Abstract: To study the influence of the unloading loading process of the deep excavation on the underlying shielded tunnel, the Midas GTS NX is used to establish a three-dimensional numerical analysis model of the shielded tunnel and the deep excavation in a subway construction project near Beijing. The numerical simulation is performed based on the specific engineering geological characteristics, geotechnical parameters, excavation support type etc. The analytical results indicate that, the distribution patterns of the displacement and stress of the shielded tunnel by the ratio k of the distance from the bottom of the excavation to the centerline of the tunnel and the diameter of the tunnel during the unloading-loading construction process of the excavation are analyzed. The results show that: the excavation unloading loading construction has little effect on the stress of the underlying shielded tunnel, but it has great effect on the deformation of the top of the underlying shielded tunnel and changing the distance between the bottom of the excavation. The horizontal axis of the underlying shielded tunnel can effectively slow down the deformation of the shielded tunnel during the construction. The k is in the range of 4.0-4.5 has little effect on the displacement of the tunnel.

Key words: Deep Excavation, Tunnel Deformation, Unloading Loading, Finite Element Model, Time History Analysis