geotechinical engineering & Geographic Information Sysytem

Electrical Resistivity

Surface electrical resistivity surveying is based on the principle that distribution of electrical potential in the ground around a current-carrying electrode depends on electrical resistivities and distribution of the surrounding rocks and soils. Usually practice in the field is to apply an electrical direct current (DC) between two electrodes implanted in the ground and to measure difference of potential between two additional electrodes that don't carry current. Usually, the potential electrodes are in line between the current electrodes, in principle, they can be located anywhere. The current used is direct current, commutated direct current or AC of low frequency (typically about 20 Hz). All analysis and interpretation are done on basis of direct currents. Distribution of potential can be related theoretically to ground resistivity’s and their distribution for some simple cases, notably, case of a horizontally stratified ground and case of homogeneous masses separated by vertical planes. For other kinds of resistivity distributions, interpretation is usually done by qualitative comparison of observed response with that of idealized hypothetical models.