Study On Stability Characteristics Of Stope Roof In Mining Gently Inclined Medium Thick Orebody

The mining of gently inclined medium thick orebody has always been a technical problem,and the roof stability is an extremely complicated research that cannot be ignored in the mining process.Compared with other types of roof,the caving process of stope roof is very complicated,its influencing factors are various,roof accidents are sudden,the exposed area and span of stope roof are larger,so it is more difficult to control.In this thesis,the underground mining project of a phosphate mine in Jinning,Yunnan is taken as the engineering background.The fracture law of gently inclined roof under the condition of room-pillar mining is studied by roof theoretical mechanical model analysis and numerical simulation,which provides a theoretical reference for similar underground mining of gently inclined phosphate rock.The main research contents and conclusions of the thesis are as follows:(1)The natural geographical conditions,engineering geological conditions,mining technical conditions and underground mining schemes of the phosphate mine area are investigated and analyzed in detail.After fully understanding the geological data of the mining area,the main rock masses of the mining area are sampled on site,and standard specimens are prepared for indoor physical and mechanical parameter tests.In order to make the test data more reliable,the Hoek-Brown strength empirical criterion will be used to reduce the rock mass parameters.(2)Based on the theory of rock beam,two-dimensional bending deformation mechanical models with two ends fixed and one end fixed and the other end simply supported are established,and the expressions of bending moment and deflection of the gently inclined beam model under non-uniform load are calculated by using the principle of statically indeterminate structural force method.The deflection curve of the model with fixed ends is parabola symmetry distribution,and the deflection value decreases with the increase of dip angle and increases with the increase of ore body buried depth and beam length,and the maximum deflection value point is located at the center point of the beam.The deflection trend of one-end simply supported model is the same,but the deflection curve is asymmetric distribution,and the maximum displacement point shifts upward.(3)Combining the theory of small deflection of thin plate in elastic mechanics and the work reciprocal theorem of bending thin plate,three three-dimensional mechanical models of the roof with four sides fixed,two opposite sides fixed and two opposite sides simply supported,and four sides simply supported are established and solved,and the formulas of stress,bending moment and deflection of gently inclined top plate under non-uniform load are obtained.According to the analysis of the actual engineering situation,it can be seen that the breaking law of the gently inclined roof is similar to that of horizontal roof,and the upper surface of the roof is in the "O" type breaking mode along the periphery,and the lower surface is in the "X" type breaking mode.(4)The numerical simulation results of the roof stability characteristics under the room-pillar mining of gently inclined phosphate rock show that the stress of rock mass on both sides of the gob changes obviously during underground mining of gently inclined phosphate rock,and the pressure relief area appears on the roof above the goaf,the stress increases continuously around.The maximum settlement displacement is0.025 m at the central position of the goaf roof,and the farther away from the goaf,the smaller the influence of rock mass displacement.The plastic zone of the roof is square,the middle part of the lower surface is mainly tension-shear failure and the failure mode around the roof is mainly shear failure.The shear failure element is annular and surrounds the middle tension-shear failure zone.