Seismic Characterization of Subsurface Soils at Ikot Abasi, Nigeria Through Integrated Geotechnical Investigations

Abstract

Subsurface exploration programs comprising borehole drilling, sampling, in-situ testing and geophysical profiling were conducted at Ikot Abasi in southern Nigeria to comprehensively evaluate seismic properties of the near-surface soils. Laboratory index testing of soil samples provided classifications and insights into the complex stratigraphy consisting of interbedded sand, silt and clay deposited under fluvial-deltaic and marine conditions characteristic of the Niger Delta region. Shear wave velocity profiling utilizing multi-channel analysis of surface waves generated high-resolution small-strain shear modulus logs. Derived Vs30 values classified the site according to international codes. Empirical correlations developed between in-situ penetration resistance, grain characteristics and shear wave velocity closely matched field measurements, validating the regression models' capability to reliably estimate seismic response from index parameters. Simplified methods incorporating normalized penetration resistances and dynamic properties assessed the stability of soil strata against liquefaction. The systematic approach aligned with established protocols and furnished robust microzonation/design data. In conclusion, the integrated field and analytical investigation techniques enhanced geological comprehension and validated predictive seismic characterization of the heterogenous subsurface deposits at Ikot Abasi.