Sinkhole Risk Evaluation by a Subsurface Cone Penetration Test

As Florida’s population is expanding and greater fluctuations in groundwater levels are being recorded, Central Florida has been experiencing a higher frequency of sinkhole occurrences than ever before. Sinkholes are formed when the soluble limestone bedrock weathers and creates cavities at its interface with the overburden finer-grained soils. The overburden soil then erodes into the limestone fissures, thus weakening the strength and holding capacity of the soil above. This initial stage of a sinkhole is referred to as soil raveling and is the most effective time to perform soil improvement measures, such as grouting, to mitigate further expansion of the subterranean void. Geotechnical engineers and scientists use subsurface exploration techniques such as standard penetration test (SPT) and cone penetrometer test (CPT) to stratify soils and estimate soil properties. These in-field tests can be implemented to detect and evaluate areas of soil raveling which may be a sign of a potential sinkhole. In this study, the authors present the current practice to assess the risk of sinkhole by using SPT and CPT as well as the raveling index (RI). Additionally, a 2D CPT imaging technique is presented to estimate the dimension of raveled soil zone and its engineering applications are discussed.