FINITE ELEMENT INVESTIGATION INTO THE PERFORMANCE OF EMBEDDED PLATE ANCHORS IN SAND

As offshore energy and other development extend to deeper waters, conventional platforms are increasingly being replaced by floating facilities. Also, up to 60 percent of wind power development is anticipated to be in deeper waters that require floating platforms moored to the seabed by anchors. Seabed soils at sites often contain sandy soil strata; therefore, practical development of offshore wind power requires anchor systems that are suitable for deployment in sands, such as piles, suction caissons and direct embedment plate anchors. Of these options, plate anchors are particularly attractive due to their compact size, light weight, variety of installation techniques, and highly efficient and suitable for a wide range of soil conditions. However, more reliable predictive models for plate anchor performance in cohesionless soils are needed for mooring systems to be securely designed. The limited research focus on plate anchor performance in cohesionless soil, particularly for deep embedment, has triggered a strong motivation for this research. Therefore, extensive small and large deformation finite element simulations were conducted to study the effects of anchor embedment depth, with special emphasis on characterizing the transition in the anchor behavior from a shallow to a deep failure, considering elastic soil behavior (in terms of Rigidity Index Ivr) in evaluating anchor performance. Additionally, there is a significant gap in knowledge concerning the keying behavior of direct embedment plate anchors in sand after installation, and the corresponding irrecoverable loss of embedment. Finally, most previous plate anchors research have focused on either horizontal or vertical anchor orientations while the effect of inclined orientations has received limited attention. The predictions showed that at shallow anchor embedment depths, rigidity index Ivr has negligible influence on anchor capacity while the performance of deeply embedded anchors is strongly influenced by rigidity index Ivr. This study developed an empirical model for predicting anchor pullout capacity as function Nvq (Dvr, γ ', z/D), describing the transition in the breakout factor Nvq from the shallow mode to its maximum value Nvqvmvavx. In regard to the keying process behavior, the large deformation finite element analyses showed that the angle of orientation α at which the maximum pullout capacity occurs increases with increasing e/B ratio, ranging between 75 degrees and 85 degrees. Also, the predictions revealed that as the loading eccentricity ratio e/B increases, the loss in anchor embedment vz/B during rotation decreases. However, once the eccentricity e greater than or equal B, a minimal loss in anchor embedment can be achieved regardless of the plate thickness. A linear relationship was observed between the maximum loss in anchor embedment and anchor pullout angle theta at any e/B ratio. In regard to the pullout capacities of inclined plate anchors in cohesionless soil. An empirical equation was proposed to estimate the breakout factor of an inclined anchor at any inclination angle theta between 0 degrees and 90 degrees. Also, the observations showed a significant sensitivity of the breakout factor Nq to the plate width B