Evaluation of the Geotechnical Properties of Residual Soils in Two Different Basement Complex Areas of Nigeria

Rocks from the Basement Complex areas of Nigeria weather to produce residual soils of varying geomechanical properties. Two such soils from the zone of accumulation were collected from Ore (Ors) and Abuja (Abs). The soils were understudied for their suitability for use as construction materials by subjecting to geotechnical analyses in order to evaluate their index and engineering properties. Ors with clays, silts, sands and gravel of (17, 22, 60 & 01) % respectively, and specific gravity of 2.57 g/cm3 is classified as a silty sand with clays whereas Abs is clayey sands with gravels. Their index properties are in the order: LL, (43.45 & 51.7) %; PI, (12.14 & 31.57) %; linear shrinkage, (8.57 & 12.1) %; free swell, (11.1 & 22.5) %; liquidity index, (-1.10 & -0.09); group index, (3.30 & 9.54); and plasticity plots, (ML & CH) for Ors and Abs respectively. Similarly, their engineering characteristics are as follows: maximum dry density, (1.52 & 1.49) g/cm3; optimum moisture content, (22.0 & 22.5) %; change in void ratio, (0.18 & 0.39); change in porosity, (0.05 & 0.10); cohesion (20.65 & 31.65) KN/m2; shear strength, (86.63 & 88.9) KN/m2; and CBR, (27.86 & 26.79) % respectively. Overall, this study shows that whilst Ors has superior analytes properties, both soils can be used as subgrades in flexible pavement design as well as for many other common construction purposes.