INVESTIGATING THE RESPONSE OF OFFSHORE FOUNDATIONS IN SOFT CLAY SOILS

摘要

A series of tests were conducted in a drum centrifuge with the aim of investigating the performance of typical offshore foundations on soft normally consolidated clay. The foundations consisted of spudcan footings and suction caissons. These types of foundations are being considered for use in various offshore applications including as foundations for mobile drilling rigs (jack-ups) and offshore wind turbines. A special loading device was designed so that combined loading could be applied to the footing. This device could apply the same ratio of horizontal to moment loading as that applied to the foundations of mobile drilling units. The main aim of the investigation was to compare how the performance changes as the foundation is varied. This is important when considering the use of a jack-up rig for a permanent facility, a concept that is increasingly being considered. In such a case there are concerns about the long-term suitability of the spudcan footing, with the amount of sustainable rotational fixity being of particular interest. A total of 64 experiments were carried out investigating areas that include a) comparing the vertical loading response in both compression and tension, b) using a fixed arm to apply predominantly horizontal loading, and c) using a hinged arm to apply a distinct ratio of horizontal to moment loading. Interestingly in the case of the spudcan footing considerable back-flow of the soil was observed during the installation phase. The combined load response of spudcans under these conditions is an area that has not been investigated thoroughly.