Uplift capacity of plate anchors under loop current loads

The suction embedded plate anchor is a new foundation to moor floating structures in deep water. The short-term uplift capacity of plate anchors under undrained conditions is usually taken as the design capacity in practice. However, the sustained uplift capacity of the plate anchors subjected to seasonal loop currents may be much lower than the short-term capacity. The reason is that suction is diminished gradually due to dissipation of the excess pore pressures in clayey seabed. Here a large deformation coupled finite element approach based on frequent mesh regeneration is proposed to reproduce the pull-up of the plate anchors to loop currents, in which the modified Cam-clay model is adopted to describe the constitutive behaviour of normally consolidated clay. The large deformation coupled approach is validated by comparing the numerical short-term capacity factors with the limit solutions under undrained conditions. The allowable hold time of sustained loads against different loading amplitudes is investigated, and the dependence of allowable hold time on soil permeability is studied as well. For a given hold time, the long-term capacity may be reduced significantly with increasing permeability. If the hold time of the loop currents is 3 months and the permeability of soil is 10-8 m/s, the current loading amplitude needs to be as low as 60 % of the short-term capacity to keep the stability of plate anchors.