Study On Roof Stability And Collaborative Control Of Gob-side Entry Retaining By Roof Cutting In Deep Mine

Gob-side entry retaining by roof cutting(GERRC)has the technical advantages of canceling section coal pillar,relieving the tension of mining connection and eliminating gas accumulation in upper corner.It is one of the key technical methods to improve coal recovery rate,reduce roadway driving rate and realize safe and efficient mining in deep mine.GERRC has a long service cycle,complex roof stress and many factors affecting roof stability,which puts forward higher requirements for roadway roof control.This paper is aimed at the problem of roof stability and collaborative control in deep mine,the structural evolution characteristics of direct roof and main roof,the mechanism of pre splitting blasting seam formation and stability,the pressure relief effect of cutting blasting parameters,the full cycle deformation mechanism of direct roof and retaining roadway and roof are studied by using the comprehensive research methods of similar simulation,numerical calculation,theoretical analysis and engineering verification The main conclusions are as follows:(1)It is clear that the whole cycle mechanical structure of the direct roof and the main roof is cantilever beam structure.Through similar simulation,the structural evolution characteristics of direct roof and main roof are analyzed.It is concluded that presplitting and roof cutting can relieve pressure.On this basis,the key problems of roof stability control are put forward.(2)The blasting parameters to ensure the seam formation and the integrity of the rock mass and the cutting parameters for the optimal pressure relief effect are obtained.Taking the air return roadway of 7135 working face in Qidong Coal Mine as the engineering background,the crack propagation law under the conditions of shaped charge blasting,ordinary blasting,different linear charge density and different blast hole spacing,and the roof pressure relief effect of different top cutting depth and cutting angle are analyzed by numerical simulation.It is concluded that the blasting hole spacing and linear charge density(charge length)are the key to roof seam formation and rock mass integrity The best pressure relief effect is obtained when the cutting depth is 9m and the cutting angle is 80°.(3)The main roof crack formation and stability criteria of the roadway with cut roof under the dynamic static coupling effect are proposed.Based on the stress wave attenuation formula in rock stratum,the main roof crack forming criterion based on tensile strength is established,and the minimum quantitative relationship between the charge length and the hole spacing is obtained.Based on the mechanical characteristics of the main roof under the dynamic static coupling effect,the main roof mechanical model is established,and the main roof stability criterion with tensile strength as the critical index is obtained The maximum quantitative relationship between the length of fixed charge and the distance between holes is revealed,and the propagation law of blasting stress wave in the main roof is alternately changed by tension and pressure,and the main roof of roadway is continuously subjected to the action of tensile and compressive stress at the same position.(4)The whole cycle mechanical model of the direct roof is established,and the deformation mechanism of the direct roof is obtained.This paper analyzes the whole period roof structure and stress characteristics of the direct roof of the cut roof and retaining roadway,establishes the full cycle mechanical model of the direct roof of the roadway,obtains the expression of the deformation mechanism of the roadway roof,and obtains the quantitative relationship between the roof deformation before and after the roof cutting,the deformation amount of the roof during the retaining period,and the quantitative relationship between the temporary support position and the support stiffness.(5)The mechanism of collaborative support in Roadway with roof cutting and roadway retaining is obtained.This paper analyzes the mechanical characteristics of coordinated deformation between the direct roof and the main roof during the roadway retaining period of the roof cutting roadway,establishes the combined mechanical model of the direct roof and the main roof,obtains the calculation expression of the shear stress between the direct roof and the main roof,obtains the interlayer dislocation criterion,analyzes the quantitative relationship between the interlayer shear difference and the bolt rod support mesh,preload and the temporary support stiffness The results show that the interlayer displacement of temporary support has significant buried depth effect.(6)The coordinated control idea of roof cutting roadway and roof control technology during roadway retaining in 7135 working face of Qidong Coal Mine are comprehensively put forward.By investigating the effect of roof cutting blasting and roof support support,the distribution law of roof deformation and working resistance of stack support during the period from primary mining to roadway retaining stability is obtained,which verifies the rationality of theoretical calculation and roof control technology.Figure[84]Table[17]References[151]...