Model experiments to measure yield thresholds and trajectories for plate anchors and develop a new anchor concept
The motivation of this research was to experimentally measure yield thresholds and dive trajectories of model plate anchors and develop a new anchor concept: The Flying Wing Anchor®. The objectives of this study were to (1) develop the understanding of pure loading yield thresholds of simple shaped bearing plates in clay under undrained loading, investigate how the undrained shear strength, sensitivity and plasticity of soil affects the pure loading yield thresholds and compare experimental measurements with theoretical predictions (2) asses the initiation of post-yield movement and dive trajectory of bearing plates, (3) optimize the design of the Flying Wing Anchor® concept based on pure loading yield thresholds, initiation of post-yield movement and dive trajectory in clay, (4) develop a simplified plasticity model to predict the initiation of post yield behavior, dive trajectory and the ultimate holding capacity of the new anchor concept in clay and compare theoretical predictions with experimental measurements. The methodology focuses on experimental testing of model plates and Flying Wing Anchor® concepts in undrained clay. The theoretical calculations are compared with experimental measurements. The pure loading yield thresholds of the bearing plates in clay under undrained loading were measured. The post-yield movement analysis showed an anchor vertically embedded into soil should initially rotate from vertical to dive deeper with drag loading. The initial Flying Wing Anchor® concept is the one-wing Diamond anchor and further optimization resulted in bi-wing concepts of Paloma and the final concept of Speedy anchors. The new anchor concept dives deeper into soil when loaded in tension. At the ultimate embedment depth, the holding capacity is maximized. The lower shear resistance enables deeper penetration into soil. The holding capacity is maximized over the full anchor surface in bearing due to high resistance in normal loading. Anchor can be pulled out of soil in pure shear and reused. Scaled model tests show the new anchor is a promising sustainable and efficient foundation solution for deep-water offshore wind turbines due to efficient installation method, sustained high capacity and horizontal trajectory during failure that prevents anchor to slide out of soil.