Exploring Geophysical Methods to Identify and Mitigate Karstic Features at Robinson Lake Dam

Robinson Lake Dam is an existing, unregulated, earthen dam that poses multiple dam safety concerns. The City of Franklin, Tennessee, proposed to redevelop the area to include a recreational lake with a rehabilitated dam embankment. The dam site lies within the Carters Limestone formation, which contains limestones prone to development of karstic features. Three existing sinkholes exist in the downstream area of the dam embankment, and water is seeping through the right abutment at an estimated rate of 200 gallons per minute (757 liters per minute). To design rehabilitation measures for the dam, the limestone bedrock was evaluated by performing rock coring, water pressure tests, and three geophysical survey methods. The purpose of this paper is to detail the comprehensive subsurface investigation program consisting of geotechnical test borings and geophysical survey methods for the design of seepage mitigation measures. The mitigation measures include a targeted foundation grouting program, focused in areas of encountered karstic anomalies from the subsurface investigation program to reduce the potential for seepage and sinkhole development.