There are many things to consider before carrying out any new construction and excavation works. Above the surface, it can be relatively straightforward as everything is visible. However, for works below ground there are many things to be considered.
Tests need to be undertaken to determine what might be hidden from the eye that can provide obstacles throughout the building and digging process as a resistivity survey, sometimes referred to as the earth resistance survey is carried out with the use of a resistivity meter
What is a resistivity meter?
A resistivity meter is an electronic measurement device used for soil surveys, locating ground water, and even surveying for underground structures. A meter determines the flow of electric current through the ground when probes are inserted into the earth at regular intervals. The level of resistivity is calculated as the amount of resistance to current flow, determining the different compositions of soil based on the readings.
How does a resistivity meter work?
Dry soil proves to have a very high resistance level as soil and dirt are poor conductors, whereas the presence of water allows electric current to pass freely. Taking readings from the probes offers a good synopsis of the soil composition, which is important when preparing foundations or drilling shafts.
The meter measures wider ranges of current and resistance than a standard electric multi-meter, with the Wenner method, named after the American inventor Dr Frank Wenner being a common calculation in measuring resistivity.
Major applications in which a resistivity metre is used includes underground contamination detection, ground water and mining resources exploration, seawater intrusion detection, bedrock detection for pile foundation, archaeological studies, borehole and cross-hole investigation, urban engineering exploration, real-time monitoring of landslides and tailings dams, geological mapping, sediment detection in rivers, lakes, and reservoirs, dam seepage and leakage detection and cavity exploration. Geomatic services also occasionally use a resistivity metre.
A resistivity meter can also measure salts in the earth, which is an aid to which materials which do not rust to use as salts contribute to corrosion. By inserting protective rods, called anodes, corrosion can be prevented, which is especially useful near to pipelines and metallic structures.
Structures such as transmission towers and buildings, and electrical substations could have electrical or lightning protection grounding rods, so a survey carried out by a resistivity meter will offer pointers to the best location for the grounding equipment to be placed.
Digging up the past
A resistivity meter is used to find the location of ancient artefacts and underground structures by archaeologists. Because the electrical resistance of soil changes around open areas, graves and buried rooms can be detected. Some of the greatest examples of such work can be seen by visiting the world’s leading archaeological museum. Many valuable finds of historical significance have been found with the use of a resistance survey.
In conclusion
Resistivity Meters are electronic meters which measure the resistivity of fluids, slurries or semi-solids and are essential to carrying out surveys where any works take place below ground level.
