The Deep Ground Rod in a Three Layer Soil - A New Approach

Abstract

The aim of this paper is to present a practical method based on a new approach in order to compute the rod ground resistance when buried in a three-layer soil. This electrode is frequently used although it requires a mechanical hammer to bury the rod, through a three-layers soil. The originality of this new approach is a two-layer equivalent soil model replacing the initial three layer soil one, enabling the rod resistance computation to be obtained using Tagg formula for rods in a two-layer soil. The authors have used measured values available in a scientific paper, have drawn the apparent resistivity curves from those values according to IEEE Std. 80-2000, and have obtained the soil parameters using the Pirsen method. From the three- layer soil, a two- layer equivalent soil has been derived and the Tagg formula has been used to compute the deep rod resistance. No numerical methods have been used in this calculation, which just requires a practical formula. The theoretical results agree with the published measurements in the field. For rods with length of 24m, 30m and 36m the proposed method has errors of -9.4%, 0.0% and 2.6%. In order to ensure that these results are not due to redundancy, the IEEE two layer model is deduced from the resistivity curve, and the use of Tagg formula leads to errors of 22.6%, 23.8% and 12.8% for the already referred lengths, and are bigger than the ones obtained from the authors suggested method.