A Simplified Approach to Resistivity Survey

The resistivity survey is among the common methods in archaeological geophysics. This aims to detect and map subsurface archaeological features and patterns without the need to dig through the ground. This is done for various reasons. Among them is the site construction. Surveying the area is among the first phase in planning its construction. The condition of the ground underneath must be ascertained before the construction starts.

The survey aims to test and gather relevant information about the mineral and fluid content of the soil, porosity and degree of water as well as the saturation in the rock underneath. These are all very important factors to consider for the proper foundation of the structures. As the earth’s lithosphere move a bit every once in a while, it is best to know the current condition of the earth before digging through.

This study has been commonly used for hydrogeological, mining and geotechnical purposes. It may be the first step towards mining, digging for water system, checking the current waterways or testing the mineral content of the ground. Recently, it was also used for environmental purpose that aims to test the safety of the ground.

This uses four sets of electrode. One pair will be carrying the current towards the ground of the site of interest. Another set will measure the voltage the moment the current hits any material underneath. The ratio between the voltage and the electric current is the resistance. This will be determined and recorded in ohms. This is the basis for the information that will be noted.

Generally speaking, any fine and densely packed damp silty materials can easily let the current pass through. Hence, the resistance is less. On the other hand, a stony deposit or bottoms with more expansive space both offers high resistance. With the noted information, the condition of the earth may be estimated.

A different array of cathode is also used to reach different levels. Some are compact enough to reach the bottom part of the earth, while others are used to reach only a minimum distance. The distance to be determined will depend on how large the area that needs to be tested.

After the information has been gathered, the resistance on different areas will be recorded. The data will be interpreted accordingly. Afterward, the underground condition will be mapped for future reference. This will be the basis for the planning of the site construction.

One of the benefits a company can get from this technology is the relevant information that it can get without having to dig through the ground. Blindly digging through may cause much damage on the pipelines, waterways, underground cables and the likes. This will be an additional cost to the company and are much of a hassle to the residents.

However, the resistivity survey also has its limitations. Among the common limitation is that it needs an ideal condition of the soil during the testing and data gathering. The soil must not be not too dry or too wet. Its greatest limitation, though, is the inability to determine lateral changes in the layer resistivity. This limitation may result to an error in interpretation and is very crucial to the construction.

Advanced Geosciences, Inc. (AGI) with headquarters in Austin, Texas, specializes in manufacturing and development of high-resolution geophysical instruments for resistivity survey and IP imaging. (http://www.agiusa.com/)


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