To relieve the axial stress induce rature high-pressure pipelines in deepwater, current design methods leave the pipe unburied and allow the formation of the lateral buckles along the pipeline in a controlled manner. However, this approach requires a better understanding of the interaction between the seabed soil and the partially embedded pipeline under both vertical and lateral movements. Research has been carried out to examine the two soil-pipe interaction mechanisms, vertical pipe penetration and lateral pipe movement, involved in the installation and operation of an on-bottom offshore pipeline. The findings reported in this thesis improve the current knowledge of pipe-soil interaction in clay. A series of physical model tests was conducted to investigate the behaviour of pipe penetration and lateral pipe movement in clay. The experiments were carried out using short pipe sections in a I g model tank equipped with a transparent Perspex window in the front panel, from which high quality images were obtained for the measurement of the soil deformation in the tests using an image analysis technique. The computational limit analysis, Discontinuity Layout Optimisation (DLO), was adopted to back-analyse and compare with the experimental results. In addition, parametric studies were conducted using DLO to investigate the effects of the change in soil geometry and soil condition on the pipe resistances and soil flow mechanisms for the vertical pipe penetration and the lateral pipe sweep processes. Experimental results showed that pipe penetration, prior to the fully embedded flow-around failure mechanism at very deep penetrations, involves four distinct stages in development of the failure mechanism from 'soil heave' to 'local flow-around' at shallow and deep pipe embedments, respectively. Good agreement was observed between the experimental and numerical results. The results of the parametric studies suggested that the onset depth of the fully embedded flow-around failure mechanism is strongly dependent on the undrained strength profile and tensile strength of the soil. The lateral resistance of a partially embedded pipe under different loading conditions was measured at both small and large lateral displacements. Results showed that the lateral resistance is strongly affected by the change in soil geometry, soil heave induced by the initial penetration and formation of the active berm in front of the pipe during lateral movements. Based on the results from the numerical and experimental studies, design equations are proposed for the predictions of (i) the pipe penetration resistance at both shallow and deep embedments, and (ii) the lateral resistance of a partially embedded pipe under combined vertical and horizontal loads at both small and large lateral displacements.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:577564 |
| Date | January 2012 |
| Creators | Lee, Yat Sun |
| Publisher | University of Sheffield |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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