HR: 08:30h
AN: NS21A-03 INVITED    [Abstracts]
TI: Ground-Truthing Seismic Refraction Tomography for Sinkhole Detection in Florida
AU: * Hiltunen, D R
EM: dhilt@ce.ufl.edu
AF: University of Florida, Department of Civil and Coastal Engineering 365 Weil Hall, Gainesville, FL 32611, United States
AU: Hudyma, N
EM: nhudyma@unf.edu
AF: University of North Florida, Division of Engineering 4567 St. Johns Bluff Road South, Jacksonville, FL 32224, United States
AU: Quigley, T P
EM: tquigley@ufl.edu
AF: University of Florida, Department of Civil and Coastal Engineering 365 Weil Hall, Gainesville, FL 32611, United States
AU: Samakur, C
EM: chandra.samakur@dot.state.fl.us
AF: Florida Dept. of Transportation, 1109 South Marion Ave, MS 2011, Lake City, FL 32025, United States
AB: In order to provide effective return of storm water runoff to the subsurface aquifer, the Florida Department of Transportation (FDOT) constructs detention basins adjacent to its transportation facilities. These basins serve as a collection point for runoff within a local drainage area, and the overburden soil above the aquifer provides a natural filter for contaminants in the surface runoff water. However, the geologic setting for many of these basins in Florida is karst, limestone bedrock at shallow depth, and the concentration of water flow in these basins leads to frequent development of sinkholes. These sinkholes are an environmental hazard, as they provide a direct, open conduit for contaminant-laden runoff water to return to the aquifer rather than percolate through the overburden soil. Consequently, FDOT is keenly interested in all aspects of sinkholes, including factors leading to formation, methods of early detection, and effective methods for rapid repair. Recently, FDOT has engaged in a research effort to evaluate the capabilities of a wide range of geophysical investigation tools with regard to detection of sinkhole-prone areas within sites being considered for construction of detention ponds. The geophysical techniques evaluated have included ground penetrating radar (GPR), multi- electrode electrical resistivity (MER), seismic MASW, and seismic refraction tomography. In addition to geophysical testing at the research sites, extensive traditional geotechnical site characterization has been conducted, including boring and sampling of soil and rock, standard penetration tests (SPT), and cone penetration tests (CPT). The proposed paper will evaluate the capabilities of seismic refraction tomography. Comparisons between refraction tomograms and borehole logs, SPT soundings, and CPT soundings suggest that the refraction method can map the laterally-variable top of bedrock surface typical of karst terrane. During a recent ground proving exercise at the University of North Florida/University of Florida karstic limestone geophysical/ground proving test site in central Florida, the limestone bedrock surface was mapped along several survey lines using both intrusive and geophysical techniques. Analyses of site data revealed a highly erratic limestone bedrock surface. Analysis of seismic refraction data demonstrated that the refraction tomography software system was able to reveal the undulating bedrock surface. However, the tomography data revealed marked differences in the compression wave velocities at the top of the bedrock surface at various locations along one of the survey lines. Compression wave velocities were highest within slots or valleys and lowest at the tops of blocks or pinnacles. Ground proving via cone penetration tests and geotechnical borings appears to corroborate this finding, and demonstrates the importance of measuring multiple material parameters during site characterization activities in complex terrane. Finally, two sinkholes formed in the detention pond directly over two valley/bowl features after refraction testing was completed, demonstrating that refraction tomography has potential in identifying areas at risk for sinkhole development.
DE: 0900 EXPLORATION GEOPHYSICS
DE: 0935 Seismic methods (3025, 7294)
SC: Near-Surface Geophysics [NS]
MN: 2007 Fall Meeting