Study On Mechanical Properties Of Large-diameter Underwater Shield Tunnel With Double-lining

With substantial construction of the shield tunnels,the problems exposed during the long term use of segment lining are becoming more and more obvious.Segment lining is hard to fully meet the safety and durability requirements of the structure,especially in the case of large section,deep buried and complicated geologic conditions.Considering the potential risk,the double-lining has become a widely accepted structure to ensure the safety of tunnels.At present,there are few projects of shield tunnels with double-lining structure,the change rule of the stress state of segment and secondary lining under different conditions is deficient.Therefore,it is necessary to study the mechanical properties of double-lining structure.Based on Wuhan Metro Line 8 cross-river tunnel,this paper studies the mechanical properties of double-lining structure under different conditions.The main research work and results are as follows:(1)The radial compressive links and tangential springs are applied to simulate the mechanical effect between the segment and secondary lining.By three-dimensional numerical calculation model of double-lining structure,the mechanical state of the segment and secondary lining under typical section condition is analyzed.The results show that when the segment lining is fully loaded,the mechanical state of the segment lining has little change after the secondary lining applied.Since the secondary lining does not bear external load,the internal force is much lower than the segment lining.The deformation of double-lining is consistent.(2)The effect of water level change on mechanical properties of double-lining structure is studied.As the water level rises,the axial force of the double-lining structure increases linearly,and the secondary lining increases more than the segment lining.As the water level drops,the axial force of the double-lining structure decreases linearly,and the segment lining decrease is greater than the secondary lining.From the variation value,the fluctuation of water level has little influence on the bending moment and deformation of the lining.The internal force and deformation growth of the segment of double-lining structure are relatively lower and smaller in the same working conditions.(3)The influence of different structural parameters on the mechanical properties of double-lining is obtained by numerical calculation.The overlapping structure improves the integrity of the segment and secondary lining,the anti-deformation performance is betterthan the compound structure.The strength degradation of the segment lining makes the secondary lining enter the bearing state,and the internal force increases.And the secondary lining can effectively reduce the structural deformation increment.With the bending rigidity of the segment joints increases,the bending moment of the segment lining is increased,the bending moment of secondary lining and the deformation of the structure decreases.The sensitivity of the bending moment of the segment lining to the joint stiffness decreases with the secondary lining applied.(4)The effect of the secondary lining strength and thickness on the mechanical properties of the double-lining structure is proved by numerical simulation.A three-dimensional longitudinal double-lining model is used to study the change rule of the longitudinal equivalent bending stiffness of the tunnel.The results show that the longitudinal bending stiffness of the tunnel is increased with the secondary lining applied.The function and position of the secondary lining concrete construction joint are discussed.