ENGINEERING GEOLOGICAL EVALUATION OF LATERITIC SOILS FROM PARTS OF AKURE, SOUTHWESTERN NIGERIA

Abstract

Lateritic soils are mostly used as filling materials for Civil engineering construction works. There is a need to establish the Engineering properties of these soils before they are used as foundation materials, in order to avoid failure of foundation that will in turn affect the structure. It is in this regard that the Engineering Geological Evaluation of Lateritic Soils from parts of Akure was carried out. A total of 31 samples were collected from 3 laterite locations, 10 from Fiwasaye (FS) underlain by granite gneiss, 9 from Futa northgate (FNG) underlain by quartzite, and 12 from Ijare (IJR) underlain by charnockite. Samples were taken from 3 horizons in FS and FNG, and 4 horizons in IJR. Laboratory analyses such as particle size distribution (PSD), hydraulic conductivity (HC), atterberg limits (liquid limit (LL), plastic limit (PL) and plasticity index (PI)), compaction (maximum dry density (MDD) and optimum moisture content (OMC)) and triaxial tests from which allowable bearing capacity (qa) was determined, were carried out to determine the index and engineering properties using British standard (BS) and American Society for Testing and Materials (ASTM). PSD for FS, FNG and IJR showed that gravel, sand, silt and clay ranged from 0.4 to 83.6%, 4.1 to 45.7%, 5.5 to 28.2% and 2.5 to 54.2%, 0.7 to 38.5%, 26.6 to 74.4%, 12.5 to 19.3% and 1.9 to 28.1%, and 0 to 40.6%, 10.2 to 43.3%, 14.1 to 35% and 30.8 to 50.9% respectively. HC for FS, FNG and IJR ranged from 1.93 x10-8 to 1.19 x 10-2cm/s, 6.12 x10-7 to 9.63 x 10-4cm/s and 2.56 x10-8 to 6.38 x 10-6cm/s respectively. LL for FS, FNG and IJR ranged from 18.7 to 54.3%, 21.1 to 41.3% and 31.4 to 35.5% respectively. PL for FS, FNG and IJR ranged from not plastic to 28.6%, not plastic to 23.5% and 19.3 to 27.3% respectively. PI for FS, FNG and IJR ranged from null to 19.1%, null to 19.5% and 12.5 to 37% respectively. FS, FNG and IJR showed a MDD range of 1416 to 2172kg/m3 and OMC of 9.3 to 34%, 1721 to 2065 kg/m3 and OMC of 11.3 to 21.2% and 1462 to 2017 kg/m3 and OMC of 14.4 to 32.5% respectively. FS, FNG and IJR showed qa ranging from 150.67 to 549.31KN/m2, 231.69 to 681.74KN/m2 and 374.6 to 1013.63KN/m2 respectively. Most of the soils from FS and IJR are poorly graded and have poor compaction characteristics while most of the soils in FNG are well graded and have good compaction characteristics. Therefore, soils from FS and IJR are not suitable as filling materials for foundation and so should not be used because of the dominance of silt and clay sized particles which will make them experience volume changes while soils from FNG are fairly suitable as filling materials for foundations.