Application of Geophysical Resistivity Surveys in Site Investigation for Building Foundation in Makurdi

Subsurface heterogeneity in alluvial and basement complex terrain presents significant geotechnical risk for building foundations if not adequately characterized during site investigation. This study applies two-dimensional electrical resistivity tomography to subsurface characterization of four proposed building development sites in Makurdi, Benue State, North Central Nigeria. Wenner-Schlumberger and dipole-dipole electrode arrays were deployed along perpendicular profile lines at each site, with electrode spacings of 2 m and maximum depths of investigation of approximately 20 m. Data inversion was performed using RES2DINV software to generate two-dimensional resistivity cross-sections. Interpretation of resistivity profiles at each site identified subsurface features including clay lenses, weathered basement zones, possible void spaces, and water-saturated horizons at variable depths. One site exhibited a near-surface resistivity anomaly interpreted as a laterally discontinuous clay lens at 3 to 5 m depth, indicating potential differential settlement risk. Geophysical interpretations were validated against available borehole logs and cone penetration test results where available. A professional foundation recommendation was derived for each site specifying appropriate foundation type, minimum depth, and areas requiring additional investigation or ground improvement. The study demonstrates the cost-effectiveness of two-dimensional electrical resistivity tomography as a rapid, non-destructive pre-design site investigation tool and provides a standard operational workflow for geotechnical practice in the Benue River basin environment. Keywords: electrical resistivity tomography, site investigation, foundation design, Makurdi, geophysics