Spotlight on RCC17 January 2013
Ted Warren highlights some major RCC projects worldwide and explains what he thinks are the essential ingredients for building a successful project.
Although there have been many applications of a dry mixed zero slump concrete dating back to as early as the 1970s, one of the first applications of RCC for use in the construction of a dam was for an emergency backfill operation of the newly constructed Tarbela dam on the River Indus in Pakistan. Other dams also being designed and constructed included Willow Creek RCC dam, completed in 1983 by the US Army Corps of Engineers. Until 1990 RCC dams were limited in height to generally under 100m but after that time we started to see these dams approaching 150m. A decade later dams like the 188m Miel dam and the 155m tall Ralco dam in Chile were successfully being designed and built in extremely difficult natural terrain and extreme weather conditions. Both of these dams were a substantial achievement for that time as they were the two tallest RCC dams in the world when completed in 2002 and 2004 respectively. It became apparent to dam engineers around the world that RCC dams could be built successfully to heights that rivaled many tall thin arched conventional concrete dams, CVC gravity dams and CFRDs.
Four of the tallest RCC dams currently under construction include:
- Diamer Basher dam on the Indus River - the dam will be 272m high and construction began in 2010.
- Gibe III on the Omo River. Construction started here in 2008 and the dam will be 249m high.
- Bunji dam on the Indus River. The structure will stand 190m high and construction began in 2011.
- Dasu dam, also on the Indus River. Construction began in 2011 to build a 190m high structure.
- Grand Ethiopian Renaissance Dam on the Blue Nile. Once complete the dam will stand 145m tall. Construction began in 2011.
The above examples illustrate the development of RCC dams and the relative size of projects over the last 40 years. It should be noted that these dams will be in the top ten tallest of all dams, of all types, and largest by volume of concrete. The Grand Ethiopian Renaissance Dam will contain some 10Mm3 RCC while Diamer Basher is expected to contain some 17Mm3 making them the tallest and largest RCC dams when completed sometime this decade.
A common misconception by some inexperienced contractors and designers is that RCC dams are very easy to design and construct. This misconception leads to the incorrect assumption that the proper expertise, procurement of resources and most importantly the proper implementation of these resources are not required.
Team work is an essential component of successful RCC projects. Every project has large obstacles to overcome and can prove to be difficult even for very experienced engineers with extensive RCC dam experience. Many RCC dams have built successfully by contractors with no RCC experience but they have had many RCC experts, RCC materials experts, design consultants as well as construction consultants who corroborated well with the constructors throughout the course of project implementation.
Some significant successful projects and their details are featured below:
Ralco dam, Bio Bio region southern Chile
The Ralco dam was an engineering achievement is every aspect:
- 155m tall containing 1.6Mm3 RCC.
- Four overtopping events.
- Rain and snow and extreme weather conditions.
- International and local protest adversely affecting access to the project.
- Extremely difficult terrain.
- GERCC upstream face with excellent performance.
- Sustained two earthquakes with no damage:
- Ralco remains in the top 12 RCC dams worldwide still today nearly ten years after completion.
Yeywa RCC dam in Myanmar
- Remains in the top 12 fastest constructed RCC dams.
- 134m tall containing 2.34Mm3 RCC.
- High cementitious RCC mixture 75C+145 KG Pozzolan with excellent results.
- Grout enriched facing system with excellent results.
- Comprehensive coring, testing and Q/C programme.
- One planed overtopping event.
- Logitudinally integrated CVC cofferdam to protect the powerhouse.
- Staged construction of RCC placement operations for planned overtopping.
- Integrated spillway for further protection of the right abutment and powerhouse construction.
Gibe III Ethiopia ( under construction)
- 249m tall.
- 6Mm3 RCC
- One of the most sophisticated conveyor systems in the world with an 'all conveyor' deliver system containing some 400m of conveyors and 2x40 ton Mobil Concrete placers by RCC Conveyors Inc.
- Three river diversion tunnels.
- 4x8m3 horizontal Twin shaft RCC mixers capable of some 960m3/hr .
About the author
Ted Warren is a construction civil engineer who has worked on many projects in various countries worldwide. Starting his career early in the US working on highways, bridges, land development and small earthen dams throughout Fairfax county Virginia, he first became involved with RCC dams in 1991. At Pennsylvania's Siegrist RCC dam he was a field engineer and then later the RCC placement superintendent for the main dam and stilling basin. This was the first RCC dam in the state of Pennsylvania, and at that time there were only 15 such RCC dams in the US and about 50 worldwide. (As of 2012 there are some nearly 600 large [ICOLD > 15m tall] RCC dams built or under construction worldwide.)
Warren's work at Siegrist inspired his career and furthered his passion for building large dams and associated hydroelectric projects. Since then he has been involved with over 20 RCC dams in 14 countries containing over 10Mm3 of RCC in total. These range from 15m to the tallest currently under construction - the Ethiopian Gibe III dam at a height of 249m tall. Warren's role has generally been as a resident engineer but he has also has been involved in many short term assignments as an advisor on RCC projects worldwide.
Ted Warren is currently the chief resident engineer at the Song Bung 4 hydropower project in Vietnam. Email: [email protected]