Geotechnical Characterization of Sandy Soils in the Niger Delta Using SPT-N Values

This study provides a comprehensive geotechnical characterization of sandy soils in Nigeria’s Niger Delta, focusing on Standard Penetration Test (SPT-N) values, effective overburden pressures, grain size distribution, and friction angles. A total of 71 soil samples were collected from five representative sites—Kana Ataba, Okansu Bridge, Otuogori Bridge, Rumuibekwe Bridge, and GRA—spanning coastal, wetland, peri-urban, and urban environments. Field investigations followed ASTM D1586 procedures, while laboratory programs included unit weight determination, grain size analysis, moisture content assessment, and consolidated drained triaxial compression for shear strength evaluation. SPT-N values ranged from 4 to 51 (mean = 28.3, CV = 39.7%), indicating very loose to very dense sands with marked spatial heterogeneity. Friction angles (φ) varied from 26° to 38° (mean = 31.6°, CV = 8.6%), showing relative uniformity in shear strength despite depositional variability. Effective overburden pressures spanned 26.1–304.8 kPa (mean = 157.8 kPa, CV = 48.4%), while grain size distribution (D50) ranged from 0.002–2.008 mm, reflecting contrasting depositional energy conditions. Statistical analysis confirmed significant spatial variability in SPT-N values (Kruskal–Wallis H = 14.65, p = 0.005), whereas friction angle and effective stress did not differ significantly (p > 0.05). This study establishes the first regional geotechnical database for Niger Delta sandy soils, integrating in-situ and laboratory data to capture both variability in penetration resistance and consistency in frictional strength. The findings provide essential baseline parameters for pile capacity estimation, settlement prediction, and bearing capacity assessment, supporting safer and more cost-effective infrastructure development in complex deltaic environments. Beyond regional application, the database contributes to geotechnical practice in deltaic systems worldwide.