Soil resistivity testing is performed for a variety of important applications, including:
Cathodic protection is a method used to reduce steel oxidation through an electrochemical process. Cathodic protection is used to protect buried or submerged pipelines, bridges, and large steel structures from corrosion, breakdown, and rust when an electrolyte (like water with salt and minerals) is present.
Aggregate materials—like sand, gravel, crushed stone, slag, and recycled concrete—provide bulk and strength to concrete or asphalt. Large aggregate quarries and sand and gravel pits are located around most populated areas because of the high cost of transporting aggregate. (In fact, the cost of transportation from the mine to the consumer may even be higher than the actual cost of the aggregate.)
The ASTM G57 standard (also known as the four-pin Wenner method) is used to determine the properties of soil.
Early Methods Of Groundwater Exploration
To best understand how electrical resistivity surveys for groundwater exploration work today, it’s important to understand where resistivity testing began.
Having an accurate image of the subsurface beneath a body of water is beneficial in myriad use cases, including:
The Institute of Electrical and Electronics Engineers (IEEE) Standard 81-2012 “Guide for Measuring Earth Resistivity, Ground Impedance, and Earth Surface Potentials of a Grounding System”, suggests the fall-of-potential grounding test to be used to evaluate the capacity of an electrical grounding system—it is often used by subcontractors to power engineers.
Land subsidence is the act of land moving downward, or subsiding. In many cases, land subsidence can signify the formation of a sinkhole, which you can read about in this article. Land subsidence could also signify the presence of an expansive clay.
Water in the atmosphere reacts with carbon dioxide and forms a weak carbonic acid. As the slightly acidic rainwater moves through fissures in the limestone, it begins to dissolve and widens the fissures—which eventually creates air or water filled pockets. When those pockets become expansive, they’re called “caves” or “voids.” This is a common natural phenomenon in limestone or dolomite known as karstification—but it can be dangerous, expensive, and life-threatening when the ceiling of a void weakens and caves in. This is known as a “sinkhole.”
At the most basic level, electrical resistivity (ER) (as used in geophysics) is the measurement of ground variations gathered by applying a small electric current across an array of electrodes.