Load-time failure envelopes for suction caissons under sustained vertical loading

Suction caissons are established as a reliable anchoring system to moor a range of offshore floating facilities. Under sustained loads, generally characterized by long durations, the caisson holding capacity against uplift loading, that relies on suction pressures induced within and at the base of the soil plug, is expected to reduce over time, due to the equalization of pore water pressures. The scarcity of studies addressing this sustained loading problem has motivated this study, in which the response of suction caissons in soft clay subjected to sustained vertical uplift loads is investigated through finite element simulations and centrifuge model tests. Results are presented in the form of failure envelopes in the load-time plane, correlating, for each failure mechanism detected, the load level to the corresponding holding time. The findings of this study are consid-ered useful for concept design purposes, when sustained loads govern the caisson design.