Desiree Willis, Technical Writer, The Robbins Company

Powering up neighboring nations will get a bit easier with a new hydroelectric project in Laos. The hydro scheme on the Nam Theun River will include a 5.5km long headrace tunnel excavated using a Robbins shielded TBM. Contractor CMC di Ravenna has ordered a 7.6m diameter single shield machine from Robbins for the project and it is currently being assembled at the Robbins manufacturing facility in Solon, Ohio, ready for shipment in July 2009.

Location of the new project in Laos

The project will double the generating capacity of the current Theun Hinboun installation from 220MW to 440MW. The new station will draw water from the Nam Theun River, the largest tributary of the Mekong, and will work in conjunction with the existing Theun Hinboun power station built by CMC di Ravenna in 1998. Electricity from the plants will be sold to neighboring Thailand where current power supplies are struggling to meet demands.

The Robbins TBM has been designed for squeezing ground conditions and will feature an articulating cutterhead and overcutters capable of cutting 100mm beyond the nominal tunnel diameter. Ground conditions along the tunnel alignment comprise alternating strata of sandstone, siltstone, and mudstone. A precast concrete segmental lining of five segments and a key in each 280mm thick ring will line the tunnel to an internal diameter of 6.9m.

CMC di Ravenna will construct multiple structures on the project for owner Theun Hinboun Power Company, Ltd, a joint venture of the Laos Government, Norwegian contractor Statkraft, and GMS Power of Thailand. These structures will include a 1,000m starter tunnel and a 45m deep TBM reception shaft as well as a 65m high regulating dam about 20km upstream of the existing Theun Hinboun powerhouse; a new water intake; and a 1km long steel lined penstock.

The new station is scheduled for completion in 2012.