keywords: Geotechnical properties, Engineering properties, Foundation design, River crossing.
Geotechnical properties of soils along some coastal communities in parts of the southern Niger Delta was carried out with a view of linking the upland and some coastal communities in the southern Niger Delta and the determination of engineering properties of the subsoils for bridge foundation design. Field studies comprised of drilling of 6 boreholes which included cone penetration tests and standard penetration tests. Laboratory studies included classification tests, triaxial, consolidation and California bearing ratio (CBR). The results revealed that the soil profile consists of a top organic clay (CL) from 0 – 3m, underlain by 6 m thick clayey sand (SC) layer, which is in turn underlain by 10m thick layer uniformly to poorly graded (GP-SP) sands and gravelly. Water table was encountered at the depth of 0.1-1.6m. The clay layers have the following average values: moisture content 80%, LL 76%, PL 26.6%, PI 49.9%, and average organic content of 5.6%. The shear strength ranges from 13.67kN/m2 – 40.87 kN/m2, optimum moisture content (OMC), maximum dry density (MDD) and soaked California bearing ratio (CBR) range from 13-22.7%, 1.09 – 1.88mg/m3, and 1 – 34% respectively. Cone penetration test (CPT) met refusal at 8m depth. A 400mm diameter pile transferred to a depth of 30m produce allowable bearing load of 7.6 x 107kN. Based on the soil profile and the mechanical design parameters, pile foundation terminating at the depth of 30 meters was recommended at river crossings.