An approximate expression for the equivalent resistivity of a two-layer soil

The lightning induced voltages on aerial and underground lines depend on the value of soil resistivity. Most calculating methodologies were developed considering the soil as a homogeneous and isotropic medium. However, actual soil is better represented if stratified into horizontal layers of different resistivity values. This paper presents a simplified expression for the calculation of the resistivity value of a uniform soil that can represent a two-layer stratified soil in lightning induced voltage calculations.