3D Finite Element Analysis of Ultimate Capacity of Suction Caissons under Multi-line Loading

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Development of ocean energy sources is significant to the current U.S. renewable energy and energy independence strategy. Geotechnical site investigation and foundation design are critical, and often costly, aspects of offshore development, however are subject to risks and uncertainties associated with design forces from the dynamic ocean environment and heterogeneous seafloor geology. Consequently, geotechnical issues have been a key factor in delays and cost overruns for some European offshore wind farms. This research seeks to reduce barriers to offshore renewable energy development associated with design and construction of foundation systems for floating technologies such as tidal, wave, ocean current, and deep water wind through advancement of a novel integrated foundation system for multi-device developments. This novel system is comprised of a network of interconnected suction caissons, which are large diameter, hollow cylinder, closed cap, pile-type foundations named for their installation by internal underpressure (i.e., suction) developed during pumping of water from the gap formed between the seafloor and cap. When used in an interconnected network to moor multiple devices, suction caissons have the potential to significantly alleviate development costs by reducing the total number of installed foundations.This goal of this research is develop the basic engineering knowledge necessary to transform the use of offshore suction caissons in clay soils from single to networked, multi-line mooring anchors. This research will lead to development of three dimensional numerical models used to predict ultimate capacity and deformation of a suction caisson under taut, orthogonal multi-line loading. The models will be calibrated/validated using both published literature and results from a physical modeling study of multi-line caisson behavior under monotonic and cyclic loading previously conducted by the principal investigator. The model will be further developed to investigate the effects of vertical load attachment point, number of lines and radial attachment angles, and load inclination with respect to caisson height on predicted capacity. This research effort will result in numerical modeling and analysis tools that will allow for continued investigation of multi-line loaded suction caisson capacity for a variety of offshore applications.