Subsoil Engineering Characterization and Foundation Design in Derived Geological Coastal Sands of Ilaje Area of Ondo State, Nigeria

Abstract

Engineering subsoil evaluation and foundation design have been undertaken at Ilaje area of Ondo State, Nigeria. The aim of this study was to examine the geo-electrical and geotechnical parameters of the subsoil to sustain building structures and also provide appropriate foundation design alternatives. A total of six VES stations were occupied and complemented with geotechnical analysis of seven soil samples collected at two cone penetration test locations. The result showed that all the determined geotechnical parameters of the subsoil fall within the specification recommended for foundation material by federal ministry of works and housing of Nigeria. The VES showed a predominant (66.67%) HKQ curve type. The upper 5 m is characterized by moderate thickness and high resistivity (average of 450ohm-m) values to sustain structural load. An average allowable bearing capacity of 150 KN/m2 was recommended for design of bases/footings for shallow foundation at a depth not less than 1.0 m. The obtained settlement values are less than 50 mm and within tolerable limit, for foundation width ranging from 0.5 to 3.0 m. However there was drastic reduction in settlement values (below 25mm) when the foundation width was increased to 2 and 3m. The allowable capacity of the driven pile ranges from 64 – 115 KN, 206 – 347 KN, and 418 – 677 KN at 5m, 10 m and 15 m respectively. The allowable bearing capacity for bored piles ranges from 34 – 69 KN, 85 – 165 KN, and 146 – 268 at depth levels of 5 m, 10 m, and 15 m respectively.