ABSTRACT
Cambrian and Ordovician limestones and dolostones are exposed in the Valley and Ridge Physiographic Province of the southeastern United States. These lithologics are prone to extensive solutioning at the current- and paleo-water table by chemical decomposition by ground water and thus form karstic terrains. Because of the prominence of karstic features, any engineered structure or rock/soil slope or dewatering plan must account for the heterogeneous nature of karst. Presented herein are three case studies of engineering impacts in karstified limestones and dolostones.
Case A - A detailed geotechnical investigation was implemented to determine the foundation conditions and to estimate grout take quantities for an embankment dam in northwest Georgia. The site investigation involved extensive core drilling and test pitting. Based on this investigation, the Ordovician limestones beneath the dam were determined to be slightly karstic with cavities filled with firm to stiff clay. Upon excavation of the core trench and construction of the grout curtain, the limestones were found to be highly karstic with preferential solutioning both parallel and perpendicular to the dam axis. This required significant modifications to the design of the dam.
Case B - Extensive dewatering for a limestone quarry during a drought year caused a drastic modification of the surface and ground water flow regime. Flow from the dewatering area became muddy indicating piping of solution cavity infilling. Surface creeks became disappearing creeks and small sinkholes began to form in the stream alluvium along the dry creek beds. Local buildings were impacted by the karstic activity. This resulted in the eventual closure of the quarry.
Case C - The demand for water in northwest Georgia has increased for the last few years. To meet this demand, local city municipalities have developed high quality, high yield springs. High yield springs are generally located in karstic limestones/dolostones. Site investigations at one site indicated that the foundation was in highly karstic Cambrian limestone and not suitable for a large clear well and associated structures. However, due to land constraints, the municipality had to construct the clear well at this location. This resulted in difficult design and construction of the foundation of the structures.
