February 2010, saw contractor CMC di Ravenna launch the first ever TBM to be used in Laos. The 7.6m diameter Robbins Single Shield TBM is excavating a new 5.5km long 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 100mm beyond nominal tunnel diameter.
Ground along the tunnel alignment consists of alternating strata of sandstone, siltstone, and mudstone supported by a final lining of 280mm thick, pre-cast concrete segments in a 5+1 ring, to provide a 6.9m i.d.
The machine was assembled in Robbins Solon, Ohio, USA manufacturing facility and shipped to the jobsite along the Nam Theun River, the 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 20m per day, but expect to reach 30m per day as tunnelling progresses,” said Barbàra.
CMC di Ravenna is constructing the tunnel for project owner Theun Hinboun Power Company, Ltd.–a JV 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 220MW to 440MW. 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