Journal of Geography, Environment and Earth Science International

Ten soil samples were collected randomly from Ihiala area at a depth of about 1m using hand auger and shovel for evaluation as a sub-grade material in road construction. These samples were analyzed to determine their chemical and geotechnical properties of pH, natural moisture content, specific gravity, particle size distribution, atterberg limits, Optimum Moisture Content (OMC), Maximum Dry Density (MDD) and California Bearing Ratio (CBR). The pH values ranges from 3.77 to 4.87 in samples 1 to 8 and 10. Silica/sesquioxide ratio values ranges from 0.08 to 0.84 in samples 1 to 8 and 1.66 in sample 9. The result of pH, chemical component analysis and silica/sesquioxide ratio analysis confirmed all the samples to be laterite except sample 9. American Association of State Highway and Transportation Officials (AASHTO) soil classification system, classified samples 1 and 7 as under A-6 soil group; samples 2, 5, 8 and 9 fall under A-2-4 group; sample 3 fall under A-7 group; samples 4, 6 and 10 were grouped under A-4. Using the Unified Soil Classification System (USCS), sample 3 is classified under SM (Silty Sand) while all other samples are grouped under SC (Clayey Sand). The MDD of the soil samples ranges from 16.6 to 18.8 KN/m³ with their OMC ranging from 10.8 to 16.00%. The CBR of the samples ranges from 2% to 11% which shows that not all can be used for sub-grade. Generally, using the Nigerian Federal Ministry of Works and Housing (NFMWH) specifications, sample 2 is a good sub-grade material; samples 6, 7, 3, 5, 8 and 9 are fair for sub-grade while samples 1, 4, and 10 are not suitable for sub-grade. It is recommended that stabilization techniques should be applied on these samples that are not suitable for sub-grade in order to improve their strength.