NGA_DC_Resistivity - Geophysical Services Environmental...

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Northwest Geophysical Associates, Inc. P.O. Box 1063, Corvallis, OR 97339-1063 (541) 757-7231 Fax: (541) 757-7331 www.nga.com [email protected] D.C. Resisitivity Figure 2 - Schematic Illustrating Basic Concept Of Electrical Resistivity Measurement Geophysical Services Environmental Groundwater Geotechnical · · © 2000 Northwest Geophysical Associates, Inc. INTRODUCTION D.C. resistivity (electrical resistivity) techniques measure earth resistivity by driving a direct current (D.C.) signal into the ground and measuring the resulting potentials (voltages) created in the earth. From the data the electrical properties of the earth (the geoelectric section) can be derived. In turn, from those electrical properties we can infer geologic properties of the earth. In geophysical and geotechnical literature, the terms "electrical resistivity" and "D.C. resistivity" are used synonymously. The term "vertical electric sounding" (VES) is also used to refer to soundings using the D.C resistivity method. The terms "resistivity" or "electrical" are often used to refer to the same methods or techniques, although "electrical" is sometimes used to encompass a broader range of techniques including the electromagnetic methods. APPLICATIONS Electrical resistivity of soils and rocks correlates with other soil/ rock properties which are of interest to the geologist, hydrogeologist, geotechnical engineer and/or quarry operator. Several geologic parameters which affect earth resistivity (and its reciprocal, conductivity) include: · clay content, · groundwater conductivity, · soil or formation porosity, and · degree of water saturation.
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