Reduction factor for the ground resistance of the foot in substation yards

Limited thickness of the surface layer of gravel in a substation yard decreases the ground resistance of the foot from its value for the infinite thickness of the surface layer, by reduction factor C. The foot is usually represented by an equivalent circular plate of radius 8 cm. This paper presents method and equations to accurately determine the reduction factor for the circular plate. The equations are valid for any depth of the upper layer. The data is presented in the form of graphs. A simple empirical equation for determining the value of C is also presented