A computational procedure for simulation of suction caisson behavior under axial and inclined loads

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Maniar, Dilip Rugnathbhai

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This dissertation documents the development of a computational procedure and its application to the analysis of suction caisson behavior under axial and inclined loads. The study is a part of a comprehensive research project on improving current understanding and developing effective procedures for the design of deep-water anchors. A suction caisson is a hollow cylinder capped at the top. In deepwater applications, it is lowered and allowed to penetrate the seafloor under its self-weight, and then pushed to the required depth with suction applied by pumping water out of the caisson interior. Use of suction caissons as foundations for deep-water offshore structures and anchors for mooring lines has been increasing in the last decade. Although researchers are attempting to understand behavior of suction caisson by means of field tests, laboratory tests, and numerical simulations, several issues and uncertainties related to capacity estimation and failure mechanisms are still not resolved. The objectives of this study are to develop a computational framework for the simulation of suction caisson behavior considering axial as well as inclined loads and including effects of both self-weight and suction installations, and verify the development by conducting simulations of laboratory tests carried out by fellow researchers on caisson models at The University of Texas at Austin. The procedure developed in this work is applicable to the axisymmetric problems of caisson installation and pullout under axial load. Water-saturated porous finite-elements are used in the representation of the soil domain while the caisson is discretized using solid finite-elements. Nonlinear behavior of the clayey soil is described by means of a bounding-surface plasticity model. The soil-caisson interfaces are modeled with a contact algorithm based on a slide-line formulation. Various remeshing tools are developed to eliminate the need for a priori specification of the caisson penetration path. The developed formulation is used to obtain results for slurry consolidation, caisson installation, reconsolidation or setup of soil following installation, and caisson axial pullout. Three-dimensional caisson models subjected to horizontal and inclined loads are analyzed using the ABAQUS/Standard computer program. The deformed geometry and state of the caisson-soil system obtained from axisymmetric simulation of the installation process are specified as initial conditions to carry out the three-dimensional analysis. The computed behavior of the caisson is compared with laboratory obix servations. Computed axial as well as horizontal load capacities match well with measured capacities from the laboratory tests. The interaction between ultimate horizontal and vertical loads is computed. In general, good agreement is found between calculated and measured caisson behavior, thus verifying the validity of the procedure.