American Society of Civil Engineers

Raising a Rattlesnake: Rattlesnake Hollow Ash Pond Dam Crest Raise

by James C. Pegues, P.E., M.ASCE, (Supervising Principal, Earth Science & Environmental Engineering Department, Southern Company, 42 Inverness Center Parkway, Bin B426, Birmingham, AL 35242)
Section: Geotechnical Engineering Construction Problems, pp. 2202-2211, (doi:

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Document type: Conference Proceeding Paper
Part of: GeoFlorida 2010: Advances in Analysis, Modeling & Design
Abstract: The Rattlesnake Hollow Ash Pond, located in north-central Alabama, was originally constructed in the 1950s with a rock fill dam to provide ash storage for a fossil-fueled electric generating plant. The dam underwent a major renovation in 1979, with a crest raise of approximately 17 m (55 feet), bringing the total height of the dam to approximately 44 m (145 feet). A second crest raise was proposed in early 2004. Feasibility studies and preliminary design evaluated the impact of various crest raise configurations, focusing on stability and seepage issues. After evaluation of options, the decision was made to raise the existing dam 6 m (20 feet) using a steep-sided upstream section consisting of roller compacted concrete (RCC), rock fill on the downstream slope, and a silty clay central core and a granular vertical drain between. Final configuration of the new dam resulted in a maximum height of approximately 50 m (165 feet) and a centerline length of about 500 m (1650 feet). Construction began in late 2006, and was completed in the fall of 2007.

ASCE Subject Headings:
Rock-fill dams