Research On Control Technology For Roof Caving In Gob-side Entry Retaining In Upper Roadway Within Deeply Inclined Coal Seam

By a comprehensive research method combining theoretical analysis and UDEC numerical simulation is adopted.Based on the research results of domestic and foreign scholars on the stability of the roof of the inclined coal seam along the goaf,combined with the production geological conditions of the Changcheng No.3 Mine.The factors affecting the stability of the direct roof above the backfill,including the dip angle of the coal seam and the tensile strength of the roof are studied,and the caving law and mechanism of direct roof above the backfill are analyzed.Aiming at the different geological conditions that may cause the roof caving,the support effects and feasibility of the roof support schemes are discussed.Main results are as follows:(1)Through the stress analysis of the direct roof above the backfill of the inclined coal seam,the mechanical model of the inclined coal roof is established,and the limit equilibrium area of the direct roof above the backfill is analyzed.The width of the limit equilibrium area of the direct roof is determined.The result indicates that the dip angle of the coal seam and the tensile strength of the direct roof are the main factors affecting the stability of the direct roof above the backfill in the inclined coal seam along the goaf.(2)The roof caving happens when the dip angle of the coal seam is 35°,and the tensile strength of the direct roof is 2MPa,or when the dip angle of the coal seam is 45°,and the tensile strength of the direct roof is 2MPa and 3MPa.(3)The dip angle of the coal seam and the mechanical properties of the roof will directly affect the tangential displacement of the direct roof above the backfill along the goaf,the development of the crack in the roof rock mass,the degree of damage and the amount of separation between the direct roof and the main roof.The larger the dip angle of the coal seam,the longer the tangential displacement of the roof rock mass,the more serious the fracture development of the roof rock mass,the greater the damage degree,and the smaller the amount of separation between the direct roof and the main roof.The greater the tensile strength of the direct roof,the shorter the tangential displacement of the roof rock mass,the smaller the fracture development of the roof rock mass,the smaller the damage degree,and the smaller the amount of separation between the direct roof and the main roof.(4)When the dip angle of coal seam is small,the top and bottom of the direct roof will be bound by the tangential stress,and the tangential displacement at the middle of the direct roof will be the largest.When the coal seam dip angle increases,the top binding force will gradually become smaller,and the tangential displacement at the top of the direct roof will the same as that at the middle of the direct roof.The tensile strength of the roof only affects the amount of its tangential displacement and does not affect the distribution of tangential displacement in the normal direction.(5)The position of the maximum amount of separation between the direct roof and the main roof is close to the backfill.The larger the dip angle of the coal seam,the more obvious this feature is.However,the position of the maximum amount of separation does not change with the changes of the tensile strength of the roof.The tensile strength of the roof only affects the amount of separation,without affecting its distribution.(6)Through the UDEC numerical simulation,the different roof support schemes are proposed for different mine geological conditions that cause caving of the direct roof above the backfill.The support effects are compared and the reasonable support parameters are determined.