Nature and engineering characteristics of foundation soils in Ibeju Lekki area of Lagos, southwestern Nigeria.

Abstract

An investigation of the geotechnical properties of foundation soils was carried out in Ibeju Lekki area of Lagos, Southwestern Nigeria. This was with a view to establishing the nature and engineering characteristics of the subsoils and their behaviour under structural loading. Twenty-five (25) Standard Penetration Tests (SPT) and thirty-five (35) Cone Penetration Tests (CPT) were carried out while thirty-three (33) soil samples were collected. In-situ test parameters (cone resistance and SPT number of blows), index properties (natural moisture content, grain-size distribution and consistency limits), shear strength parameters, compressibility properties, Califonia Bearing Ratio (CBR) and moisture-density relationship were determined in compliance with specifications of the British Standards (BS) 5930, 8004 and 1337. The subsoils in the shallow groundwater level area, were a combination of soil types (clay-sized particles = 9 – 12 % , silt -sized particle= 2 - 9 %, sand = 62 - 87 %, gravel = 2 – 28 %), variable consistency (L = 43 - 118% and I = 19 – 69 %) and shear L P 2 0 strength parameters (C = 20 – 100 kN/m and = 1 - 9 ). For shallow foundation within 1.0 m and 2.0 m, a total u 2 settlement of 23.65 mm was estimated to occur under assumed loading intensity of 45 kN/m with allowable 2 bearing capacity of 121 kN/m . For deep foundation, the allowable loading bearing capacity for a pile of 600 mm diameter set at 8.0 m would be 940 kN. CBR and compacted density results indicated a sub base thickness range of 100 mm - 150 mm for a proposed road layer compacted at optimum moisture content to take care of probable groundwater fluctuation in the area.

Keywords: Creek, Strength, Settlement, Foundation and Subsoils