121. Reducing Leakage at Concrete-Faced Rockfill Dams in China

A major challenge in the construction of concretefaced rockfill dams is controlling leakage. New systems developed by Chinese dam designers are performing well, even at very high dams. Since the late 1990s, numerous dams in China have been designed and built utilizing concrete-faced rockfill construction. Construction on the first Chinese dam of this type, the 95 m high Xibeikou Dam, commenced in 1985 and was completed in 1990. This construction technique also is being applied to larger dams. For example, the 233 m high Shuibuya Dam, the 185.5 m high Sanbanxi Dam, and the 180 m high Hongjiadu Dam are under construction. Altogether, 14 concrete-faced rockfill dams more than 100 m high have been completed in China since 1998, and nine more are scheduled for completion by 2009. The concrete facing on the upstream slope of these dams consists of adjoining slabs, which are typically between 12 and 18 m wide and as much as 150 m long. One of the key problems in concrete-faced rockfill construction is controlling leakage through the joints between the concrete slabs, often referred to in China as water stop. The most problematic joints with respect to controlling leakage are the perimeter joints, which are at the contact between the face slabs and the dam's foundation. These joints may develop 5 cm openings or shear displacements, and exhibit as much as 10 cm of settlement. From 1994 to 1998, the China Instititute of Water Resources and Hydropower Research (IWHR) conducted a research program to investigate ways to improve water stop treatments used on large concrete-faced dams. The program was initiated to support upcoming construction projects, particularly Shuibuya Dam, which was to be the highest concrete-faced rockfill dam proposed in the world to date. Design engineers estimated that using concrete-faced rockfill construction at Shuibuya Dam would save nearly US$1 billion and reduce construction time by a year, relative to other construction methods. However, experience at other high dams of this type in Europe and South America showed that excessive leakage could jeopardize the success of the project.