| The roadway with composite roof in the coal mine is gradually increasing with the mining depth.As a special underground rock with weak interlayer,the composite roof of coal roadway is characterized by low overall strength,wide difference of lithology,loose structure and poor self-stability.The stress field in rock mass redistributes after the roadway excavation,the combined effect of overburden and horizontal tectonic stress contributes to the bending deformation or even destruction of compound roof strata in various degree.This invalids the roof support structure system,induces large scale cave and other engineering disasters,threats the mining safety,and restricts the efficient production of coal mining.At the same time,numberous theoretical researches and engineering practices show that the bearing mechanism and supporting structure of the composite roof cannot be reasonably explained,based on the forgoing roadway roof deformation and failure mechanism and the existing support theory.Therefore,effectively controlling the deformation and failure of the composite roof and improving the overall stability of the roadway are becoming an urgency need in safety mining.This paper is on the basis of the summarizing and analyzing of forgoing roadway roof support researches,the physical and mechanical parameters of rock mass,and the bearing properties of it before or after anchor,the failure pattern of strata after the caving and the height of balance arch are systematically researched,based on the theoretical analysis,experimental study,numerical simulation and field practice in the groove of compound roof in 40303 working face of a coal mine in Binchang,Shaanxi province.After that,a bearing model named arch-beam is proposed,and new support approach on compound roof is developed,and applied to the groove of composite roof supporting design in 40303 workingface.The main achievements of this paper are as below:(1)The fundamental physical and mechanical parameters of the complex roof of the 40303 working face in Bingchang are analyzed,on the basis of the field sampling and laboratory test including uniaxial compression test,three axial compression test,tensile test and shear test carried out on the composite roof of the return roadway in40303 working face,and mechanical parameters like uniaxial compressive strength,tensile strength,elastic modulus,Poisson's ratio and angle of internal friction parameter test are obtained.The results indicates the differences of the compressive strength,elastic modulus and Poisson's ratio exists in single layer and composite rock mass,at uniaxial compressive condition,different rock mass transverse strain ofdifferent sizes and mutual constraints in composite layered rock,which results in adhesive confining stress,different strength of rock mass strength based on the order from small to large damage.(2)The field detection of the lithology and fracture distribution of the complex roof of the 40303 working face in Bingchang with the drilling and peeping method is used.The test results illustrates that the roof with depth of 0~0.4 meter is circumferential fissure sandstone;0.4~1.6 meter is sandy mudstone with oblique cracks and accompanied by a small amount of seepage of water;1.6~2.2 meter is circumferential crack development,with a small amount of water leakage,broken limestone layer;2.2~5.11 meter is mudstone with for circumferential fissures and seepage the phenomenon;5.11~7.71 meter for the distribution of circumferential fracture zone and a large area of water siltstone;7.71~11.84 meter is the sandstone with obviously longitudinal crack distribution,these phenomena show that the ventilation roadway roof of 40303 working face has the typical characteristics of compound roof.(3)The basic support characteristics of roadway composite roof before and after anchorage are theoretically investigated.A compound roof rock beam in the vertical load and horizontal tectonic stress,beam formation mechanics model of loads,structural mechanics and material mechanics theory,the maximum deflection in the lower layer of rock beams across the maximum bending moment and maximum tensile stress formula is deduced based on the proposed composite rock beam and combination rock beam stress under the combined action of bending moment and deflection,the maximum tensile stress and the relation formula of roof thickness,roadway span,and horizontal lateral pressure in the vertical and horizontal structure.The results show that the deflection and span under composite roof rock beam,the maximum bending moment and maximum tensile stress are increased as the reduction of the thickness of the rock beam;the thickness of rock beam increases the deflection and cross side composite roof rock beam,the maximum bending moment and maximum tensile stress increases with the span of tunnel and horizontal side the pressure increasing.The additional bending moment produced by the roof strata under horizontal tectonic stress increase the bending moment and the maximum tensile stress of the rock beam under the vertical stratum pressure to a certain extent,which aggravates the tensile failure of the composite roof.(4)The caving arch shapes and vertical height of the composite roof strata after the deformation and failure under the combined action of vertical stratum load and horizontal tectonic stress are studied.Under the combined action of vertical stratumload and horizontal tectonic stress,the roof of composite roof deflate to a certain stage and form caving and initial equilibrium arch and limit equilibrium arch.When the lateral pressure coefficient is smaller than 1,the level of the upper strata of composite roof in a certain range in vertical strata load plastic damage range is large,oval shaped to form vertical natural equilibrium arch,conversely,when the lateral pressure coefficient is greater than 1,the upper part of composite roof in a critical range in vertical load under the rock stratum the plastic damage range is small,oval shaped to form the natural balance of the horizontal arch.Considering the instability modes of the roadway support,the scope of the natural balance arch of the composite roof will further expand,and changed into a hidden balance arch and an extended hidden balance arch,on the basis of the natural balance arch,it will be turned into the stealth balance arch and the extended stealth balance arch.(5)The similar material model test on return roadway of 40303 working face crossheading composite layered roof is explored,the deformation and failure forms,under different lateral pressures and thickness of composite layered roof are studied.The results show that the same thick compound roof rock increases with the lateral pressure coefficient on vertical load,the level of load displacement under the effect of the roof strata displacement distribution curve on the center of the tunnel is symmetrical and the roof span to the ends decreased gradually;in the vertical direction,the same section of shallow roof displacement deep roof displacement increased significantly.The lateral pressure has a significantly effect on morphology distribution of the composite roof balance arch,the specific performance is: the level of lateral pressure coefficient is smaller than 1,the composite roof caving arch is elliptic in vertical direction;when increases the lateral pressure coefficient,the composite roof damage range in the vertical direction doesnot change much,while the damage range along the horizontal the direction of the rapid increase.When the pressure coefficient of the horizontal side is greater than 1,the shape of the caving arch of the composite roof distributes in the horizontal direction.The simulation test phenomenon further validates the reasonableness of the theoretical study.(6)The design method of composite roof bolt(cable)support is proposed based on the model of ‘arch – beam' bearing structure.On the systematically analysis of existing compound roof support theory and method,based on the established mechanical model of roadway bearing structure of compound roof ‘arch-beam',the design of compound roof support is put forward,and the roof bolt and anchor support parameters also are determined by the composite beam theory and equilibrium arch theory.(7)Numerical analysis is carried out to investigate the deformation and failure of the composite roof of coal roadway under different support conditions.The numerical analysis model is established in return roadway of 40303 working face crossheading composite layered roof by use of FLAC3 D software,based on the actual excavation conditions of the boundary conditions and support conditions are set up,and the relationship between the depth of the composite roof and the side pressure coefficient of the coal roadway are studied.The results show that the vertical displacement of the composite roof is closely related to the pressure coefficient of the horizontal side.When the lateral pressure coefficient is low,the vertical stress plays a leading role.When the lateral pressure coefficient is large,the horizontal tectonic stress plays a leading role.With the increase of the lateral pressure coefficient,the shape of the plastic failure range of the composite roof is gradually transferred from the vertical ellipse to the ellipse in the horizontal direction.The comparative analysis between the original support and the improvement plan shows that the optimized bolt support parameters can effectively support the composite roof of the roadway,and the supporting effect is obviously optimized.(8)The basic problems of the original support scheme and the optimum design of the supporting parameters of the composite roof of the roadway in 40303 working face are analyzed.according to investigate the combination effect of load of loose rock mass in the balance arch and horizontal tectonic stress on the return roadway of40403 workingface,the maximum tensile stress is calculated,results show that in the original support scheme,anchor and cable length are shorter,and it is hard to form a Tab.arch beam supporting structure,and resulting in caving roof instability.By using the support theory of ‘arch-beam' bearing structure,the supporting parameters of the original bolt(cable)length,anchoring length and spacing in 40303 working faces are optimized,and the on-site application effect is monitored.The results show that the optimized bolt(cable)support parameters can effectively control the deformation and failure of the super composite roof,and the stability of the roof can be greatly improved. |
PDF Full Text Request