Effect of longitudinal joints on seismic response of the large shield tunnel in liquefiable soils

In view of the damages to shield tunnels in recent strong earthquakes, this paper focuses on the effect of longitudinal joints on the seismic response of the shield tunnel in liquefiable soils. First, the normal and shear behaviors of high-strength concrete interface at the joint were studied through direct shear tests under monotonic and cyclic loadings. The results show that the flatness rather than the roughness is the dominant factor influencing the behavior of the interface. As the confining stress and cyclic number increase, the total contact area increases, thus resulting in the increases of the normal stiffness and the friction coefficient. Based on the testing results, the seismic response of a shield tunnel in liquefiable soils was studied using numerical analysis. According to the results, the longitudinal joints have a significant effect on the seismic response of the shield tunnel. When neglecting the joints, the tensile stresses in concrete, the tunnel uplift and the surface deformation remarkably decrease, and the shield tunnel becomes less vulnerable to earthquakes. Due to the soil liquefaction, the joints located near the waist are more likely to get opened and corresponding bolts bear large tensile forces, which are the main reasons for the common damages to shield tunnels. Based on this experimental and numerical study, the effect of the joints and the seismic damages of the large shield tunnel are better understood, consisting an important step in the development of appropriate specifications for the seismic design of the large shield tunnel.