Application of the pole-dipole resistivity technique to the detection of solution cavities beneath highways

Using a multiconductor electrode cable and a 30-post switching system, pole-dipole electrical resistivity measurements with a linear electrode array demonstrated a strong correlation between resistivity anomalies and subsurface voids at four sites in Florida. Solution cavities below the water table are filled with a groundwater-solute mixture characterized by lower electrical resistivity than the enclosing country rock (Eocene and younger limestone). Air-filled cavities above the water table exhibit high resistivity anomalies. Confirmation drilling of postulated cavities and other anomalies suggests the method can be used with confidence to locate highway-threatening solution cavities with diameters as small as 3 to 5 m to a depth of 25 to 30 m.--Modified journal abstract.