Numerical investigation on the suction caisson response considering seabed trenches and cyclic loading

As anchors of floating offshore structures, suction caissons endure cyclic loads transmitted by mooring chains. The moving chains repeatedly cut into the seabed, triggering the formation of trench, which further reduces the stability of suction caisson. However, the coupling effects of cyclic loading and trenches on the movement of suction caisson remain unexplored. To address this issue, finite element analyses were conducted to investigate the coupling effect of cyclic loading and trench on the movement of rigid suction in clay, employing a bounding surface constitutive model. The influences of cyclic amplitude, mean load, trench depth and width on the anchor behaviour are analysed. The results show that movement at the fixed loading point on the rigid caisson nonlinearly increases with the amplitude (qam) and mean (qme) of cyclic loading on a trenched seabed. This increase becomes pronounced when qam exceeds 0.15, and qme surpasses 0.35 the caisson's bearing capacity (qref). Additionally, trench dimensions significantly influence the caisson's movement. Specifically, trench depth has complex influence on the caisson's movement pattern, and increasing trench width results in larger movement, especially beyond a certain width. Considering the seabed trenches and cyclic loading, these findings offer valuable insight into the suction caisson movement. •Cyclic patterns have nonlinear effects on suction caisson's movement, with key thresholds of cyclic loading triggering significant movements.•The study reveals that seabed trenches significantly influence the movement mechanisms of suction caissons, and identifies the dimensions thresholds of trench that mark significant changes in suction caisson's movement as trench sizes evolve.•Optimal mooring points for suction caissons were determined under cyclic loads with seabed trenches.