Abstract: Illegal temporary surface surcharge can induce additional ground stress, which may cause adverse effects or damage to the existing shield tunnel structure. However, current methods for predicting tunnel longitudinal responses to surface surcharge generally simplify the tunnel as an Euler-Bernoulli beam resting on Winkler foundation, which ignores the shearing deformation of shield tunnel and cannot consider effect of the burial depth on the coefficient of subgrade reaction. In this study, a new analytical method is developed to evaluate the existing shield tunnel deformation subjected to surface surcharge, considering the tunnel shearing effect and the burial depth of the tunnel. In the proposed method, the shield tunnel is treated as Timoshenko beam resting on Winkler foundation and the effect of burial depth of shield tunnel on the coefficient of subgrade reaction is considered. The effectiveness and feasibility of the proposed method is verified by a three-dimensional finite element analysis and measured data from a case. Parametric analysis indicates that a shallowly buried shield tunnel suffers large settlement when the distance between the load center and tunnel axis is relatively close. Increasing the equivalent bending stiffness and the coefficient of subgrade reaction would remarkably reduce tunnel settlement. The tunnel settlement was hardly sensitive to equivalent shear stiffness. However, increasing equivalent shear stiffness would significantly reduce the dislocation between the adjacent rings. In general, the proposed method will serve to be theory support for reasonably predicting the shield tunnel responses to surface surcharge.

Key words: surface surcharge, shield tunnel, theoretic analysis, deformation of tunnel