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The Tennessee Valley Authority (TVA) constructed the Bear Creek Dam in 1969 to provide flood control, recreation, water supply, and economic development benefits. The dam is located in Franklin County, Alabama, and is one of two dams in the Bear Creek Project. The structure consists of an earth dam, a concrete overflow spillway with a highway bridge carrying County Road 37 across the spillway and dam, an intake tower, lined tunnel, and an outlet structure. The Dam is approximately 1,200-feet long at the crest and is 68-feet high at the maximum section. The crest of the overflow spillway is at elevation 602 and the crest elevation of the dam is 618.
The Dam is a homogeneous rolled fill embankment constructed from compacted residual soil. The Dam is founded on karst rock consisting of the Mississippian age Bangor Limestone underlain by the Pennington Shale and Bangor Limestone. During construction, the existing overburden on the right abutment was excavated to competent rock and approximately 900 feet of the foundation was grouted using both vertical and angled grout holes. The existing overburden was left in place along the remaining portion of the Dam to the spillway on the left abutment.
Seepage was observed at the downstream toe of the Dam after first filling the reservoir in 1969. A grouting program was successfully performed in 1972 to reduce the seepage flow in the area from the right abutment to near the spillway. However, by 2004, the seepage had again increased to about 800 gallons per minute and TVA initiated another grouting program on the left side of the Dam. Two partial grout lines were installed before the work was halted due to flooding.
In addition, TVA has revised the PMF and determined that the earth dam would be overtopped by this flood.
TVA requested proposals on methods of providing a cutoff for the seepage and providing seismic stability and PMF capacity for the embankment dam as part of the NEPA process. In response to this proposal, Paul C. Rizzo Associates, Inc. (RIZZO) proposed constructing a deep seepage cutoff wall using either the secant pile or plastic concrete slurry wall technique and alternative modifications to the existing dam to provide a dam capable of existing seismic and PMF demands.
RIZZO's Scope of Work included the following major tasks:
- Phase I Conceptual Design and Design Report;
- Phase I Site Investigations; Field boring investigations, Surface and down hole geophysical investigations, pumping wells and piezometers to study ground water regime.
- Design of Cutoff Wall and Water Barrier;
- Geotechnical analyses and Report;
- Seismic evaluation of Intake Tower;
- PMF Development;
- Final Design, Construction Drawings and Technical Specifications;
- Request For Proposal Assistance to TVA, and
- Construction Oversight.
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