Centrifuge Experiments Investigating the use of Jetting in Spudcan Extraction

摘要

Jack-ups usually operate at a number of sites during their design life, which necessitates their retrieval at the end of deployment on any of those locations. In clay soils, the process may however be difficult due to the potentially high extraction resistance. One option believed to ease the spudcan extraction is to use a jetting system at the invert of the spudcan to break the suction generated during the extraction and hence to reduce the extraction resistance. The feasibility and the performance of such a jetting system have been investigated in a geotechnical centrifuge. At 200g, the reduced scale spudcan models a 17.1 m diameter spudcan, which is penetrated up to 1.5 diameters into normally consolidated clay and held at operation load for the equivalent of 4.5 years. The main parameters investigated include the flow rate during jetting, the extraction rate and the direct load applied during extraction. The results demonstrate the feasibility of reducing the extraction resistance through jetting provided that the jetting flow rate is sufficiently high with respect to the extraction rate and that the extraction rate is high enough to ensure undrained behaviour.