Determination of Subsurface Geotechnical Properties for Foundation Design and Construction in Akenfa Community, Bayelsa State, Nigeria

Abstract

This study aims at establishing the sub-soil types and profile to ascertain the geotechnical characteristics of the underlying soils in Akenfa in Yenagoa, Yenagoa Local Government Area of Bayelsa State, Nigeria and recommend appropriate foundation design and construction of projects in the area. Three (3) geotechnical boreholes were drilled at the site to obtain baseline data on geotechnical properties of the soil and water level monitoring, the boreholes were advanced with the use of a cable percussion boring rig and were terminated to a maximum depth of 30m. The particle size distributions of a number of representative samples of the cohesionless soils were determined by sieve analysis. The results show that the samples are low to medium plasticity silty clay. The lithology revealed intercalations of clay and sand in thin layers to a depth of 2.0 m below the existing ground level. Underlying this clay is a stratum of loose to medium dense sand and dense sand. The sand is well sorted grading from fine to medium as the borehole advances. The laboratory analysis showed that the silty clay has undrained shear strength of 48 kPa. The loose sand has a maximum SPT (N) value of 12 while the medium dense sand has maximum SPT (N) value of 28. Considering the nature of the civil structures to be sited in the area, it is anticipated the load and the moderate compressibility of this near surface silty clay and the underlying loose silty sand be supported by means of raft foundation founded within the clay layer. It is recommended that studies on the geotechnical characteristics of the area be carried out as it provides valuable data that can be used for foundation design and other forms of construction for civil engineering structures in order to minimize adverse effects and prevention of post construction problems.