Shinagawa drive exceeds rate expectations

Excavation rates on the tunnel portion of the Shinagawa section of the Central Circular Route of the Tokyo Metropolitan Expressway in Japan hit 550m in April, a Metropolitan Expressway Company (MEX) spokesperson told T&T yesterday. This exceeded the already high target rate of 400m per month.

“To reach and exceed this goal, we adopted several innovations to reduce the cycle time of excavation,” said the spokesperson. “The system that enables the assembly of segments during excavation was used, rather than the conventional method, in which the segments are generally assembled after excavation. Also, segments of the greatest previously used width, 2m, were employed.

“Another challenge was the construction of large-section shield tunnel with a diameter of 12.3m and an excavation length of 8km. To achieve large-section and long-distance excavation, a large-scale cutter bit was used to eliminate the need to change the bit during excavation.

“However, in the case that the cutter bit must be changed, it can be switched at any time using the ‘relay bit method’.”

The 12.3m od, 11.5m id, 8km long drive for MEX was contracted to Kajima. A 12.55m Kawasaki EPB shield machine was selected for the project due to its minimal environmental impact and previous successful use. As T&T went to press the machine had been driven 4.5km through mudstone in the Kazusa Group that was found to be stiff and stable.

Shinagawa project manager for Kajima, Masami Moriguchi said, “Constructing a large-diameter tunnel in a densely popular area is not uncommon in Japan, though on this project total excavated volume is around 1M cubic metres, the same as a medium-sized earth dam. That’s a lot of muck!”

Moriguichi previously worked on the 6km 79th Street water tunnel project in Chicago, Illinois, US and the Yoyogi tunnel on the Central Circular Route, Shinjuku section.

Tunnelling work on the Shinagawa section of the Central Circular Route was made the joint responsibility of MEX and the Tokyo Metropolitan Government (TMG). TMG had to excavate a 5.8km section.

Work began on the JPY 400bn (USD 4.9bn) project in 2005 and will be finished in 2013. Other ongoing works as T&T went to press included the connection to link the existing Central Circular Route Shinjuku section with the under construction Shinagawa section, an open cut excavation. MEX also told T&T that thankfully there was no structural damage due to the 2011 Tohoku earthquake.