Yangtze River Tunnels (Chiangjiang Under-River Tunnel Project), China

In late 2008 the first tunnel of the Chiangjiang under-river tunnel project to cross the Yangtze River in China will be completed. The tunnel is the first of a twin-tunnel complex which will be fully completed by 2010 in time for the World Expro in Shanghai.

Each of the tunnels will be able to take three lanes of traffic and are 7.47km long, being tunnelled at depths of 65m under the river bed. They will have two levels with three-lane traffic above and services and safety facilities below with additional space for a metro. The tunnels are being constructed by the Shanghai Changjiang Tunnel & Bridge Construction Co Ltd and the Chinese partner Shanghai Tunnel Engineering Co Ltd (STEC).

The tunnelling is being carried out using one of the largest S-317 Mixshield tunnel boring machines (TBM) ever built. The TBM for the first tunnel, one of two for the project, has a diameter of 15.43m, total length of 135m and a total weight of 2,300t. It was constructed by Herrenknecht AG after a contract awarded in spring 2005 and was handed over to begin operations at the end of April 2006. The TBM was constructed in four months at a site in Shanghai Wuhaogou (Pudong), 6km from the tunnelling site.

The construction of the second identical TBM (S-318) for the second tunnel was started in the middle of 2006. The main drives, providing cutterhead power of 3,500kW and weighing 170t each, were fabricated in Germany and transported to Shanghai by ship. The tunnel project will employ 1,500 construction workers and is expected to cost in excess of $1.5bn.

THE PROJECT GOAL

Shanghai is a large industrial city and is short of space to accommodate the large number of workers resident in the city. The Chinese want to create one of their first eco cities in the middle of the Yangtze River Delta. The new city, called Dongtan, has been designed by Arup and is being developed by the Shanghai Development Company. The initial phases are expected to be completed by 2010.

The new city will incorporate every possible green technology to save energy and water. There will be waste and heat recycling, water treatment and communal heating/hot water systems. The amount of car traffic will be carefully controlled and limited to the periphery of the city.

The new city will be constructed on the island of Chongming which will be connected to the Changxing river island (600,000 residents) with a bridge. In turn, Changxing Island will be connected to the Shanghai mainland at Pudong by the two new 7.47km tunnels.

START OF TUNNELLING

The tunnelling with the S-317 was started in a 26m-deep launch tunnel on 6 September 2006 from Shanghai and breakthrough to the island is expected at the end of 2008.

The S-318 TBM began parallel tunnelling on 8 December 2006, with a distance between tunnel centre lines of 23m, and breakthrough is expected at the start of 2009.

The Mixshield machines work on the hydroshield principle and will have to withstand water pressures of 6.5bar and excavate a mixture of sand, clay, broken rock and groundwater (206,033kN thrust and 39,945kNm torque). The technology allows tools on the cutting wheel to be changed from within the shield at atmospheric pressure, with six cutting wheel arms accessible. This will mean that hazardous diving operations are not required.

The two machines will have to install a total of 7,500 lining segment rings for the two tunnels; each of the rings is made up of 11 segments, weighing up to 16t. The final interior diameter will be 13.7m. The two tunnels will require the disposal of 2.7 million cubic metres of earth by the time they are completed.