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This technical note examines the suction caisson extraction mechanism under steady seepage conditions using a series of centrifuge tests supported by finite-element predictions of these tests. An approximate methodology for prediction of the extraction resistance is subsequently proposed, which is shown to provide a simple means for estimation of suction caisson extraction resistance in un-aged free-draining materials.

The carbonate sediments found offshore on the North West Shelf of Australia can generally be described as silts with varying proportions of clay-sized and sand-sized carbonate particles. This paper investigates the undrained shearing response (as measured under simple shear and triaxial conditions) of two sediments with different grading curves. The importance of the fines content in controlling the density and hence dilatancy and undrained strength of the materials is demonstrated. The paper discusses the importance of fabric to the behavior of these soils and provides guidance on how undrained strengths of soils of this nature may be assessed with a knowledge of a material’s in-situ water content (or void ratio) and composition.

The trend towards taut-wire mooring systems, instead of catenary chains, to anchor floating facilities for offshore exploration requires high-capacity anchoring systems capable of withstanding vertical loading components. Conventional drag anchors have very limited vertical capacity, and this has led to the development of alternative drag-in plate anchors, or vertically loaded anchors (VLAs). VLAs are installed in a similar way to conventional drag anchors, but they are ultimately loaded normal to their plate surface, and thus act like embedded plate anchors. A critical issue in the overall mooring system design is the ratio of the pull-out load to the anchor installation load, and this is termed the performance ratio. The performance of a model VLA was modelled in a geotechnical centrifuge, with particular attention to the performance ratios. Whilst the performance ratios obtained were much lower than expected, the testing proved that VLAs provide a simple and inexpensive alternative to other anchoring systems.

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