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New Geotechnical Report Discusses Foundation Failures in Estill County

Lexington, KY. (September 4, 2008) - Severe foundation problems have occurred in numerous building structures and one road in Estill County as a result of their foundations being sited on the Devonian Chattanooga Shale and Crab Orchard Formation.  These foundation problems caused heaving of concrete foundations, cracked flooring and walls, broken sewer and utility lines and some building subsidence, resulting in millions of dollars in expensive remediation.  Such damages can occur in the Devonian Shale when pyrite is oxidized to form secondary sulfates, which can swell when exposed to just a small amount of water or humidity, a reaction sometimes called pyrite swelling.  That’s the conclusion of a 5 year study conducted by research staff with the Kentucky Geological Survey at the University of Kentucky.

Warren H. Anderson, a geochemist and mineralogist in the Survey’s Energy and Minerals Section, conducted an investigation to determine the cause of these problems in an effort to provide detailed geologic data to the construction industry to prevent future construction and development problems when building in Estill County.  His report, Foundation Problems and Pyrite Oxidation in the Chattanooga Shale, Estill County, Kentucky, has been completed and is available on-line at the KGS web site.

“The Chattanooga Shale formation includes a variety of organic material, clay, silt, and iron-sulfide minerals, mainly pyrite, also known as fool’s gold,” says Anderson. “What happened with the building foundations in Estill County is that pyrite, exposed to moisture during construction excavation and subsequent rainfall, began to swell as a result of the growth of sulfate crystals. This is a chemical reaction between water and pyrite, and it creates crystal growth.  These new crystals can grow to many times their original size creating heaving of foundations. 

“In the case of the Crab Orchard Formation under the Irvine Bypass roadway, it appears that expanding clays are the primary problem, although if parts of the bypass are sited in the Chattanooga Shale, you will have the same problems as the school and hospital have,” Anderson explains. “The swelling can actually lift building foundations and road beds, causing a variety of structural problems, including subsidence and heaving.”

Estill County Middle School, the Carhartt clothing factory and the Marcum and Wallace Hospital auxiliary building have suffered damage as a result of the swelling of the formations, along with a section of pavement on Ky. 499 (the Irvine Bypass).

“Because the Chattanooga Shale can be found over a wide area of eastern and west-central Kentucky, zones of pyrite in the shale could cause the same kind of damage in other locations outside Estill County,” Anderson cautions. “It would be a good idea to try to avoid such zones because remediation can be an expensive and disruptive process.”

His report includes some recommendations for avoiding the damages seen at the Estill County sites. Among them are:

1. Avoid construction and excavation in the pyrite zone of the Chattanooga Shale. Avoid using Chattanooga Shale aggregate as construction fill. Conduct minimal excavation into the shale to reduce pyrite oxidation.
2. Keep water away from the foundation, preferably through the barrier method. Drainage ditches or drain tile can still accumulate sulfates from weathered shale material and cause heaving. Drainage ditches and tile did not solve the middle school problem.

Suggested remediation measures for cases of existing damage are also included in the on-line report, which can be accessed using free Adobe Acrobat Reader software and downloaded at the KGS web site: http://kgs.uky.edu/kgsweb/olops/pub/kgs/ri18_12.pdf