Uplift capacity of suction caissons under sustained and cyclic loading in soft clay

A series of centrifuge tests were conducted on instrumented model suction caissons in normally consolidated, lightly over-consolidated. and sensitive clays, to investigate the uplift capacity and external radial stress changes for sealed caissons subjected to sustained loading and cyclic loading. The external shaft friction ratio during vertical pullout for these two types of loading was analyzed from the radial stress measured at failure, then the corresponding reverse end-bearing capacity factor was derived from the pullout capacity. Tests results were compared with those under monotonic undrained pullout. For caissons under sustained loading, the holding capacity was found to be 72-85% of that under monotonic undrained loading. Radial stress reduction around the caisson shaft reduced the external shaft friction ratio to 0.67-0.75. while dissipation of the "passive" suction at the caisson tip reduced the reverse end-bearing capacity factor to 7.5-9.4. Under cyclic loading, the uplift capacity of the caisson was found to be 72-86% of the monotonic capacity. Repeated loading reduced the external shaft friction ratio to 0.65-0.80, while the reverse end-bearing capacity factor reduced to 6.4-9.0.