Abstract:
Preparation for cutoff wall construction at Boone Dam in Sullivan and Washington Counties,
Tennessee required an assessment of subsurface conditions and implementation of slurry control
grouting. The initial phase of slurry control grouting consisted of a low mobility grouting (LMG)
program intended to minimize the risk for slurry loss during cutoff wall construction and to provide
an interim risk reduction for soil transport related failure modes. To achieve this objective, LMG was
used in alluvium, residual soils, and epikarst to fill voids and move soft clays. A secondary objective
of the LMG program was to utilize sonic drilling data for exploratory purposes. Drilling action,
soft/rapid advancement zones, water losses during drilling in rock, and interpretation of recovered
material below the base of the embankment were then integrated with a follow-on high mobility
grouting (HMG) program in the epikarst and competent rock zone.
This paper will describe the development and implementation of the LMG program by describing the
LMG test program, evolution into the LMG exploratory grouting, observations made during the LMG
programs, and lessons learned. In 2015 and 2016, a total of 533 LMG holes were drilled (30, 550
linear feet of drilling) and 23, 029 cubic feet of LMG was injected. A test Slurry Control Cell was
performed with permeability testing before and after LMG grouting that indicated effective slurry
control. A review of LMG injection/take data revealed that a substantial and consistent grout take
reduction trend, by order of hole, occurred in the alluvium, residual soils, and epikarst. Normal and
unusual inclinometer and piezometer responses to LMG grouting are described along with
investigation measures undertaken as a result of unusual responses. Lessons learned are provided
regarding LMG as an investigation tool, mix design, LMG slump, grout mixing, test cells, and
grouting as a result of unusual instrumentation responses.