Center Hill Dam
Center Hill Dam lies on the Caney Fork River in northern DeKalb County, about 50 miles east of Nashville. Since construction, seepage problems through the dam’s karst limestone foundation has required diligent monitoring, subsurface investigations, and grouting. Despite past work, seepage has increased to an unprecedented level of approximately 130 cubic feet per second under normal lake operations. Foundation conditions are deteriorating because clay-filled joints in the rock within the rims and dam foundation are eroding. This chronic erosion jeopardizes the earthen embankment dams, the abutments, and the integrity of the rims, resulting in a high potential for dam failure.
This $106 million rehabilitation project for the Nashville District of the US Army Corps of Engineers presented one of the most challenging dam safety and stability issues in the USACE inventory.
Key Challenges
GEI teamed with Bauer Foundation Corp. of Odessa, Florida to provide design engineering and Quality Control services for the project. Chronic seepage and erosion problems jeopardized the earthen embankment dam, the abutments, and the integrity of the rims, resulting in a high potential for dam failure. Before this work was completed, Center Hill Dam was ranked Dam Safety Action Classification I, which is the highest category of risk and urgency for dam safety major rehabilitation.
Prior to this work, a report titled “Major Rehabilitation Evaluation Final Report” led by GEI founder Steve Poulos PhD, PE, evaluated seepage problems and provided justification for the Center Hill Dam Foundation Remediation project. The primary feature of work in the rehabilitation was the installation of a 1,000-foot-long concrete seepage barrier wall installed through both the dam embankment soils and the underlying bedrock. This seepage barrier has a minimum 30-inch thickness and extends to depths more than 300 feet through rock with unconfined compressive strengths up to 32,000 psi. To increase dam safety, the barrier wall was installed inside an 88-inch-wide concrete encasement wall which is up to 200 feet deep.
GEI served as the technical lead for the project, and provided engineering for all items related to dam safety, on-site construction management, and quality control for construction activities. GEI was responsible for all submittal work, for the design of concrete pile and drilled shaft foundations for the slurry plant, for the design of a subsurface exploration program to evaluate the integrity of the soil rock interface, and for the design of a treatment plan for the epikarst zone below the embankment. GEI also designed a major rockfill extension of the dam in the upstream direction, and provided all civil, mechanical, plumbing, and electrical system design for the work platform along the upstream side of the main dam earthen embankment. GEI provided oversight and quality control during the construction of approximately 100,000 square feet of encasement wall panels in the earth embankment and approximately 200,000 square feet of concrete barrier wall panels.