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As a discontinuous ring structure, segmental longitudinal joints are a weakness of shield tunnels and play an important role in the determination of tunnel deformation caused by ground pressure. A longitudinal joint bending test is first carried out by employing a detailed 3D numerical model for the Shanghai Metro tunnel. This reveals that the joint stiffness varies nonlinearly with the axial force and bending moment. Based on numerical results, an analytical model for determining the joint rotational stiffness is provided, which takes the influence of the mechanical behavior of the concrete and steel bolts, the geometrical dimensions of the joint cross section and the subjected loads into account. Then, a simplified fitting equation is proposed, which has been verified by the experimental test results. This reveals that the results obtained from the proposed fitting equation are in good agreement with the experimental results before the joint reaches the limit state. Therefore, this proposed equation can be preliminarily adopted for the simulation of joint bending behavior and the determination of tunnel deformation in the tunnel design stage. [ABSTRACT FROM AUTHOR]

Surcharge due to improper soil dumping and irregular backfilling often causes excessive deformation along the adjacent shallow tunnel in soft-soil areas. Tunnel structures are usually modelled with beam elements where the bending of the concrete segments is considered while the shearing dislocation between segmental rings is usually ignored. In this work, a Timoshenko beam was used to consider such dislocation of a shield tunnel under surcharge and a Pasternak foundation was used to account for the tunnel–soil shear effect. A numerical method was then developed to assess the effect of surcharge loading on the longitudinal responses of the underlying tunnel based on a two-stage method. The proposed solutions were verified using a case history from Shanghai and a three-dimensional numerical simulation from the literature. Results of a further parametric study showed that the deformation induced by surcharge loadings would be underestimated without the shearing-induced dislocation of tunnel segments, which could overpredict the serviceability of the underlying tunnel in surcharge accidents. [ABSTRACT FROM AUTHOR]