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概要

Geotechnical Considerations in Shoreline Protection and Land Reclamation in Kula, Eastern Niger Delta

Nwankwoala HO and Orji MO

The investigation is to determine the suitability of the study site for the design and construction of a shoreline protection and also carry out reclamation exercise at the adjoining lands. Nine (9) number boreholes were drilled to a maximum depth of 20.0 m below the existing ground level using a cable percussion rig and nine (9) numbers Cone Penetrometer Testing using 2.5 tonne CPT equipment. The lithology reveals intercalations of clay and sand in thin layers to a depth of 2.0 m below the existing ground level. Only borehole 3 revealed the clay layer to a depth of 5.0 m. 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 intended structure, the anticipated load and the moderate compressibility of this near surface silty clay and the underlying loose silty sand, it is suggested that the cellar slab be supported by means of raft foundation founded within the clay layer. Where the proposed project precludes the use of raft foundation, pile foundation should be employed to transmit the anticipated load from the cellar slab to the underlying sand stratum and that such piles should be closed-ended, straight-shaft steel pipe piles driven into the sand stratum and all driven piles should undergo pile load test to confirm their working load and consequent estimated settlement.