Stratigraphic Constraints to Shallow Foundation Design in the Coastal Zone of Nigeria

Abstract

The coastal zone of Nigeria comprises the Beach ridges and mangrove swamps. The zone is underlain by an alternating sequence of sand and clay with a high frequency of occurrence of clay within 10m below the ground surface. The proximal location of compressible clays to the surface increases the influence of imposed loads, with the consequence of consolidation settlement. The impact of imposed load is exacerbated by the thickness and consistency of the compressible layer. A chart based on dimensionless coefficients to facilitate the design of shallow foundation in environments typified by a 3-layer stratigraphic model comprising sand-clay-sand has been presented. In areas with comparatively thin upper sand layer, the placement of fill consisting of cohesionless materials of about 1.5m drastically reduces the induced load to a safe and allowable range thereby allowing shallow foundations with significant loading to be supported in the coastal zone.

Keywords: coastal zone, clay, stratigraphy, foundations