A series of centrifuge tests have been performed to investigate the uplift behaviour of a shallow skirted foundation resting on clay subjected to various sustained loadings expressed as a fraction of the undrained bearing capacity in compression. Displacements, uplift loads, total and pore pressures underneath the foundation were monitored during testing to provide insight on the development of negative pore pressure (suction) at the foundation base and on the mechanism triggering breakout. The results indicate that the displacement rate and the time the uplift load can be sustained depend on the magnitude of the load, but also on the time the foundation experienced consolidation prior to uplift. Breakout was not observed at a relatively large time scale under low sustained loadings, while the foundation was pulled out directly under high loading levels. At intermediate loadings, breakout was inferred from the sudden increase in displacement rate. The breakout mechanism of the foundation is also discussed based on the observation of pore pressure variations underneath the foundation.
The outcomes of the present study have the potential to provide a better understanding of the suction mechanism for offshore foundations and to provide guidelines for offshore retrieval operations.