Case History Illustrating the Challenges of Foundation Design and Construction in Karst Terrain

This paper discusses the challenges associated with design and construction of foundation systems for a Corporate Campus located in Chester County, Pennsylvania that is underlain by Karst terrain. A comprehensive subsurface investigation was implemented to develop adequate foundation systems and related site work precautions. Because there was evidence of sinkhole activity prior to any construction work, and the subsoils revealed some variability from a consistency/density standpoint, the selected foundation system design included a combination of soil improvement using compaction grouting for shallow foundations and deep drilled-pier foundations. After construction activities began, several occurrences of solution activity were documented and repaired. During construction of drilled-pier foundations at one of the structure locations, a significant number of voids and discontinuities in the rock were encountered. The impact of these discontinuities and voids was dramatic to the effort and time necessary to complete the drilled pier foundation construction for this structure. After careful consideration of potential cost and schedule impacts, the foundation design for remaining structures was modified to eliminate the use of drilled piers and incorporated only compaction grouting for support of shallow foundation systems. Interaction of the Geotechnical Engineer, Construction Manager, Owner, and Contractor began early in the construction process and this interaction became critical to the project success as work proceeded on this project