Simplified FELA-based evaluation of suction caisson bearing capacity in layered sands

Evaluating the bearing capacity of a foundation situated on layered soils is crucial for ensuring offshore wind structure stability under varied loading conditions in its service. This study uses finite element limit analysis (FELA) to investigate suction caisson behavior in one- and two-layered cohesionless soils from the Bohai Sea under purely vertical and combined loading. A key innovation is the introduction of a simplified method to analyze ultimate vertical bearing capacity, employing a theoretical retaining wall model that aligns closely with FELA results. The effective interface frictional angle is proposed as a parameter for assessing caisson performance under lateral loads and moments. The research also explores failure modes and combined load yield surfaces, considering soil layer thickness. The research indicates that as the internal friction angle of soils rises, the critical rupture angle for the active sliding body progressively increases, leading to the mobilization of deeper soil layers. The failure mode of suction caissons under lateral loading remains consistent, while moment loading results in deep rotational failure. Additionally, the study confirms the accuracy of existing elliptical equations in describing failure envelopes and introduces new findings on the influence of soil layer thickness on eccentricity parameters and failure envelope characteristics.