Grouting in Karst Terrane—Concepts and Case Histories

Throughout the United States and especially on the east coast, development pressures have increased construction atop carbonate rocks. A myriad of concepts and techniques for identifying and remediating karst hazards has been proffered, many reasonable, some not so. Only remediation by grouting is discussed herein. The difference between effective and ineffective technique for both the identification and remediation of karst are related to the nature of the subsurface, the likely failure mechanism, and the type of construction. Bedrock character, bedding orientation, tectonic alteration, glacial activity, nature of the overburden, as well as the location and size of soil or rock cavities, will influence the failure mechanism in some way. In addition, the nature of any planned or existing construction can modify the manner, extent and procedures of the grouting operations. Any cost-effective grouting program in solutioned carbonates must consider all of the above concerns. Grouting can be as simplistic as filling the "throats" of isolated sinkholes with an appropriate "flowable fill" to a full-fledged exploratory/grouting program using compaction and/or slurry grouting techniques below a major structure. Developing an accurate cost estimate varies from quite difficult to impossible. Case histories of successful remediation operations that consider these concepts are presented herein.