefficient method,according to the degree of water inrush danger on the floor,the No.8 Mine were divided into water inrush danger zone,relative danger zone,transition zone,relative safety zone and safety zone.The research results show that:（1）FALC^3D numerical simulation results show that as the slope length and burial depth of coal mining face increase,the depth of floor disturbance damage also increases.In the future,when the third level coal mining operation is performed,the maximum damage depth of the floor is between 16.12 and 23.22m.（2）Through the analysis of the influence factors weight value of each floor water inrush,it is found that faults,effective aquiclude thickness and aquifer water pressure are the most important factors affecting water inrush from coal seam floor.（3）The zoning results of the two evaluation methods show that part of the working faces of the 30,31,33 and 34 mining areas at the three levels of the well field are all faced with large water inrush pressure of ordovician limestone from the floor.