Sarah Elkhatib

Bio: Sarah Elkhatib is an academic researcher from University of Western Australia. The author has contributed to research in topics: Drag & Finite element method. The author has an hindex of 4, co-authored 5 publications receiving 102 citations.

Installation And Pull-Out Capacities of Drag-In Plate Anchors

Abstract: 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.Copyright © 2002 by ASME

Foundations of offshore wind turbines: A review

Abstract: Offshore wind is a source of clean, renewable energy of great potential value to the power industry in the context of a low carbon society. Rapid development of offshore wind energy depends on a good understanding of technical issues related to offshore wind turbines, which is spurring ongoing research and development programmes. Foundations of offshore wind turbines present one of the main challenges in offshore wind turbine design. This paper reviews the present state of knowledge concerning geotechnical and structural issues affecting foundation types under consideration for the support structures of offshore wind turbines, and provides recommendations for future research and development.

The undrained bearing capacity of a spudcan foundation under combined loading in soft clay

Abstract: Mobile jack-up drilling rigs are typically supported by individual, large diameter spudcan foundations. Before deployment, the suitability of a jack-up to a location must be shown in a site-specific assessment under loads associated with a 50-year return period storm, which ultimately need to be resisted by the foundations. The capacity of the spudcans under combined vertical, horizontal and moment loading is therefore integral to the overall site-specific assessment of the jack-up. In soft clays, spudcans can penetrate deeply into the seabed, sometimes up to several footing diameters, with soil flowing around the downward penetrating footing, sealing the cavity. Although this is generally believed to provide some additional bearing capacity to the footing, no detailed study or formal guidance is available to date. This study, therefore, investigates the influence of soil back-flow on the failure mechanisms and quantifies the effect on the capacity of a spudcan under general loading through finite element analyses. A closed-form analytical expression is developed that describes the capacity envelope under combined loading, applicable to embedment depths ranging from shallow to deep.

Influence of padeye offset on bearing capacity of three-dimensional plate anchors

Abstract: This paper reports advanced three-dimensional large-deformation finite element analyses investigating the effect of the padeye offset on the behaviour of plate anchors. The analyses varied the normalized padeye offset from 0 to 0.5 and identified two counterbalancing effects on the anchor bearing capacity induced by the padeye offset. These are the change in anchor inclination with respect to the direction of loading (detrimental due to the reduction of bearing area) and the reduction of loss of embedment (beneficial, as the anchor mobilizes stronger soil). The results provide insights to optimize the design of plate anchors. The underlying concepts also have applications for other types of anchors.

Probabilistic combined loading failure envelopes of a strip footing on spatially variable soil

Abstract: Failure envelopes written directly in terms of the applied vertical, horizontal and moment loads are finding increased popularity in the design of shallow foundations. However, these are deterministically derived and assume a spatially homogeneous soil without any variation in properties. The spatially variability of soil strength under a strip footing is accounted for in the results of this paper through the Random Finite Element Method, which combines spatial variability analysis, finite element simulation and Monte Carlo simulation. A multitude of combined loading failure envelopes are derived from finite element analysis of a soil domain with randomly generated and spatially varying values. This has allowed the size and shape of the failure envelopes to be defined for distinct levels of their probability of occurrence. These provide guidance for the reliable design of strip footings on clays in heterogeneous soil conditions, and have particular application offshore where horizontal and moment loads can be proportionally large.

A plasticity model to assess the keying of plate anchors

Abstract: Suction-embedded plate anchors (SEPLAs) have been developed to answer the growing need for anchors to withstand significant vertical loading. The concept combines the advantage of suction caissons (known penetration depth and location) and ‘drag-embedded' plate anchors (efficiency and low cost). The main issue associated with SEPLAs relates to the keying process, as the anchor is first loaded, and the associated loss of embedment and reduction in capacity. The paper presents a plasticity model developed to predict the trajectory and load development during anchor keying, and up to peak load. Rigid plasticity is assumed, allowing the kinematics of the anchor to be determined from a yield surface and associated plastic potential. The trajectory and performance of a typical SEPLA are predicted using the model, and are compared with results from centrifuge tests and large-deformation finite-element analysis. The anchor loss of embedment ranged from ∼0·2 to 1·5 times the anchor height for loading inclinations ...