Subsurface characterization and shear strength evaluation for infrastructure stability: A case study of university of Ilorin teaching hospital, Ilorin, Nigeria

This study integrates geophysical and geotechnical methods to assess subsurface properties and soil shear strength for engineering applications. Electrical resistivity techniques, including Schlumberger vertical electrical sounding, Werner horizontal profiling, and dipole-dipole inversion models, were used to characterize the subsurface. The results revealed significant variations in resistivity, with high-resistivity zones 1400 – 4354 Ωm corresponding to stable materials such as dry sand, compacted soil, or rock, while low-resistivity zones 15.5 – 153 Ωm indicated weaker formations, including clay and water-saturated soils. These findings highlight potential stability concerns, particularly in areas with high moisture retention. Direct shear tests were conducted to evaluate the soil’s mechanical behavior under varying normal stresses of 5 kg, 10 kg, and 15 kg. The results demonstrated an initial strain-hardening phase followed by peak shear strength and plastic deformation. Higher normal stress enhanced shear resistance, confirming a direct relationship between applied stress and shear strength. The computed cohesion values ranged from 50 to 100 kPa, and internal friction angles varied between 28° and 32°. Profile 2 exhibited higher cohesion, suggesting stronger bonding suitable for static structures, while Profile 3 showed greater frictional resistance, making it more appropriate for retaining walls and embankments. Overall, the study confirms that subsurface variability significantly influences soil strength and stability. Understanding these parameters is crucial for infrastructure planning, ensuring foundations and load-bearing structures are positioned on competent ground. Unlike previous Nigerian studies that often treated geophysical and geotechnical data separately, this study integrates multi-array resistivity with direct shear testing to provide a site-specific geophysical-geotechnical correlation model for infrastructural stability assessment. The findings emphasize the need for site-specific evaluations, considering factors such as water infiltration and cyclic loading, to mitigate potential structural failures.