Numerical Investigation of Uplift Behavior of Circular Plate Anchors in Uniform Sand

Abstract

Embedded plates provide an attractive anchorage alternative for mooring floating structures owing to their light weight and high efficiency. They can be installed through a variety of means, including suction, driving, or dynamic installation. A primary measure of anchor performance is monotonic drained capacity, which increases with increasing embedment depth owing to increased soil strength and the diminishing effect of the free surface. While the performance of plate anchors in clay has received thorough coverage in the research literature, attention to plate anchors in sand has been relatively limited, particularly for deeply embedded plates. This paper presents a numerical study of the monotonic capacity of circular, horizontally oriented anchors in sand, subjected to centric loading. The finite-element study investigates a range of anchor embedment depths from 1 to more than 20 plate diameters. This depth range is sufficient to characterize the transition of the anchor behavior from a shallow to a deep failure mechanism, for which the latter has an associated depth-independent dimensionless breakout factor. The study employs a large-displacement finite-element analysis employing a Mohr-Coulomb soil model with a nonassociated flow rule. Key soil properties considered in the analysis include the friction angle, dilation angle, and rigidity index of the soil. At shallow anchor embedment depths, the rigidity index has a negligible influence on anchor capacity. However, the performance of deeply embedded anchors is strongly influenced by all three parameters considered in the study. Finite-element solutions proved to be in good agreement with previously published lower-bound plastic limit analyses. Comparisons to experimental data showed good agreement in terms of overall trends of anchor capacity versus depth. For design purposes, this research developed an empirical model for predicting anchor monotonic drained capacity as a function of relative density and anchor embedment depth.