Integrated 1D and 2D geoelectric subsurface imaging around some distressed buildings within Ilara-Mokin Town

Integrated geophysical investigation using 1D and 2D electrical resistivity techniques were employed for post-foundation investigation around some distressed buildings in Ilara-Mokin, Ondo State, Nigeria. The study was carried out with the aim of characterizing subsoil materials and determining the probable cause(s) of foundation failure within the area. Five (5) traverses with varying lengths from 16 – 57 m were established. The Vertical Electrical Sounding (VES) using the Schlumberger array and combined Horizontal Profiling (HP)/Vertical Electrical Sounding (VES) using the dipole-dipole array techniques were adopted for this study. Qualitative interpretation was done by visual inspection of the pseudosections generated using the DIPROTM software while VES data were interpreted through partial curve matching and later refined by computer iteration technique using Resist Version 1.0. The pseudosections revealed lithological layers interpreted as the topsoil, weathered layer, partly weathered/fractured basement and fresh basement rock. Though these layers were not clearly defined partly due to the inhomogeneous properties of the soil material. The average depth to bedrock was observed to be 5 m with possible fracture zones occurring along traverses 2 and 3. The 1D and 2D images delineated very low resistivity and water clay formation, due to the swampy environment around the study site. The study concluded that the building foundation failures are caused by the incompetent water saturated clayey materials underlying the foundation structures.