Electrical Resistivity soundings

Electrical resistivity is a bulk soil property (similar to density) that characterizes the flow of electrical current through that material. It is particularly useful in grounding grid design to properly size grounding elements or in the case of poor soil resistivity, improve the soil. 

The easiest way to picture the collection of resistivity data is a resistivity instrument which supplies a current source (battery), a current meter, and a voltage meter. Current is passed through the ground by way of electrodes spaced at known geometry. The voltage drop is measured between the potential electrodes, and based on the known geometry (distance between electrodes) resistivity can be calculated. 

The two most common arrays in which electrical resistivity data are collected are the Wenner and Schlumberger arrays. The Wenner array maintains equal spacings (a) between electrodes and the Schlumberger array maintains a much smaller spacing between the inner (potential) electrodes while varying the outer (current) electrode spacing. 

Mapes In-Situ uses the ABEM Terrameter (1000 and 4000) for resistivity soundings and is capable of performing measurements with spacings (a) of up to 500 meters between electrodes. 

Resistivity profiling can be carried out with the same equipment; however, a multi-channel system that collects data at different spacings automatically is much more efficient. The ABEM Terrameter 1000 and 4000 can also be used for resistivity profiling (imaging). Resistivity imaging is ideal for archeological investigations, mine void or karst topography delineation, groundwater exploration, and soil/groundwater pollution investigations.