Stress Distribution Characteristics And Coal And Rock Rupture Law Of Different Dip Seams Under True Triaxial Mining Conditions

Before the coal seam mining,the coal and rock mass is in a state of stress balance.As the mining work progresses,the original stress balance is destroyed and different stress zones are formed in the coal rock.The coal rock is deformed and destroyed.The rock mass after the overburden rock fractures falls down.The upper and lower part of the goaf form a curved subsidence zone,a fracture zone and a fall zone.The rock formation below the goaf is affected.The supporting pressure bulges toward the goaf,and a water guiding damage zone,a protective belt and a pressurized water guiding belt are formed below the goaf.Different from the horizontal coal seam,the mining of the inclined coal seam will cause the stress distribution characteristics and the deformation movement of the rock layer below the overburden and the goaf to be uneven and asymmetrical.Under different propulsion schedules,the periodic compression and overburden and the lower strata of the goaf are The amount of deformation is also different.In order to explore the stress field and fracture law of coal and rock during mining,this paper takes a coal mine of Furong Company of Sichuan Coal Industry Group as the research object,and combines theoretical analysis,three-dimensional similar simulation physical experiment and numerical simulation experiment based on FLAC3 D to horizontal and inclined coal seams.The stress distribution characteristics and fracture law of coal and rock during mining are studied,and the following main conclusions are obtained:(1)The mining of the coal seam destroys the original stress balance.As the coal seam advances,the front bearing pressure is formed in front of the working face,and the lateral bearing pressure is generated on both sides.The pressure relief state appears in a certain range of the working surface,and the coal seam advances.Afterwards,the fallen rock blocks in the goaf fill the goaf,which plays a supporting role,causing the overburden stress to rise again.The stress value after the recovery is close to the original rock stress.(2)After the coal seam is recovered,the overburden layer in the goaf is subsided downward,and the floor rock layer is bulged upward,and the deformation is concentrated in the middle of the rock stratum.With the increase of overburden strata,the sinking amount of coal rock gradually decreases,the range of deformation occurs,and the deformation in the plane gradually decreases from the middle to the periphery.As the depth of the bottom plate increases,the influence of the bottom plate against mining increases gradually,and the in-plane deformation gradually decreases from the middle to the periphery,which generally exhibits the characteristics of “lower intermediate height”.(3)The mining of coal seams is accompanied by the occurrence of tensile expansion and shear slip of the rock stratum,and the fractured rock formation forms a fracture field.In the horizontal section of the rock formation,the fracture distribution is of the "O" shape,and the vertical section is "elliptical".According to the distribution characteristics of the plastic zone of the coal and rock in the goaf,it can be inferred that the fracture zone in the overburden is mainly caused by shear failure,and the rock formation forms the fall zone after the tensile failure.The maximum failure height of the overburden is about 43 m.The maximum damage depth is around 22 m.(4)Under different propulsion conditions,the existence of dip angle leads to the uneven distribution of stress in the working face of the inclined coal seam.The isostatic contour of the unloading pressure is “arched” in the overlying strata,and the “spoon”shape in the stratum of the stratum.The upper side stress concentration coefficient at both ends of the surface is lower than the lower side;the larger the working surface width,the denser the stress contour in the lateral stress concentration area of the working surface,and the displacement range and displacement of the rock layer below the overburden and goaf are enlarged.The greater the coal dip angle(12°,30°,45°),the more obvious the asymmetric characteristics of the stress distribution;the displacement of the rock under the overlying strata and the goaf in the gently inclined coal seam is similar to that of the horizontal coal seam,and the “spoof” shape of the steeply inclined coal seam The center of the displacement contour is biased toward the underside of the work surface.