Study On Prediction,evaluation And Prevention Of Bed-separation Water Disaster In Multi-seam Mining In Wulunshan Coal Mine

Coal mine multi-seam mining is affected by inter-layer lithology combination,interlayer spacing and mining production conditions and other factors,resulting in many mining problems,such as roof separation water damage,roof secondary fracture and strong mine pressure,threatening coal mine safety production.Based on the superposition mining of 8 coal,6^-3coal and 3 coal in Wulunshan Coal Mine,this paper carried out field hydrogeological mapping on the basis of analyzing the hydrogeological and engineering geological conditions of the mine.Based on the drilling data of No.1 mining area,the contour maps of coal seam thickness,coal seam and rock stratum,and rock stratum spacing are plotted to analyze the occurrence law of coal seam roof strata in a mining area.Combined with the water inrush situation of the working faces of 8 coal and 6^-3coal,through field investigation,theoretical analysis and numerical simulation,the separation position,breaking distance and height of water flowing fractured zone of 6^-3coal are mainly studied.In addition,the water inrush risk zoning of 6^-3coal and 3 coal in the first mining area is divided,and the prevention and control measures for the water disasters in the first mining area are put forward.(1)Through the drilling data during exploration and supplementary exploration in Wulunshan Coal Mine,it is concluded that the spatial occurrence of 8 coal and 3coal in the first mining area has little change and is relatively stable.The thickness of6^-3coal varies greatly.The roof lithology combination of each coal seam is fine sandstone,siltstone,mudstone,coal and limestone.The maximum heights of 8 coal,6^-3coal and 3 coal calculated based on the standard formula are 35.3 m,36.83 m and34.98 m,respectively.Considering the influence of disturbance of close coal seam group,the maximum height of 6^-3coal seam is calculated to be 37.6 m.Based on the key layer theory,the 6^-3coal conduction height is predicted to be 39.86 m.(2)Based on the traditional key layer theory and the modified key layer method,the key layer positions of 8 coal,6^-3coal and 3 coal working faces were identified and compared.Combined with the water inrush position of working face and the calculated fracture distance position,it was analyzed that the separation layer of the1601 working face developed under the fine sandstone at the bottom of 3 coal in the upper section of Longtan Formation.Through the 3DEC discrete element software to simulate the overburden caving law of three-layer coal mining,it can be concluded that the development characteristics of separation are consistent with the theoretical judgment of separation position in the previous paper.(3)The analytic hierarchy process(AHP)and entropy weight method were used to select the thickness of 6^-3coal,the thickness of aquifer in the range of 6^-3coal roof to the bottom interface of Changxing Dalong Formation,the development height of 6^-3coal water flowing fractured zone,the distance between the thickest rock layer in the range of 10-30 m of 6^-3coal roof and 6^-3coal roof,the thickness of 8 coal,the thickness ratio of mudstone,the thickness of 6^-3coal to K₂ limestone,and the thickness of protective layer.The AHP-EM evaluation model was constructed by GIS software to determine the comprehensive weight.The risk of water inrush in 6^-3coal face was divided:the 1601 working face of 6^-3coal in the first mining area is in the dangerous area and the more dangerous area,and the 1603 working face is part of the safer area.(4)The analytic hierarchy process(AHP)and entropy weight method were used to select 6 indexes such as 3 coal thickness,6^-3coal thickness,8 coal thickness,3coal conduction height,3 coal aquifer thickness,and 3 coal conduction height distance from sub-critical distance.The AHP-EM evaluation model was constructed by GIS software to determine the comprehensive weight,and the risk of water inrush in 3 coal working face was divided.The risk of water inrush in 1 partition 3 coal mining is in a relatively dangerous and dangerous area,the western part of the mining area is in a dangerous area,the northern part of the mining area is in a relatively safe area,the eastern part is in a relatively safe area,the southern risk distribution is complex,and the overall risk is relatively dangerous.(5)Based on the large well method,the predicted water inflows of 1601,1603and 1301 working faces in the first mining area are 52 m³/h,53.7 m³/h and 42.77 m³/h,respectively.Based on the catchment corridor method,the predicted water inflows of1601,1603 and 1301 working faces in the first mining area are 79.3 m³/h,106.1 m³/h and 65.7 m³/h,respectively.Combined with 6^-3coal working face roof aquifer water abundance research and actual water inrush situation put forward prevention measures.