ABSTRACT

All dimensions are approximate The vertical penetration of spudcan foundations, as used in mobile jack-up rigs, has been studied with a view towards understanding the mechanisms of soil deformation underneath and around spudcan foundations during deep penetration. Drum centrifuge model tests and finite element (FE) analysis have been conducted. The experimental work carried out on uniform kaolin clay with undrained shear strength (su) of 13 kPa and 18 kPa. A half-spudcan model was placed against a transparent window in the centrifuge in order to visualize soil flow during penetration. It was found that a cavity (or hole) was formed above the spudcan during initial penetration until a point where the soil flowed back over the top of the spudcan. Contrary to offshore design guidelines, flow of soil above the spudcan is not due to cavity wall failure, since the stability number Ns for cavity depth is around 2.4. Instead, flow is due to a change in the base failure mechanism to one that involves rotational flow around the spudcan. The bearing capacity factor (Nc) measured in these tests ranged between 10 and 12 in the two soil samples