Geotechnical and Suitability Studies for Subgrade and Sub – Base Construction Materials Around Baba – Ode and Obada Areas Southwestern Nigeria.
Lateritic soils from Baba – Ode, in Ilorin, Kwara State and Obada in Oyo State, Southwestern Nigeria were investigated with respect to their geotechnical properties and their suitability for subgrade and sub – base construction materials. Four disturbed lateritic soil samples A and B (Baba – ode in Ilorin) and samples C and D (Obada in Oyo state) were selected for grain size analyses, specific gravity tests, atterberg limit tests, compaction, California bearing ratio and shear box tests. Atterberg consistency limit test show that samples from Baba-ode has liquid limit ranges of 27.0 - 30.0%, plastic limit 16.2 - 19.5%, plasticity index 10.5 - 10.8%, shrinkage limit 7.4 - 9.1% while those from Obada has liquid limit ranges of 22.5 - 31.0%, plastic limit of 13.3 - 21.5%, shrinkage limit of 5.5 - 7.4% and plasticity index of 9.2 - 9.5%. They have California Bearing Ratio (CBR) values within 2-3% (mean = 2.75%) and 2% (mean = 2) in Baba-ode while Obada samples are 2-4% (mean = 2.75%) and 1-3% (mean = 1.5%) respectively. Optimum water contents for Baba-ode samples are 15.0% and 13.0 - 14% for standard and modified proctor respectively while those of Obada are 11.0 -15.0% for standard proctor and 10.0 - 14.0% for modified proctor. The cohesion of Baba-ode samples are within 70 90Kpa with mean of 79Kpa and angle of internal friction (ɸ) ranging from 260 - 320 with mean of 280 for standard and modified compaction energies respectively while Obada samples fall within 30- 40Kpa with mean of 35Kpa and the angle of internal friction ranges from 22o –280. Geotechnical analysis suggest that the soils are good to fair as erosion resistance in canal construction because of its high bearing capacity and can also be used as sub – grade and base course in road construction.
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