Influence of Deep Excavations on Nearby Existing Tunnels

In Shanghai, a number of new underground passages are being constructed, often requiring deep excavations. When the excavations are in the vicinity of existing tunnels, it is necessary to assess the influence of these excavations on existing tunnels such as displacements of the lining and additional loads on the lining. This paper presents a finite-element parametric study of tunnel behavior caused by nearby deep excavation. This study investigates the effects of several parameters that may affect the tunnel response. These parameters are: Relative position of the tunnel with respect to the excavation, tunnel diameter, excavation dimensions, and tunnel protection measures. The results reveal that the influence of the excavation on the underlying tunnel is significant in a range of ∼5 × excavation width measured along the tunnel axis; unloading further than 10 m away from the axis of the tunnel has little effect on the tunnel structure. Based on the study in this paper a better understanding of the interaction between deep excavations and tunnels will be obtained.