Abstract: In order to study the deformation with time of the tunnel structure and surrounding soil on the adjacent subway shielded section tunnel induced by the excavation and unloading of a deep foundation pit in soft soils, the excavation control measures are necessary. This paper presents the case history of a deep excavation construction adjacent to the Metro Line 4 in Nanchang City. A commercial threedimensional finite element software was used to establish the numerical analysis model. The entire excavation process was numerically simulated. The impact of the deformation of the excavation supporting structure and the surrounding soil on the safe operation of the subway was evaluated. The results show that, with the increase of the excavation depth at the foundation pit, the greater the deformations at the adjacent ground surface, bottom of the excavated area, at the surrounding supporting structures and at the shielded subway tunnel structure. The deformation monitoring should be focused on the horizontal deformation of the tunnel segments. During the excavation, the measures such as stepwise and block excavation should be adopted to reduce the impact on the adjacent tunnel in active operation.

Key words: deep excavations in soft soils, subway tunnels, numerical simulations, deformation with time, risk control