After seven months of tunneling and more than 16 project records, two Robbins EPBMs working on the Guang-Fo metro project in China are pushing well ahead of schedule. The 6.3m diameter machines are running more than a month earlier than program and are on track for breakthroughs in August and October 2009, respectively.

16 records to their name since January

Records include a best month of 377m (1,235ft) - higher than any of the 16 TBMs that have worked on the Guang-Fo Metro Project. "The excavation speed of these machines has been praised by the project owner, Guangzhou Metro Company, many times," said Mr. Ju Yicheng, Vice Chief Project Engineer for contractor China Communication Construction Corp., 2nd Navigation Engineering Bureau Ltd. (CCCC). "We believe the high rates are a combination of fewer equipment breakdowns and efficient project management."

Ground conditions comprise weathered granite, coarse sand, and silt with operating earth pressures of up to 4 bar. Four independent foam injection points in the cutterhead are used to consolidate the face and create a smooth flow of muck in the mixed ground conditions. Active articulation systems have also allowed the machines to negotiate curves of 200m (820ft) radius with no ring deformation. Active articulation allows the front shield to adjust independently of the machine's thrust cylinders, applying even pressure to each ring in tight curves.

The Robbins EPBs are boring twin 2.6km long tunnels for the Guang-Fo line of the new metro, which will connect the neighboring cities of Guangzhou and Foshan. The line is part of the Chinese government's Inter-city Rapid Rail Project, which aims to link up nine cities in Guangdong Province, including Shenzhen and Dongguan, by 2015.

Desiree Willis, Technical Writer, The Robbins Company

Two Robbins EPBMs are on the project

Two 6.3m (20.5ft) diameter EPBMs are supplied by Robbins to China's first ever high-speed, intercity rail link. The first machine was launched in December to excavate Lot 12 of the Guangfo line that will shorten travel times between the cities of Guangzhou and Foshan to just 40 minutes. The second machine is now being dismantled in a local workshop for shipment, assembly and launch on a parallel tunnel in February. Assembly of both machines and their back-up systems is performed in Guangzhou under direction of the Robbins EPB Division.

The EPBs will bore parallel tunnels connecting the three stations of Jushu, Xilang, and Hedong. Starting from a common 16m (53ft) deep shaft, the twin tunnels will be excavated in two sections of a total linear length of 2.6km (1.6 miles).

Pearl River Delta cities

Both disc cutters and soft ground cutting tools will be used on the machines to bore through complex mixed-face, waterbearing geology including weathered rock, coarse sand, and silt at ground water pressures of up to 4 bar. As the machines advance, they will erect a precast concrete segmental lining of 300mm (12in) thick and with 5 segments and a key in each ring.

Tunneling is scheduled to be complete within the year. The 33km long (20 mile) Guangfo line with 21 stations is aligned all underground and is part of the Chinese government's Pearl River Delta Inter-City Rapid Rail Project that aims to link nine cities in Guangdong Province by 2015, including Guangzhou, Shenzhen and Dongguan.

www.RobbinsTBM.com

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