ENGINEERING GEOLOGICAL INVESTIGATION OF SUB SOIL AT IKERE-EKITI, SOUTHWESTERN NIGERIA.

Abstract

This project determine the engineering geological investigations of sub soil at Ikere-Ekiti, Southwestern Nigeria. In order to achieve this, eighteen (18) disturbed samples were collected at a depth of one (1) meter. Ikere Ekiti falls within the basement complex of Nigeria, with Biotite Granite, Charnockites and porphyritic granite to be the dominant rock types. The samples were subjected to the following geotechnical tests: particle (grain) size tests, natural moisture content test (NMC), Atterberg limit tests, linear shrinkage test, compaction tests, California bearing ratio tests(CBR)and specific gravity tests. The fine content of the particles size analysis values range between32.9% and 54.6% while the coarse content range between 45.4% and 67.1%. The NMC values range between 4.3% and 14.4%, while the linear shrinkage values range between 7.1% and 11.4%. The maximum dry density (MDD) values range between 1518 kg/m3 and 1906 kg/m3 and its moisture content values range between 15.3% and 24.3%. The CBR values range from 2% to 24%. The specific gravity values range between 2.64 and 2.74. The liquid limit values range between 31.8% and 53.8%and the plasticity index range between 11.8% and 27.3%. Most of the sampled soils values is within the normal clay and the remaining 11.1% (samples. 2 and 4) are inactive clay. The clay minerals are in the range of illite and kaolinite group. This is in agreement with the activity values i.e. normal active to inactive clays. The linear shrinkage values has 22.2% of the sampled soils to be within the stipulated standard of FMWH (1976) of good sub base, sub grade and base materials. The Atterberg limit tests show medium to high plasticity which implies medium to high compressibility. Compaction characteristic shows that most soils fall within fair to good rating. Based on AASHTO classification, 78.8% of the sampled soils are classified as A-2-6 soil type, which are good foundation materials while the remaining 22.2% falls into A-7 soil group .Conclusively, all the tests adequately show that the

sampled soils in Ikere Ekiti are not completely suitable for sub-grade and sub base materials but some level of stabilization can help improve the strength of the soils.