The first of the pair of 15.43m diameter TBMs – the world’s largest – excavating road tunnels below the Yangtze river, at Changxing Island near Shanghai, has holed through some months ahead of schedule.
Excavation of the twin tunnels commenced in September 2006 and by January last year both of Herrenknecht’s Mixshields were in the ground. Previously, the first machine (S-317) was expected to reach its target shaft on Changxing Island towards the end of this year. However, the shield holed through on 21 May some 20 months after commencing its drive.
Geology along the alignment of the tunnels, which are spaced 23m between centres, comprises sand, clay and rubble. Starting at an excavation depth of 26m below the river, the machines reached a maximum depth of 65m when boring the 7.17km long tubes.
The second Mixshield (S-318) was launched three months after the first machine and if the lag remains then it may breakthrough at its target shaft on Chanxing Island in or before August.
The tunnels are being built by Shanghai Changjiang Tunnel & Bridge Construction Development co Ltd to link Chanxing Island, in the Yangtze, with the mainland at Pudong. The tunnels are part of a larger transport project to link Pudong with another river island – Chongming.
The tubes will be fitted as double decked, the upper level of each tunnel taking a three lane road while the lower level provides space for service and safety installations, and possibly a future metro line.
Breakthrough at the Yangtze Breakthrough at the Yangtze
