Empirical Relationships Between Seismic Velocities and Geotechnical Parameters in the Lagos Basin

This study develops empirical relationships between seismic wave velocities measured in situ and standard geotechnical parameters in the Lagos Basin, South West Nigeria. Correlating geophysical measurements with geotechnical data improves the utility of seismic surveys for geotechnical engineering applications and reduces the number of costly laboratory tests required for site characterisation. The Lagos Basin's coastal plain sand and alluvial sedimentary sequences present specific geotechnical characteristics that may not be accurately predicted from correlations developed in other geological environments. This study compiles a co-located dataset of in-situ seismic measurements (MASW shear wave velocity and seismic refraction P-wave velocity) and geotechnical parameters (SPT N-value, unconfined compressive strength, CBR, plasticity index, and relative density) from 68 site investigation projects in Lagos State. Sites span Lagos Island, the mainland, and peri-urban areas covering diverse geological conditions from reclaimed coastal sediments to lateritic basement materials. Statistical analysis derives regression equations between Vs, Vp, and geotechnical parameters, assessing correlation strength and confidence intervals. Findings reveal strong power-law correlations between Vs30 and SPT N-value (R-squared of 0.84) in the granular coastal sediments, with distinct regression families for loose coastal sands, lateritic fills, and clay-rich estuarine sediments. Vp shows weaker correlation with unconfined compressive strength in the weathered basement zones. The study produces a Lagos Basin-specific Vs-N value correlation chart for geotechnical practice and recommends its adoption in the Lagos State Ministry of Works geotechnical site investigation guidance.

Keywords: seismic velocity, geotechnical parameters, MASW, Lagos Basin, empirical correlation.