Calculation Models And Mechanical Behaviors For The Prestressed Composite Lining Of The Shield Tunnel

The prestressed composite lining which composed of an outer segment lining and an inner prestressed lining is a new composite lining of the shield tunnel.It is proposed firstly for the Yellow River Crossing Tunnel in the Middle Route of the South-to-North Water Division Project in China,which presented an innovative solution for the shield water conveyance tunnel in poor geological conditions with technical difficulties such as large cross section,deep buried depth,high internal pressure,high anti-seepage requirement,etc.However,since the Yellow River Crossing Tunnel is the only case for the prestressed composite lining all over the world,the relevant design theories,calculation models and engineering experiences are not perfect enough,and the stress transmission mechanism and the mechanical behavior of the lining are still not clarified.Therefore,combined with the results of the in-situ monitoring and model tests,theoretical analyses and numerical simulations are used as the main methods to present the calculation model and reveal the mechanical behavior of the prestressed composite lining of the shield tunnel.The main research contents and achievements are as follows.(1)Detailed three-dimensional finite element models are established for the segmental joint with gaskets and the segmental joint without gaskets,respectively.The numerical bending tests are performed to compare the bending moment-rotation curves of the two joints,and the results reveal that the elastic gasket has a significant effect on softening the joint.Based on the interface model of the segmental joint,an analytical model for the segmental joint with gaskets are proposed,and the reliability of the analytical model is verified by comparing the analytical results with the the numerical bending test results.Besides,parametric analyses are carried out for the mechanical behavior of the segmental joint by the analytical model,and the influences of the parameters related to the elastic gasket and the bolt on the the mechanical behavior of the segmental joint are obtained.(2)A simplified three-dimensional solid-spring model is proposed for the segmental joint to perform the bending test,and the reliability of the simplified model is verified by being compared with the detailed three-dimensional finite element model and the analytical model.Based on the solid-spring model,a numerical model of the whole segmental lining is established to analysis the distribution of the deformation,stress,axis force and bending moment for the segmental lining subjected to external loads.With the consideration of the staggered joints,a two-dimensional beam-spring model is proposed for the whole segmental lining,and it is verified by comparing it with the three-dimensional solid-spring model.The influence of the parameters related to the elastic gasket and the bolt on the mechanical behavior of the whole segmental lining are revealed.(3)A three-dimensional finite element model is established for the Xiaolangdi desilting tunnel,and it is verified by the in-situ monitoring results.A three-dimensional simplified shell model and a two-dimensional simplified beam model are proposed for the prestressed lining with circular anchor cables,and the reliability of the simplified models is verified by being compared with the three-dimensional finite element model.Combining the three-dimensional finite element model results with the simplified model results,and at the point of view of stresses,axis forces and bending moments,the mechanical behavior characteristics of the prestressed lining with circular anchor cables under the condition of the anchor cable is tensioned or the tunnel is filled with water are revealed.Beside,the weakest region of the prestressed lining concrete is pointed out.(4)The stress transmission mechanisms of the prestressed composite lining with three joint surface treatments,which the inner lining and the outer lining are separated by the membrane,bonded together and connected by the rebar,are theoretically analysed.Combining the theoretically analysis with the simplified segmental lining model and the simplified prestressed lining model,a beam-springs-beam model is proposed for the prestressed composite lining.By adopting the proposed model,the influences of the membrane stiffness,bond strength and rebar quantity on the stress transmission between the inner lining and the outer lining of the prestressed composite lining are revealed,and the influences of the load variation caused by different inner lining construction timing,seepage between the inner lining and the outer lining and overload operation of the lining on the force and bending moment of the the prestressed composite lining are indicated.(5)The proposed beam-springs-beam model for the shield tunnel prestressed composite lining is adopted to study the Yellow River Crossing Tunnel of the Middle Route Project of the South-to-North Water Division Project.Combining the beamsprings-beam model calculation results with the three-dimensional finite element calculation results and the full-scale experimental results,the stresses,deformations,axis forces,bending moments of the rebar model and membrane model for the prestressed composite lining of the Yellow River Crossing Tunnel is compared and analyzed,respectively.The mechanical behavior characteristics of the prestressed composite lining is revealed,and it is indicated that the membrane model has advantages with respect to material utilization,safety margin,waterproof,drainage,structural stability,etc.