The first of 15 TBMs started tunnelling last month on the 36.1km long twin-bore Line 3 on the Guangzhou metro, in southern China.
The refurbished Mixshield TBM is one of 11 Herrenknecht machines that will be used on Line 3. The majority of these were used on Line 2, completed last year, although four new machines were ordered for the project. Two new EPBMs ordered from Wirth and two slurry TBMs from Mitsubishi complete Line 3’s 15 machine line up.
Seventy per cent of the line is being built with the 6.3m diameter machines, to give a finished internal diameter of 5.4m. The rest of the line is being constructed with NATM.
Line 3 runs from the north of Guangzhou to the south, passing under three rivers, and through some difficult water-bearing ground. The top layer of ground is soft, made up of mostly sand and marl, above sedimentary rock, sandstone and silt. The machines are also expected to encounter veins of granite.
Ground freezing will be used near the station boxes, and some of the bigger buildings will require underpinning. Overburden ranges from 2m to 30m.
However, the engineers are confident in their machines. Ju Shi Jian, the senior engineer for the client, Guangzhou Metro, told T&TI that they should complete construction by the first half of 2005, ready for an operational start of June 2006. Consultant to Guangzhou metro is the Design Institute of Guangzhou Metro Corporation.
Guangzhou’s 18.5km long Line 1 was completed in 1999, while the 18.6km long Line 2 should be fully operational later this year.
An estimated US$6bn will be spent on Guangzhou’s metro system between 2003 and 2010, when 120km of tunnels will be built.
