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the seabed, whereas mobile foundations include the steel catenary risers that form response. Ultimately the method will be

Pipelines would be best designed to rest on the sur- trenches where they touch down on the incorporated into a design tool for use by face of the seabed to minimize the sliding seabed—which actually assist by easing industry. resistance of the foundation. This encour- this fatigue hotspot. Other examples are The Centre for Offshore Foundation ages sliding rather than overturning. the installation of drag or plate anchors Systems has a long-established relation-

A critical design feature of mobile and lateral buckling of subsea pipelines. ship with industry and development of foundations is that the predominant Mobile foundations are a logical evolu- a design tool for mobile foundations will mode of displacement is translation, tion of the now widely-accepted practice be carried out with input from opera- since overturning could lead to over- of allowing seabed pipelines to move in tors, consultants, and contractors with an stressing of connectors between the a controlled manner to accommodate interest in the technology. The motiva- pipes and structure. A mobile foundation operational loading. tion for the project was driven by indus- could be provided with sloping sides to try needs and the output of the research

Leading the way assist in the desired translational motion will be used by industry, so we will work should it settle into the seabed. Australia is well positioned to lead tech- with our industry colleagues to develop a nology development of mobile founda- usable and practical solution.

Where can mobile tions. Not only is it recognized foundations be used?

worldwide as a centre of excel-

Mobile foundations have particular lence for seabed engineering, but potential in deep water or remote oil Australia has substantial stranded and gas felds that have been identifed gas reserves, which coupled with offshore Australia and elsewhere. Australia’s geographic remoteness

A pipeline heats up as hot oil or gas provides complementary drivers.

passes through it. This, in turn, causes The industry is interested thermal expansion along the length of the in a scientifc basis for under- pipe and increased loading to the founda- standing the behavior of mobile tions supporting the connected pipeline foundations, but to date virtu- infrastructure. To resist these loads can ally no information is publically require a massive foundation. available.

Alternatively, a mechanical arrange- World-frst experimental ment can be introduced to relieve the testing of mobile foundations

Schematic of a possible mobile subsea foundation.

Image from the Centre for Ofshore Foundation Systems, loads, with the pipeline termination at prototype scale is now being

University of Western Australia.

being mounted on sliding rails. However, carried out at the Centre for this solution involves a moving part Offshore Foundation Systems

Conclusion that must remain operational during the (COFS) at the University of Western life of the project, and the foundation Australia (UWA), supported by a three- Costs associated with mobilizing a sec- footprint is still large because it must year Australian Research Council grant, ond installation vessel for subsea founda- encompass the slider arrangement. to create a design framework for industry tions are particularly signifcant for the

As an alternative, a compact mobile for mobile foundations. bottom line of smaller developments and foundation can be designed to undergo UWA is ideally placed to carry out when vessels have to be brought in from controlled and limited sliding across the research, as host of the National far afeld.

the seabed to absorb some of the loads Geotechnical Centrifuge Centre, which Mobile foundation technology offers caused by this thermal expansion of the houses the busiest geotechnical centri- an economic solution to a present chal- connected pipelines. fuge in the world. Geotechnical centri- lenge to offshore development, and

While some parallels exist between the fuge modelling enables small scale mod- will contribute to unlocking the huge mode of operation of a mobile foundation els of geotechnical systems to be tested hydrocarbon reserves located offshore and a sleigh or ski, mobile foundations at accelerated gravity levels (up to 400x Australia and elsewhere that are cur- would not be intended for long distances Earth’s gravity), allowing feld-scale soil rently “stranded”. of travel. stresses to be accurately replicated. Stress

The movement would be limited to similitude is critical to capture the true Susan Gourvenec is just a few meters at most, as a pipeline response of geotechnical systems, while a Professor at the is turned on, heats up, and expands, and feld scale tests of offshore geotechnical Centre for Offshore back again during shutdown, when the systems are prohibitive. Foundation Systems pipeline cools down and contracts. A frst campaign of geotechnical cen- at the University of

The movement is periodic over the trifuge modelling of a prototype mobile Western Australia. lifetime of the facility, each time the foundation has been undertaken at UWA Gourvenec has more pipeline is started-up or shutdown, and observations of the foundation under than 15 years of but would be suffcient to relieve loads realistic feld conditions are promising. geotechnical engineering experience, both on the foundation and within the The next stage is to develop a theoret- with particular interest in offshore pipeline. ically-based framework to describe the geotechnics. She is a consultant offshore

Mobile foundations will add to a port- soil mechanics response of the seabed geotechnical engineer to industry and folio of seabed infrastructure designed during the periodic cycles of foundation member of the ISO and API Committees to allow movement. Other examples sliding, in order to predict the foundation for Offshore Geotechnics.

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