Video: Development of Anchor Penetration Models for Cable Burial Risk Assessment
- Fraser Gibson (Ryder Geotechnical) | Robbie Williams-Crew (Ryder Geotechnical)
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- Offshore Technology Conference
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- 2020. Copyright is retained by the author. This document is distributed by OTC with the permission of the author. Contact the author for permission to use material from this document.
- 7 Management and Information, 7.2 Risk Management and Decision-Making, 7.2.1 Risk, Uncertainty and Risk Assessment
- CBRA, Risk Assessment, Anchor Penetration Model, Cables
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An anchor penetration model is an important aspect of a cable burial risk assessment as the model is there to predict the depth a given anchor will penetrate to, once deployed. There are a number of variables that influence the penetration depth of anchor, which are as follows: Anchor size; Fluke length; Fluke angle; and Soil type. The anchor size is considered as the weight, in kg, of a given anchor required to stop a vessel of a given displacement tonnage. The fluke length and fluke angle vary depending on the type of anchor, manufacturer, and anchor size. Current industry guidance presents a number of example values with respect to fluke lengths, and vessel displacements; however, these are generic values and are not necessarily suitable for all cable scenarios.
This paper presents a methodology that can be used to develop a detailed anchor penetration model for a given region for input into a cable burial risk assessment. The process is applicable for any region, and for specific vessels in that region, thus reducing the conservatism in the overall required penetration depth. The above variables are presented along with a number of factors that can influence the overall penetration depth, and how these should be treated.
The model has been implemented on a number of projects, and compared against the limitations of current industry practice. The results indicate that for a given anchor penetration prediction, by using a more appropriate regional model, the predictions are less conservative, leading to a reduced burial depth requirement.
Cable burial and protection is a critical aspect for a given windfarm development; however, overconservative burial depths can increase the installation cost significantly, and increase the time required for installation, leading to greater exposure time for the cable and offshore personnel. More accurate predictions at the planning stage can remove these conservatisms, introducing a more efficient installation and operation phase.