EMPIRICAL RELATIONSHIP BETWEEN ELECTRICAL RESISTIVITYAND GEOTECHNICAL PARAMETERS: A CASE STUDY OF FEDERAL UNIVERSITY OF TECHNOLOGY CAMPUS, AKURE

Abstract

Electrical resistivity measurement and geotechnical tests were carried out at a part of the Federal University of Technology, Akure Campus. The apparent resistivity and geotechnical parameters distribution at the depth of 1 and 2 m were obtained with the aim of establishing an empirical relationship between the two parameters. The electrical resistivity data was acquired at ten (10) locations that cut across the geology that underlay the study area. Schlumberger configuration was adopted with electrode spreading corresponding to the depth of interest (1 and 2 m). The geotechnical analyses were carried out on twenty (20) soil samples taken at the depth of 1 and 2 m from the ten sounding locations where apparent resistivity (a) values were determined. The geotechnical tests conducted include; natural moisture content, grain size analyses, specific gravity, Atterberg limits, compaction, California bearing ratio (CBR) and unconfined compression tests. ArcGIS 10.1 software was used to generate maps showing the iso-resistivity as well as the geotechnical parameter distribution across the study area at 1 and 2 m depth. It was observed that they all correlate with the composition of the weathering end-product of the geology of the study area. The apparent resistivity values obtained within the study area ranges from 45 to 487 m and 8 to 701 m at the depth of 1 and 2 m respectively. The apparent resistivity values obtained were plotted against each of the geotechnical parameter using Microsoft Excel software, and the trend line was used to obtain the resultant linear empirical equation as well as the coefficient of correlation. From the correlated plots at both depths, it was observed that specific gravity, maximum dry density and California bearing ratio exhibit a direct relationship with apparent resistivity. Other analyzed parameters such as moisture content, clay and silt content, liquid limit, plastic limit, plasticity index, linear shrinkage, optimum moisture content and unconfined compression shear strength exhibit an inverse relationship with apparent resistivity. Almost all the cross plots at both depths show a relatively good correlation with coefficient of correlation (R) ranging from 0.52 to 0.93, except for plastic limit that weakly correlates with apparent resistivity, whose coefficient of correlation is 0.34 and 0.38 at 1 and 2 m depth respectively, and plasticity index with coefficient of correlation of 0.44 at 1 m depth.