Instrumented Packers at TVA's Boone Dam-Paper

Paper

Pdf Summary

The paper describes the use of instrumented packers during TVA’s Additional Drilling and Grouting Program (ADGP) at Boone Dam, Tennessee. Following discovery of a sinkhole and seepage in 2014, TVA undertook extensive foundation remediation. The ADGP used a two-line curtain of high-mobility grout below the planned concrete cutoff wall to verify design assumptions and treat deeper rock.<br /><br />Earlier packer designs measured pressure during water testing but could not reliably withstand grout injection because grout could block the pressure-transmission tube. The contractor developed a revised design using a pressure transmitter connected to a fluid-filled bladder at the injection point. Sensors were calibrated against a reference gauge and kept within 5% accuracy.<br /><br />Direct pressure measurements helped maintain safe injection pressures and avoided uncertainties associated with estimating downhole pressure from surface readings. Conventional calculations depend on line-loss estimates and assumptions about local groundwater pressure, both of which can vary. During grout injection, calculated effective pressures sometimes exceeded measured pressures at shallow depths, then became substantially lower with depth. This divergence suggests that relying solely on calculated pressures could create dam-safety risks. Instrumented packers also supported monitoring for potential hydraulic fracturing or movement of defects.<br /><br />The authors recommend continued development and broader use of instrumented packers, noting that designs with witness tubes can produce inaccurate results. They also caution that ADGP data came mostly from deep, relatively intact rock with very low grout takes; further testing in more fractured, karst-affected rock is needed to explain pressure differences under typical grouting conditions.

Keywords

instrumented packers

grout injection

Boone Dam

TVA

ADGP

dam remediation

downhole pressure

foundation grouting

pressure measurement

hydraulic fracturing