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Highlights • Model tests are conducted to study longitudinal bending behavior of shield tunnel subjected to longitudinal axial forces. • A regressed equation is obtained based on the model test results. • A modified longitudinal equivalent continuous model that incorporates longitudinal axial force is proposed. • The longitudinal bending stiffness efficiency is highly dependent on longitudinal axial forces. Abstract Longitudinal bending stiffness efficiency (LBSE) is a key parameter for analyzing longitudinal behavior of shield tunnel. The LBSE is defined as the deformation ratio of a uniform beam to the corresponding segmented non-uniform beam when subjected to the same load. Traditionally, the LBSE is treated as a constant, which can be evaluated by various longitudinal equivalent continuous models (LECMs). However, the effect of longitudinal axial forces (N) on the LBSE is often excluded. In this study, model tests are designed to investigate the LBSE subjected to longitudinal axial forces. The tests reveal that the LBSE is not a constant and it increases with the increasement of longitudinal axial forces. A regressed equation is obtained to revise the traditional LBSE based on the model test results. A modified LECM is proposed to calculate the LBSE, and the analytical results fit with the model tests well. The highlight of the proposed model is that the effect of longitudinal axial force is included. According to the analytical analysis, the LBSE is related to λ (=N · r /2 M), in which r is distance from segment rings' center to bolts, N is longitudinal axial force, and M is bending moment. When λ = 0, the modified LECM reduces to the Shiba-LECM. When λ increases from 0 to 1, the LBSE increases from Shiba-LECM result to 100%. When λ ≥ 1, the LBSE remains 100%. [ABSTRACT FROM AUTHOR]

It has been widely recognised that near-fault ground motions can be distinctly different from far-fault ground motions, in terms of their amplitudes and spectral characteristics, and there are a number of studies investigating the effects of near-fault ground motions on the structural response. However, only a few studies focus on underground tunnels, and most of them consider vertically incident seismic waves, neglecting the wave passage effect which is critical for long tunnels. This paper investigates the consequences of near-fault pulse-like ground motions on the seismic tunnel response, with an example of a tunnel embedded in saturated poroelastic soil. The input motions are represented by obliquely incident P1 waves, and the wave passage effect along the longitudinal direction is considered by a 2.5D modelling technique. The seismic tunnel response for near-fault pulse-like and far-fault ground motions is compared. Additionally, artificial ground motions, which have consistent acceleration response spectra with the near-fault pulse-like ground motions, but without velocity pulses, are generated to gain further insight into the contribution of velocity pulses. It is shown that the near-fault pulse-like ground motions can noticeably increase the tunnel internal forces, due to large seismic energy associated with the velocity pulses. For pulse-like ground motions with similar acceleration response spectra, the fling-step velocity pulse can be more detrimental to the tunnel than the forward-directivity velocity pulse. Moreover, the amplification effect of the near-fault pulse-like ground motions on the tunnel internal forces tends to be more prominent for large vertical angles of incidence, highlighting the significance of considering the oblique incidence case for seismic design. • Interaction of the tunnel and saturated poroelastic soil for obliquely incident seismic waves. • The longitudinal tunnel response due to the wave passage effect. • Near-fault pulse-like ground motions tend to increase internal forces in the tunnel lining. • Effects of forward-directivity and fling-step velocity pulses. • Influences of pulse-like ground motions are more prominent for large vertical angles of incidence. [ABSTRACT FROM AUTHOR]

Segmented tunnels are widely used nowadays. However, most existing studies on the seismic response of underground tunnels are based on the model of continuous linings, without considering the segment joints. This paper presents a numerical study aiming to investigate the factors that affect the seismic response of segmented tunnels, with a step further than previously, considering obliquely incident seismic waves. The numerical simulation is carried out by a 2.5D coupled finite element-boundary element (FE-BE) model, which can properly simulate the soil-tunnel interaction for obliquely incident seismic waves and predicts both the transverse and longitudinal seismic responses of the tunnel. It is shown that the joint distribution is one of the critical factors that determine the seismic responses of the segmented tunnel, and the influence of the segment joints tends to be more pronounced when they are located near the positions of large transverse bending moments in the tunnel lining. Compared with the homogeneous tunnel, the reduction in the transverse bending moment and axial force of the segmented tunnel is significant, while it is minor in the longitudinal bending moment and axial force, and the effect of the segment joints highly depends on the soil-tunnel relative stiffness. In addition, the influence of the spectral characteristics of the input motions on the tunnel responses is highlighted. • Dynamic soil-segmented tunnel interaction for 3D obliquely incident seismic waves. • The segment joints lead to smaller tunnel internal forces while larger deformations. • The effects of the segment joints on the tunnel longitudinal internal forces are small. • The effects of the segment joints highly depend the soil-tunnel relative stiffness. • Input motions with significant long-period spectral accelerations cause large tunnel responses. [ABSTRACT FROM AUTHOR]