The Mechanism Of Preventing Rib Spalling And Engineering Application Of Injecting Water Into Coal Wall In Loose Thick Coal Seam Workface

The rib spalling in workface and roof falling bring great threat to coal mine safety production,and seriously affect the advancing speed and output of workface.In loose thick coal seam,due to the soft coal body and the large mining height,the development of crack in front of the workface and rib spalling of coal wall are more serious in the mining process.Therefore,it is of great engineering value and practical significance to carry out the research on the mechanism and engineering application of water injection to prevent rib spalling of the coal wall in loose thick coal seam workface to ensure the safe production of it.Based on the engineering research background of the ?811 loose thick coal seam workface of Luling Coal Mine of Huaibei Mining Group,this thesis comprehensively uses indoor tests,theoretical analysis,numerical simulation and on-site monitoring methods to research mechanism and engineering applications of water injection in the coal wall to prevent rib spalling of the ?811 loose thick coal seam workface.Mainly includes:(1)Using X-ray diffractometer and scanning electron microscope,the mineral composition and microscopic morphology of the ?811 loose thick coal seam were analyzed.There is a large amount of clay mineral kaolinite in the coal seam of ?811 workface.It has the characteristics of soft,strong water absorption and easy expansion by water absorption,and has good plasticity and high adhesion.At the same time,there are many tiny cracks in the coal seam,more pulverized coal particles,and low natural moisture content,which provides the feasibility for preventing and controlling rib spalling of coal wall through water injection in the ?811 loose thick coal seam face.(2)Through the tests of uniaxial compressive strength and shear strength of coal samples,the relationship between uniaxial compressive strength,peak strain and moisture content of coal samples with different moisture content,as well as the relationship between shear strength,cohesion,internal friction Angle and moisture content of coal samples were studied.The compressive strength of coal samples decreases slowly with the increase of moisture content,while the peak strain increases first and then decreases.The shear strength and peak strain of coal samples increase first and then decrease with the increase of moisture content,while the cohesion and internal friction Angle of coal samples increase first and then decrease with the increase of moisture content.Considering the variation of compressive strength,shear strength,peak strain,cohesion,internal friction Angle and moisture content of coal sample,the optimum moisture content of coal wall by injecting water to prevent rib spalling in?811 loose thick coal workface is determined.(3)According to the distribution law of lead abutment pressure of workface,the mechanical model of deformation and failure of coal body and rib spalling of ?811 loose thick coal workface was established The expressions of the range of fracture zone and plastic zone of coal body in front of loose thick coal seam workface were deduced by using Mohr-Coulomb criterion.The relationship between the width of fracture zone,plastic zone and coalbody cohesion,internal friction Angle,retaining force,mining height,mining depth and other parameters are analyzed,which provides a theoretical basis for the determination of water injection parameters(the depth of water injection hole)of ?811 loose thick coal seam.(4)According to the geological conditions of the ?811 loose thick coal seam workface,using COMSOL numerical calculation software,the factors affecting the coal seam water injection effect such as hole spacing,pressure,position(orifice and hole bottom)and time are simulated and analyzed,and their influence laws are analyzed,so as to provide a theoretical basis for determining the best physical parameters of coal wall water injection in ?811 loose thick coal seam.(5)Based on laboratory test,theoretical analysis,numerical simulation,and field monitoring results,design the shallow hole high pressure water injection scheme and water injection parameters of the ?811 loose thick coal seam workface of coal wall,including injection hole spacing,position,the angle,number,depth,time and pressure,etc.,and has carried on the engineering practice of coal wall shallow hole high-pressure waterflood to prevent rib spalling.When the coal seam reaches the optimum moisture content,the working resistance of supports in ?811 workface is reduced compared with that before water injection,and the problem of rib spalling coal wall in workface is well controlled.Figure[54]Table[9]Reference[80]...