Other electrical methods

Vertical electrical sounding (or VES) represents a method for investigating the variation of resistivity with depth. This technique involves a series of resistivity measurements to be made with increasing progressive distances between current (A-B) and potential (M-N) electrodes, according to a four-pole device of various types. Current is fed into the ground through the two outer electrodes A and B; the potential difference generated in the subsurface as current passes between A and B is measured through the two middle electrodes M and N. From the measurements of potential difference (ddp) and current intensity (I), the apparent resistivity (R) of the soil is obtained. By increasing the distance between electrodes A-B and M-N, measurements can be extended to deeper and deeper layers. By plotting the apparent resistivity values on a logarithmic diagram, the apparent resistivity curves are constructed from which, with the help of a mathematical model, the values of the actual resistivities and the thickness of the layers with different resistivities can be traced.

The Self-Potential method consists of a type of passive geoelectrical survey that allows the measurement, by means of a pair of non-polarizable electrodes, of changes in the electrical potential in the subsurface due to an electric field generated by natural sources (hydraulic, thermal, and chemical). The components of Spontaneous Potential are mainly: Electrokinetic Potential, generated by groundwater flow, and Electrochemical Potential, generated by the difference in solute concentrations as a result of oxide-reduction reaction between water and the rocks with which it comes in contact.

The Arc Testing Method is an electrical investigation methodology for locating “leaks” in exposed geomembranes, as long as they are dry, clean, and do not have excessive ripples that could result in possible shielding of current flow. It is based on the principle of creating a high voltage by means of a probe above the insulating membrane and an electrode outside the investigated area to close the electrical circuit in cases of holes, cuts, or defects in the welds.

The OHMEX method consists of an electrical investigation for locating “leaks” in HDPE geomembranes buried by a hydraulic headwash or man-made material. It is based on the principle of creating an electric current flow between electrodes placed in contact with the geomembrane and outside the investigated area; respectively, where holes, holes, cuts or defects in welds are present, the electric circuit is closed and high potential values are measured.