| The stress distribution of surrounding rock of roadway with inclined composite roof is complex,and the distribution of deformation and plastic zone is obviously asymmetrical,which often leads to great difficulty in roadway support and seriously restricts the safe and efficient production of coal mine.Therefore,it is of great significance to study the anchorage mechanism and stability control of roadway with inclined composite roof.In order to solve the technical problems of serious asymmetric deformation of surrounding rock and difficult to control during the service period of such roadway,this paper takes the return air roadway of a working face in a mining area of No.4 inclined coal seam in Yongning Coal Mine as the background,and the coal seam inclination is between 20° and 45°.Laboratory test,numerical simulation,theoretical analysis and engineering monitoring are adopted.To tilt the compound roof of roadway surrounding rock stress distribution and failure mechanism,prestress and anchorage Angle of45 ° inclined bedding rock anchorage control mechanism of the key problems are studied,and on the basis of the optimized support scheme,supporting and experiment was carried out,in order to realize the compound roof of roadway stability control,which is a reference for similar type of roadway surrounding rock control.The main conclusions are as follows:(1)Based on theoretical analysis and field investigation,the stress distribution,deformation and failure characteristics and failure mechanism of surrounding rock of return air roadway in a mining area of no.4 inclined coal seam in Yongning Coal Mine are studied.The main conclusions are as follows:(1)The asymmetric stress distribution characteristics of roof,side and floor of roadway are as follows: Stress concentration occurs at the left and right corners of the roof,and the stress concentration on the left side of the roof is greater than that on the right side,the peak value of stress concentration on the lower side of the roadway is greater than that on the right side,and the stress concentration degree on the left side of the floor is greater than that on the right side.(2)The concrete deformation and failure characteristics of roadway are as follows: the roof has the characteristics of oblique triangular caving arch and layer separation,and the damage is most obvious at the left corner of the roof.The deformation of the left side is obviously larger than that of the right side,and the displacement of the roadway side is asymmetrical.Due to asymmetric load on both sides of roadway floor,uneven floor heave occurs on both sides of roadway floor,which poses a threat to roadway safety production.(2)Based on the laboratory test and numerical simulation,the stress distribution characteristics and deformation and failure of the specimens without anchor and with anchor were compared,and the anchoring mechanism of prestressed anchor cable was clarified.Under the side pressure of the prestressed anchor cable,the stress uniformity of the laminated rock mass was improved with the rapid increase of the axial load of the anchor cable.By sharing the external forces,the tensile,shear and bending deformation of prestressed anchor cable can effectively delay the crack propagation and normal and tangential deformation,which makes the crack propagation need to provide higher external load.Due to the high resistance characteristics of prestressed anchor cable,the fractured surrounding rock is extruded and formed a new bearing structure under the constraint strengthening of anchor cable,and the bearing structure of bedded rock mass is strengthened jointly with the anchor cable.At the same time,the interconnecting compressive stress zone formed by prestressed anchor cable can effectively improve the compressive shear strength,deformation capacity and residual strength of stratified rock,and limit the further deformation failure of rock mass.(3)The test results show that the evolution process of anchor cable axial force can be divided into sharp increase,slow increase delay and slow decrease stages.In the rapid growth stage,under the action of anchor cable,the lateral constraint of specimen increases and the crack propagation is inhibited.In the slow delay stage,the anchorage structure of bedded rock mass is strengthened under the action of high resistance of anchor cable.In the slow drop stage,the anchor cable fracture and tray loosening lead to the axial restraint decline of the bedded rock mass,and the anchor solid strength decreases rapidly.(4)Based on the similar simulation test system,the variation rules of surrounding rock stress and displacement of inclined bedding rock mass under different anchoring angles are simulated,and the following conclusions are drawn: When the anchorage Angle is 45°,the elastic modulus,peak strength and residual strength of the specimen increase by 16.71%,14.29%and 18.64%,respectively,compared with the anchorage Angle of 90°.With the optimization of anchoring Angle,the constraint effect of anchor cable on rock mass dilatation is enhanced,and the bulk strain of specimens with anchoring Angle β=45° is 18.47% lower than that of specimens with anchoring Angle β=90°.The discontinuous deformation of specimens is weakened,and anchor cable has strong constraint ability on rock mass dilatation.(5)The influence of different anchoring angles on the stress distribution characteristics and deformation and failure law of inclined bedded rock mass was studied by numerical simulation,and the following conclusions were drawn: The anchoring Angle can effectively improve the stress concentration of the bedding plane and surrounding rock.When the anchoring Angle is 75° ～ 90°,the stress concentration on both sides of the top of rock mass is large.When the anchoring Angle is 45°,the stress concentration on the top of rock mass decreases most significantly,and the stress distribution of the bedding rock mass is more uniform.The elliptical compressive stress zone formed by anchor cable anchoring provides resistance for rock mass sliding along the bedding plane and enhances the crack stopping effect of rock mass.When the anchoring Angle is 45°,the compressive stress zone of the specimen is closely connected and the total area is large,and the anchoring cable has a good effect.(6)The similarity simulation test system is used to study the influence of different prestresses on mechanical properties of inclined bedding rock mass,and the following conclusions are drawn: The prestress of anchor cable is positively correlated with the bearing capacity of bedded rock mass.When the prestress increases from 0.5k N to 0.7k N,the elastic modulus,peak strength and residual strength of specimens increase by 66.14%,46.62% and26.27%,respectively.That is to say,increasing the prestress of anchor cable can effectively improve the overall anchoring strength of bedded rock mass.With the increase of prestress,the brittleness index of anchor decreases gradually.When the prestress increases from 0.5k N to0.7k N,the post-peak brittleness index decreases by 17.9%.The increase of prestress greatly limits the progressive failure of surrounding rock,such as slab and block slip.Increasing the prestress can effectively reduce the dilatancy deformation failure of rock mass.When the prestress increases from 0.5k N to 0.7k N,the volume strain decreases by 34.8%.(7)Based on numerical simulation,the influence of prestressed anchor cable on the stress distribution characteristics of inclined bedded rock mass is studied,and the following conclusions are drawn: the application of prestress reduces the heterogeneity of stress distribution of bedded rock mass,and the uniformity of stress distribution increases with the increase of prestress of anchor cable;Under the action of the prestressed anchor cable,the rock mass around the anchor cable forms an oval stress compression zone,which limits the further deformation and failure of the rock mass.With the increase of the prestressed anchor cable,the compression zone overlapped with each other,and finally made the whole joint in the compression state.(8)Aiming at the return air roadway in a mining area of No.4 coal seam in Yongning Coal Mine,the reasonable prestress and anchorage Angle of anchor cable are designed.The stability of roadway support structure is verified by monitoring and analysis of roadway convergence,anchor rod and anchor cable working load,which provides scientific basis and reference for roadway support with inclined composite roof. |
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