One of the ways to install plate anchors in deep seabed is to drop the anchor system from the sea level and allow it to initially embed in the seabed under its own weight. Further dragging would cause the anchor to rotate and embed further into the seabed. There could be difficulties of getting the anchor plate horizontal or mooring line to be perpendicular to the plate where the maximum pullout capacity could be achieved. As part of the investigations, various aspects of the plate performance were examined through centrifuge testing in which the plate orientation and pullout angles were varied. It was presumed that dynamic stability of the anchor (during field installation) can be achieved by having the plate in biwing configuration. Therefore, the performance of the biwing anchors having different spacing between the plates was also examined in the centrifuge testing program and the findings were compared with predictions obtained through finite-element modeling (FEM). Both pullout directions and the plate angles considerably influenced the pullout capacity factors. The comparison between the predicted pullout capacity using FEM and measured pullout capacity for biwing anchors at shallow embedment depths was excellent. However, the FEM-predicted pullout capacity was noticeably lower than the measured ones for deep anchors. Pullout capacity of biwing anchors at shallow embedment depth increased as the spacing between the plates S increased from 0 to 0.5B. However, there appears to be a slight reduction in the performance in deep embedment anchors. This is also reflected in FEM findings. @en

Offshore wind developments are moving towards deep-water regions where energy is abundant, visual impact is minimised and the larger turbine sizes can make the energy production more cost-effective. One of the key challenges facing the industry is the development of reliable substructures. While fixed foundation systems are widely used for shallow-water (<60 m) developments, permanent anchors are seen as one of the most viable mooring solutions for floating structures in deep water. In the current study, the pull-out behaviour of square plate anchors in clay was investigated using large-displacement finite-element analysis. The anchor capacity and failure mechanism were considered for a range of embedment ratios and undrained shear strengths. Three distinct modes of anchor failure identified in previous studies were examined through the analysis of four descriptors including: the pull-out capacity of the anchor, the pull-out displacement required to mobilise this capacity, the energy absorbed by the anchor during pull-out and the variation of the pull-out capacity with respect to a normalised overburden pressure. The findings of the study are presented in the form of a series of charts that can aid design through understanding of the factors controlling the development of anchor failure modes, in addition to identifying the transition point between different failure mechanisms.@en

This paper presents data from an initial development stage of an 'umbrella anchor' concept. The anchor can be pushed into sand deposit in a folded arrangement to reduce installation loads. When a pull-out load is applied to the mooring line, the anchor deploys to create a large embedded plate anchor. Physical modelling was carried out in saturated sand-bed with the anchor installed at depths of up to 1.6 m and loaded vertically. During installation, liquefaction was generated at the tip of the anchor to reduce the penetration resistance. This enabled the anchor to be installed quickly and accurately to a target depth. The anchor could provide pull-out resistances comparable to anchor that was wished-in-place at similar depths. The observed behaviour provided encouraging preliminary results and suggests that, with further development and analysis, the concept could potentially be used for commercial applications. @en

This paper presents an experimental and analytical study to investigate the effect of shape on the pull-out capacity of shallow horizontal plate anchors in sand under drained loading conditions. Novel dynamically penetrating plate anchor concepts have been proposed for use in the offshore energy sector. These anchor concepts may have shapes that are atypical, and the analysis of pull-out capacity of these shapes may be needed for design. Most of the research on the capacity of shallow horizontal anchors has focused on square, rectangular or circular shapes. Physical and analytical modelling was used to study the capacity of circular, square, triangular and kite-shaped plate anchors. The 1g physical model results indicated that the circular anchor had the highest capacity, which was up to two times higher than the square anchor, which had the lowest capacity of all shapes included in this study. The equilateral triangle and kite shapes had capacities that fell between the circle and the square shapes. A new generalised non-associated flow limit equilibrium model was developed to predict the pull-out capacity of shallow plate anchors with convex polygon anchor shapes. The model was most accurate at embedment ratios of 4 or less, with a bias of less than 10%.@en

In recent times, interest in dynamically installed foundation systems for deep-sea construction has increased; however, these foundation systems are still under development and need quantification of various soil parameters with different perspectives. For the design of dynamically installed foundations, it is essential to assess the strain-rate effect on very soft soils. The T-bar has been widely used to characterize soft offshore sediments, such as silt and clay, and there is extensive existing literature on the interpretation of test results. Strain-rate dependence has not previously been fully examined for T-bar tests in very soft clay at very high rates of penetration. This paper examines this aspect using a physical model test. A 65-cm-thick kaolin clay bed was formed using vacuum consolidation. A T-bar was driven into the clay bed at rates that varied from 0.1 cm/s to 60 cm/s. The tests revealed that the resistance factor increased by 9 % for every 10-fold increase in the penetration rate for the material tested in this research.@en

Offshore wind developments are moving towards deep water where the energy is abundant and visual and sound interference is minimised. However, construction in deep water poses several challenges to developers, among which are the high cost of operation and material transport. The current study addresses the behaviour of a novel foundation system (pending US patent) that aims at minimising the cost of deployment for emerging offshore wind facilities. To this end, the preliminary results of an offshore field test on the small scale dynamically installed anchor are presented and the testing methodologies are briefly outlined. The results provide insights into the behaviour of the anchor as it is released into the water column, impacts with the seabed, and finally, achieves it maximum penetration depth. This is enabled through a detailed study of the data obtained from an accelerometer built into the anchor, which tracks the anchor motion over the course of its deployment. Overall, the findings in this research contribute to an enhanced understanding of the behaviour of dynamically installed anchors as perceived through field tests.@en

This paper addresses scaling issues related to small-scale 1-g model tests on plate anchors in sand under drained loading conditions. Previous centrifuge studies from the literature have suggested that the results of conventional 1-g model testing are inaccurate because of scale effects. Other studies have suggested, however, that scaling errors can be reduced in 1-g model tests if the results are presented in dimensionless form and the constitutive response of the model soil is representative of the prototype behavior. There are no experimental studies in the literature that have tested the validity of this approach for plate anchors. A simple 1-g scaling framework was developed for vertically loaded, horizontal plate anchors. Small-scale 1-g model tests were performed on square plate anchors in dry sand, and combined with existing centrifuge and 1-g model test data from the literature to test the scaling approach for both capacity and deformation. The 1-g model tests provided a reasonable representation of the full-scale prototype behavior when the scaling approach was applied.@en

This paper addresses scaling issues related to small-scale 1-g model tests on plate anchors in sand under drained loading conditions. Previous centrifuge studies from the literature have suggested that the results of conventional 1-g model testing are inaccurate because of scale effects. Other studies have suggested, however, that scaling errors can be reduced in 1-g model tests if the results are presented in dimensionless form and the constitutive response of the model soil is representative of the prototype behavior. There are no experimental studies in the literature that have tested the validity of this approach for plate anchors. A simple 1-g scaling framework was developed for vertically loaded, horizontal plate anchors. Small-scale 1-g model tests were performed on square plate anchors in dry sand, and combined with existing centrifuge and 1-g model test data from the literature to test the scaling approach for both capacity and deformation. The 1-g model tests provided a reasonable representation of the full-scale prototype behavior when the scaling approach was applied.@en