At 65 feet high and 700 feet long, Greenbrier Creek Dam impounds a reservoir used for recreation and raw water supply for the City of Mt. Sterling, Kentucky. This significant hazard earthen embankment and its associated normal pool elevation have been raised by 10 feet twice since the project’s original construction in the early 1960s. Through the years, the dam has experienced numerous slope stability and seepage issues, and bedrock scour has occurred within the spillway channel, which is comprised of interbedded dolomite and highly erodible shale. Schnabel has worked with the city to rectify these issues since August 2022.

Since the early 1990s, several sloughs and sinkholes formed adjacent to the site’s right downstream groin. In 2013, a grouting program was implemented at the right abutment to address conduit-like leakage through the bedrock. Recurring slope instability has also been documented at various locations on the downstream slope since 2015. Given the history of issues and worsening existing conditions, a decision was made in 2022 to partially draw down the lake. Schnabel joined the team that same year.

Since then, Schnabel has performed numerous geophysical tests using a variety of methods. The team has also conducted historical and ongoing InSAR analysis, geotechnical exploration and laboratory testing, and is designing Interim Risk Reduction Measures to slow the progression of apparent ongoing failure mechanisms.

A robust, automated instrumentation and monitoring program was also implemented for continuous near-real-time data acquisition. Several prisms, automated piezometers, a reservoir gauge, a crackmeter, tiltmeters, an automated total station, and a weather station are among the key components of the program. Conceptual alternatives for a replacement dam are also in development and include an embankment dam with a labyrinth spillway and a Roller Compacted Concrete dam.

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