Yield Surface of Deeply Buried Square Anchors Under Out-of-Plane Loading

Anchors are widely used offshore as foundation systems to moor floating platforms and renewable energy devices to provide uplift resistance in vertical or resistance in inclined direction. Most of the available research work has concentrated on in-plane loading. However, any failure of a single mooring line in a storm can cause out-of-plane loading on the remaining anchoring system. This research targets how this out-of-plane loading can affect the trajectory and ultimate holding capacity of the anchors. This paper presents results of a numerical investigation of the undrained bearing capacity of deeply buried square plate anchor in clay under six degrees-of-freedom loading. Finite element analyses are conducted to define the combined loading yield surface (or yield surface for the anchor in its current position) and an analytical expression of the yield surface is proposed and written directly in the six degrees-of-freedom loads. This analytical expression allows implementation of the yield surface in a plasticity approach, where the load-displacement relationship of the anchor can be described. The method to achieve this and also an illustration of how this framework on a simple plate anchor can be extended to predict the performance of more complex anchor geometries is described at the end of the paper in a description of future research.