Characterization of problematic subsurface soils in Eha-Amufu using integrated investigation approach: implications for earth works

Abstract

Mapping of the subsurface is a vital procedure during construction. It enhances hazard zonation, planning and protection of engineering structures. The present study centres on an area susceptible to foundation instability and building collapse in Enugu State, southeastern Nigeria. The study followed an integrated research method by employing a geotechnical approach and geophysical surveys such as electrical resistivity and remote sensing performed using Landsat, Aeromagnetic and shuttle radar topography mission (SRTM) images. Geotechnical data revealed that the subsurface comprised soils with higher fines (69%) than coarse (31%) grain sizes, high liquid limit (27–76%), plasticity index (9–46%), natural moisture content (6.0–14.8%) as well as low specific gravity (2.49–2.67) and coefficient of permeability (2.27 × 10–8–1.81 × 10–4 cm/s). Shear strength parameters- cohesion (13–35 kPa) and internal friction angle (9–21°) were low to moderate as well as the coefficient of consolidation (0.04–3.84 m2/mN) and coefficient of volume compressibility (0.05–0.29 m2/year). These properties are reminiscent of silty-clay soil of high plasticity and compressibility. The low soil resistivity with values ranging between 10 and 170 Ωm and aeromagnetic signal strength of 8.74 × 10–5 nT/km confirmed the silty-clay classification. The moderate to high lineament density determined from the remote sensing methods indicates the influx of moisture from higher surrounding grounds into the area to initiate high groundwater regime and flooding as observed in the fieldwork, which consequently triggers the activity of clay minerals present in the clay.