The problem of shield tunnel uplift is a common issue in tunnel construction. Due to the decrease in shear stiffness at the joints between the rings, uplift is typically observed as bending and dislocation deformation at these joints. Existing modeling methods typically rely on the Euler-Bernoulli beam theory, only considering the bending effect while disregarding shear deformation. Furthermore, the constraints on the shield tail are often neglected in existing models. In this study, an improved theoretical model of tunnel floating is proposed. The constraint effect of the shield machine shell on the tunnel structure is considered using the structural forms of two finite long beams and one semi-infinite long beam. Furthermore, the Timoshenko beam theory is adopted, providing a more accurate description of tunnel deformation, including both the bending effect and shear deformation, than existing models. Meanwhile, the buoyancy force and stratum resistance are calculated in a nonlinear manner. A reliable method for calculating the shear stiffness correction factor is proposed to better determination of the calculation parameters. The proposed theoretical model is validated through five cases using site-monitored data. Its applicability and effectiveness are demonstrated. Furthermore, the influences of soil type, buried depth, and buoyancy force on the three key indicators of tunnel floating (i.e. the maximum uplift magnitude, the ring position with the fastest uplift race, and the ring position with the maximum uplift magnitude) are analyzed. The results indicate that the proposed model can provide a better understanding of the floating characteristics of the tunnel structure during construction.

Download PDF:

Keywords: Analytical solution, Conceptual model, Matrix transfer method, Shield tunnel, Timoshenko beam theory, Tunnel uplift