Imaging of Deep Sinkholes Using the Multi-electrode Resistivity Implant Technique (MERIT) Case Studies in Florida

Abstract

Surface geophysical methods have been extensively utilized for sinkhole investigations. While surface geophysical methods can penetrate to depth where sinkhole development occurs the resolution is typically poor. A detailed understanding of deep raveling zones into sinkhole throat through a new and novel geophysical technique was developed by the authors. The authors performed over 750 sinkhole investigations on residential properties over a five year period of time, in each case geophysical methods of Ground Penetrating Radar (GPR) or Electrical Resistivity (ER) were performed. Over 1500 confirmatory Standard Penetration Test (SPT) drillings were performed of the geophysical anomalies. In a very large percentage of the geophysical surveys performed, the location, size and depth of the raveling zones into the sinkhole throat could be clearly identified. The authors developed a novel geophysical technique called The Multi-Electrode Resistivity Implant (MERIT) to address the need to image deeper into karst formations to help identify the location of deep raveling zones and sinkhole throats. The purpose of this paper is to present case studies of the application of MERIT technology. Three case studies are presented in this paper. The first case study focuses on the first application of MERIT at the Bordeaux Village in Tampa, Florida where a sinkhole swallowed a car in 2010. The MERIT survey was able to image the car in the sinkhole throat. This case study demonstrates the ability of the MERIT technique to identify the location of the sinkhole throat by identifying the depth and location of the car, a large conductive ER anomaly. The second case study focuses on a pipeline in Orlando, Florida being threatened by sinkhole development on the adjacent property. MERIT was able to identify size and depth of raveling of soils into the sinkhole throat near the pipeline. The results of the MERIT image were critical in engineering design to address the treatment to the pipeline. In the third case study MERIT technology was applied to a proposed roadway through an extensive karst region of Lake County, Florida. Initial geotechnical investigation indicated a potentially large and deep sinkhole feature. MERIT was able to provide a concise geologic structure including the identification of the locations sinkhole throat at 52m deep. MERIT has been shown to identify details of the complex geology and geometry of karst formations. In particular the techniques ability to provide improved image capabilities of the raveling zone and sinkhole throats has significant engineering applications for assessment, risk analysis, and remediation of sinkholes