On the measuring methods of the soil electrical resistivity

The design of grounding systems must guarantee the electrical safety of installations and be based on the actual conditions of the site. The electrical resistivity of the soil is the most significant parameter upon which the design should be based and should allow a multi-layer modelling. In this paper, the authors illustrate the major techniques and configurations for soil electrical resistivity measurement, and discuss advantages and drawbacks of each. The convention to be adopted to correctly identify the depth of investigation for vertical electrical soundings associated with the electrode arrangement, independently of the measurement technique, is also discussed. The data inversion, a mathematical procedure by which the measured values of apparent resistivity are processed to determine the true values of soil resistivity, is presented. This paper is meant to be a reference for practitioner engineers, who must perform soil electrical resistivity surveying to produce reliable results for a proper grounding electrode design.