Engineering Geological Properties of Coastal Plain Sands in Selected Areas in Ikoyi Area, a typical Coastal Sedimentary Terrain

ABSTRACT

Coastal plain sands in some selected areas of Ikoyi, in Lagos, Dahomey basin southwestern Nigeria have been investigated with respect to their geotechnical properties to determine their suitability as construction materials and to recommend suitable foundation type for the proposed developments. Representative samples collected from each sites were subjected to standard engineering tests and CPT method was used for calculating the bearing capacity of the soil. The cone resistance values (Qc) ranges from 8-158 kg/cm³, 20-160 kg/cm³, 32-166 kg/cm³ for Sokoto street site, Parkview estate site, and Delta street site respectively. Correlating this result with standard penetration test values, it shows dense soil at 3m, 10m and 45m for Delta Street site, medium dense soil at 2m and 30m for Parkview estate site, and medium dense soil at 3m, 29m and 30m for Sokoto Street site. The undrained triaxial test revealed that undrained cohesion ranges from 47-70 KNm^-2, 44-95 KNm^-2, and 15-30 KNm^-2 with no angle of internal friction for Sokoto Street, Delta Street and Parkview estate site respectively. These values show that the soils have low bearing capacity due to low undrained cohesion and angle of internal friction. The geotechnical analysis result show that for the proposed building (tower) on the three sites, shallow foundation cannot be supported because the foundation pressure exceeds the bearing capacities of the soil across the three sites at shallow depth and the loads needs to be transferred to more competent soil layer at deeper depth via a non- displacement (or replacement) pile.