ABSTRACT
In the underground section of about 2 km long in the Tokyu Toyoko Line, a triple-spectacle-shape tunnel was constructed by shotcreting method in 210m section around Tammachi Station. There are few similar examples to refer to design, and thus planning was performed using FEM analysis. In construction planning, attention was given to the treatment of confined groundwater, measures for face stability and settlement prevention. Methods of excavation that would not cause unsymmetrical earth pressure were considered. A monitoring system that can automatically observe and plot data such as track settlement and ground behavior was introduced for the safety of ongoing train operations. On the 55 m long section of tunnel that has the mushroom cross section, monitored results has fully reflected into primary design and excavation steps. This paper describes the series of technical matters from geological investigations, the design and observational construction in the triple-spectacle-shape tunnel.
