Abstract
Subway tunnels are mostly located in strata with an uneven pressure. This uneven pressure is usually manifested by lateral pressure coefficients less than 1. To adapt to the unevenness of the stratum load, in this study, we propose a new shield tunnel lining structure—outer circle and inner ellipse shield tunnel lining structure—whose outer contour remains circular and the inner contour shape of the structure is designed according to the load conditions. We used the stiffness step discounting method to obtain the calculation coefficients used in the force method formulas and established the calculation model of the outer circle and inner ellipse shield tunnel linings. The force method was then used to determine the force distribution characteristics of the outer circle and inner ellipse shield tunnel lining structure. During the verification, it was sufficient to analyze whether the waist structure rigidity met the safety conditions. This simplifies the design elements. The internal space area of our proposed design is expanded by 0.86 m2 compared to the internal space area of the equal stiffness shield tunnel lining design.
Highlights
Shield tunnel linings have been widely used in urban subway tunnel construction. e thickness and shape of the linings are two important design factors influencing the safety of the tunnel and have a considerable impact on the project cost
Chen et al [2, 3], studied an acceptable shield tunnel lining thickness for a large-diameter highway tunnel located in the plateau region. ey found that a change in the thickness of the shield tunnel lining has a small effect on the axial force of the shield tunnel lining structure and that an increase in the lining thickness results in an increase in the bending moment of the shield tunnel lining structure
There are still shortcomings in the results of numerous studies: (1) scholars have studied in-depth the effect of reducing the thickness of the shield tunnel linings on the structure, but the object of their study was still a structure of equal stiffness with uniform thickness, and the effect of ground load was not taken into account; (2) some scholars conducted studies on variable-section lining structures, but there are few published studies on this aspect, and there is a lack of relevant theoretical studies. erefore, in this study, when the lateral pressure coefficient is less than 1, we propose an outer circular inner elliptical shield tunnel lining with a circular outer profile
Summary
Shield tunnel linings have been widely used in urban subway tunnel construction. e thickness and shape of the linings are two important design factors influencing the safety of the tunnel and have a considerable impact on the project cost. Huang et al [6] studied the effect of shield tunnel lining thickness on structural forces using model tests. E change in the bending moment value is the most significant, and a larger shield tunnel lining thickness will result in a larger bending internal force and a reduction in the structural deformation capacity. They concluded that additional lining thickness may not benefit the structure itself and will only cause a waste of the material. Ji [14] studied the building limits and structural mechanical characteristics of rectangular shield tunnel linings and proposed rectangular variable section shield tunnel linings. All the above results were compared with those of the equal-rigidity shield tunnel linings when the loading conditions are same to draw relevant conclusions
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