Application of radial electrical resistivity profile array for mapping deep vertical fractures in a proposed engineering construction site within the University of Ibadan Campus, Southwestern Nigeria

Abstract

In this study we demonstrate the efficacy of radial electrical resistivity profile array in delineating deep narrow linear fracture that could constitute weakness in the subsurface, thus hindering foundation material in providing necessary support to proposed engineering construction, in the southeastern part of the University of Ibadan Campus, southwestern Nigeria, where nearby buildings show stress induced failure traceable to defect in foundation upon which the buildings were founded. Six electrical resistivity profile arrays were occupied at 0°/180°, 307210°, 607240°, 907270, 1207300° and 1507330° orientations to complete a clockwise 360° sweep at 30° interval. The radial profile array enabled subsurface features to be intersected at relatively high angle, thus making measurement of linear features of limited lateral extent feasible irrespective of their orientations. Low resistivity distribution which decreases in value with depth (300-8 $\Omega$ m) characterizes the northern part of the study area while relatively higher value that increases with depth (420-4150 $\Omega$ m) dominates the south. The occurrence of a narrow strip of low resistivity zone (8-170 $\Omega$ m) at 20 m, which gains prominence with depth, dividing relatively resistive zone in the southern part of the study area indicate the presence of a deep vertical fracture whose detection is essential to guide further foundation geotechnical studies as well as aid the design of appropriate foundation that would support the proposed engineering structure.