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Record-setting headway under high overburden Jul 2011
Desiree Willis, Technical Writer, The Robbins Company
Mountains soar more than 1,400m (4,600ft) above the tunnel alignment where two Robbins gripper TBMs are making record advance through exceedingly difficult conditions.
West Qinling intermediate breakthrough

West Qinling intermediate breakthrough

The project site, high in China's West Qinling Mountains and about 10 hours from the nearest town, may not seem like the most hospitable site to build a railway tunnel but the reality is turning that notion on its head with two 10.2m (33.5ft) diameter rock TBMs advancing at rates much higher than any ever recorded for TBMs in the 10 to 11m diameter range. Peak rates of 235m (771ft) in one week, and 841.8m (2,761ft) in one month during Spring 2011 beat the previous long-standing rates for TBMs of this size set by a Robbins machine on Chicago's TARP project of the mid-1980s of 185m (607ft) in one week and 685m (2,247ft) in one month.
"The Robbins machines have a good performance, we are very happy with the weekly rates, and hope for even better monthly rates," said Chief Engineer and Vice Project Manager Xu Jinlin for contractor China Railway Tunnel Group Co. Ltd. (CRTG).
The 18th Bureau of CRTG is managing the Left Line Tunnel, while China Railway Construction Corporation (CRCC) is managing the Right Line Tunnel. The parallel 16.6km (10.3 mile) routes are just 40m apart and are located approximately 1,000m above sea level, about halfway up Qinling Mountain.
The 685m per month record-setter of its class

The 841.8m per month record-setter of its class

The record-breaking Left Line machine broke through into an intermediate adit on May 28, 2011 at the 5.5km mark. It is now undergoing planned maintenance and inspection before setting off on the remainder of the drive in several weeks' time.
Rock has consisted mainly of phyllite and limestone, often with high quartz content, with intermediate fault zones of breccia and clay. A 600m (2,000ft) section of badly broken rock was also encountered.
Despite the conditions, only about 100 cutters have been changed on the Left Line machine to date. The Right Line machine, launched a month later and running about 1,000m behind its twin, is also experiencing good cutter wear.
To combat the tough conditions, the machines have been designed specially with adaptable ground support systems that replaced the roof shield fingers. A new roof shield canopy contains mesh pockets, rather than fingers, for installation of support by workers under the safety of the shield structure.
Twin portals of the parallel mountain bore headings

Twin portals of the parallel mountain bore headings

Other design aspects include improved ring beam installation, separate rock bolting and probe drilling drills, and upgraded materials handling.
"The ring beam erector and the segment hoist have both performed very successfully. Overall, the machine is good," said Wang, Spare Parts Manager & Engineer for CRCC.
The West Qinling tunnels are part of the Chinese Government's Lanzhou to Chongqing Railway project, an extensive 820km (500 mile) long scheme that will link the capital of Gansu Province, Lanzhou, with Chongqing, the central China mega-city of more than 35 million people. The entire railway is expected to open in 2014.
References
Robbins consolidates presence in China - TunnelTalk, March 2011

           

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