Design of direct on-seabed sliding foundations

Andrew Deeks, Hongjie Zhou, Henry Krisdani, Fraser Bransby, Phil Watson

Research output: Chapter in Book/Conference paperConference paper

15 Citations (Scopus)

Abstract

This paper describes a new framework for the geotechnical design of pipeline-related foundations (e.g. foundations for PLETs and Tees) designed to slide directly over the seabed during pipeline operation. This approach can present considerable savings in terms of fabrication and construction costs because of reduced foundation sizes. Over the design life, a pipeline is likely to endure many thermal/pressure load cycles due to product and flow rate variations during operation. These cycles result in the foundation sliding back and forth across the seabed within a footprint. These loads and corresponding motions impose cyclic shear stresses on the soil that can (i) degrade foundation bearing capacity and (ii) cause additional foundation settlement. Often the key design consideration is whether or not the cumulative settlements will eventually compromise the integrity of the pipeline system to which the PLET and its associated foundation are attached. In addition to consolidation and creep, two key mechanisms are shown to control cyclic foundation settlement: (i) bearing mechanism induced burial and (ii) cyclic shear stress driven soil volume reduction. Their relative significance depends on the soil conditions (soil state) and input pipeline movements. The paper presents key aspects required for the design of direct on-seabed sliding foundations, including the soil parameters and associated testing required. Validation of the design approach is illustrated by comparison to laboratory model tests performed on carbonate soils. The impact of soil properties on potential foundation performance is illustrated with a design example and the importance of conducting site specific soil testing and settlement analyses is emphasised. It is also illustrated that close integration of the pipeline, structural and geotechnical analysis is necessary to reliably quantify system performance of these novel foundations.

Original languageEnglish
Title of host publicationASME 2014 33rd International Conference on Ocean, Offshore and Arctic Engineering
PublisherASME International
Volume3
ISBN (Print)9780791845417
DOIs
Publication statusPublished - 2014
Externally publishedYes
EventASME 2014 33rd International Conference on Ocean, Offshore and Arctic Engineering, OMAE 2014 - San Francisco, United States
Duration: 8 Jun 201413 Jun 2014

Conference

ConferenceASME 2014 33rd International Conference on Ocean, Offshore and Arctic Engineering, OMAE 2014
CountryUnited States
CitySan Francisco
Period8/06/1413/06/14

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