This exercise presents a detailed numerical study using PLAXIS 2D for the analysis of a braced excavation carried out above an existing tunnel as part of an urban metro construction project. The primary objective is to model and evaluate the construction of a cross-passage situated directly over a newly built tunnel, considering the complex interaction between the staged excavation, temporary support elements, and the underlying tunnel lining system.

The analysis captures the challenges inherent to deep excavations in urban environments, such as ground movement control, potential tunnel deformation, groundwater management, and structural loading from nearby surface infrastructure. A braced excavation support system, composed of soldier piles, struts, and cross-lot elements, is employed to minimize ground deformation and ensure the stability of the excavation during all construction phases.

The modelling approach includes the simulation of soil improvement through injection above the tunnel crown, staged construction of the braced excavation, and the sequential construction of the cross-passage.