Evaluation or Resistivity Tests for Design of Station Grounds in Nonunirorm Soil

The actual soil formation at a prospective station site usually can be approximated by an assumed 2-layer stratification. The method of establishing characteristic parameters of such a formation by 4-electrode tests is reviewed. As the main result of this study, curves are presented to determine, from these parameters, the apparent resistivity values to he used in computing the resistance of a grounding grid in a 2-layer soil. During the design of such a grid, the maximum touch and step voltages that might occur during a ground fault have to be evaluated in addition to the station ground resistance.