Using a three dimensional finite element method of analysis, an analytical feasibility study on suction piles was conducted. Elastoperfectly plastic soil properties were used to evaluate the effect of various cross-sectional shapes on the overall performance. Results of soil stresses and pile displacements under vertical, horizontal, and inclined loads were evaluated and compared.
The US Navy is currently conducting a technical feasibility study pertaining to the construction of Mobile Offshore Bases (MOBs). This is expected to be a self-propelled, floating military base with a runway on top and other supporting facilities below such as living quarters, material storage areas, docking facilities for transport ships, etc. The proposed dimension of the MOB is approximately 1,500 meters by 150 meters. It is intended to be a forward-deployed, self-contained military base floating in deep waters. The South Dakota School of Mines and Technology is participating in this MOB feasibility study to provide an adequate mooring technique for this very large floating structure. The MOBs are expected to be controlled by dynamic positioning. However, during storage, repair, or lay-up periods, or for hybrid mooring, conventional mooring techniques may be needed. Suction piles are currently being investigated analytically and experimentally to provide the necessary mooring capacity. Suction piles typically have a large diameter (up to 30 meters to date) with a relatively small length-to-diameter ratio. They are installed by applying a suction pressure inside the pile, which acts as an external surcharge to push the pile into the seafloor. They may be retrieved later by applying a positive pressure inside the pile. This paper describes the results of an analytical performance study on suction piles, using a three-dimensional finite element method of analysis. Three cross-sectional shapes that were thought to be able to provide adequate bearing resistance against various external loads were selected.