Jornal de Geologia e Geofísica
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Geotechnical Evaluation of Foundation Conditions in Igbogene, Bayelsa State, Nigeria

Nwankwoala HO and Adiela UP

Geotechnical studies were carried out to investigate the foundation conditions in Igbogene, Etelebou in Bayelsa State, Nigeria. The evaluation was carried out by means of three (3) number boreholes to a maximum depth of 30 m below the existing ground level using the cable percussive rig. Field and laboratory investigations reveal a near surface stratigraphy of clay to an average depth of 6 m underlain by loose silty sand to a depth of 10 m below the existing ground level. Underlying this clay layer, the formation presents a stratum of sand which extends to the maximum depth of investigation. Field and laboratory analysis carried out on relatively undisturbed soil samples of the silty clay showed the undrained shear strength of this near surface soil to lie between 40 and 56 kPa with a mean value of 47 kPa. However, the 1.0 m thick peat embedded between 3.0 m and 4.0 m will great increase the compressibility of this clay. Pile foundation is recommended, considering the anticipated load and the very high compressibility of peat under imposed load. Piles should be straight-shaft, closed-ended steel pipe piles and driven into the medium dense sand. Pile load test should be carried out on all piles to confirm working load and estimated settlements.