An Economical Pre-Mining Tool
Electrical Resistivity Imaging is a sophisticated geophysical surveying tool that can be utilized to map and characterize the subsurface geology over a large area quickly and at significant reduced costs compared to random placement of standard penetration test boring.
What is Electrical Resistivity?
Electrical resistivity measurements involve the passing of an electrical current underground and measuring its resistance to flow. Different earth materials, such as clay, sand and limestone, and subsurface cavities resist the flow of electrical current differently. Substantially greater contrasts in the degree of resistance are used to identify and locate boundaries among different materials as well as the presence of cavities.
This technique helps mining companies improve accuracy and reduce time and costs before mine development commences. Moving overburden is expensive and time consuming and ERI surveying detects target materials before excavation.
How Does ERI Work?
ERI data can be collected using multiple types of arrays. The level of subsurface clarity and the depth limits of the modeled ER data are primarily dependent on the type of array and the total spread of the electrode array. Geohazards will utilize the best array for your situation.
Measurements of ERI are made with Advanced Geosciences SuperSting R8 8-channel Resistivity Meter with an incorporated switch box and a passive electrode cable system. The resulting data is processed utilizing EarthImager 2D or 3D, a computer program that produces two-dimensional or three-dimensional vertical cross section models of the subsurface.
Here is an example of the 2D data processing that can be obtained utilizing ERI.
This 215 foot long ERI traverse depicts low-resistivity clayey materials overlying relatively higher resistivity limestone. The maximum depth penetration for this traverse was approximately 46 feet. The dark and lighter blue zones extend from the surface to approximately 10 to 15 feet below the land surface. The greens and yellow zones represent the underlying limestone bedrock. The vertical blue zone in the middle of the traverse represents a possible infilling of overlying soils into a fracture or cavity in limestone. This anomalous subsurface zone is an area where a sinkhole may form and would be a recommended area for further exploration with an SPT boring.
ERI surveys can be completed in a relatively short period of time. Typically 4 to 5 traverses can be measured in a day and projects covering large areas can be completed in less than a week.