Numerical simulation study on influence of soft ground settlement on deformation of small diameter tunnel in Tianjin

Aiming at the problem of longitudinal deformation of existing drainage shield tunnels caused by settlement in soft strata, taking a drainage shield tunnel with an outer diameter of 3.5 m in the soft soil strata of Tianjin as the engineering case soil, a soft soil creep constitutive model is adopted. By establishing a 3D stratum-tunnel numerical model, the stratum settlement law after the completion of the drainage tunnel and its influence on the tunnel are studied, and the deformation differences of the drainage tunnel in full-pipe and empty-pipe states are further compared. The research results show that: (1) In the "tunnel + no inspection well" section, the surface and the tunnel as a whole show uniform settlement. When the stratum is consolidated for 100 years, the average surface settlement reaches about 0.27 m, and the maximum tunnel settlement reaches about 0.15 m. (2) In the "tunnel + with inspection well" section, the stratum shows uniform settlement, with the maximum settlement reaching about 0.31 m after 100 years of stratum consolidation; while the tunnel shows non-uniform settlement, with the maximum settlement reaching about 0.18 m after 100 years of consolidation. Obvious differential settlement occurs at the connection between the tunnel and the inspection well, reaching about 0.03 m and 0.07 m at 10 years and 100 years of stratum consolidation, respectively. (3) The settlement of the drainage tunnel in the full-pipe state increases significantly. When the stratum is consolidated for 100 years, the maximum settlement increases from 0.15 m in the empty-pipe state to 0.18 m, but the settlement trend remains unchanged, and the longitudinal curvature radius is almost the same as that in the empty-pipe state.