华北水利水电大学水利水电工程毕业设计外文翻译

DESIGN CONSIDERATIONS OF A HIGH ROCKFILL DAM

NAM NGUM 2 CFRD, LAO PDR

Ruedi Straubaar1, Eva van Gunsteren2 and Stephen Moll3

1Geotechnical and Dam Engineering Expert, Pöyry Energy Ltd. (formerly Electrowatt Engineering Ltd.)Hardturmstrasse 161, CH-8037 Zurich, Switzerland

E-mail: ruedi.straubhaar@

2 Project Engineer and Assistant Project Manager for Nam Ngum 2, Pöyry Energy Ltd. (formerly Electrowatt Engineering Ltd.) Hardturmstrasse 161, CH-8037 Zurich, Switzerland

E-mail: eva.van-gunsteren@

3 Dam Engineer, Pöyry Energy Ltd. (formerly Electrowatt Engineering Ltd.) Hardturmstrasse 161,CH-8037 Zurich, Switzerland

E-mail: stephen.moll@

Abstract: Nam Ngum 2 dam, a large concrete face rock fill dam (CFRD) of 182 m height, is under construction and impounding is scheduled to start at beginning of April 2010. The dam is situated in a narrow valley and founded on sedimentary rock of variable strength.

Dam design principles comprising dam zoning, face slab design and instrumentation are outlined. Foundation treatment including grouting

and measures below the plinth are presented. The properties of the available rockfill materials and their influence on the dam zoning are discussed.

Emphasis is given to the rockfill properties and placement procedures which influence dam behaviour during construction, impounding and operation.

Key words: CFRD, Rockfill, Face Slab, Instrumentation

1Nam Ngum 2 Hydropower Scheme

The Nam Ngum 2 (NN2) hydropower scheme is located on the Nam Ngum river in Lao PDR, about90 km north of the capital city of Vientiane and some 35 km upstream of the existing Nam Ngum 1dam and powerhouse. With an installed capacity of 615 MW, the project will produce energy for the Thai electricity grid. A significant component of the scheme is the 182 m high concrete face rock fill dam, with a volume of 9.5 M m3 and a crest length of 500 m. The dam will impound a reservoir with a volume of approximately 4.2 M m3.

Construction of the NN2 Project commenced in late 2005 and is scheduled for completion in the second half of 2010. Rock fill placement in the dam body commenced in January 2008, and will be finished in early November 2009. Face slab construction, which is divided into an upper and lower stage, commenced in December 2008 and will be

completed by beginning of April 2010, when impounding will begin. The reservoir will fill during one rainy season, enabling commissioning to take place during the second half of 2010.

2Considerations with respect to dam deformations

Concrete face rock fill dams are considered inherently safe for a wide range of weak and strong rock fill (Cooke 1991) and deformation of the rock fill is often assumed not being a governing concern provided the dam is well engineered and the dam foundation is of adequate quality. It is often assumed that dam settlements are a simple function of the dam height and that they are not likely to exceed 1 % of the compacted fill height with horizontal deformations less than 50 % of the settlements. Predictions are also often made based on laboratory tests and dam deformation analyses.

2.1 Rock fill testing performed for NN2 CFRD

For the construction of the NN2 dam quarried rock of sedimentary formations are available. The source material, consisting basically of sandstone and siltstone, has been investigated by drilling, quarry trials, laboratory testing and trial embankment construction. The essential tests are index property tests, compressive strength and basic friction angle tests. Tests were also performed on saturated specimen, which normally gives more representative lower values.