GEOTECHNICAL PROPERTIES OF SOME OFFSHORE NIGER DELTA CLAY

ABSTRACT

Offshore geotechnics in Nigeria is the exclusive preserve of the International Oil Companies (IOC) causing paucity of data in the public domain on offshore geotechnical investigations in Nigeria and recently, indigenous oil companies who have the resources and economic impetus to conduct such investigations. Due to the cost implications of such investigations, there is insufficient understanding of the geotechnical behaviour of clays from the offshore Niger Delta Basin. Clay as a constituent mineral, size fraction and earth material in the offshore combines two of the more challenging problems of geotechnical engineering – the clay and water problem. As a cohesive earth material, clay presents with unique challenges in engineering and being totally submerged and consequently fully saturated, the dimension of submersion is added to the existential clay problem in offshore geotechnics. This work provides clay focused geotechnical field and laboratory data from five Niger Delta offshore locations. A preliminary analysis to the end of characterizing the geotechnical properties of the clays is also provided. The results of field and laboratory investigation shows that the clays are high moisture content soils with reduced effective unit weight due to their perpetual submersion with dominant fine fractions that are highly plastic except when substantially sandy. Laboratory tests coupled with visual observations also indicate that the clays are very soft to soft and sometimes firm with high compressibility. These properties have serious implications for engineering structures on the seabed.