EXTRACTION FORCES FOR OFFSHORE FOUNDATIONS UNDER UNDRAINED LOADING

Centrifuge model tests have been carried out under controlled laboratory conditions to simulate the installation of jack-up spud can-type foundations into beds of uniform clay having undrained shear strengths in the range of 12-40 kPa. Much of the previously published field data relating to removal of objects from the seabed covers sites with ill-determined strength profiles but generally rather lower strengths. Results are presented that indicate that the, underbase adhesion necessary to sustain substantial breakout resistance is not obtained until a compressive bearing pressure approaching that required for a substantial penetration, i.e., surface failure, has been previously applied. Once compressive failure is approached then breakout forces increase towards the compression capacity but rarely achieve the theoretical upper limit of equality between tension and compression under undrained conditions. © ASCE.