Pages: (15-40 )
Abstract
This study integrated magnetic and electrical resistivity investigation to characterize and evaluate the subsurface
materials and recognize geologic features (faults/fractures/contacts) that may affect foundation stability in Ilishan-
Remo, a sedimentary terrain in southwestern Nigeria. Three traverses were established for ground magnetic and 1D
Schlumberger Vertical Electrical Sounding (VES) surveys. The magnetic data were corrected for diurnal variations
and offset, and processed into profiles. The profiles identified geologic structures (fault/fracture/contact zones) that
often associated with weak zones that can compromise the integrity of civil engineering foundations underneath the
examined traverses. The VES data were interpreted to reveal a typical subsurface sequence of topsoil, lateritic layer,
clayey sand/sand, sand/sandstone. Results indicated that zones underlain by competent lateritic and clayey sand
materials with relatively high resistivity values (> 300 Ωm) and high thickness values are more suitable for foundation
purposes. Conversely, areas characterized by low resistivity values (< 200 Ωm), indicative of clayey or water-saturated
materials, were identified as geotechnically weak and unsuitable for shallow foundation systems without
improvement. Structural anomalies detected in the magnetic profiles corresponded with areas of low resistivity and
thicker weak layers, confirming their geotechnical significance.
Keywords: ound magnetics, Vertical Electrical Sounding (VES), Schlumberger Array, Subsurface Evaluation, Sedimentary terrain.,