Hello S. Jeyaratnam,
It sounds from your question that you are trying to conduct one of two different grounding tests. Either you are (A) trying to measure the resistance-to-ground of a metal grounding electrode system, or you are (B) trying to measure the soil resistivity of the earth.
(A) The resistance-to-ground of an electrode system is often measured using a test method called the 3-Point Fall-of-Potential test. This test method measures the effectiveness of a grounding electrode system in relation to the soil/earth at some distant point. Here is a link with more info: https://www.esgroundingsolutions.com/about-electrical-grounding/how-to-do-electrical-grounding-system-testing.php
(B) The soil resistivity of the earth at your site is important to understand if you are trying to design a grounding system. A common test method for measuring soil resistivity is the Wenner 4-Point (or 4-Pin) Method. Here is a link with more info: https://www.esgroundingsolutions.com/about-electrical-grounding/what-is-soil-resistivity-testing.php
One other option comes to mind and that is you may be trying to install grounding electrodes and are trying to determine the most effective distance to space them. The Spacing of electrodes deals with a theory known as the Sphere of Influence. Basically you want to space your electrodes out 2-times (2X) the length of the electrode. So, if you are installing 3-meter grounding rods, you would want them spaced at 6-meter intervals. Here is some more information on the Sphere of Influence:
Please let me know if this provides you with enough detail and information to answer your question. If not, please do not hesitate to send over site plans and specifications so that we might better understand your issues.
The Engineering Team at E&S Grounding Solutions