ABSTRACT
Constructed as part of the Osaka Municipal Subway No. 7 extension, Nishi-Nagahori Station crosses below an existing tunnel of Osaka Municipal Subway No. 5. Construction of a station in such circumstances would normally involve use of conventional underpinning techniques, whereby a drift would be excavated below the existing tunnel, and piles installed from within the drift to temporarily support the existing structure from below. In the case of construction of Nishi-Nagahori Station, various conditions, including the extremely small clearance between the two structures, dictated that such methods were unsuitable. A new technique known as the ‘Suspension Method’ was therefore developed, eliminating the need for such a drift. This paper reports on the design and construction results achieved using the method for this project.
