Mechanical behavior of quasi-rectangular segmental tunnel linings: Further insights from full-scale ring tests

Compared with traditional circular shield tunnels and rectangular shield tunnels, quasi-rectangular shield tunnels have advantages in space efficiency, bearing capacity and applicability in urban areas. This new type of cross-section was first utilized in Ningbo Metro Line 3 in China, a full-scale ring test of corresponding lining structure was conducted to investigate the bearing mechanism of the structure preliminarily. In order to investigate the influence of segmental reinforcement, longitudinal joint position and shear bearing capacity of a T block on the mechanical behavior of a structure, two more full-scale ring tests are conducted. The failure process, structural convergence deformation, joint deformation and bolt strain of the lining structure are obtained. The bearing mechanism and robustness of the structure under unexpected circumstances are analyzed as well. The experimental results show that: (1) Optimization of segmental reinforcement and bolt position has little effect on the mechanical performance at elastic stage. (2) With the same joint configuration, an increase in the segmental reinforcement has a minor effect on the performance of the longitudinal joint. The robustness of the structure is not improved significantly either. (3) When the shear bearing capacity of the T block is guaranteed, the optimization of longitudinal joint bolt position can improve the mechanical performance of the structure significantly. When the overall rigidity of the structure is raised, the ultimate bearing capacity increases by 30% and the failure mode is ductile. As a conclusion, in order to increase the robustness and overall safety of a quasi-rectangular segmental tunnel lining, shear bearing capacity of T blocks should be strengthened to ensure that the segment would reach its bending moment bearing capacity first. The bolt hole of the positive moment joint should be moved inward while that of the negative moment joint should be moved outward as well.