Abstract:
Between 2015 and 2021, the Tennessee Valley Authority (TVA) constructed a composite seepage
barrier composed of a multi row grout curtain and a secant pile concrete cutoff wall at Boone Dam to
mitigate the risks of failure by internal erosion and piping. During implementation of the grout curtain,
TVA observed measurements and trends in the dam safety instrumentation that indicated deformation
of the embankment was occurring, resulting in cessation of grouting to evaluate the displacement. The
objective of this paper is to provide a representative description of the forensic investigations completed
following the dam safety observations which concluded that hydraulic fracturing during grouting was
the root cause of the displacement. Some fracturing of soft foundation soils was anticipated during
reinforcement of the karst foundation. However, grout was found to have travelled vertically and
parallel to the axis of the embankment through the compacted fill. The paper is organized to present an
overview of the geology, a chronological summary of the observations, the forensic analyses and
investigations completed to identify the root cause of the movement. The paper further discusses
specification revisions which incorporated these lessons learned into practices during completion of the
grouting program. This paper highlights the importance of designing a grouting program specific to
the conditions of the bedrock being grouted and the overlying soils. The paper further demonstrates the
importance of interpreting grouting signatures and dam safety instrumentation in real time and the value
of constantly evaluating grouting performance and treatment protocols over the project duration.