Prediction of the additional structural response of segmental tunnel linings induced by asymmetric jack thrusts

Abstract

When a shield machine moves along a curved alignment or corrects a deviation, the asymmetric thrust of the propulsion cylinder generates an additional bending moment at the front end of the tunnel. This yielding moment causes the longitudinal deformation of the tunnel, the dislocation between adjacent segmental rings, and other structural defects. However, the related mechanism is far from deeply understood. Thus, this paper reports a case study of shield tunneling along a curved alignment. To this end, an analytical model for calculating the additional response of the segmental lining under asymmetric thrusts was established, where the shield tunnel was simplified to a Timoshenko beam on Winkler’s foundation. Then, the performance of the analytical model was verified via convincing numerical simulations, and an in-depth sensitivity analysis was conducted to explore the effect of the critical parameters. Subsequently, the action range of the additional bending moment and the influence of the heterogeneity of the ground caused by the shield tail grouting on the performance of the tunnel were discussed. The research results demonstrate that the proposed analytical model is reliable and applicable to calculating the additional responses of the segmental lining subjected to asymmetric thrusts. Compared with the stiffness of the foundation, the shear stiffness of the shield tunnel affects the structural behavior of the tunnel more notably. The impact of the additional bending moment is classified under two stages due to the nonlinearity of the equivalent bending stiffness of the tunnel caused by the longitudinal axial force. The action range of the additional bending moment decreases nonlinearly with increasing the stiffness of the foundation and the shear stiffness of the tunnel. When the longitudinal inhomogeneity in the stiffness of the foundation caused by the shield tail grouting is considered, the shear force on the tunnel and the dislocation between neighboring rings increase remarkably.