报告人：Prof. Dave White, University of Southampton
报告题目：DESIGN BENEFITS OF AN EVOLVING SEABED: ARRESTING PIPELINES AND FREEING FOUNDATIONS
I’ll use this presentation to talk about the geotechnical research theme of ‘whole life’ changes in seabed strength. Two example applications will be described: one to stabilise pipelines and the other to ‘free’ foundations.
The ‘whole life’ changes in strength arise from both monotonic dead loads and cyclic live loads. The gain in strength caused by dissipation of pore pressure following cycles of loading is highlighted. This is an aspect of soil response that has not been emphasised in past research and practice, perhaps due to a historic focus on surface-piercing offshore structures that must be designed against storm loading. In contrast, different forms of loading with slower cycles are the dominant action on modern subsea facilities.
Two flowlines in Shell’s Malampaya development provide an elegant case study of changing seabed strength. These pipelines were ‘walking’ progressively in one direction, close to their inlet. A new stabilisation concept was invented, trialled and then installed to remediate this behaviour, all within a period of 12 months. Results from laboratory testing and field trials will be shown, and the role of changing seabed strength will be described.
Long term gains in seabed strength add to the stresses that can be locked into a pipeline, potentially causing buckling. This load can be relieved by redesigning the end connections via a ‘free foundation’ that can translate across the seabed in response to expansion and contraction of the pipeline. This concept will be illustrated via recent centrifuge testing and novel analytical models. ‘Free’ foundations can be smaller than conventional foundations, leading to a reduction in installation costs.
I have been Professor of Infrastructure Geotechnics at the University of Southampton since late 2017, and am involved in the development of the UK: CRIC National Infrastructure Laboratory. I previously held the Shell Chair of Offshore Engineering at the University of Western Australia, and was the Director of the ARC Research Hub for Offshore Floating Facilities (offshorehub.edu.au). My research is focussed on geotechnics, pipeline design and the broader theme of offshore engineering, primarily for energy developments. I am a Co-Director of the EPSRC Offshore Renewable Energy Supergen Hub.