Remedial Grouting, Phase II, Red Rock Dam, Pella, IA

Red Rock Dam is owned and operated by the US Army Corps of Engineers, Rock Island District. The dam is located between Knoxville and Pella in South Central Iowa. The dam forms Lake Red Rock, the largest lake in the state. The primary purpose of the Lake is flood control, but like many Corps lakes, recreation is also an important use.
The dam is a 5200 foot earth embankment dam with a concrete outlet works. Construction began in 1960 and started impounding water in 1969. The geology underlying the dam is very complicated with broken and solutioned limestone, partially solutioned gypsum, weakly cemented sandstone, underlain by dolomite. During construction, a three row grout curtain was constructed in a core trench. Extremely high volumes of grout were placed throughout the length of the dam. On the left abutment a 3 to 5' gypsum lens degraded over the years. During high water conditions, downstream piezometers on the left abutment were free flowing!