Grouting for Karst Risk Reduction Based on Geophysical Investigation Methods

Modern site investigations combining geophysical imaging with conventional exploratory borings can offer a significant improvement in the cost effective application of grouting for Karst risk reduction. This paper provides case histories of projects where the authors have utilized geophysical imaging to improve the understanding of subsurface conditions on difficult Karst sites when conventional soil borings or soundings failed to provide adequate data to arrive at a cost effective solution. The addition of modern imaging techniques allows for more accurate and cost-effective grouting designed to target specific Karst features rather than simply blanketing an area with grout injections. This paper provides 3 case histories where the grouting contractor utilized geophysical methods to study the work area prior to grouting for the purpose of minimizing the cost of the grouting program. One of these case studies describes the use of geophysical methods to locate the active Karst features beneath a water-filled pond and select an appropriate grouting pattern for remediation. Two other case studies within this paper present the use of Geophysical imaging to allow the cost effective use of cap grouting beneath proposed shallow foundations in an area with active Karst features instead of converting the structures to a deep foundation system of drilled shafts or micropiles.