3D Electrical Resistivity Imaging (ERI) for subsurface evaluation in pre-engineering construction site investigation

Three Dimensional (3D) Electrical Resistivity Imaging (ERI) was carried out for pre-construction foundation investigation of a proposed engineering construction site within the University of Ibadan Campus, south-western Nigeria, where some distressed structures (offices and hostels) have been reported to show stress induced cracks attributed to incompetent foundation support from rocks upon which they were constructed.
The 3D grid of resistivity data generated along parallel and equally spaced profiles stations presented the resistivity distribution of the subsurface as well as delineated zones of relatively high resistivity values (450–4500Ωm) in the east and lower resistivity zones (15–300Ωm) in the west. The study also delineates zones of isolated low resistivity values (10–50Ωm) at the mid and west end of the field. The generated resistivity distribution sections, maps and 3D model indicate spatial variation in resistivity value which varies both laterally and vertically. The variation which is attributed to differences imposed by underlying rock’s structural and geological rock composition resulted from complex rock coexistence as schist (quartz- and amphibolitic-schist) and quartzite coexist as underlying rocks of the proposed construction site, especially since these rocks respond to weathering differently.
The generated subsurface resistivity model guided selection of geotechnical investigation points which captures spatial variation in subsurface physical properties as recorded by the measured subsurface resistivity. Better guided geotechnical investigation provided needed information required to design appropriate foundation support for the proposed engineering structure.