Comparison of SPT-N Correlations for Different Geological Formations in the Niger Delta Region of Nigeria

Abstract This study developed region-specific empirical correlations for estimating Standard Penetration Test (SPT)-N values across different geological formations in the seismically active Niger Delta region of Nigeria. Extensive in-situ and laboratory geotechnical investigations were conducted to obtain SPT blow counts and characterize engineering properties of soils representing the loose Benin sands, stiff Agbada sands, and indurated Akata shales. A database of over 1500 SPT-N data points and soil parameters was compiled from 50 borehole logs spanning Rivers, Bayelsa, Akwa Ibom, and Delta states. Multiple linear regression analyses were performed to derive generalized and formation-specific SPT-N predictive models relating blow counts to depth, effective stress, and geological unit. The developed correlations showed good agreement (R2 > 0.68) with measured field values. Comparisons with existing empirical models from literature validated the accuracy of the customized regional approach. Predicted SPT-N values allowed estimating shear wave velocities based on established relationships, enabling classification of sites according to seismic design categories. This study highlights the need for developing geology-specific correlations to properly characterize the spatially varying geotechnical properties across the structurally complex Niger Delta subsurface. The generated predictive models enhance regional subsurface investigation for geohazard assessment and foundation design.