Abstract:

During foundation pit excavation, deformation often occurs to the tunnel lying underneath, as a result, the normal operation and safety of the Metro tunnel lying underneath cannot be guaranteed. In this paper, the influence of the excavation of foundation pit on the deformation of the underlying tunnel and the surrounding soil mass in complex ground is studied, and the influence of the variation of the ratio between the excavation width of the foundation pit and the diameter of the tunnel (L/D) and the influence of the variation of the ratio of the modulus of the complex ground (E2/E1) on the deformation of the soil mass and the tunnel are analyzed in detail, with the development of the underground space along the running tunnel from Mingfa Square Station to Nanjing South Railway Station on Line 3 of Nanjing Metro as an example. Conclusions drawn are as follows: 1) When L/D＜3, the rebound of the floor of the foundation pit and the deformation of the underlying tunnel increase as the excavation width of the foundation pit increases; when L/D≥3, the rebound of the floor of the foundation pit and the deformation of the underlying tunnel are not influenced by the excavation width of foundation pit; 2) When E2/E1＜8, the rebound of the floor of the foundation pit and the deformation of the underlying tunnel reduce dramatically as the ratio of the modulus of the complex ground increases; when E2/E1≥8, the rebound of the floor of the foundation pit and the deformation of the underlying tunnel are not influenced by the ratio of the modulus of the complex ground.

Key words: complex ground, foundation pit excavation, Metro tunnel, numerical analysis, deformation