Two Main Beam TBMs launched in China

The first ever Robbins Main Beam TBMs with a redesigned ground support system replacing roof shield fingers were launched in the mountains of Gansu Province, China in June and July. The two 10.2m machines will bore the twin 16.6km West Qinling rail tunnels under high cover.

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.

Ground in the tunnels consists of 30 to 80 MPa UCS sandstone and phyllite rock beneath more than 1,400m 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. Robbins vice president Brian Khalighi said, “We believe this systematic use of mesh with roof bolts and steel straps will be adequate support for the geology.”

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, 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, were assembled at a local workshop and transported to the jobsites, where they were assembled on bridges spanning a deep valley. The first machine, for the Left Line, was launched at the end of June and has excavated over 100m after being walked through a 2km long adit tunnel. The second machine, for the Right Line, was launched on 17 July. The TBM tunnels are just 40m apart and are located approximately 1,000m 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 long scheme that will link the capital of Gansu Province with southwestern Chongqing, a mega-city of over 35 million people. The new railway, at a cost of USD 11.3bn, will shorten transport times from 17.5 hours to 6.5. The entire railway is expected to open to traffic in 2014.