Big Wins for Robbins TBMs under High Cover

Jul 13, 2011

Construction site, general

Main Beam TBMs score Two World Record Advance Rates

At up to 1,400 m (4,600 ft) of cover and more than 10 hours from the nearest town, China’s West Qinling Mountains may not seem like the most hospitable site to build a rail tunnel. Two Robbins TBMs are turning that notion on its head, however, with world record advance rates in exceedingly difficult conditions. The first of two 10.2 m (33.5 ft) Main Beam Machines advanced 235 m (771 ft) in one week, and 841.8 m (2,761 ft) in one month during Spring 2011—rates much higher than any ever recorded for TBMs in the 10 to 11 m diameter range. The previous long-standing rates, from a Robbins machine at Chicago, USA’s TARP project, were for 185 m (607 ft) in one week and 685 m (2,247 ft) 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 Mr. Xu, Chief Engineer & Vice Project Manager 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 two parallel 16.6 km (10.3 mi) routes are just 40 m (130 ft) apart and are located approximately 1,000 m (3,280 ft) above sea level, about halfway up Qinling Mountain.
The record-breaking Left Line machine at West Qinling also broke through into an intermediate adit tunnel on May 28, 2011 at the 5.5 km (3.4 mi) mark, where it is now undergoing planned maintenance and inspection. Within several weeks the machine will be launched again to bore the rest of its tunnel.
Ground has consisted mainly of phyllite and limestone, often with high quartz content. Crews have also encountered fault zones of breccias and clay, as well as a 600 m (2,000 ft) long section of badly broken rock. Despite the conditions, only about 100 cutters have been changed on the Left Line machine so far. The Right Line machine, launched a month later and about 1,000 m (3,280 ft) behind, is also experiencing good cutter wear.
To combat the tough conditions, the machines have been specially designed with adaptable ground support systems that replaced the roof shield fingers in the L1 area. The new roof shield canopy contains mesh pockets, rather than fingers, for installation by workers under the safety of the shield structure. Other design aspects include improved ring beam building, separate roof and probe drills, and materials handling. “The ring beam erector and the segment hoist have been very successful. Overall, the machine is good,” said Mr. 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 820 km (500 mi) long scheme that will link the capital of Gansu Province (Lanzhou) with southwestern Chongqing, a mega-city of over 35 million people. The entire railway is expected to open to traffic in 2014.

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