Dam Safety Instrumentation Performance of Boone Dam during Remediation Grouting-Paper

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Boone Dam, an embankment dam founded on weathered karst limestone, was placed under heightened safety precautions after a sinkhole appeared near its downstream toe in October 2014 and mud later discharged into the tailrace—signs of possible internal erosion. The Tennessee Valley Authority lowered the reservoir and developed a composite seepage barrier to reduce long-term dam-safety risks.<br /><br />The remediation combined two rows of low-mobility grouting (LMG), two rows of high-mobility grouting (HMG), and a concrete cutoff wall. LMG was intended to stabilize soils and weathered rock, fill larger voids, and help prevent slurry loss during wall construction. HMG targeted open fractures in deeper, more competent limestone and helped reduce seepage. Work was completed in stages, with extensive instrumentation used to monitor dam response.<br /><br />Piezometers recorded short-lived pressure increases during grouting, generally greater during HMG than LMG. Some increases in foundation pressures dissipated within one or two days; embankment responses were usually small. Repeated HMG treatment produced weaker pressure responses, suggesting reduced hydraulic connectivity. Longer-term trends showed groundwater levels rising upstream of the grout rows and falling downstream, consistent with reduced seepage across the dam foundation. These patterns persisted before construction of the cutoff wall.<br /><br />The grouting programs also helped control slurry losses during cutoff-wall excavation. No excessive losses occurred; the maximum observed rate was less than 1 cubic foot per minute. Overall, instrumentation indicated that the treatments reduced hydraulic gradients and supported construction of the cutoff wall with minimal slurry-loss risk. The reported groundwater observations were made while the reservoir was at a restricted level, approximately 30 feet below normal summer pool.

Keywords

Boone Dam

embankment dam

karst limestone

sinkhole

internal erosion

seepage barrier

grouting

cutoff wall

piezometers

groundwater levels