ELECTRICAL RESISTIVITY INVESTIGATIONS USING NON-LINEAR FOUR-ELECTRODE CONFIGURATIONS

Simple direct current, electrical resistivity surveys have emerged as an important procedure in reconnaissance investigations of shallow subsurface karstic cavities. Linear, Wenner-array configurations of four electrodes or pole-pole variations are traditionally employed, but space availabilities, particularly in developed areas, often preclude maximum depth capabilities.

This research, conducted in north-central Florida, demonstrates that certain non-linear patterns of current and potential electrodes yield results consistent with those from Wenner arrays, but can be deployed to accommodate potentially impeding structures. Field tests demonstrate that a sounding pattern of current electrodes with sequentially increasing spacing along a line of interest and similarly-spaced potential electrodes oriented parallel to the line, but offset by a spacing unit, can duplicate results from more traditional electrode patterns. Interpretations of the data permit identification of distinct sand, clay, and limestone lithologies within the upper approximately 100 feet. This new “box pattern” offers an opportunity to conduct surveys in limited-access areas, and provides the option of “directional” results to more specifically locate the source of anomalies.