Robbins EPBs undercut Downtown Zhengzhou

Dec 10, 2010

Dual TBMs hollow out New Metro under Low Cover

Zhengzhou, a city of 7 million people, is set to become a crossroads for rail commerce in China. The country's future main routes, traveling between Beijing and Guangzhou (North-South), and between Xuzhou and Lanzhou (East-West), will intersect in the city. The plan includes up to four rail lines in Zhengzhou itself, which will eventually link up to the national lines. Excavation of Zhengzhou Metro's new Line 1 tunnels began on September 28, 2010 when the first of two 6.3 m (20.7 ft) diameter Robbins EPBs was launched from a 16 m (52 ft) deep shaft.
The second machine is scheduled for a launch in late October. Both TBMs, for the 11th Bureau of the China Railway Construction Corp. (CRCC), will excavate under downtown Zhengzhou with cover as low as 8 m (26 ft). The parallel 3.6 km (2.2 mi) tunnels will pass through four intermediate stations between the Kaixuan and Tongbo areas of the city. The ground is expected to consist of clay, fine sand, loess, and some pebbles, with little groundwater.
"The most critical issue for this project is passing under Xi Liu Lake, a large body of water with a depth of 1.0 to 2.0 m (3.2 to 6.6 ft). The distance between the bottom of this lake and the top of the tunnel is just 7.0 m (23 ft)," said Steven Zhu, Robbins Project Manager. The tunnel will also pass beneath building foundations and a highway interchange bridge. In order to reduce settlement, foam and bentonite will be injected for soil conditioning. The advance rate and the material removed will be continuously and closely monitored to prevent subsidence.
As the machines bore, they will line the tunnel with 300 mm (12 in) thick concrete segments in a 5+1 arrangement. Curves with radii as small as 200 m (656 ft) will be negotiated using active articulation to prevent segment deformation. Line 1 of Zhengzhou Metro will consist of 26 km (16 mi) of tunnel and 22 stations once complete in 2013. The Zhengzhou Metro company has invested 10.2 billion Yuan in the six rail lines, which will total 188 km (117 mi) by their completion between 2015 and 2030.

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