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

Video Transcription

Video Summary

The presentation reviewed low-mobility grouting (LMG), begun in 2015 as part of an exploratory program ahead of cutoff-wall construction. The dam’s problematic epikarst zone—weathered, often highly permeable rock beneath foundation soils—created a risk of slurry loss. LMG aimed to reduce that risk while also revealing weak zones and other subsurface conditions.<br /><br />More than 500 holes were grouted using staged injection, with closer-spaced holes added where grout takes were high. Primary, secondary, and tertiary holes showed progressively lower grout takes, and follow-up permeability tests indicated substantial improvement. However, piezometer trends suggested that higher-order grouting may have become less effective and could have caused damage.<br /><br />Key lessons included using LMG as an investigation tool, carefully matching grout mix to purpose, and ensuring geology suits tight spacing. Because flow meters could not be calibrated reliably at low rates, crews tracked grout volume by stroke count. In discussion, the 150-psi refusal pressure was tied to typical overburden depth; grouting stopped when dam instrumentation approached established deformation thresholds.

Keywords

low-mobility grouting

epikarst zone

cutoff-wall construction

grout injection

permeability tests

dam instrumentation