Engineering properties of residual soils in part of Southwestern Nigeria: implication for road foundation

The impact of roads on the socioeconomic development and progress of any country cannot be quantified. A geotechnical investigation of subsoils along Isinbode-Ara road, stretching in southeastern to northwestern direction of 7 km distance within Ekiti State, Southwestern Nigeria, was carried out. This investigation follows the British Standard Institution, such as moisture content, particle size distribution, specific gravity, Atterberg limit, compaction, consolidation and California bearing ratio. Results of investigation showed that the moisture content, specific gravity, liquid limit, plastic limits and plasticity index ranged from 7.2-25.9%; 2.64-2.77; 24.0-61.1%; 19.2-26.2% to 4.35-38.90%, respectively. Grain size distribution showed the fine and coarser fractions range from 13.0-66.5% to 32.6-84.8%, respectively. The maximum dry density and its optimum moisture content ranged from 1.48-2.07 g/cm(3) to 11.3-30.3%, respectively. Soaked CBR results ranged from 3 to 44%. Two classes of subsoils, namely A-2-4 and A-2-6 (granular materials) and A-6 and A-7-6 (clayey soils), were identified and rendered suitable and unsuitable road construction materials, respectively. This investigation revealed that the subsoils are poor road construction materials due to its fine fractions and plasticities, which should be put into consideration during its foundation design and construction stages.