Settlement Response of Existing Metro Tunnels Induced by Parallel Symmetric Shield Tunneling: A Model Test Study

Parallel shield tunneling in close proximity to existing metro tunnels induces additional settlement deformation of existing structures, which poses a challenge to operational safety. In this paper, a self-developed Φ200 mm model shield machine test system is adopted to carry out model test research on the settlement response of existing tunnels induced by parallel symmetric shield tunneling. A 1:30-scaled 3D-printed refined assembled segment model is fabricated based on similarity theory, and high-precision distributed optical fiber sensing technology is used for deformation monitoring. The influences of vertical spacing of tunnels, center spacing of new tunnels, axis angle and stratum loss rate on the settlement of existing tunnels are analyzed. The results show that the settlement curve of the existing tunnel arch presents a normal distribution shape, and the maximum settlement occurs near the new tunnel side. The settlement of existing tunnels decreases with the increase in vertical spacing between new and existing tunnels, and increases with the increase in stratum loss rate and center spacing of new tunnels. The research results can provide experimental support for safety control of parallel shield tunnel construction.