Conleth O’loughlin

The Performance of Dynamically Embedded Anchors in Calcareous Silt

The Omni-Max anchor is a new type of dynamically installed anchor featuring a mooring arm located close to the anchor tip that is free to rotate about the anchor length. An experimental programme has been undertaken on a geotechnical centrifuge to assess the anchor performance in calcareous silt. The testing programme includes (i) anchor drops and measurement of the penetration depth, and (ii) anchor pull and assessment of the anchor trajectory. An anchor embedment model based on strain rate enhanced shearing resistance is capable of satisfactorily predicting anchor embedment using model parameters that are similar to those used for clay. The diving behaviour of the anchor, post keying, is demonstrated, provided that the initial embedment after impact is deep enough to prevent a shallow mechanism to develop during anchor keying.© 2013 ASME

The Dynamically Embedded Plate Anchor: Results From an Experimental and Numerical Study

Dynamically embedded plate anchors are rocket shaped anchors that penetrate to a target depth in the seabed by the kinetic energy obtained through free-fall. After embedment the central shaft is retrieved leaving the anchor flukes vertically embedded in the seabed. The flukes constitute the load bearing element as a plate anchor. This paper provides an overview of an experimental and numerical study undertaken to provide the first performance data for this anchor concept. The experimental work includes geotechnical centrifuge modelling and field tests using three different reduced anchor scales, whereas the numerical work focused on investigating anchor capacity for a rage of geometries, embedment depths and seabed conditions. The experimental work indicates that expected tip embedments are in the range 2 to 3.3 times the anchor length and depend on the impact velocity, anchor mass and shear strength of the soil. As with other plate anchors, the anchor needs to key before maximum capacity can be mobilised. Both the centrifuge and field experiments show that this keying and pullout behaviour is typical of other vertically installed plate anchors, where the main issue is the loss in embedment during keying. Both the experimental and numerical studies showed that the capacity of the DEPLA is much higher than that of other dynamically installed anchors with capacities up to 40 times the dry weight of the plate and plate bearing capacity factors of about 15.

A Release-to-Rest Model for Dynamically Installed Anchors

AbstractDynamically installed anchors are torpedo-shaped anchors that are installed by dropping them through the ocean such that they self-bury in the soft seabeds typically encountered in deep wat...

Anchor and Chain Reaction During Inclined Pullout in Clay

Plate anchors have attracted much attention in offshore deep water development. This paper studies anchor rotation and chain reaction during plate anchor inclined pullout when it is installed vertically in clay. Both numerical simulation of strip plate anchor and centrifuge model tests on square anchor are conducted in uniform and normally consolidated (NC) clay. In the numerical analysis, Remeshing and Interpolation Technique with Small Strain model (RITSS) is used to simulate large movements of the anchor. In the centrifuge model tests, a transparent “soil” is used to observe anchor rotation and chain reaction during anchor pullout. It is found that plate anchors reach ultimate capacity (Nc ≈ 11.7) when they are fully rotated to a position perpendicular to the pullout direction. During anchor pullout at 60° to the horizontal, the loss of embedment during keying-in ranges from 0.38 B to 0.58 B for square and strip anchors in uniform and NC soils. The loss of anchor embedment in NC clay is about 4% ∼ 23% higher than that in uniform clay depending on the soil strength profile in the NC soil.Copyright