Comprehensive Foundation Rehabilitation at Bear Creek Dam

The Tennessee Valley Authority (TVA) Bear Creek Dam is a high-hazard potential embankment dam in northwest Alabama that provides water supply, flood control, and recreation benefits. Since its initial filling in 1969, the dam has experienced significant seepage through its karst limestone foundation. After experiencing limited or temporary success at controlling seepage using supplemental grouting programs and downstream seepage collection systems, TVA elected to embark on an extensive rehabilitation effort for the existing dam's deficiencies, as follows: (1) foundation seepage leading to a potential loss of embankment material at the foundation contact and (2) the potential loss of the embankment dam as a result of overtopping during the potential maximum flood (PMF). Paul C. Rizzo Associates, Inc., was hired to design a permanent solution for the dam's deficiencies. Performance of this rehabilitation consists of construction of a downstream roller-compacted concrete reinforcement structure to prevent loss of the dam during PMF overtopping and installation of a composite seepage barrier consisting of a two-line grout curtain with cutoff wall panels at select locations to reduce potentially hazardous foundation seepage. The existing emergency spillway as well as the existing sluiceway tunnel and associated intake structure were preserved as a part of this new construction. This article presents the means and methods employed to effectively treat the karst limestone geology present at the Bear Creek Dam, with emphasis on the evolving nature of the design and construction of the final seepage barrier, whereby continuous, 'real-time' evaluation of the geologic conditions encountered during each phase of the foundation treatment process was used to tailor the scope and design of the next step of the rehabilitation.