Study On Mechanical Response Characteristics For Reinforced Ribs Of Shotcrete In Cold Regional Tunnels

The reinforced ribs of shotcrete are widely used in the supporting of weak surrounding rock because it is convenient to construct,economical and effective.the researches on the supporting structure mainly focus on the structural form design,reinforcement mechanism and support effect under the load of surrounding rock.And the influence of temperature variation on the deformation and internal force of the supporting structure has not been involved,which affects accurate evaluation of bearing characteristics of reinforced ribs of shotcrete in cold regional tunnels.Firstly,the influence of temperature variation on the bearing characteristics of reinforced ribs of shotcrete is analyzed qualitatively based on three mechanical models including fixed arch,fixed arch with elastic support and fixed arch-elastic foundation beam related to qualities of surrounding rock mass.Then,the expressions of internal forces and deformation under combination actions of surrounding rock mass pressure,gravity load and temperature variation are deduced based on the three mechanical models,and the corresponding calculation programs are written.Finally,the internal force and deformation of reinforced ribs of shotcrete in cold regional tunnels is analyzed through the example of Jimingyi Tunnel,which provides technical support for evaluation of bearing characteristics of reinforced ribs of shotcrete in cold regional tunnels under different surrounding rock conditions.The main research contents are as follows:(1)Mechanical response of reinforced ribs of shotcrete is analyzed based on the model of fixed arch.And the mechanical model of internal force-deformation of reinforced ribs of shotcrete is established under combination actions of surrounding rock mass pressure,gravity load and temperature variation with the method of structural mechanics.Then the analytic solutions of the internal force and the deformation of reinforced ribs of shotcrete are derived,and the corresponding calculation programs are written and verified,which is used to study the responses of bending moment,axial force,shear force and deformation of reinforced ribs of shotcrete when the temperature inside and outside the structure changes synchronously at-38.1? and 31.5?.The results showed that:Temperature variation on the inside and outside of the structure has little influence on the internal force but has a greater influence on the deformation of the reinforced rib.When the temperature is lowered synchronously by 38.1?,the settlement of the vault has increased by 46.61%.(2)Mechanical response of reinforced ribs of shotcrete is analyzed based on the model of fixed arch with elastic support.And the mechanical model of internal force-deformation of reinforced ribs of shotcrete is established under combination actions of surrounding rock mass pressure,gravity load and temperature variation with the method of structural mechanics.Then the analytic solutions of the internal force and the deformation of reinforced ribs of shotcrete are derived,and the corresponding calculation programs are written and verified,which is used to study the responses of bending moment,axial force,shear force and deformation of reinforced ribs of shotcrete when the temperature inside and outside the structure changes synchronously at-38.1? and 31.5?.The results showed that:Temperature variation on the inside and outside of the structure has little influence on the internal force but has a greater influence on the deformation of the reinforced rib.When the temperature is lowered synchronously by 38.1?,the settlement of the vault has increased by 25.21%.(3)Mechanical response of reinforced ribs of shotcrete is analyzed based on the model of fixed arch-elastic foundation beam.And the mechanical model of internal force-deformation of reinforced ribs of shotcrete is established under combination actions of surrounding rock mass pressure,gravity load and temperature variation with the method of structural mechanics,elastic foundation beam and load transfer.Then the analytic solutions of the internal force and the deformation of reinforced ribs of shotcrete in variable temperature field are derived,and the corresponding calculation programs are written and verified which is used to study the responses of bending moment,axial force,shear force and deformation of reinforced ribs of shotcrete when the temperature inside and outside the structure changes synchronously at-38.1? and 31.5?.The results showed that:Temperature variation on the inside and outside of the structure has little influence on the internal force but has a greater influence on the deformation of the reinforced rib.When the temperature is lowered synchronously by 38.1?,the settlement of the vault has increased by 25.54%.