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The city is located on the southern bank of the Chang Jiang (Yangtze), but new areas are being developed on the northern bank.
The river which is around four km wide at the tunnel site is crossed by several bridges. A new link will cross the river at the location of a small flat island which is separated from the south bank by a narrow river arm. The connection includes a minor bridge (600 metre span) and a large diameter tunnel.
The bridge will span the narrow river arm between the island and the south bank. Under the main channel between the island and the north bank the river will be crossed in a tunnel. The tunnel will be 3,710 metres in length and have two tubes, each with three traffic lanes and utility and emergency escape galleries beneath the road deck.
Also, there will be cross tunnels connecting the two main tunnels. The tunnel tube will have an internal diameter of 13.3 metres and an external diameter of 14.5 metres. The ground conditions are challenging with soft alluvium strata under the river. The strata are mainly silt and fine sand. The tunnel has a maximum depth below the Yangtze mean water level of around 55 metres and the cover to the tunnel will be between 5.5 and 30 metres.
The tunnel will be bored with two large diameter slurry tunnel boring machines. At the design stage this size of TBMs has only been used in a couple of places around the world, and a couple of similar projects are in their initial stages. Certainly, the combination of large diameter, sub-aqueous tunnelling in soft soil conditions, as in Nanjing, is unique.
Torsten MølgaardSenior Project DirectorTel.: +45 56 40 28 89
Assistance in preparation of TBM specification
Nanjing Yangtze River Tunnel Co. Ltd.
Tunnel length 3.7 kmTwo slurry TBMs, diameter 14.5 metresSoft river depositsWater pressure: 5.5 bar