Back-Analysis of Deep Embedment of a Heavy Pipeline in Very Soft Clays

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4. Back-Analysis of Deep Embedment of a Heavy Pipeline in Very Soft Clays

Pipe-soil interaction forces are key elements in the design of offshore pipelines in very soft clays. These forces are highly influenced by the pipeline as-laid embedment. It is therefore important to accurately predict the range of embedments in the field, in order to bracket the interaction forces to consider in design to satisfy all limit states. Although methodologies exist, uncertainties remain when making these predictions. A major uncertainty relates to the approach to adopt, and the level of soil remoulding to consider, to account for dynamic lay effects, when dealing with heavy pipelines in very soft clays for which large embedments are anticipated. A back-analysis of the embedment of a heavy pipeline in very soft clay is presented and comparisons are made with common design methodologies. The objective of the back-analysis was to use the outcomes in future pipeline designs at the site. The pipeline as-laid survey has confirmed that the embedment was large. A second survey has revealed that further embedment took place over a period of 2 years, which was unexpected. The main outcomes of the back-analysis are presented. In particular, the methodology and level of soil remoulding to consider to match the observed embedment is discussed. Regarding the increase of embedment, two plausible hypotheses are discussed.

5th International Symposium on Frontiers in Offshore Geotechnics (ISFOG2025)

15 - Mooring lines, Cables, Pipelines, Immersed tunnels and Risers