The Metropolitan Area Outer Discharge Channel (MAODC) is the first underground river to be constructed in Japan, under National Highway Route 16, at 50 m deep from the surface. The tunnel with its finished diameter of 10.6 m is 6.3 km long and was constructed by the slurry shield method. Many innovative technologies were used in the construction, such as a new type of segment bearing internal pressure, an automated material transportation system and an automated segment erection system. This paper presents the special features of MAODC including design, construction, and the latest tunneling technologies.
MAODC is designed to eliminate flood damages caused by small- and medium-size rivers in the middle reaches of the Naka River and the Ayase River, which mn through the eastern part of Saitama Prefecture, Japan, as shown in Fig.1. The Naka/Ayase River basin is a low-lying area surrounded by the Edo River, the Tone River and the Ara River. As the discharge capacity in this basin is not enough, when it rains heavily, a wide area is flooded and does not dry for a long time. Moreover, this area has recently become heavily urbanized, so many houses are damaged when flooding occurs. Therefore, a comprehensive flood control project has long been needed in this area and rapid completion of the project is expected. MAODC consists of a tunnel, five shafts, a pressure adjustment reservoir and a pump station as shown in Fig.2. When the rivers rise due to a storm, water flows over the crest of weirs at each intake structure, flows through the tunnel and is pumped out at 200 mTsec to the Edo River at the pump station. The tunnel is constructed under National Highway Route 16 at 50 m deep from the surface, to expedite project completion.
