The two main suction pile design methods that are generally applied and accepted within the industry are 3D Finite Element analysis and limit equilibrium. The limit equilibrium method involves assuming a number of failure mechanisms with the mechanism offering the least resistance adopted for design. The limit equilibrium suction pile design software CAISSON has been developed and validated by Cathie Associates for Technip. It is currently in use for rapidly and reliably determining the critical failure mechanism and ultimate holding capacity of initiation, mooring and hold back suction piles in clay. CAISSON has been developed as a stand-alone program written in Visual Basic with a user-friendly program interface implemented to allow for efficient computations. The failure mechanisms employed in CAISSON were identified initially using 2D FE results from PLAXIS. The failure mechanisms identified were further calibrated using 3D FE modelling in ABAQUS and FLAC to account for the influence of side shear within the limit equilibrium equations adopted in CAISSON. The current version of CAISSON can analyse suction piles with L/D aspect ratios from 0.5 to 5 installed in clay of uniform or linearly increasing undrained shear strength. Additional program features include computation of inverse catenary shapes for anchor chains, anisotropic undrained shear strength profiles, pile tilt and pile misalignment. The development and validation of CAISSON is presented in this paper along with a case study and a short parametric study to identify the significance of the CAISSON input parameters that govern the ultimate holding capacity of suction piles. Planned upgrades to CAISSON will also be presented.

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