Study On Coal And Rock Pillar Setting For Safe Mining Of Coal Seam No.8 Near Loose Seam In Bayi Mining Area Of Xinhu Coal Mine

When China’s coal mines are mining near the coal seam under the loose layer,the water diversion fracture zone formed due to the damage of coal seam overburden may cause the loose layer water to collapse into the underground through the water diversion fracture zone,resulting in mine water disaster.In order to ensure the safe production of coal mines,huge thick coal and rock pillars are usually reserved.However,the retention of coal pillar will cause a large number of coal resources backlog and reduce the recovery rate of mine resources.Based on the collection and sorting of geological and hydrogeological data of Xinhu coal mine,this paper analyzes the characteristics of "three separation" and "four inclusion" of loose layer in shallow block in 811 and 814 working faces of Bayi mining area,the lithology and combination characteristics of overburden in 8 coal seam,and the thickness of 8 coal seam,and studies the failure characteristics of overburden in 8 coal seam by using numerical simulation and "three down" procedures,The height of reserved coal pillar is calculated according to the allowable mining grade,and the feasibility evaluation of safe coal pillar is carried out.The main research results are as follows:(1)The bottom plate depth of the third water resisting layer in the study area is 464.7～481.8m,the average depth is 474.58m,the thickness is 192.8～235.55m,and the average thickness is 216.23m.It has good water resistance and blocks the hydraulic connection between the water of aquifer Ⅰ,Ⅱ and Ⅲ,the "four aquifers" water and the sandstone water of coal measures.The buried depth of the fourth aquifer group floor is 468.3～496.65m,the average depth is 481.12m,the thickness is 0～21.3m,and the average thickness is 5.43m.There are great differences in lithological performance,great changes in thickness,and most sections are missing.The sedimentary thickness is generally thin and gradually thicker from East to west.According to the results of pumping test,the unit water inflow is 0.00723858～0.06097 L/(s·m),and the permeability system is 0.067447～1.82308m/d,Water rich property is weak.(2)The thickness of coal seam 81 is 0.85～3.88M,with an average thickness of 2.55m.The roof types are direct roof type,direct roof+main roof type and main roof direct covering type;The thickness of coal seam 82 is 1.41～2.84m,with an average thickness of 2.32m.The roof type is main roof+direct roof and direct roof.The spacing between coal seams 81 and 82 in the study area is 3.17～3.86M,with an average spacing of 1.86M.The lithology is mainly mudstone.There is magmatic rock between coal seams 2013-1 and 2014-11.(3)The bottom plate depth of bedrock weathering zone is 490.75～535.70m,with an average of 514.70m;The thickness is 10.81～50.08m,with an average of 27.30m.Due to the influence of weathering and groundwater,the rocks in the weathered zone have developed fissures,resulting in dissolution or argillization,with strong water separation capacity.The overburden thickness of coal seam 8 is 77.91～368.5m,the average thickness is 252.84m,the sand mud ratio is 0.31～2.19,and the average is 0.83.According to the mechanical test of overburden of coal seam,the overburden type is medium hard rock.(4)According to the "three down" regulations,the height of the caving zone of coal seam 81 is 12.62m,the height of the caving zone of coal seam 82 is 10.98m,the height of the water conducting fracture zone of coal seam 81 is 45.16m,and the height of the water conducting fracture zone of coal seam 82 is 50.48m.The height of the caving zone of coal seam 8 combined mining is 10～11m and the height of the water conducting fracture zone is 51～55m by FLAC3D numerical simulation.According to the four water bearing and sedimentary characteristics,the mining grade of coal seam 8 is determined as grade I,and the thickness of protective layer is 4 times the cumulative mining thickness of coal seam.The calculated height of waterproof coal pillar is 74.22m.Comprehensively,the vertical height of waterproof coal pillar is 75m.FIG.[33]Table[25]Reference[76]...