Electrical Resistivity Imaging

Electrical Resistivity Imaging (ERI) provides a 2D, a pseudo 3D or a 3D image of the survey area. This testing technique provides imagery of the different types of soil as they interact with the electrical current induced in to the soil. ERI can be used to identify:

· Depth to the Bedrock

· Rock Fracture Mapping

· Karst Features

The depth of this testing technique is limited to the length of the survey line distance. On average, ERI depth of survey is 20 to 25 percent of the line length. Therefore, if that survey line is 100 feet long the expected depth will be between 20 and 25 feet below land surface (bls). Depending on the target of the investigation, the spacing of the electrodes will dictate the length of the line. Survey lines can have a max of either 56 or 112 electrodes depending on the type of system being used. The benefit of ERI over Seismic Refraction is how ERI testing will continue through the strata instead of stopping at a hard refractor such as rock.

In some cases, such as transmission line pathways, solar farms or wind farms, the soil conductivity is essential. This information can provide the engineer with the data necessary to design the proper grounding grid or cathodic protection system necessary for their project. Four Oaks Geophysics is able to test soil resistivity testing using Wenner Array or four pin method (ASTM G57-06) to log the soil resistivity values throughout the survey area.