Ground proving three seismic refraction tomography programs

During a recent ground-proving exercise at the shared University of North Florida and University of Florida karstic limestone geophysical and ground-proving test site in central Florida, the limestone bedrock surface was mapped along several survey lines with both intrusive and geophysical techniques. Analyses of the site investigation data revealed a highly erratic limestone bedrock surface, which is common in karst terrane. Analysis of seismic refraction data demonstrated that three commercially available refraction tomography software systems can 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. This variability is attributed to the geologic history of the limestone, which includes how the limestone was formed and how the limestone weathered. 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 terranes.