Long-Term Grouting of a Karst Foundation at Logan Martin Dam, Alabama: Fid-Bau Portal

Long-Term Grouting of a Karst Foundation at Logan Martin Dam, Alabama

Bruce, Donald A. / Greene, Brian H. / Craig Findlay, R. / Williams, Bobby E. / Williams, John H. / Mickwee, Richard L.

Seepage through the karstic limestone foundation below Logan Martin Dam, AL, developed when the reservoir was first filled in 1964, producing springs in the downstream channel, on the riverbanks and eventually at the embankment toe. After a large sinkhole developed on the downstream face of the east embankment on April 9, 1968, the first of many remedial grouting campaigns began, and they continue to this day. This paper reviews the long history of grouting performed at the dam site. There have been many changes and improvements to the means and methods of grouting in recent years that have led to success in mitigating underseepage and improving dam safety. New challenges continue to present themselves. In 2012, exploration conducted at the site revealed that the upper 15 meters (m) of the karst under a rock buttress (“bolster”) at the base of the east embankment had about 30 percent voids, raising collapse concerns. In response, a method utilizing discrete grout columns formed using low mobility grout (LMG) was developed, evaluated and then fully implemented. This application of LMG column stabilization is unique and the paper discusses the development and assessment of the method, as well as full implementation of the remediation, including instrumentation and monitoring. Finally, the on-going work to continue deep curtain high mobility grouting along the axis of the east embankment of the dam is reviewed. The use of real-time grout monitoring, balanced stable grouts, an extensive instrumentation program and the development of a 3D geologic model are guiding the way forward towards assuring dam safety while guaranteeing power generation.