Scour and sedimentation of submarine pipelines: closing the gap between laboratory experiments and field conditions (Keynote)

Predicting changes to subsea pipeline embedment due to sediment mobility is critical to many aspects of pipeline design, including on-bottom stability, thermal management, fatigue analysis and flow assurance. Motivated by this requirement, significant advances have been made over the last few decades in un-derstanding the mechanisms of pipeline scour and sedimentation. This has led to the development of predic-tive models and formulas, based predominantly on laboratory experiments. However, despite these developments uncertainties still remain in predicting scour and sedimentation in actual field conditions. One reason for this continued uncertainty is that previous laboratory experiments have often focused on idealised testing conditions, consisting of uniform sandy sediments and steady or stationary near-bed current and wave velocities. Although these idealised conditions enable systematic studies, they are not representative of the range in marine sediments and metocean conditions observed in practice; hence extrapolation is necessary. A second reason for uncertainty is that there has only been limited comparison of laboratory results with field data, and so quantitative validation is lacking. Noting these areas of uncertainty, in this paper we review a col-lection of recent studies completed at the University of Western Australia (UWA) which each aim to close the gap between laboratory experiments and actual field conditions, and therefore reduce uncertainty in predicting changes in scour and sedimentation in the field. These studies focus on three aspects of work: (i) the effect of variations in marine sediment properties on the rate of pipeline scour; (ii) the effect of time-varying seabed velocities on pipeline scour; and (iii) comparisons of laboratory based estimates of scour and sedimentation with field data. In each study an emphasis is placed on developing reliable predictive models and formulas that better represent field conditions, or are validated against field observations. It is argued that these models allow for improved predictions of pipeline scour and sedimentation, and may be used to form a rational design approach for subsea pipelines