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Client: International Design-Build Construction Consortium, Thailand / Japan
Location: Laos, Southeast Asia
Completion Date: Ongoing
Capital Cost: Over $1.0 Billion US
Project Highlights: Bid & Final Design Services for the Two Main Civil Works Packages. KC will also be providing construction services starting 2005.
The Nam Theun 2 Hydroelectric Project is the most important project in a long-term collaborative effort between the Lao People’s Democratic Republic (Laos) and Thailand to develop up to 3000
MW of hydropower energy in Laos for export to Thailand. The Nam Theun River, a major tributary of the Mekong River, is situated on the Nakai plateau between the Mekong River (the Lao-Thai border) and the Annamite Mountains delineating the eastern border of Laos with Vietnam. The
project entails a trans-basin diversion of waters from the Nam Theun River to the Project’s powerhouse located at the base of the Nakai escarpment and from there to the Xe Bang Fai
River, another tributary of the Mekong.
Klohn Crippen (KC) has been involved with the Nam Theun 2 Project since the mid 1990’s when we first evaluated the project layout and recommended a RCC dam and integral spillway rather than
a concrete face rockfill dam and separate spillway. Subsequently, KC carried out value engineering reviews and site investigations and preliminary design for the RCC dam layout.
In March 2002 the project development company, the Nam Theun 2 Power Company Ltd. (NTPC), led by Electricte de France (EDF) proceeded with project implementation by calling for
competitive Design-Build tenders. The tender call was structured into three civil works packages (CW1, CW2 & CW3) and two electrical-mechanical work packages (EM1 & EM2).
KC was retained by an International Design-Build Construction Consortium for bid design engineering of the two main civil works packages comprising the hydro facilities; namely, CW1 and
CW2. The D-B Consortium used KC’s bid design to successfully bid these two civil works packages. KC commenced final design services for the advance construction works in April 2004 in order
to meet schedule constraints. KC’s main final design effort will commence in late 2004 and continue until early 2006. Project in-service is 2009.
Work Package CW1 includes the roller compacted concrete (RCC) Nakai Dam structure and integral reinforced concrete spillway structure, the diversion tunnel, upstream and downstream RCC cofferdams, 10 saddle dams (4
of which are major earth structures), site access and the headrace channel. The CW1 package earthworks are very extensive, including over 4.2 million cu.m. of excavation for the headrace
channel and over 0.5 million cu.m. of earth embankment design associated with the reservoir saddle dams.
The construction planning for the main dam and diversion system was problematic as the annual Nam Theun flood is very large and could not be accommodated for the diversion design. Consequently, KC devised an innovative diversion scheme that has the construction of the Nakai
Dam being done based on dry-season windows over three years with the site area being flooded during the wet seasons. Using RCC construction for the main dam and both the upstream and downstream cofferdams provided the ability to overtop these structures, without failing, during
the wet season. If RCC construction were not employed, it would have meant a requirement for a much larger capacity and higher cost diversion system. This would undoubtedly have impacted overall project economics.
Work Package CW2 includes the intake structure, intake gates, headrace tunnel, surge shaft, pressure shaft, pressure tunnel, penstock tunnel, units’ manifold, the main powerhouse and
adjoining pelton units powerhouse, the tailrace and associated powerhouse area buildings and other civil structures. The underground works for Work Package CW2 are large in scale and
complex in design. This is especially true for the pressure shaft, pressure tunnel and penstock tunnel sections of the conveyance system where the normal pressure head is over 350 m (not incl.
transients). The steel lined portions require massive steel cans of considerable thickness. The steel manifold is a double bifurcation structure with critical support and pressure design requirements.
The low pressure headrace tunnel is a large diameter structure that is fully concrete lined.
The power from Nam Theun 2 will be supplied to Thailand under a Power Purchase Agreement (PPA) that NTPC negotiated with the Government of Thailand through the state utility the Electricity Generating Authority of Thailand (EGAT).
Services:
- Site investigations
- Preliminary design
- Final design
- Value engineering reviews
- Bid design
- Construction services (2005)
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