Laos launches its first TBM
TBM Recorder Laos launches its first TBM Mar 2010
Desiree Willis, Technical Writer, The Robbins Company
A Robbins single shield TBM is the first TBM to be used in the country of Laos in Asia. The 7.6m diameter machine was launched in February by contractor CMC di Ravenna to excavate the 5.5km long headrace for the expansion of the Theun Hinboun hydroelectric scheme to provide power to neighboring Thailand.

The first ever TBM to be used in Laos

"We chose the single shield TBM based on ground conditions and the type of tunnel lining needed," said Luca Barbàra, Far East Manager for CMC di Ravenna. The Robbins TBM has been designed to accommodate moderate squeezing ground conditions. An articulating cutterhead fitted with overcutters makes the machine capable of excavating 100mm beyond the nominal tunnel diameter. Ground along the tunnel alignment consists of alternating strata of sandstone, siltstone, and mudstone. To support the ground and provide final lining, 280mm thick, pre-cast concrete segments are being used in a 5+1 arrangement for a finished i.d. of 6.9m.
The machine was assembled in the Robbins manufacturing facility in Solon, Ohio, USA before being shipped to the jobsite on the Nam Theun River, the largest tributary of the Mekong River. Machine startup by an experienced crew went smoothly, with no significant TBM or equipment problems. "We are presently excavating at about 20m/day, but expect to reach 30m/day as tunneling progresses," said Barbàra.
CMC di Ravenna is constructing the 5.5km long tunnel for project owner, Theun Hinboun Power Company, Ltd, a joint venture of the Laos Government, Norwegian contractor Statkraft, and GMS Power of Thailand. Once complete, the Theun Hinboun Expansion Project will double generating capacity of the existing Theun Hinboun power station scheme from 210 MW to 440 MW. The new contract brings CMC de Ravenna back to the Nam Theun region after building the existing power station in 1998. Other recent progress at the site has included the initial phases of a new 70m high reinforced concrete dam adjacent to the power station. Crews redirected the flow of the Nam Theun River through a diversion channel in preparation for dam building and placement of reinforced concrete began in February 2010.

Right: The 7.6m diameter TBM is designed for squeezing ground, with an articulating cutterhead and overcutters.


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