Use of Geophysical Methods for Sinkhole Exploration
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2020-10-01
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Edition:Final Report
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Abstract:Karst geology is characterized by the presence of sinkholes and voids, which may pose significant risk to existing infrastructure. Sinkhole formation is often observed near active quarries, where dewatering operations can alter regional groundwater flow patterns leading to subsidence and increased void formation. In these areas, identifying locations which may be susceptible to sinkhole formation requires an ability to map the rock surface and any dissolution features within the rock. Traditional geotechnical explorations alone are not well-suited to this effort as they only provide subsurface information at discrete points and therefore may miss voids within the rock or may provide incomplete information in areas of highly variable rock surfaces. Geophysical methods offer a means to produce continuous profiles of the rock surface and possible locations for voids but interpreting the results of these tests in karstic geology can be challenging. This study uses 2D electrical resistivity and seismic surveys at sites with active sinkholes, repaired sinkholes and pinnacled rock in Alabama. Resistivity data is collected using 2D dipole-dipole and strong-gradient arrays. The seismic data is processed using a full waveform inversion (FWI) technique. Subsurface profiles interpreted from the geophysical surveys are compared to geologic information and borehole data from previous site investigations, where available. Results from the geophysical surveys are found to be consistent with borehole data regarding variation of bedrock depth and identification of possible sinkhole features. Potential limitations and sources of error pertaining to each survey type are considered. The results of the geophysical surveys are used to create a sinkhole investigation plan, which seeks to integrate the various sources of information in order to provide a comprehensive and cost-efficient characterization of sinkhole sites. Recommendations for implementation of the findings from this study and areas for future research are discussed.
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