Robbins Single Shield launched in Laos

The first TBM ever to excavate in Laos was launched in February. The 7.6m diameter Robbins Single Shield TBM will dig a new hydroelectric tunnel for the Theun Hinbourn Expansion Project, which will provide power to neighbouring Thailand.

Contractor CMC di Ravenna is constructing the 5.5km long tunnel for the project owner Theun Hinboun Power Company, a joint venture of the Laos Government, Norwegian contractor Statkraft, and GMS Power of 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 was 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, 280mm thick, pre-cast concrete segments will be used in a 5+1 arrangement, making a finished tunnel diameter of 6.9m.

The machine was assembled in Robbins Solon, Ohio, manufacturing facility and shipped to the jobsite along the Nam Theun River, largest tributary of the Mekong. Machine startup went smoothly, with no significant TBM or equipment problems.

“We are presently excavating at 20m per day, but expect to reach 30m per day as tunneling progresses,” said Barbàra.

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. Placement of reinforced concrete began in February.