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The Tokyo Tunnel - G-Cans

24 August 2010

Introduction
The Tokyo flood tunnels – G-Cans project started construction in 1992 and completed in 2004, about 12 years later. It was just in time to be tested in tyhoon 22 in 2004 when 14 families were reported to be affected instead of 236 families before the completion of the project. The tunnel collects water from Tokyo downtown district and discharge it into the Edogawa river.


The Tunnel
The tunnel is 10m in diameter and about 6.3 kilometers (four miles) long. It is buried 50 metre under the ground in the Tokyo suburbs.

It has 5 concrete silos, each having a diameter of about 32 metres and is about 70 metres tall.

The tunnel is connected to a gigantic water tank measuring about 78m width, 177m long and 25m tall (or 350,000 m3). The tank is propped by 59 numbers of gigantic pillar, each weighing about 500 tons. As the pillars look like those in ancient temples, some named this water tank “the underground temple of Tokyo”.

Connected to this water tank are series of water pump that have a total output of 14,000 hp or 10 MW. They can discharge flood water up to 200 m3 per second or one Olympic pool water in 10 seconds.

The Cost
Estimated to be about US 2.0 billion

The Volume
The tunnel can hold approximately 640,000 m3 of flood water.


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