Centrifuge Model Study on Vertical Pullout Behavior of Square Plate Anchors in Normally Consolidated Clay

As oil and gas extraction has reached increasingly deep water in recent years, floating platforms are now more widely used than conventional facilities. The mooring of floating systems can be problematic since significant vertical loading is imparted to the foundation systems. Consequently many different types of anchors have been developed to resist the pullout forces, and compared with conventional anchors SEPLA (suction embedded plate anchor) is more widely used because of its lower cost and shorter installation time. The vertical uplift capacity of plate anchors has been studied extensively. However most of the studies were based on theoretical and numerical analysis or tests in 1g conditions. In the present paper, 50g and 100g centrifuge model tests are performed to analyze the pull-out behavior of plate anchors in normally consolidated soft clay and the soil flow mechanism during the uplift process. The anchor is idealized as square in shape. Load-displacement curves and vertical pullout capacity are obtained in a series of wish-in-place tests. The contributing factors are also examined, with special attention paid on the anchor embedment ratio (H/B). Half-anchor tests are performed to study the soil movement patterns surrounding the anchor during the uplifting process, by using PIV (particle image velocity) method and the close range photogrammetry technique. Results are presented in the form of capacity factor (Nc) and are also compared with previous numerical and empirical solutions. Full-flow mechanism (soil flows around the anchor with local failure in shear) is observed in the half-anchor tests. This study with centrifuge model test provides insightful information on the uplifting pullout capacity of plate anchors as a part of foundation systems of floating platforms, as well as the flow and failure mechanism of surrounding soil.