Analysis of apparent resistivity in a multi-layer earth structure

An expression for the apparent resistivity in an earth structure with an arbitrary number of layers is derived for the Wenner four-electrode method. The expression is arrived at by performing an analysis of apparent resistivity in a multilayer structure as an extension of studies that have concentrated on the two-layer model. Applying a series of parameter data to this expression enabled the preparation of ρ-a curves for such a multilayer structure, and these curves were compared with actual ρ-a curves obtained from two case studies. The results showed good agreement, indicating that the proposed expression and parameter estimation technique could be practically applied to ground design problems. In particular, earth parameters for a multilayer structure obtained through the proposed method can be used for calculating the ground resistance required by deep-driven rods in a particular geologic formation