Design and Performance of a Deep Excavation Sharing a Common Wall with a Metro Station in Service

Substructures are always affected by soil unloading in adjacent deep excavation. However, the unloading effect can be reduced with rational design and construction schemes. This paper presents the design and performance of a deep excavation in Shanghai, China. The deep excavation is distinctive because it shares a retaining wall with an operating metro station with a length of 150 m. During construction, potential large heaves of the metro lines are expected due to unloading effect in the excavation. To reduce the unloading effect and protect the metro station in service, a temporary partition wall is constructed paralleling to the metro station with a distance of 18 m away from its external wall. Thus the whole excavation is divided into two independent pits and the dimensions of the small one are 18 m by 150 m. Therefore, the unloading effect on deformation of the metro station can be reduced and the metro station can be protected. To confirm the efficiency of this construction scheme and ensure the safety of the metro station, a comprehensive field monitoring program is conducted throughout the construction period. Deformation behaviors of both the supporting system and the metro lines are presented in this paper. Results show that the deformations of the supporting system are well controlled and the maximum uplift of the metro lines is only 15 mm, which is less than the allowable value, i.e. 20 mm.