Seven Dynapac rollers were used on the Nam Theun 2 dam project—one of the world's largest hydroelectric dam designs. Located in the central highlands of Laos, the $1.25 billion project features a 39-meter-high roller-compacted concrete (RCC) dam, which will produce electricity for the neighboring areas, including Thailand.
The entire project will include a 436-meter-long concrete gravity structure, spillway, 13 smaller earth-saddle dams, headrace channels, and roadworks. Together 450 square kilometers of reservoir space will be created to flood the Nakai Plateau.
Contractor Italian-Thai Development, Bangkok, Thailand, is using four Dynapac machines—two large articulated tandem rollers, CC422 and CC421, and two small CC102 steel-and-rubber drum units—to compact the layers of concrete atop the dam crest.
“Italian-Thai Development wanted the flexibility that the different sizes offer,” says Anucha Burapachaisri, director of Dynapac's Thai distributor MEC Group. “The large machines, of course, do the bulk of the work, but the CC102s are here being used to complement them by compacting cross-joints and in the restricted corner spaces.”
The dam's design calls for a continuous supply of stiff, zero-slump concrete and damp gravel mixed with local aggregate, portland cement, and water. The mix is placed in layers 30 centimeters thick, followed by two to four passes by the Dynapac rollers. A fine water mist then is applied to cure the concrete.
In one eight-hour shift, a complete 30-centimeter-thick, 150-square-meter layer is laid on the crest from each abutment to accommodate the number and size of machines needed on the project.
An additional three rollers are compacting the 145 kilometers of access roads to the jobsite and roads around the saddle dams. Two Dynapac CA252D smooth-drum compactors are used to grade, compact, and maintain these areas because of the machine's ability to work with clay and loam—soil found in heavily forested hills. The third and last CA252D roller is concentrating work on a substation transformer site on the banks of the Mekong River.
Designers Klohn Crippen Berger, Vancouver, British Columbia, Canada, recommended a RCC dam and integral spillway over other alternatives such as a concrete face rockfill. This is due to the lesser volume of materials that would be needed to construct the dam and the speed in which it could be built. Speed was key on this project not only because it saved money, but because the Nam Theun river area floods throughout the year.