Induced polarization (IP) is the Earth’s capacity to hold an electric charge over time. IP measures the voltage decay curve after the injected current is shut off. The higher the IP, the longer over time the charge is held—IP decays over time, typically a few seconds but sometimes up to minutes, and will eventually disappear. IP is especially useful for mineral exploration applications.
Inversion is the mathematical process of calculating cause from a set of observations. In resistivity work, it is used to calculate the resistivity of different formations in the ground from a set of readings taken at the surface or between boreholes.
Have you ever prepared for a vacation, only to arrive at your destination and realize you’d neglected to pack important attire and equipment for your holiday? Recently, in my haste to prepare for a trip, I didn’t make a list and found myself in this very situation—I ended up wearing wool sweaters and jeans in an 80-degree climate.
In the 1980s and early 1990s, geophysicists became largely disenchanted with electrical resistivity because of the inadequacies of Vertical Electrical Sounding (VES). Specifically, the VES method assumes that the imaged geology is horizontally layered and that each layer is homogeneous. Of course, this often isn’t the case, causing some project managers (and their clients) to become fed up with the unusable results.
Throughout most of the 20th century, Vertical Electrical Sounding (VES) was the dominant geophysical resistivity method. It has been used all over the world for three primary purposes: geotechnical investigation, groundwater exploration, and mineral exploration. VES is performed using either the Wenner electrode configuration described in the ASTM G57 standard or using the Schlumberger electrode configuration. (The Schlumberger method is most commonly used for groundwater and mineral exploration, because it is less labor intensive than the Wenner method.)
A switch box with a grid of electrode take-outs. Make your own electrode setup. Great for labs and boreholes.
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. The electrolyte serves as a conduit for the electron flow from the anode to the cathode. In steel structures where no electrolyte is present (like a steel building), they are best protected by galvanizing (zinc coating) or simply painting.
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: