Study On Reducing F22 Normal Fault Protection Coal Pillar In W3₂20 Face Of Qianyingzi Coal Pillar

With the rapid development of the national economy,the consumption rate of coal resources has also accelerated.The simple structure is now in the stage of exhaustion.Qianyingzi coal mine mainly mines 3₂coal,with complex structure,high fault density and large width of reserved fault protection coal pillar.The W3₂20 working face studied in this paper is located in the second mining area on the West Wing of F22 normal fault.Due to the dual water effect of fault water and the fourth aquifer of the overlying Cenozoic loose layer("four aquifers")on the working face in the mining process of the working face,during the preliminary design,the width of fault protection coal pillar is 60M-80M,and the coal pressure reaches more than 200000 tons,resulting in serious waste of resources.Therefore,it is very important to study the reduction of F22 normal fault protective coal pillar in W3₂20 working face.Taking the fault protection coal pillar of W3₂20 working face in qianyingzi coal mine as the background,on the basis of consulting the latest frontier research results at home and abroad on the working face under the influence of"double water",combined with the lithology characteristics of F22 normal fault in qianyingzi coal mine,this paper determines the research content of W3₂20 working face and formulates the research technical route.The hydrogeology of the working face and the water abundance of F22 fault are analyzed,the underground advanced geophysical exploration is designed,and the underground drilling holes are designed and constructed for abnormal areas;The rock samples around the fault zone and working face are drilled,the rock mechanical parameters of W3₂20working face are determined through indoor uniaxial compressive strength experiment,the mining model of working face is constructed,and the evolution characteristics of stress,strain and displacement of W3₂20 working face are simulated by FLAC^3Dsoftware;Using the theoretical calculation formula,the"two zones"height of the overlying strata of W3₂20working face is calculated,and the width of fault protection coal pillar of W3₂20 working face is determined in combination with the"engineering analogy method",and the following research results are obtained:(1)F22 normal fault is the boundary fault of the West No.2 mining area of qianyingzi coal mine,with an extension length of 6.6km.The fall of F22 fault is between0m and 360m.F22 normal fault is near W3₂20 air roadway,with a fall of 60m?100m.The fault protection coal pillar is reserved for more than 60m in the original design;The coal thickness of W3₂20 working face is 1.7m?4.6m,with an average of 3.29m and an average inclination of 5°?25°,with an average of 10°.It belongs to a gently inclined coal seam.The designed upper mining elevation of the working face is-240.0m(roof)level,the lowest elevation of bedrock surface is-194m,and the minimum sand control coal pillar is46m.Comprehensive mechanized coal mining and all caving method are adopted to manage the roof.(2)According to the drilling data of water 4 around the working face,the thickness of"four aquifers"in the mining area of the working face is 1.85m?13.85m.According to the pumping test data of water 4holes,the unit water inflow q=0.0004186l/(s*m)and the permeability coefficient k=0.0056m/d,belonging to the aquifer with weak water yield.Water leakage occurred during the construction of drilling holes 27-2,40-5 and 29-1,and the leakage is between 5m~3/h and 19.2m~3/h;According to the pumping test results of 29-8and 40-2,the water level elevation is between-2.82m and 20.65m.According to the detailed rules for water prevention and control in coal mines,the mining grade of water body is class II water body,and sand proof coal pillar can be reserved for mining;3₂coal roof and floor sandstone fissure aquifer,with weak water yield,is a static reserve,which has little impact on the safety production of the working face(3)According to the three-dimensional ground earthquake,the drop and swing range of F22 normal fault on the working face side are found,and no suspected collapse column with diameter greater than 20m is found;Before roadway excavation and mining,the transient electromagnetic method and radio wave pit penetration were used for 12 times of advance exploration.The transient electromagnetic method did not find an obvious abnormal area of low resistance,indicating that the F22 normal fault is a water rich fault with weak water bearing property;Six structural anomaly areas were found in radio wave pit penetration,and there was no collapse column feature.(4)Nine groups of underground exploration drilling yards are designed in the adjacent W3₂21 working face and W3₂22 working face,and 26 F22 fault exploration boreholes are designed and constructed,with a total work amount of 2840m;23 fault exploration holes were designed and constructed in W3₂20 working face,with a total work amount of 1307m.All the detection holes have no water outflow,indicating that the water bearing conductivity of the fault is poor,which provides a basis for reducing the fault protective coal pillar.(5)The roof of coal seam 3₂in the working face is composed of mudstone and siltstone,and the overlying rock belongs to medium hard rock.According to the uniaxial compression test results of rock samples,the mining analysis model of W3₂20 working face affected by faults is constructed.The mining stress,strain and displacement under different protective coal pillar widths are simulated and analyzed by FLAC^3D.It is determined that the protective coal pillar width of F22 fault can be reduced from 60m to30m.(6)According to the"three down"coal mining code,the overburden type of W3₂20working face is soft?medium hard,the mining grade of water body is class II,and the collapse zone is not allowed to affect the"four inclusions".The type of safety coal pillar that can be reserved is sand control safety coal pillar.According to the maximum mining height of 4m,the engineering analogy method of measured data of the mine is used to calculate that the sand control safety coal pillar is 25.32m;According to the"three down"mining code,the safe coal and rock pillar requiring sand control is 24.8m;The guidelines for coal pillar reservation and coal pressure mining of buildings,water bodies,railways and main shafts and roadways are adopted,and the safe coal pillar requiring sand control is44m;Both are less than the 46m actually reserved,so the mining is feasible.(7)The mining of W3₂20 working face began in December 2021.When the paper was completed,100000 tons of originally designed fault protective coal pillar had been mined,and there was no safety production accident of fault water and"four aquifer"water.It shows that the ideas of geophysical exploration,drilling verification,FLAC^3Dnumerical simulation software to simulate mining evolution characteristics and theoretical formula calculation adopted in this paper are feasible,and have the prospect of popularization and application in similar working faces.Figure[62]Table[26]Reference[79]...