INTEGRATED GEOPHYSICAL INVESTIGATION OF FOUNDATION CONDITION BENEATH A BUILDING SITE IN FUPRE FOR CIVIL ENGINEERING CONSTRUCTION PROJECT. (2D WNENNER AND SEISMIC REFRACTION METHOD)

ABSTRACT An integrated geophysical investigation involving 2D Wenner electrical resistivity and seismic refraction methods was conducted at the FUPRE building site to evaluate subsurface conditions for civil engineering foundation design. Three major subsurface layers were delineated across all profiles. Seismic refraction results showed average P-wave velocities of approximately 265 m/s for the first layer, about 445 m/s for the second layer, and about 890 m/s for the third layer. These velocity values correspond to: a very soft and loose topsoil layer with low stiffness, a moderately compacted lateritic or sandy–clay unit with improved load-bearing capacity, and a dense lateritic or weathered basement layer representing the most competent foundation material. The average resistivity values also support this layer classification, with low resistivity in the topsoil, moderate values in the intermediate lateritic zone, and high resistivity in the competent deeper layer. Integrating both methods reveals that the topsoil layer is unsuitable for direct foundation loading due to its low velocity and weak mechanical properties. The second layer is generally adequate for shallow foundations, especially where it is sufficiently thick and laterally continuous. The third layer, characterized by high seismic velocity (>850 m/s), is the most competent horizon, suitable for heavy structural loads or deep foundation anchorage. Overall, the integrated geophysical results indicate that the site is suitable for building construction once the weak topsoil is removed or bypassed, and foundations are properly seated on the moderately compacted lateritic layer or extended to the deeper competent layer where necessary. The study demonstrates the effectiveness of combining resistivity and seismic techniques for reliable engineering site characterization in the Niger Delta environment.