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Seabed scour around marine structures in mixed and layered sediments

Porter, KE; (2016) Seabed scour around marine structures in mixed and layered sediments. Doctoral thesis , UCL (University College London). Green open access

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Abstract

The inherent uncertainty in the prediction of seabed scour depth at offshore structures such as wind turbines is currently a significant barrier to realising optimised, cost effective foundation design. One significant aspect thought to contribute to this uncertainty which has not been extensively studied is the variation in the sediment properties in the marine environment where sediment beds often consist of complex mixtures of materials stratified with depth. This research project encompasses the design and execution of an extensive laboratory study investigating this aspect of the scour problem. Two uniformly graded sands were used to build a range of simplified mixed and layered sediment beds, as a first step to improving understanding of scour behaviour in these situations. A variety of hydrodynamic conditions including unidirectional current, tidal and wave-current flows were tested to ensure relevance to the marine environment. As part of the experiment design a detailed review of scour measurement techniques was conducted leading to the implementation of a photogrammetry system which delivered high resolution, high accuracy scour hole profiles. This study has led to a number of original results. In a layered bed of fine sand overlying coarse sand interaction effects at the grain scale resulted in an enhancement of scour depth in the underlying coarse sand. Bimodally distributed mixed sands were found to alter significantly the scour time development curve. Novel scour tests under a spring-neap tidal cycle in the clear water regime indicated a considerable lengthening of the time to equilibrium. A review of prediction methodologies was undertaken and modifications proposed to take into account the research outcomes. This project has demonstrated that the configuration of the sediment bed is highly influential on scour development, and will contribute towards the future development of more sophisticated design models for implementation in industry.

Type: Thesis (Doctoral)
Title: Seabed scour around marine structures in mixed and layered sediments
Event: UCL
Open access status: An open access version is available from UCL Discovery
Language: English
UCL classification: UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science > Dept of Civil, Environ and Geomatic Eng
URI: https://discovery.ucl.ac.uk/id/eprint/1476108
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