Deformation Response Research of the Existing Subway Tunnel Impacted by Adjacent Foundation Pit Excavation

Abstract

The excavation of foundation pits is one of the most important factors causing changes to the initial stress state of its surrounding soil, thus affecting the safety of nearby existing subway tunnels. In order to study the deformation in metro lines induced by adjacent foundation pit excavation, a three-dimensional model based on an actual engineering case was established, and the deformation regulations of the retaining wall, surrounding soil, and tunnels were investigated, which also validated the model’s feasibility. Additionally, the deformation and strain response of the subway tunnel under different selection parameters of the enclosing structure and soil were studied. The results showed that, after the foundation pit excavation, the soil inside the pit underwent an uplift, the surrounding soil outside of the pit showed vertical settlement, and the retaining wall created a deformation towards the interior of the pit. Mechanical parameters of plate elements have a small influence on the deformation of metro lines. Axial strain and maximum displacement of the subway tunnel increase with the increase in the soil’s Poisson’s ratio, and on the contrary, they decrease with the increase in the m-value and $G_{0,\mathrm{ref}}$ . The maximum responses of the subway tunnel came from changes to $G_{0,\mathrm{ref}}$ and $\upsilon$ . These analysis results can be used for the safety evaluation of subway tunnel operation, design, and construction in other similar engineering settings.