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Published:
Mar 7, 2024Keywords:
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Estimating the Depth of Investigation in Electrical Resistivity Survey: Laboratory Measurements
Dr. Albert Asare
Abstract
The depth of investigation in geo-electrical resistivity surveys is an important parameter required to make a reasonable interpretation of the measured apparent resistivity. Even though it is generally accepted that, the wider the electrode spread the deeper the investigation, no definite relationship has been developed between the depth of investigation and the current electrode spread (AB) for geological formations, especially in Ghana. The most commonly used depth factor for Schlumberger array (AB/2) for example, have been found not to be accurate from field observations. This study thus explores the depth of investigation for the Schlumberger and Wenner arrays through a laboratory study. A rectangular wooden box filled with compacted silty sand to different depths was placed directly on the natural ground, and the interface between the silty sand and natural ground was investigated through geo-electrical sounding. The vertical electrical sounding curves were inspected for points of conspicuous changes in apparent resistivity, which were attributed to the change from the silty sand to the natural ground interface. Then comparing the known depths of the interface to AB, it was established that, for both the Schlumberger and Wenner arrays, the depth of investigation is about 0.26 of AB (i.e., ~AB/4).
