Integrated Geotechnical Assessment of Subsurface Construction at Federal University Gusau, Zamfara State, Northwestern Nigeria

Abstract

This study presents an integrated geotechnical assessment of subsurface construction at Federal University Gusau, Zamfara State, Northwestern Nigeria, to evaluate the suitability of the campus subsurface conditions for sustainable building development. An integrated approach involving field geological mapping, vertical electrical sounding (VES), and geotechnical laboratory testing was employed to characterize subsurface stratigraphy and assess the engineering properties of foundation materials. Twenty (20) VES stations were surveyed across the study area using the Advance Detector Model Technology Zone (ADMT ZN300) instrument to determine resistivity variations and delineate subsurface layers. The results revealed a three-to-four-layer geo-electric sequence comprising topsoil/lateritic overburden (0.5–6 m thick; 24–394 Ωm), weathered basement (8–15 m thick; 150–735 Ωm), fractured basement (200–750 Ωm), and fresh basement bedrock occurring at depths greater than 15 m with resistivity values of 750–1200 Ωm. Geotechnical analyses showed that the lateritic overburden exhibits variable engineering properties, with some locations characterized by low undrained shear strength (cu = 15–35 kPa) and high compressibility, making them unsuitable for shallow foundations without ground improvement. In contrast, the fresh basement bedrock exhibits high bearing capacity (>500 kPa), indicating its suitability as a competent foundation horizon. Structural mapping of seventeen outcrops revealed an average dip of 19.2° and dominant NE–SE structural trends, which may influence foundation orientation and groundwater flow. The study therefore recommends the use of deep foundation systems, such as pile or raft foundations extending to the fresh basement bedrock, particularly for multi-storey structures, alongside comprehensive site-specific geotechnical investigations before construction and avoidance of uncompacted lateritic clay zones. The findings provide essential baseline geotechnical and geophysical information for infrastructure planning and sustainable development at Federal University Gusau and other Basement Complex terrains in Northwestern