RESAP | Soil Resistivity Analysis


The RESAP (Soil Resistivity Analysis) computation module is used to determine equivalent earth structure models based on measured soil resistivity data.


RESAP's main screen.



Technical Description

Correctly interpreted soil structures are essential for the analysis of grounding systems, cathodic protection scenarios, electromagnetic induction (EMI) problems, and for the computation of transmission line parameters.

RESAP compares field data to apparent resistivities produced by different soil models, and automatically determines a soil structure yielding a closely matching electric surface response.

In addition, RESAP can be used to approximate the real earth structure using a simplified model based on a reduced number of layers specified by the user. It can also be used to generate limiting soil models, e.g. to ensure that safety requirements are met with a conservative margin despite the fact that the soil structure model exhibits local variations (multiple soil models within the geographical area of interest).


Resulting soil structure from a RESAP analysis.



Technical Highlights

With RESAP, you can develop four fundamental types of soil models:

  • Uniform soils.
  • Horizontally layered soils (any number of layers may be specified).
  • Vertically layered soils, oriented arbitrarily with respect to the electrode array used for the measurements (presently restricted to two layers).
  • Exponentially varying soils, useful for computing transmission line parameters, or to represent frozen soils.


Technical Features

  • Input soil resistivity data for multiples traverses and obtained from Wenner, Schlumberger, Dipole-Dipole or Unipolar methods, or specify your own arbitrary arrangement (General method). Continuously vary the ratio of current probe spacing to potential probe spacing (e.g. a traverse may start as a Wenner – but finish as a Schlumberger configuration).
  • Data can be specified in the system of units of your choice (i.e. metric or imperial) and consistent with your instrumentation (e.g. apparent resistance, apparent resistivity).
  • Optionally specify depth of current and potential probes, for additional accuracy (especially beneficial for smaller electrode spacings).


    Electrode arrangements supported by the application.
    Probe depths can also be accounted for.

  • Identify additional equivalent soil structures by guiding the convergence process with varying initial estimates, and conservatively base your grounding system design on a soil structure corresponding to a worst-case scenario that accounts for seasonal variations.
  • Use the locking feature to have the program calculate a soil model incorporating, partially or totally, the horizontal layer characteristics that you have specified.


    Specification of starting and constrained values for the parameter optimization process.

  • Choose between three powerful least-square optimization algorithms (Steepest-Descent, Levenberg-Marquardt, or Simulated Annealing).
  • Control the process by customizing the iteration parameters and the stop conditions.
  • The high-precision digital filter ensures apparent soil resistivities are computed quickly and accurately.