| The coal and rock mass of fault zone in the steeply dipping coal seam is weak in strength and complex in stress.Fault slip and periodic rupture of roof force dynamic load on tailgate during working face is mining,it leads to large deformation failure such as coal wall and roof caving,causes failure of supporting structure,affects the normal production of the mine seriously.Therefore,it is of great significance for the safe and efficient mining of steeply dipping coal seam to study the mechanism of surrounding-rock large deformation or damage,explore support control methods,provide theoretical and technical support for the stability control of surrounding rock in tailgate under this kind of geological conditions when tailgate across fault zone.Taking the tailgate of the 3115-14 steeply dipping working face of Taiping coall mine as the engineering background,the main influencing factors and the mechanism of the deformation and damage of the surrounding rock passing through the fault in the tailgate are analyzed,failure mechanism of different support structures under dynamic load is analyzed,principle of large deformation control and technology of support control of surrounding rock in tailgate that across fault are put forward.The main conclusions are as follows:(1)The influence range of the advanced bearing pressure of working face mining is 50m in front,about 5.32m in front,the peak value of bearing pressure is 16.36MPa～29.37MPa,and the dynamic load coefficient is between 1.36～3.36.The mining of the working face is easy to induce fault activation,resulting in large deformation and damage of the roof of the tailgate,coal wall pieces,etc.,and the failure of support such as roof metal mesh breakage and bolt tray falling.Dynamic load strength and fault location are the main influencing factors for the deformation and damage of the tailgate passing through the fault in steeply dipping working face.(2)When the stoping tailgate is affected by the fault zone,the surrounding rock stress environment is complex,the fault zone is prone to produce additional stress and the barrier effect is significant,and the surrounding rock stress distribution is not uniform,which is manifested as the vertical stress concentration degree is larger away from the fault zone side,and the horizontal stress release range is larger near the fault zone side.The deflection angle of the principal stress direction near the lateral wall of the fault zone is larger,and the stress path is transferred away from the fault wall.The deformation of surrounding rock and the failure range of plastic zone are large.With the increase of dynamic load strength,the concentration degree of vertical stress on the left side and the release range of vertical stress on the roof increase,the main stress direction of the roof and the right side deflects greatly,and the stress path transfers along the left side of the rock layer.The deformation of the roof and the left side wall and the failure range of the plastic zone are obviously increased,and the large deformation characteristics of the tailgate are further highlighted,revealing the large deformation failure mechanism of the surrounding rock across the fault of the tailgate at the steeply dipping working face.(3)The failure mechanism of the support structure of the tailgate across fault in steeply dipping working face is revealed,and the main reason for the instability of the surrounding rock is the uncoordinated deformation of the surrounding rock in the anchor net shotcrete support tailgate under dynamic load.The tailgate in the fault zone is affected by the mining dynamic load of the working face,the surface deformation of the surrounding rock in tailgate and the force of the bolt increase continuously with different support conditions.Affected by the change of stress transfer path in fault zone,the deformation gradient of the two coal walls and floor is small in the elastic deformation stage.the deformation gradient of the roof increases first and then decreases,and mainly goes through the linear elastic deformation stage,the viscoelastic deformation stage and the plastic deformation failure stage.The mechanical models of falling body of rood and the splice body of right coal wall are established,and criterion of stability is given.When the frictional stress is less than the shear stress,the rock layer is damaged,The failure characteristics of large deformation and failure mechanism of supporting structure in tailgate over fault in steeply dipping working face are revealed.(4)The surrounding rock control principle of "regional,rigid-strength coupling support"and the combined support technology of " anchor net shotcrete+rigid-flexible support" were put forward.Under this support,the deformation of surrounding rock and the stress of anchor bolt are significantly reduced,and the roof subsidence is reduced from 36.15mm to 21.88mm,which is reduced by 40%.The deformation of left side,right side and floor heave are reduced by 91%,38%and 64%respectively.The vertical stress concentration coefficient and horizontal stress release range of tailgate surrounding rock in fault zone are reduced and evenly distributed.Field industrial tests show that this method can improve the ability of resisting dynamic load failure,reduce the deformation of tailgate surrounding rock,and effectively control the dynamic load deformation and failure of tailgate in fault zone steeply dipping coal seam. |
