Abstract

This study is aimed at investigation for foundation designs at the West Bank Creek, Lagos deep offshore. All field tests were conducted in accordance with standard geotechnical procedure. The soil profiles obtained within the depth explored at the site consist essentially of two soil zones. They are very soft silty clays and medium dense sands. Results revealed that within the depths bored, a relatively high deposit of clay overlies the boreholes from the river-bed to average depth of 3.0 m. In BHs 8, 10, 11 and 12, the clay extends beyond 3.0m thickness with varying depths ranging from 5.0 m to 8.0 m. However, prevalent deposits of sand underlie the clay to the end of the boreholes. In BHs 6 and 9, the entire holes are characterized by huge deposits of sand formation. Notably, the sandy formation exhibited appreciable Standard Penetration Test (SPT) blows indicating sands of medium densification. Based on the field investigations and comprehensive studies, the estimated volume of available sand fill material is 691,863 m³. Sand volume estimate was limited to -10.50 m from the river-bed. All the boreholes have potentials for sand borrows. Scooping of the clayey materials is required to expose the sand deposits. Dredging operation with appropriate dredger should be limited to the area covered by the survey.

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