Abstract:
On October 20, 2014 a sinkhole appeared near the downstream toe area of the earthfill embankment at
Boone Dam, followed by turbid seepage discharge into the tailrace. These events initiated a large-scale,
multi-faceted response by the Tennessee Valley Authority (TVA) and its engineering partners. Seepage
issues were determined to be related to internal erosion and loss of soils within the karst foundation.
Evaluation of grouting techniques for short-term and long-term mitigation were considered. The study was
structured to address many site-specific questions related to development of a mitigation approach to
address project objectives, viability of grouting in a karst environment with significant clay infilling,
identification and mitigation of grouting risks at Boone Dam.
A test grouting program (i.e., field study) was designed and executed to evaluate the potential for low
mobility grouting (LMG) techniques for treatment of the soil-infilled karst. Multiple test areas were
designed, each with specific objectives, hole layouts, grouting techniques, instrumentation, and engineering
evaluation factors. The program was designed to allow field adjustments to be made by the engineering
team based on observed performance and long-term mitigation strategies.
The study demonstrated that the behavior of LMG is dependent on the slump of the mix, grain size
distribution of the aggregate, and the presence or absence of fly ash. The study also demonstrated that
displacement grouting (using LMG) within the epikarst (transition zone between soil and karstic limestone)
may result in significant and sometimes unanticipated piezometric and ground responses. These findings
were instrumental in developing a long-term mitigation approach at Boone Dam utilizing the benefits of
LMG to construct a composite cutoff wall across the embankment dam.
This paper summarizes key observations of LMG and displacement grouting techniques at Boone Dam
during the test grout program and implementation of long-term mitigation measures. This paper serves as
an update to the Grouting 2017 Paper “ Boone Dam Test Grout Program: Objectives, Engineering Design
and Observations” .