Applications, Observations, and Lessons Learned from Remedial LMG Grouting-Paper

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At Boone Dam in Tennessee, a sinkhole and turbid seepage identified potential foundation erosion and prompted construction of a seepage barrier. Low-mobility grouting (LMG) was used to fill voids in weathered rock, displace weak foundation soils, reduce slurry losses during later cutoff-wall construction, and gather information about subsurface conditions.<br /><br />In 2015–2016, crews drilled 533 sonic-drilled holes totaling 30,550 feet and injected 23,029 cubic feet of grout. Testing in a designated cell showed that LMG reduced hydraulic conductivity by at least an order of magnitude. Piezometer readings also indicated reduced seepage through the foundation. The completed grouting treatment helped limit slurry losses during cutoff-wall construction, which was finished in 2022 with only minor losses.<br /><br />The work highlighted the importance of consistent grout mixing: replacing a variable “mother mix” process with full batching at mobile mixers resolved pumping problems and improved strength results. A low-slump mix (0–2 inches) performed well for displacing soft soils; higher-slump grout was used briefly for void filling but was discontinued after an unexpected rise in embankment piezometric levels and investigation confirmed a fracture.<br /><br />The authors caution that closely spaced, higher-order holes can increase stresses after voids have been filled and may mobilize foundation soils. At Boone Dam, spacing closer than five feet was ultimately ruled out. Overall, LMG proved useful both as a treatment and an investigative tool, but mix properties, injection pressures, hole spacing, and instrumentation responses require careful control.

Keywords

Boone Dam

Tennessee

sinkhole

turbid seepage

foundation erosion

low-mobility grouting

seepage barrier

hydraulic conductivity

cutoff-wall construction

grout mixing