Evaluation of earth resistivity for grounding systems in non-uniform soil structure

The variation in soil resistivity have a considerable influence on the performance of most grounding systems, affecting both the value of ground resistance, the ground potential rise, the step and touch surface potentials. This paper presents a suggested mathematical model to examine the behavior of earthing system in non-uniform three-layer soil conditions. The study of the apparent soil resistivity of a driven ground rod as well as the value obtained by the four-point Wenner method has been done and its dependence on the characteristic of each layer is discussed. A comparison between the two methods is emphasized Finally, the results demonstrate that there is a predicable relationship between the calculated results obtained by these two methods.