ABSTRACT
Laterites are soils that formed from the weathering of the basement complex and are rich in secondary oxides of Iron and Aluminum. It‟s red colouration is due to it‟s high iron content. Laterites are mostly found in Tropical regions which are characterized by distinct dry and wet seasons. Laterites are mainly used in the construction ofroads either as a subgrade or as a sub-base material. Geotechnical evaluation is one of the effective means of detecting and solving pre and post constructional problems. Three bulk samples were collected from depths of 4m, 5.2m and 7m at Onihale/Isorosi Quarry, Ijako-Ifo Southwestern Nigeria and subjected to laboratory analysis. The tests carried out on the soil samples include: Specific gravity test, Grain size distribution analysis, Consistency test, Compaction test and California bearing ratio test. The results obtained from the various tests shows that the specific gravity of the three samples are 2.65, 2.65 and 2.58 for samples CA,CB and CC respectively and this is an indication that samples CA and CB are good laterites. The specific gravity of the three samples ranges between 2.58 to 2.65 with an average of 2.63, the grain size/hydrometer test reveals that the samples are mainly sand with insignificant amount of clay and silt particles. The consistency limit test shows that the plasticity index ranges between11.25% to 15.57% with average value of 13.66%, the value is lower than the specified value of the Federal Ministry of works (1970) which is 17. The compaction test shows that the optimum moisture content of the soil samples ranges between 16.7% to 17.2% with an average value of 16.6%, the specified value for a good subgrade soil is 14.45 according to the Federal Ministry of works for roads and bridges. Based on the results of the laboratory analysis, it can be deduced that the soil can be used as a subgrade material but improvements should be done on the soil such as; addition of cement, asphalt, lime ash and bio-enzymes so as to make the soil a very good sub-grade material.
