UTILIZING MULTIPLE GEOPHYSICAL METHODS TO AUGMENT A COMPREHENSIVE DAM SAFETY INVESTIGATION: A CASE STUDY FROM THE EASTERN TENNESSEE VALLEY AND RIDGE

Tennessee Valley Authority (TVA) Dam Safety recently completed an issue evaluation study that included an investigation of the potential for migration of embankment material into foundation karst features at a dam located in the Valley and Ridge province of eastern Tennessee. A combination of land- and marine-based geophysical methods was utilized to characterize potential subsurface karst hazard or seepage pathways at the dam; methods included microgravity, self potential, electromagnetic, electrical resistivity imaging, and seismic refraction surveys. In addition to these surveys, numerous available data including foundation mapping, design information, construction records, borehole data and grouting records, dam safety performance instrumentation data, inspection records, and remote sensing data (including InSAR) were compiled, spatially referenced, and synthesized as part of this investigation. The compilation of these data in a spatial and temporal framework provided valuable insight and focus to the interpretations of the geophysical data. The resulting interpretations are based on a combination of complementary geophysical techniques that are supported by the compiled geologic and geotechnical data. Areas that could possibly represent potential seepage paths or karst dissolution were identified using this integrated approach, which effectively focuses our efforts for future investigations and highlights areas to focus on during routine dam safety inspections. Overall, the results of this study demonstrate the importance of implementing multi-faceted geophysical studies designed to address specific project objectives to gain a better understanding of the geologic conditions at a site, and then apply that understanding to inform risk estimates for geologically-based failure modes.