Project Specifics

Geosyntec evaluated the seismic stability of the Blue Ridge Dam at the Blue Ridge Hydroelectric Plant, which was constructed between 1925 and 1930 by the Toccoa Electric Power Company on the Toccoa River near Blue Ridge, Georgia. In 1939, it was purchased by the Tennessee Valley Authority (TVA). The dam is a semi-hydraulic fill earthen embankment constructed by placing compacted “dumped” fill from nearby sources on the upstream and downstream faces, portions of which were subsequently washed using water cannons to mobilize the soils, creating a sluiced fill zone and a central puddled core of fine-grained material.

Geosyntec Scope of Services

Beginning in 2013, Geosyntec evaluated the seismic stability of the Blue Ridge Dam for the modified cross section for TVA. Geosyntec’s technical approach focused on evaluating the stability and performance of the dam under the design seismic events and working with TVA’s professional staff and advisors to minimize the amount of additional remediation work needed to satisfy the requirements of TVA’s Dam Safety Program. Our team established the initial stress conditions within the embankment using seepage analyses and then evaluated the potential for the embankment and foundation soils to liquefy or experience cyclic softening during the design seismic events. We also estimated the likely magnitude of permanent deformations induced by seismic loading through numerical analyses using FLAC (Fast Lagrangian Analysis of Continua). We conducted post-earthquake limit equilibrium stability and Newmark-style deformation analyses for comparison with the results of the numerical analyses.

In 2017, Geosyntec performed the installation, connection, programming, and testing of an automated data acquisition system (ADAS) at Blue Ridge Dam, as an interim risk reduction measure that automated the existing instrumentation at the dam. During this retrofit, we installed six in-place inclinometers, five vibrating wire piezometers (VWPZs) inside observation wells, 16 remote-monitoring units (RMUs) to connect more than a dozen existing VWPZs, six RMUs for seepage-flow measurements, two seismic-monitoring stations, a radio repeater, and a base station.

Notable Accomplishments

Before conducting the field and laboratory investigations, Geosyntec mined data from previous field and laboratory investigations, optimized the number of tests, minimized the number on hours worked in the field, and reduced the overall budget. This supplemental field and laboratory data allowed us to derive site-specific soil properties, which we then used to assess the dynamic response and stability of the Blue Ridge Dam. The liquefaction and deformation analyses were complex because the embankment and foundation materials are transitional soils that straddle the boundary between coarse-grained and fine-grained soils. For the numerical deformation analyses, Geosyntec addressed this uncertainty by employing two advanced constitutive models to bracket the expected behavior range given the transitional nature of the soils. Geosyntec demonstrated that the recent remedial projects implemented by TVA improved the stability and safety of the dam for both static and seismic-loading conditions. Furthermore, Geosyntec completed the project on time and under budget on an aggressive schedule required by TVA.

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