Robbins Single Shield Launched on Laotian Hydro Scheme

May 11, 2010

Country's first TBM will help power up neighboring nation: In early 2010, contractor CMC di Ravenna oversaw the launch of the first tunnel boring machine ever to excavate in Laos. The 7.6 m (25.1 ft) diameter Robbins Single Shield TBM is digging a new hydroelectric tunnel for the Theun Hinboun Expansion Project, which will provide power to neighboring Thailand.

"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 with overcutters makes the machine capable of excavating 100 mm beyond 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, 280 mm (11 in) thick, pre-cast concrete segments are being used in a 5+1 arrangement, making a finished tunnel diameter of 6.9 m (22.6 ft).

The machine was assembled in Robbins Solon, Ohio, USA manufacturing facility and shipped to the jobsite along the Nam Theun River, largest tributary of the Mekong. Machine startup went smoothly, with an experienced crew and no significant TBM or equipment problems. "We are presently excavating at 20 m per day, but expect to reach 30 m per day as tunneling progresses," said Barbàra.

CMC di Ravenna is constructing the 5.5 km (3.4 mi) 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 current scheme from 220 MW to 440 MW. The station will utilize water from the Nam Theun River, adding to current power supplies from the existing Theun Hinboun power station built by CMC di Ravenna in 1998.

Other recent progress at the site has included the initial phases of a new 70 m (230 ft) 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. Placement of reinforced concrete began in February 2010.


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