Estimating the Depth of Investigation in Electrical Resistivity Survey: Laboratory Measurements

Albert Asare; Frederick Owusu-Nimo; Bukari  Ali; Bernard Audinada Ampofo

doi:10.4314/just.v42i1.1574

Dr. Albert Asare Kwame Nkrumah University of Science and Technology https://orcid.org/0000-0002-3351-9461
Dr. Frederick Owusu-Nimo Kwame Nkrumah University of Science and Technology
Mr. Bukari Ali Kwame Nkrumah University Of Science and Technology | KNUST Department of Geological Engineering
Mr. Bernard Audinada Ampofo Kwame Nkrumah University of Science and Technology

DOI: https://doi.org/10.4314/just.v42i1.1574

Keywords: Depth of investigation, Vertical electrical sounding, Schlumberger array, Wenner array, Apparent resistivity

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).

Author Biographies

Dr. Albert Asare, Kwame Nkrumah University of Science and Technology

Albert Asareis a lecturer at the Geological Engineering Department, KNUST, Kumasi Ghana. He joined the Department in 2020, and has since been lecturing and teaching in Principles of Geophysics, Exploration Geophysics, Hydrogeology, Groundwater development, and professions. His research interest is in the application of geophysical methods in solving environmental engineering issues like Groundwater exploration, groundwater contamination, geotechnical investigations, and groundwater development. His current research focuses on mapping seawater intrusion along the coastal communities using both the geophysical and hydrogeochemical approaches and coastal wetland studies.

Dr. Frederick Owusu-Nimo, Kwame Nkrumah University of Science and Technology

Frederick Owusu-Nimo is a Civil Engineer and Senior Lecturer at KNUST, Kumasi. He has over 10 years of experience in geotechnical, geo-environmental, and geophysical engineering. He has been involved in developing relationships between geotechnical properties and geophysical parameters of soils to aid in the use of geophysics in engineering and environmental investigations. He has also participated in characterizing illegal mining (Galamsey) sites and operations in selected districts in Ghana. Dr. Owusu-Nimo has also been involved in studies related to the geotechnical properties and characteristics of landfill waste and liner materials. He is interested in the characterization of lateritic soils and earth materials.

Mr. Bukari Ali, Kwame Nkrumah University Of Science and Technology | KNUST Department of Geological Engineering

Bukari Ali is a Part-time Lecturer at the Geological Engineering Department, KNUST, Kumasi. He has over 35 years of experience in groundwater exploration and exploitation. He has been teaching courses in principles of geophysics, exploration geophysics, hydrogeology, and groundwater development, engineering geology and geotechnical engineering. His research interest is in hydrogeology and groundwater geophysics.

Mr. Bernard Audinada Ampofo, Kwame Nkrumah University of Science and Technology

Bernard Audinada Ampofo is a Senior Technician at the Department of Geological Engineering, KNUST, Kumasi. He is a Geological Engineer and holds a masters in Geophysical Engineering from KNUST. His research interest is in the application of geophysics in in the fields of hydrogeology, environmental science, and geotechnical engineering. He has collaborated with some faculty members and postgraduate students in undertaking various research works across the country. His current research area is focused on integrating near-surface geophysics and modeling techniques in hydrogeophysics and environmental science.