Beneath the surface: detecting soil instability and subsidence risks with ERT and seismic refraction

Abstract

The dominant geotechnical challenge in deltaic zones stems from subsidence because water-saturated soft soils lead to structural failures in buildings. ERT and Seismic Refraction methods were utilized to identify sub-surface conditions at Niger Delta University Amassoma after one of its buildings collapsed into the ground. The sub-surface contains three different layers
of soil with resistivity measurements between 0.453 Ωm and 145 Ωm that represent different levels of moisture content and earth composition. Seismic refraction analysis shows shear wave velocities (Vs) between 128.23 m/s and 230.59 m/s in the upper 13.6 m, correlating with weak, highly compressible soils. N-value analysis demonstrates weak soil strength because N-values show an increase from 2.09 to 3.71 in the upper layers before reaching 9.97-11.43 at deeper levels which signifies improved stability. The results suggest that the collapsed/inking building’s foundation was most likely built on unstable, low-strength soils prone to settlement and failure. This study emphasizes the importance of deep foundation designs and soil improvement strategies for reducing subsidence hazards in similar conditions. The integration of ERT and seismic refraction provides a comprehensive assessment of subsurface instability, offering valuable insights for geotechnical engineering and safer construction in deltaic regions.