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.

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.

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.