Objective To ensure the operational safety of the existing station during the close-proximity under-crossing construction, it is necessary to study the settlement deformation characteristics of the station and the influence of construction parameters on the settlement.

Method Based on the project of a newly-built metro station in Nanjing in close proxi-mity to and under-crossing an existing metro station in water-rich sandy strata, this study is carried out through combining numerical simulation and field tests. Firstly, a numerical model of the under-crossing construction is established using Plaxis 3D finite element software. Then, the effects of excavation step length (1.0 m, 2.0 m, 3.0 m), initial support thickness (0.3 m, 0.4 m, 0.5 m), and temporary support removal length (5.0 m, 10.0 m, or complete removal) on the existing station structural settlement during the new mining method construction are analyzed, and the optimal construction parameters are determined. Finally, field measurements are conducted based on the model analysis. Monitoring points are deployed to track the law of vertical displacement of the existing station induced by the closely under-crossing construction, verifying the accuracy of the numerical model.

Result & Conclusion The vertical displacement of the existing structure shows a V-shaped distribution, and significant disturbance occurs within the range of 1.1 times the construction width of the overlapping section from the existing station central axis. Reducing the excavation step length and the temporary support removal length can effectively control the vertical displacement of the existing station, while the change in initial support thickness has a relatively small impact on the vertical displacement of the structure. Compared with an excavation step length of 3m, that of 1m can reduce the maximum vertical displacement of the structure by 63.6%. Finally, with reference to various specifications and considering factors such as construction space and construction economy, optimized construction parameters are proposed as follows: excavation step length (2.0 m), initial support thickness (0.3 m), and temporary support removal length (5.0 m).