Geotechnical Properties of Some Soils in a Tar Sand Area of Southwestern Nigeria

Abstract

Engineering properties of some soil samples in Idiobilayo and Idiopopo areas of Southwestern Nigeria were studied with the aim of determining their geotechnical properties which can aid in the exploitation plan of the tar sands deposits in the area. A total of six sampling locations with three samples each were established in the study area. Samples of soil both disturbed and undisturbed were obtained from the trial pits to a depth of about 1.5m at 0.5m vertical interval. The disturbed samples were subsequently subjected to classification tests such as grain size distribution and consistency limits using British standards 1377 procedure. However, the undisturbed samples were subjected to permeability test. Results obtained in this study showed that the area of study is underlain essentially by sandy soils, with substantial silty content. Clay and gravel content are quite minimal. The particle size distribution curves confirmed a general dominance of silt to coarse-grained sand size particles in the soil matrix with minor but complimentary clayey and gravelly materials. Amounts of fines in the soils are less than 50% except in trial pts 4 and 5 where they are slightly above 50%. The soils consist of sand (60.0 %) and silt (35.0 %). The percentage of fines (silt and clay sized fraction) in the soils was about 38.0 %, and makes the soils good base for landfill, since recommended percentage of fines, should not be less than 20.0 %. However the obtained values of permeability coefficient of 5.5 X 10 -6 mm/s to 1.2 X 10 -4 mm/s call for the lining of the base to avoid groundwater pollution by leachates.