Numerical Simulation Study on the Impact of Foundation Pit Unloading on Adjacent Existing Subway Tunnels

Jian Xiong; Yahui Wang; Minjian Chen

doi:10.6919/ICJE.202410_10(10).0002

Authors

Jian Xiong
Yahui Wang
Minjian Chen

DOI:

https://doi.org/10.6919/ICJE.202410_10(10).0002

Keywords:

Foundation Pit Unloading; Adjacent Side; Existing Subway Tunnel; Numerical Simulation.

Abstract

To further explore the impact of new foundation pit unloading on adjacent subway tunnels in various regions, a study was conducted based on a foundation pit project in Shenzhen. A three-dimensional numerical model was created using MIDAS GTS NX finite element software to simulate the new foundation pit project and the adjacent subway tunnel. The deformation of the foundation pit support structure, the settlement of surrounding soil, and the deformation of the existing subway tunnel under different excavation conditions were analyzed and compared with actual monitoring data. The results show that during foundation pit construction, both the support structure's deformation and the surrounding soil's settlement were relatively minor. The pile-anchor support scheme effectively controlled the foundation pit's deformation. The maximum horizontal and vertical displacements of the adjacent subway tunnel, induced by foundation pit excavation, occurred near the pit's center and gradually decreased towards both sides. As the foundation pit's depth increased, the maximum horizontal and vertical displacements of the tunnel structure also increased. After the foundation pit was backfilled, the deformation gradually decreased but did not reduce to zero. The tunnel structure's maximum horizontal and vertical displacements were 2.03mm and 0.95mm, respectively. The impact of foundation pit excavation on the tunnel structure's horizontal displacement was more significant than on its vertical displacement, but foundation pit dewatering had a greater impact on the vertical displacement. Comparing the numerical simulation results with actual measurements, the overall deformation pattern of the subway tunnel was consistent with the simulation, and the actual displacement was smaller than the simulated results. The foundation pit unloading had minimal impact on the adjacent subway tunnel, ensuring its normal operation.

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