Abstract: The micro-mechanisms of suction caisson-soil interaction under the action of inclined mooring lines remain unclear. In this study, a coupled discrete element method (DEM) and finite element method (FEM) was adopted to investigate this issue from macro- to micro-scales, with a focus on the influence of mooring depth. The sand particles were simulated by DEM, and the suction caisson was simulated by FEM. The mooring line tension was simulated by controlling the roller motion. The results revealed that the differences in the evolution of the force-displacement curves were attributed to the differences in the suction caisson motion modes at different mooring depths. The mooring depth differences caused significant differences in the vertical pull-out displacement, rotation angle, and deformation of the suction caisson. The critical reverse mooring depth point of suction caisson rotation direction and pull-out displacement is located near the depth of h = 66.7% from the top of the suction caisson (i.e., 2/3 of the suction caisson depth). Moreover, the deformation behavior of the soil was analyzed at the scale of particles, ultimately determining the failure mode of the interaction between the suction caisson and the particle soil. The study showed that neglecting the mooring depth of the mooring line may lead to a misjudgment of the bearing capacity of the suction caisson and the failure mode of the soil.

Key words: suction bucket, anti-pulling, coupled DEM-FEM, depth effect, soil deformation