Swift EPBM makes its mark in Zhengzhou Apr 2011
Desiree Willis, Technical Writer, The Robbins Company
In Zhengzhou, China soft ground tunneling has made a speedy entrance. The metro's first TBM, one of two 6.3m diameter Robbins EPBMs for Zhengzhou's Line 1, achieved a project record of 720m (2,362ft) in one month.
Factory testing of the Zhengzhou EPBM

Factory testing of the Zhengzhou EPBM

Daily rates have been as high as 22 rings (33m or 108ft) in two 10-hour shifts. The rates are not only a project record amongst nine other machines, but also rank as some of the highest rates ever recorded for Chinese EPBMs in the 6-7m diameter range.
The Robbins machines were launched in November and December 2010, and have both achieved intermediate breakthroughs into a cut and cover station site, most recently on March 29, 2011. The TBMs entered the station box after excavating 1,300m through conditions that included soft, powdery soils, which are a benefit for swift tunnel boring.
"The breakthroughs went perfectly," said Zhou Shuqing, General Mechanical and Electrical Engineer for contractor CRCC, 11th Bureau.
"Machine downtime during tunneling has been minimal, and the organization of this project has been very good." Ground in later sections of the tunnels is expected to consist of clay, fine sand, loess, and some pebbles, with little groundwater.
Intermediate breakthrough celebrations

Intermediate breakthrough celebrations

Both EPBMs, for the 11th Bureau of the China Railway Construction Corp (CRCC), are excavating under downtown areas of Zhengzhou with cover as low as 8m for nearly half of the tunnel length. The 3.6km long parallel tunnels are passing through four intermediate stations between the Kaixuan and Tongbo areas of the city. All sections are expected to be completed by September 2011.
High advance rates are being achieved despite various challenges which included a section of tunnel just 7m (23ft) below Xi Liu Lake, and advancing very close to nearby building foundations and beneath a highway interchange bridge.
In order to reduce settlement, foam and bentonite are being injected for soil conditioning. Advance rates and the volume of muck extracted from the excavation chamber are being monitored closely to prevent subsidence.
Soft powdery soils made for speedy advance

Soft powdery soils made for speedy advance

Zhengzhou, a city of 7 million people, is planned to become a center for rail commerce in China. Up to four metro lines will be built in the city, while freight lines traveling between Beijing and Guangzhou (North-South), and between Xuzhou and Lanzhou (East-West), will eventually intersect in the city. Once completed, in 2013, Line 1 of Zhengzhou Metro will include 26km of tunnel and 22 stations. The Zhengzhou Metro company has invested Yuan 10.2 billion (US$1.5 billion or €1.1 billion) in the new metro lines to create a network that will total 18 km by 2015 and 2030.
Robbins EPBMs undercut downtown Zhengzhou - TunnelTalk, October 2010

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