Incremental Approach for Cyclic Displacement of Helical Anchors in Sand

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Helical anchors have experienced a renaissance of research activity in recent years owing to their suitability for mooring floating energy converters. They are relatively easy to install and exhibit large uplift capacity relative to their self-weight, yet their response to complex variable load patterns at sea remains to be fully addressed, in part due to the difficulty in constructing large deformation numerical models. The tendency is to assume uniform loading and design the anchor to remain within a stable regime, yet inevitably anchors will be subjected to extreme storm events over their lifetime. Aimed at tackling this problem, this paper provides a simple incremental approach for cyclic displacement of shallow plate anchors, one which accommodates a seamless transition from stable to meta-stable to unstable zones under variable loading. The approach indicates that, while bidirectional compression and tension loading may be particularly damaging, anchors subject to tension-only uplift loading maintain stability at loads proximal to their ultimate uplift capacity. The flexible approach described herein applies in a unified manner to both loose and dense sand, having been calibrated against 16 previously published, and 16 recent long term cyclic tests in each.

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

13 - Developmental foundation and anchoring concepts: hybrid foundations, ring anchors, helical piles, torpedo, shared anchoring