Performance Assessment of Shield Tunnel Damaged by Shield Shell Extrusion During Construction

A shield tunnel can be damaged by shield shell extrusions, such as shield tunnel floating, which may cause contact (even a squeezing action) between the shield tunnel and shield shell. To fully analyze this problem, a detailed 3D-finite element model (FEM) of a shield tunnel under the effect of a squeezing action in the shield tail, soil pressure, jacking force, and grouting pressure, was established by applying a plastic-damage constitutive model of concrete. A full-scale test of three segment rings was conducted, and the test results verified the feasibility of the constructed FEM. In this study, different squeezing positions and deflection angles of the shield shell were analyzed. The results indicated that the area squeezed by the shield shell experienced the most damage, and the tensile damage to a segment reduced gradually as the squeezing position approached the circumferential seam. The damage range gradually increased with the increase in deflection angle. The effect of the squeezing position of the shield shell on the bending moment was larger than the effect of the deflection angle on the bending moment. However, the effect of the squeezing position and that of the deflection angle on the shear force were the same.