Subway station construction ensuring safety of adjacent expressway

The Higashi Roppongi Station of the subway, Nanboku Line (Subway No.7) currently under construction in the center of Tokyo is a large-section cut-and-cover tunnel station, This station is constructed in extreme proximity to a double-deck elevated expressway where the traffic volume is heavy. Diaphragm walls were constructed as advance underground supports in a transverse direction to the tunnel before the excavation work started. Furthermore, a special method rarely employed for subway construction, a large scale submerged excavation method, was employed to ensure the safety of the expressway and conservation of the surrounding environment. This paper is a report on this special construction method and the result of analysis, prediction, and measurement of the effect on the expressway structure during the work.