New support system on West Qinling TBMs Jul 2010
Desiree Willis, Technical Writer, The Robbins Company
- Ground support has reached new heights in the mountains of Gansu Province, China. Two 10.2m (33.5ft) machines are the first ever Robbins main beam TBMs with a redesigned ground support system replacing roof shield fingers.
Redesigned ground support systems on the two Robbins TBMs
- The TBMs were launched in June and July 2010 to bore the twin 16.6km (10.3 mile) long West Qinling rail tunnels under high cover.
- The new roof shield canopy contains mesh pockets, rather than fingers, for installation of mesh by workers under the safety of the shield structure. Other design aspects include improved ring beam building, separate roof and probe drills, and more efficient materials handling.
- Ground in the tunnels consists of 30 to 80 MPa (4,300 to 11,600 psi) UCS sandstone and phyllite rock beneath more than 1,400m (4,600ft) of cover. The corresponding ground support program consists of continuous mesh and rock bolts, with either ring beams or steel straps, for the length of the tunnel.
Launch of the two 10.2m machines
- "We believe this systematic use of mesh with roof bolts and steel straps will be adequate support for the geology," said Brian Khalighi, Robbins Vice President, Kent, Washington, USA.
- Should extremely poor ground be encountered, the mesh pockets can be relatively easily modified to use the McNally Support System, patented by C&M McNally Engineering of Toronto, Ontario, Canada for exclusive use with Robbins TBMs. The McNally System utilizes steel or wood slats to provide continuous support along the roof area of the tunnel, protecting workers from falling rock.
- The two machines, for contractor China Railways 18th Bureau (Group) Co, were assembled at a local workshop and transported to the jobsites where they were assembled on bridges spanning a deep valley.
Assembly of the machine on Qinling Mountain
- The first machine was launched at the end of June and has excavated more than 100m (330ft) after being walked through a 2km adit tunnel.
- The second machine was launched on July 17. The TBM tunnels are just 40m apart and are located approximately 1,000m (3,280ft) above sea level, about halfway up Qinling Mountain.
- The parallel rail tunnels will be used for freight and will link the city of Longnan with the towns of Waina, Luotang and Fengxiang within Gansu Province. The West Qinling tunnels are part of the Chinese Government's Lanzhou to Chongqing Railway, a massive 820km scheme that will link the capital of Gansu Province, Lanzhou, with southwestern mega-city Chongqing, which has an urban population of more than 35 million people. The new railway, at a cost of US$11.3 billion, will shorten transport times from 17.5 hours to 6.5 hours and enable an annual freight capacity of 100 million metric tons. Trains will run on the double track lines at 160km/hr with a 50-train daily maximum. The entire railway is expected to open to traffic in 2014.
- Modern large diameter rock tunnels - TunnelTalk, April 2010
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