Abstract

Sub-surface investigation was undertaken by drilling boreholes within and along the Nun River Channel covering three communities of Kaiama, Opokuma and Sabagreia, Bayelsa State, Nigeria. The route extent was over 5 km long and the study was necessitated to provide materials as structural fills for road construction purposes. Eight boreholes were drilled in the three locations to a maximum depth of 14 m from the river bed. Results reveal an overlying ligh grey to dark brown, very fine grained (anhedral), soft to stiff consistency, highly plastic silty clay soil in all the boreholes. This unit varies in depth vary in depth of 1.0 to 7.0 m and is proceeding thinner towards the Sabagreia axis from Kaiama. Beneath this overburden lie light grey, medium grained sands, in BH 2 to BH 6 covering the Kaiama and Opokuma axis. The sands are about 7 to 12 m in thickness to the maximum drilled depth of 14 m. In BH 7 and BH 8 in the Sabagreia axis, the underlying sands are coarse grained in texture and about 13 in thickness to the borehole depth. It is recommended that the sand may be derived at minimum depths of about 1.0 m below the river bed in the Sabagreia area, about 2.0 m in the Opokuma region and about 4.5 to 7.0 at the Kaiama axis. Medium to coarse grained; poorly graded (well sorted) sands which display uniform size gradation in the sand range were encountered below the river bed in the area.

Key words: Soils, grain size, engineering properties, stratigraphy, Niger Delta.