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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.)
There are many different types of aggregate materials found in various geographic locations:
The ASTM G57 standard (also known as the four-pin Wenner method) is used to determine the properties of soil.
Soil tests can be performed in many ways and for a number of reasons.
To best understand how electrical resistivity surveys for groundwater exploration work today, it’s important to understand where resistivity testing began.
Brothers Conrad and Marcel Schlumberger performed the very first investigation of how electrical current moves through the ground and what you can detect using an electrical resistivity survey in the early 1900s. From their research came what is now one of the most common methods of groundwater exploration, vertical electrical sounding (VES).
VES uses four electrodes...
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.
Grounding tests are mainly used at lightning protection systems, electrical substations, and industrial sites where expensive machinery needs to be...
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.
To understand the need for land subsidence testing and monitoring, think of the need for both MRIs and X-rays. Just because a patient says his shoulder hurts doesn’t mean a...
One way that sinkholes form is when 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 and highly controlled electric current across an array of electrodes.
Electrical resistivity imaging (ERI)—also known as electrical resistivity tomography (ERT)—is a geophysical technique used to create an image of a specific portion of the Earth’s subsurface. It is created through the use of automated geophysical instruments that gather thousands of resistivity measurements via an electrode cable and multiple electrodes.