Integrated Geotechnical and Geophysical Evaluation of Soils for Determination of Building Site Suitability in Parts of Bayelsa State

Assessment of foundation conditions in the Niger Delta is complicated by shallow groundwater, lateral lithologic variability, and weak fine-grained near-surface deposits.

This study evaluates building-site suitability in selected parts of Bayelsa State, southern Nigeria, using an integrated geotechnical–geophysical approach.

Borehole logging, laboratory determination of index properties, Standard Penetration Testing (SPT), Vertical Electrical Sounding (VES), and Multichannel Analysis of Surface Waves (MASW) were combined to characterize lithology, moisture condition, resistivity structure, stiffness, and bearing competence.

The shallow subsurface is dominated by soft clay, silty clay, and sandy clay, whereas deeper horizons consist mainly of clayey sand, silty sand, and dense to poorly graded sand.

Moisture content ranges from 18.3 to 41.1%, liquid limit from 22 to 73%, and plasticity index from 6 to 41%, indicating wet and moderately to highly plastic shallow soils.

SPT N-values increase from about 6 to 20 with depth, reflecting progressive improvement in competence.

VES delineates 4–6 geoelectric layers, with shallow conductive clay-rich zones showing resistivity values of 35–63 Ùm in Amassoma and Tombia, whereas deeper sandy units in Opolo attain up to 3278 Ùm.

MASW-derived shear-wave velocity increases from about 176 to 606 m/s with depth.

Comparative bearing-capacity estimates from SPT, MASW, and laboratory testing show close agreement, with shallow values generally below 85 kPa and deeper sandy horizons commonly exceeding 120 kPa and reaching about 213 kPa.

The results demonstrate that the upper 2–3 m are generally unsuitable for untreated shallow foundations, whereas deeper sandy horizons constitute the preferred competent founding strata.