A study on the mechanical behavior of super-large diameter shield tunnels under segment removal

Purpose This study aims to investigate the deformation and cracking behavior during the opening construction process of cross-passages in super-large diameter shield tunnels. Design/methodology/approach This study first validates the accuracy of the numerical simulation model through comparison with full-scale experimental results. Subsequently, a simulation of the tunnel opening process is conducted, considering five key construction stages: initial condition, pre-support, segment removal, cast-in-place ring beam construction and support dismantling. Findings The segment removal phase is further refined to reflect the actual engineering process of segmental dismantling via static water drilling and cutting. Simulation results show that in the pre-support stage, the internal support system helps the main tunnel share the soil and water pressures, effectively reducing the overall deformation of the segment structure. During the segment removal phase, the tunnel opening experiences two cantilever effects – once during the half-ring segment removal and again during the full-ring segment removal – leading to load transfer, significant displacement and deformation, as well as cracking and failure in the tunnel lining structure. The maximum displacement occurs at the arch waist of the tunnel near the opening. Misalignments are mainly concentrated in the three central segment rings near the opening, with both longitudinal and circumferential joint misalignments peaking at the 225°arch foot of the backrest in the tunnel. Numerous cracks appear and rapidly develop along the outer arc of the opening, as well as the inner arc surfaces at the arch crown and arch bottom. In the support dismantling stage, even with the reinforcement of the cast-in-place ring beam, the tunnel structure cannot be ensured safe. As the internal support is dismantled, cracks begin to penetrate the concrete lining, with the largest crack located at the waist of the ring beam. Originality/value Utilizing Diana finite element software for numerical simulations, solid tunnel segments were modeled to simulate the process of removing concrete segments at the opening of a super-large diameter shield tunnel constructed using the mining method, with reinforcement provided by cast-in-place ring beams. The segmented cutting and removal process was refined, and the deformation and lining cracking failure of the shield tunnel during this process were analyzed.