Research On The Mechanical Properties And Stability Of Variable Stiffness Shield Tunnel Linings Structure

With the rapid development of urban underground rail transit,shield tunnel linings are widely used in shield tunnel construction.Urban underground rail transit tunnels represented by subway tunnels usually bear uneven ground.loading.Therefore,rationally designing the shield tunnel linings and giving full play to the structural capability has become a key research topic..In this paper,we study the relationship between ground load and shield tunnel linings thickness,propose the variable stiffness shield tunnel linings for shield tunnels with uneven ground load,suggest the design of variable stiffness shield tunnel linings form,derives the mechanical model of variable stiffness shield tunnel linings,and analyzes variable stiffness shield tunnel linings feasibility and stability.The main research results of the paper are as follows.(1)Considering the uneven formation load,a variable stiffness shield tunnel lining structure is proposed.The outer contour of the shield tunnel lining remains circular to facilitate construction,and the inner contour shape is a function related to the formation load.Based on the equal stress design method,the variable stiffness shield tunnel lining is given.The design method of the thickness of the shield tunnel lining is to design three types of inner contours of the shield tunnel lining,ellipse,single parabola and double parabola respectively,compare the advantages and disadvantages of the three variable stiffness shield tunnel linings and the utilization rate of internal space,and finally choose the outer contour of the elliptical inner profile.The inner elliptical shield tunnel lining is the main form of the variable stiffness shield tunnel lining.(2)Drawing on the idea of the step fold method,deduce the mechanical model of the variable stiffness shield tunnel lining,study the mechanical properties and deformation characteristics of the variable stiffness shield tunnel lining,and obtain the internal force distribution law and de formation law of the variable stiffness shield tunnel lining structure.The influence of the change of formation parameters on the mechanical properties of the variable stiffness shield tunnel lining,combined with the mechanical properties and safety requirements of the variable stiffness shield tunnel lining,the optimal size combination of the variable stiffness shield tunnel lining structure is proposed.(3)The theoretical analysis conclusion of the variable stiffness shield tunnel lining is supplemented and verified by the numerical simulation method.A variable stiffness shield tunnel lining model test platform is built,and through the model test,the internal force characteristics and deformation characteristics of the variable stiffness shield tunnel lining are analyzed,and the results are compared and verified with the theoretical analysis results.The results show that the experimental results of the distribution law of the internal force of the variable stiffness shield tunnel lining are consistent with the theoretical analysis results.In terms of bending moment,the theoretical calculation value is larger than the experimental value;in terms of axial force,the experimental value is larger than the theoretical calculation value.The experimental results of the variable stiffness shield tunnel lining displacement are consistent with the theoretical calculation results,and the displacement experimental value is greater than the theoretical calculation value.(4)Select engineering examples from different regions in China,design corresponding variable stiffness shield tunnel linings according to their geological conditions,and analyze the stability and economy of variable stiffness shield tunnel linings under different geological conditions according to the requirements of current specifications,and compare them with equal stiffness shield tunnel linings.Determine the feasibility of variable stiffness shield tunnel linings in similar proj ects in the future.The results of the study are of great practical significance for the rational design of shield tunnel shield tunnel linings,and provide theoretical guidance and engineering reference for similar projects.