Geophysical Investigation of Foundation Competence at a Proposed Housing Estate Site in Kaduna, North West Nigeria

The expansion of residential housing estates in Kaduna State, driven by a growing urban population, necessitates thorough geotechnical and geophysical site characterisation prior to construction to avoid costly foundation failures. This study investigates the geotechnical competence of a proposed 15-hectare housing estate site in Kaduna South using electrical resistivity tomography and seismic refraction. Three 200-metre ERT profiles and four seismic refraction traverses were acquired across the site following a grid layout. RES2DINV inversion produced two-dimensional resistivity models highlighting a lateritic zone of variable thickness, underlain by fractured and fresh basement. Compressional wave velocities from refraction analysis range from 400 metres per second in the weathered topsoil to 3,800 metres per second in the fresh basement, providing a basis for rippability and foundation bearing capacity assessment. Correlation of resistivity and velocity models identifies three zones of concern where weathering extends beyond 10 metres depth, suggesting low bearing capacity and potential for differential settlement. These zones are recommended for either deep foundation solutions or pre-treatment of the subgrade prior to construction. The integrated geophysical approach demonstrates its cost-effectiveness relative to dense borehole programmes in providing a continuous subsurface image across the site. Results are presented alongside geotechnical classification criteria applicable to Nigerian building codes. Keywords: resistivity tomography, seismic refraction, foundation competence, Kaduna, site investigation