Geotechnical assessment of subsoils in parts of Akwa Ibom State University, Ikot Akpaden, Akwa Ibom State, Nigeria.

Abstract

A pre-construction assessment of the geotechnical properties of subsoils in parts of the main campus of Akwa Ibom State University was carried out to determine the stratigraphy, identify and classify the soils between 0 to 7m. Six boreholes were drilled to 7m each using a hand Auger, while soil samples were extracted for different laboratory classification tests including moisture content, atterberg limit, particle size distribution, compaction and california bearing ratio. The subsurface stratigraphic profile consists of a clayey silty sand topsoil in all the boreholes excluding BH5 where it did not occur throughout the drilled depth and BH6, where it was found from 0-7m. Underlying the topsoil is a sandy silty clay layer at different depths in BH1, BH2, BH3, BH4 and in BH5, where it was found from 0-7m. The clayey silty sands were of low to intermediate plasticity (9% to 17%) with liquid limit and moisture content values of 23% to 40 % and 15% to 41.1% respectively. The sandy silty clays had a higher plasticity index (11% to 32%) and liquid limit (27% to 92%) than the topsoil. Particle size distribution curves of the sands showed poorly graded fine to medium to coarsegrained sands with minimal gravel fractions. The maximum dry densities (1700kg/m³ to 1770kg/m³) fell within the acceptable range for good backfill materials although the optimum moisture content percentages (14.3% to 16.5%) were slightly higher than the acceptable range. Therefore, the soils should be improved and a bearing capacity analysis carried out before construction for an adequate foundation design.