DEEP PENETRATION OF SPUD-CAN FOUNDATIONS ON SAND AND CLAY

A critical review is presented which draws together results from model tests and computations on the mechanisms by which the spud-can foundation of an independent leg offshore jack-up structure can penetrate deeply into the seabed through both uniform and stratified deposits. Particular consideration is given to the so-called punch-through mode in layered soil profiles, where a strong stratum overlies a weaker one. Little evidence has been found to support the mechanical basis of two methods of analysis commonly used in the offshore industry where foundations often have dimensions in excess of 10 m while conventional laboratory models have rarely exceeded 100 mm. New model tests performed in a centrifuge with stresses appropriate to offshore foundations are reported and these show different mechanisms from many unit gravity models. The need for a reappraisal of the basis of analysis is established. Where large volumes of soil are displaced by spud-can preloading, offshore analysis should explicitly address the pattern of soil flow around the foundation and the reality of post-installation geometry.