Characterization of a Karst Site using Electrical Resistivity Tomography and Seismic Full Waveform Inversion

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 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. 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 a site with previous sinkhole activity along an interstate in central Alabama. The site is adjacent to a limestone quarry. 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 then compared to borehole data from previous site investigations. 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.