Foundation Construction in a Reclaimed Marginal Land: A Case Study

A sand-filled land situated in a mangrove swamp area in the Niger Delta is to be used for the erection of a factory for the production of pre-cast concrete electric poles. The soil profile for the site comprises a hydraulically-placed top sand about 2 metres in thickness, under-lain by very soft organic clay which in turn rests on a continuous deposit of medium dense to dense sand. The ground water table is, in general, about 1.0m below the ground surface in the area. The main columns of the structures are designed to carry a maximum load of 1200 kN and require embedment depths of 2 metres. This implies that the bases of the columns will lie on or within the organic clay which is too weak to support any significant load. The option of piled foundation was considered expensive, although this had the advantage of being able to overcome construction problems associated with unfavourable ground water conditions. Ground improvement involving discriminative removal of the top sand and the weak organic clay and their replacement with well-compacted sand was adopted while de-watering of the excavation was carried out with sump pumps. Keywords : Marginal land, land reclamation, mangrove, factory construction, swamp area, sandy soil, ground water table, dewatering, sump pump, Niger Discovery and Innovation Vol. 19 (2) 2007: pp. 117-121