ABSTRACT
With more metro lines built in Shanghai of China, there are increasing cases of new interchange stations being excavated in the close proximity of an existing station. The surrounding ground movement caused by soil removal and dewatering within the excavation enclosure pose great threat to the existing metro station in service, especially those parallel to the new excavation in soft strata. To date, few case studies about protection of existing metro station parallel to the adjacent deep excavation were reported in the literature. In this study, a deep excavation, which will serve as an interchange metro station of Shanghai suburban railway Jiamin line, is taken for a case study. This project faced a big challenge for protecting the adjacent existing metro station, because of the following major factors: (1) the new excavation was parallel to the existing metro station with a minimum distance of 4.4 m; (2) the depth of the new excavation was up to 29.3 m, far below the existing metro station with a burial depth of 17.205 m; (3) considering its great excavation depth, dewatering within the underlying confined aquifer had to be conducted during soil removal to prevent hydraulic failure. The field monitoring results showed that through a series of protection measures, including basal reinforcement, zoned excavation procedure, servo support and recharging confined aquifer, both the lateral deflections of retaining walls and surrounding ground movements were well-controlled throughout the construction; the existing metro station was rarely affected by the adjacent excavation. The experience obtained from this project can provide an effective reference for similar cases in the future.
