Boone Dam - Observations of LMG Grouting in Clay-Paper

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The paper describes a low-mobility grouting (LMG) test program at Boone Dam, Tennessee, developed to help control internal erosion through the dam’s complex, karstic foundation. A sinkhole and turbid seepage observed in 2014 prompted investigation, which found seepage pathways in the epikarst—a transition zone of irregular limestone, voids, and soft, saturated clay. The remediation strategy combined LMG to fill voids or displace soft soils with a seepage barrier.<br /><br />The program included a test pit to compare grout mixes and delivery methods, followed by three test areas used to assess injection behavior, soil deformation, pore-water pressures, and suitable stage cutoffs. Results showed that grout performance depended on slump, aggregate gradation, and additives such as fly ash. A single modified mix, used at different slumps, proved suitable for both soil displacement and rock-void filling. The test pit also showed that fly ash could increase grout mobility and the potential for grout migration and hydrofracture.<br /><br />Field monitoring revealed that grouting and drilling could cause substantial, sometimes unexpected, pressure changes, heave, and lateral soil movement. LMG traveled significant distances through the epikarst, and displaced soft clay could alter seepage conditions far from an injection point. These effects make careful control of grout properties, injection rates, pressures, and stage volumes essential; pressure and volume cutoffs help limit potential damage.<br /><br />The program informed Boone Dam’s long-term mitigation approach and demonstrated the value of hole-specific grouting plans based on drilling records, downhole imaging, and previous injection performance. The authors recommend robust, continuous instrumentation and monitoring, prior assessment of site-specific failure modes, and flexibility to adjust procedures as conditions emerge. Grouting in karst beneath critical infrastructure requires particular attention to changing groundwater pressures and other dam-safety risks.
Keywords
low-mobility grouting
Boone Dam
karst foundation
internal erosion
epikarst
sinkhole
seepage barrier
grout migration
hydrofracture
dam remediation