Pyramid Geophysical Services was contracted to assist in a comprehensive evaluation of subsurface geologic and hydrogeologic conditions along a causeway in South Carolina. The causeway was experiencing slope failures and ground collapses. These failures were thought to be the result of both the presence of buried debris as well as focused groundwater erosion in the subsurface. Pyramid utilized every surface geophysical method in our toolbox to characterize this site, including electrical resistivity tomography (ERT), ground penetrating radar (GPR), electromagnetic methods (both metal detection and conductivity mapping), and seismic analysis. The combination of all these methods allowed for a comprehensive understanding of subsurface hazards, including void identification, delineating buried debris, and identifying other subsurface hazards and groundwater flow pathways and aided in developing mitigation measures.
Pyramid performed extensive GPR surveys adjacent to and surrounding open ground collapse features. The GPR, combined with other geophysical methods, helped to identify additional subsurface voids and potentially failing soils in the subsurface.
Pyramid ultimately provided the client with plan-view hazard maps identifying the locations of all possible voids, failing soils, groundwater flow pathways, and other subsurface condition information that was used in the mitigation design for the causeway.