The first of two huge TBMs is set to start tunnelling beneath the Yangtse River in China at the beginning of next month.
The Herrenknecht S-317 Mixshield is, at 15.43m diameter, claimed to be the world's largest.
The slurry TBM will bore the first of two parallel 7.2km long three lane road tunnels to connect Shanghai with Changxing, an island in the Yangtse estuary. It will be joined in December by a second machine, the S-318, which will build the second tunnel 23m away.
Shanghai is expanding rapidly: it already has a population of 20M, and 500 new vehicles are registered each day, placing huge strain on its infrastructure.
The new tunnels will connect Changxing river island, which has a population of about 600,000, to the road traffic network. They are part of a five-year, Yuan12.3bn (£850M) project which also includes an 8.8km long bridge between Changxing and Chongming island - China's third largest - set for major new development (GE November 2004).
UK consultant Halcrow, which is part of the design team for the bridge, is also involved in the design of the 8.9km long tunnels, which include cut and cover approach sections.
Shanghai Tunnel Engineering and Rail Transit Design and Research Institute, Parsons Brinckerhoff (Asia) as well as the Third Harbor Engineering Investigation and Design Institute are also involved.
The Mixshields will tunnel to depths of 65m in soft ground with high groundwater pressures up to 6.5bar. The two machines will install a total of 7500 lining segment rings, each comprising 11 segments, and excavate a total of 2.7M. m 3 of material.
Weighing 2300t, the TBMs are 125m long and are being assembled in Shanghai Tunnel Engineering Company's factory in Shanghai Pudong before being taken to site.
To allow engineers to safely change tools at the cutting wheel during tunnelling, the six cutting wheel arms are accessible from within the shield under atmospheric pressure.
The fi st TBM is expected to arrive at Changxing island at the end of 2008 and the tunnels will be open to traffic in April 2010.