Development of a Point-Based Index for Sinkhole Vulnerability Evaluation in Central Florida’s Karst Terrain

As Central Florida cities begin to grow and population and infrastructure webs out to support the increasing urban areas, contractors, and engineers are facing new design challenges caused by the variable and fragile karst landscapes. The greatest concern when constructing within karst terrain in Central Florida is the possibility of sinkholes (either cover-subsidence or collapse types). These isolated occurrences of drastic subsidence or soil collapse can wreak havoc on infrastructure supported on shallow foundation. Because of these hazards, proper site characterization is essential to ensure a practical, yet safe, design during construction phases, and the project’s life span. In this study, the authors develop a quantitative system of analyzing initial subsurface testing results (cone penetration tests) in efforts to provide a better understanding of the subsurface profiles and loose-soil anomalies. The resulting index, coined as the sinkhole raveling ratio (SRR), is developed through data processing and analysis of cone penetration tests (CPTs) performed in known sinkhole active sites. The SRR is a function of encountered soil resistance values, such as cone tip resistance (q_c) obtained from CPTs, as well as encountered stratigraphy thicknesses of the loose-soil anomalies. A major benefit of SRR is the ability to compare a group of CPTs within a project site or, on a larger spatial scale, between various sites exhibiting similar geological formations and soil types. Through a combination of SRR site analysis and by following the methodology presented in this study, a better characterization of potential sinkhole hazards can be performed for site development and design. Although the presented SRR index was formulated for specific Central Florida soils, similar empirical methodologies can be implemented for any site characterization in residual soils underlain by highly soluble, karst bedrocks.