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 which is characterized by a lower electrical resistivity than the enclosing country rock (Eocene and younger limestone). Air‐filled cavities above the water table exhibit markedly high‐resistivity anomalies. Confirmation drilling of postulated cavities and other anomalies suggests the method can be used with confidence for identification and location of highway‐threatening solution cavities with diameters as small as 3 to 5 m to a depth of 25 to 30 m.