Finite Element Analysis of Subsea Expansive Anchor Piles in Rock Seabed

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An innovative anchor template aimed at rock seabed formations for the floating wind market is proposed. GRIP (product name) anchor comprises a subsea structural template with a skirted mud mat forming a pile cap accommodating three expansion anchor piles comprised of Circular Hollow Sections (CHS). In the proposed concept, a segment of the pile is expanded to form a bulb, creating a preload between the pile exterior surface and the drilled surface of the rock cavity. This expanding mechanism creates a friction force as well as the mechanical interlock between the pile and rock, resisting axial loads. This article presents a preliminary Finite Element Analysis (FEA) of pile expansion and axial pullout at the concept stage. A 2D axisymmetric model is created with S355 steel pile with conceptual dimensions and assumed rock properties. The FEA consists of two stages: 1) expansion of the pile inside the drilled rock hole during installation and 2) axial pullout during design life. A parametric study is conducted to investigate the effects of the pile diameter and the number of expansion points in the pile. This ascertains that the expanded bulb remains in the cavity formed in the rock after unloading. For the considered rock and pile properties, the axial capacity is approximately 7MN and 10MN for Ø406mm and Ø610mm CHS piles, respectively. There is a little change in the load capacity with the number of expansion points of the pile as the failure is governed by the yielding of the steel CHS pile. The increase in capacity is directly proportional to the increase in the diameter of the pile for the same wall thickness. FEA of the proposed expansive anchor piles in rock formations provides promising results with respect to axial capacity, which needs to be verified with an experimental study.

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

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