The Use of Electrical Resistivity Tomography (ERT) for Engineering Site Investigation in the Ugbowo Campus of the University of Benin, Benin City, Nigeria

Abstract

A 2-D electrical resistivity tomography (ERT) survey was undertaken at the site of the blocks of flats in the Ugbowo Campus of the University of Benin, Benin City, Edo State, Nigeria with a view to determining the integrity of the soil in and around the location of the buildings. The survey employed the Wenner-Schlumberger electrode array for data acquisition over an area measuring approximately 200 X 200 m². Data acquisition was carried out on two (2) sets of six (6) traverses of lengths 200 m and 100 m each respectively. The electrode separation was 10 m and 5 m respectively. The study was aimed at determining the integrity of the soil where the apartment blocks are located. The values of resistance measured in the field are converted to apparent resistivity values which are then inverted with RES2DINV software developed by Geotomo and the results displayed as pseudosections. Analysis of the 2-D electrical resistivity tomography results showed wide vertical and lateral variation in resistivity along the traverses. Resistivity values in the range of 20 Ωm to 14,000 Ωm were obtained during the field survey. The results also showed that the subsurface is made up of mostly lateritic sand, gravel and basement rock. The results did not show the presence of clay, faults, cavities or any subsurface feature that poses any danger to the buildings. The results of the survey indicate that the high-rise blocks of apartments are in no danger of collapse from the effect of unstable subsurface structures.