Penetration and Pullout Capacity of Low-Skirted Suction Caissons

The bearing capacity of suction caissons is the key to the design of offshore structures. A new type of cross-shaped low-skirted suction caisson is invented to effectively improve the bearing capacity, considering inevitable “soil plug” phenomenon. The behaviors of penetration and pullout for new low-skirted suction caisson are investigated by performing model tests. A new formula for calculating the penetration resistance is suggested based on the limit equilibrium theory and the test data, which can consider the change of the lateral area of the suction caisson during penetration. The behaviors of low-skirted suction caisson under inclined loading are analyzed by carrying out finite element simulation. The effects of loading angles and loading positions on the ultimate bearing capacity and failure mechanism of low-skirted suction caissons are discussed. The research results can provide a reference for the design of suction bucket foundation for offshore structures.

Effect of Fins on Combined Loaded Suction Caisson in Deepwater Clay Soils. A Numerical Analysis

Suction piles are a form of foundation widely adopted in the offshore energy industry. Efforts to enhance the combined Vertical-Horizontal (V-H) performance of piles with the addition of fins, attracted interest from the engineering community in the beginning of the 21st century. Design of this enhancement was surfaced whilst examining foundation solutions for renewable energy projects. Studies to date have primarly considered relatively shallow waters comprising sandy soils, with the behaviour of fin-enhanced piles in very soft to soft clay soils, receiving less attention. The present study emphasis is on typical deep-water deposits of soft clay and attempts to evaluate the impact of varying fin length, shape, orientation and location, on the combined capacity of suction piles by means of three-dimensional finite element analyses. The paper investigates two types of load configuration; in the first instance loading at the pile head and secondly with the load attachment point located at approximately two thirds of the pile embedded length. These two configurations cover different foundation solutions, such as support for subsea infrastructure and anchoring for floating facilities, respectively. Optimum fin-enhanced suction pile configurations are presented for each application, with the results from this study indicating an increase of the load-carrying capacity in V-H space, whilst reducing the overall suction pile size. The efficiency of various configurations is presented with composite plots of increase in holding capacity, plotted against the increase in steel surface area. Preliminary recommendations on fin length, location, shape and orientation for typical suction pile applications are presented with intent to demonstrate the potential for cost savings and reduction in both operational and schedule risk.

Solid-Fluid Coupled Numerical Analysis of Suction Caisson Installation in Sand

Suction caissons are widely used foundations in offshore engineering. The change in excess pore pressure and seepage field caused by penetration and suction significantly affects the soil resistance around the caisson wall and tip, and also affects the deformation of the soil within and adjacent to the caisson. This study uses Arbitrary Lagrangian–Eulerian (ALE) large deformation solid-fluid coupled FEM to investigate the changes in suction pressure and the seepage field during the process of the suction caisson installation in sand. A nonlinear Drucker-Prager model is used to model soil, while Coulomb friction is applied at the soil-caisson interface. The ALE solid-fluid coupled FEM is shown to be able to successfully simulate both jacked penetration and suction penetration caisson installation processes in sand observed in centrifuge tests. The difference in penetration resistance for jacked and suction installation is found to be caused by the seepage and excess pore pressure generated during the suction caisson installation, highlighting the importance of using solid-fluid coupled effective stress-based analysis to consider seepage in the evaluation of suction caisson penetration.

Suction Caissons as Multipod OWT Foundations in Clay: Investigation of Loading Rate Effects

The paper elaborates on the bearing mechanics of suction caissons serving as the foundation system of offshore wind turbines (OWTs) supported on jacket structures. As axial loading governs foundation design in this configuration, the study proceeds to a numerical investigation of the tensile load carrying capacity of a suction caisson in clay through a series of coupled pore fluid diffusion — effective stress analyses with a hypoplastic constitutive model. The latter allows for the quantification of loading rate effects on the amount of negative excess pore pressures (passive suction) generated within the confined soil plug and their contribution to uplift caisson resistance. Based on these results, a simplified uncoupled procedure is employed to account for loading rate effects in the performance-based design of an 8MW OWT founded on a Suction Bucket Jacket (SBJ).