Theoretical Analysis and Numerical Simulations for the Safe Clear Distance of a Shallow-Buried Twin-Shield Tunnel with Small Spacing

In the construction of a twin-shield tunnel in limited underground space, the design of the clear distance between the two lines needs to consider not only the safety issues related to the interaction during excavation but also the low-carbon effect, aiming to precisely shorten the distance and fully utilize the underground space, thus saving land resources. In this paper, the earth pressure patterns in a shallow-buried twin-shield tunnel with small spacing are clarified. Furthermore, based on the Mohr-Coulomb shear failure criterion of the middle bearing pillar, a theoretical decision model for safe clear distance in it, adaptable to different geological formations, is established. In addition, its accuracy is verified through numerical simulations. At last, the quantitative influence of various parameters on the safe clear distance is analyzed using the theoretical model. The results of the study offer a theoretical foundation for the design of a clear distance between a shallow-buried twin-shield tunnel with small spacing and the parameterized measurement of the ground reinforcement needed for its construction.