Ground impedance measurement and interpretation in various soil structures

This paper discusses ground impedance measurement and interpretation using the fall-of-potential method in various soil structures. The soil structures considered include horizontally layered soils. Vertically layered soils, cylindrically layered soils, spherically layered soils, and soils with finite volumes made of different resistivity materials. The results show that applying the uniform soil based 61.8% percent rule to obtain the true ground impedance may lead to wrong values. The measurement error based on the 61.8%, rule ranges from 8% in a spherically layered soil to as much as 44% in some vertical soil models. The results in this paper offer guidance in ground impedance measurement and interpretation when a variety of fall-of-potential curves may be encountered due to different soil structures. This paper demonstrates the necessity of soil resistivity measurements in order to accurately interpret the fall-of-potential measurements