Karst Investigations: Folded or Flat, Young or Old

All karst is not created equal. Variations in the age of the formation (e.g., Florida "limerock" versus the limestones of Wisconsin) result in strength variations and hence, performance. Variations in tectonic environment can yield flat carbonates (e.g., Kentucky's Mammoth Cave) versus the folded and faulted Appalachian carbonates (e.g., Virginia's Carlsbad Caverns) resulting in unusual patterns of solutioning as well as different failure mechanisms. Thus, geotechnical investigation and analyses must understand how the depositional and tectonic constraints of these different "rocks" can result in varying problems to investigators, analysts, designers and constructors. This paper addresses the differences in possible structural failure or contamination modes that develop in these different rocks in relation to man's works. The study procedures presented are multi-phased; particularly if the geotechnical work is first used as input for planning purposes. A review of aerial photography, satellite imagery and available geologic information, as well as a reconnaissance to "ground-truth" the aerial photography and regional maps, are all generally part of the first stage of an investigation in karst areas. Subsequent phases consist of developing a geologic model of the site, then testing and refining it through field investigations and construction inspection. Direct investigation tools include test pits and borings using specific techniques, with perhaps the use of certain indirect (geophysical) tools to cautiously correlate between known hard data points. The procedures are not unique, but represent an attempt to present economical investigative concepts that recognize the nature of different karst environments.