Review of Cabling Techniques and Environmental Effects Applicable

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Review of Cabling Techniques and Environmental Effects Applicable to the Offshore Wind Farm Industry – Technical Report 3.7.8 CURRENT BURIAL TARGETS FOR THE OFFSHORE WIND FARM INDUSTRY The offshore wind farm industry has generally recognised that the main risks posed to the subsea cables derives largely from inshore fishing activity and dragging anchors from coastal vessel traffic. Typical target depths of burial between 1m and 2m have been specified for the majority of the Round 1 sites which have been developed to date. However, as the Round 2 developments move into deeper water, cable risk assessment may identify the need for increased burial depths as the possibility of anchor damage from larger seagoing vessels has to be considered. The use of burial assessment surveys may increasingly be used to establish target burial depths for cables. This procedure is explained in more detail in Section 3.10 of this report. 3.7.9 REMEDIAL MEASURES Cable burial is the primary method for protecting subsea cables. Providing the correct burial machine is selected for the designated burial task, the target depth of burial is likely to be achieved. However, occasionally reduced burial or zero burial occurs. This will usually result as a consequence of an unforeseen event such as extreme weather; the departure from the scheduled installation procedure; extreme ground conditions which were not anticipated from the original survey; or equipment failure. Remedial measures will be required if the perceived risk for the installed cable is considered too high. In many cases it will not be possible to re-engage the cable with the original cable burial machine (i.e. subsea cable plough or tracked cable burial machine with enclosed cable path). In such cases the only remedial burial option available will be post lay burial by other means. Most post lay burial machines only utilise jetting systems which straddle the surface laid section of cable and these machines have limited capability when working in hard seabeds. Alternative cable protection methodologies which are reviewed in Section 3.8.6 can also be employed as a means of remedial protection for the installed subsea cable. 3.8 Cable Protection Methods This section describes the methods which are currently used to protect subsea cables in the subsea telecommunications, power cable and oil and gas industries worldwide. Section 3.9 of this report focuses specifically on the cable protection methods which are relevant to the offshore wind farm industry. Section 3.9 does not repeat the methodologies as chronologically listed in this Section 3.8, but summarises the methodologies used on wind farms installed to date and also lists the cable protection methodologies considered relevant for current and future offshore wind farm developments. 34
This section is divided into 2 sub-sections as follows: ● ● Cable types and installation techniques A review of all cable burial methods employed by all industries worldwide to protect subsea cables Sections 3.8.1 to 3.8.5 inclusive; and A review of alternative cable protection methodologies such as rock dumping, concrete mattresses, fronds, grout bags etc. Section 3.8.6. Each cable protection method is described in detail together with explanations of which methods are commonly employed for varying seabed condition. Illustrations and figures for the methods and equipment are provided to illustrate the methodology under review. 3.8.1 CABLE BURIAL METHODS There are a diverse range of cable burial machines available in the market capable of burying and protecting offshore cables. This section of the report presents and describes these cable burial machines whilst also indicating the range of application and capabilities of each machine. This is always a subjective and sometimes controversial topic, as the performance of a cable burial machine in the offshore environment can vary from the supplier/owner specification which can tend towards more optimistic performance criteria. Therefore, the performance statements in this section of the report are based more on performance observed in the field by the authors and independent associates consulted, as opposed to the published performance criteria. In order to allow a comprehensive review of the various cable burial machines, and to be able to investigate the environmental effects associated with each machine, four categories have been established for the cable burial machines: ● ● ● ● Cable Burial Ploughs; Tracked Cable Burial Machines; Free Swimming ROVs with Cable Burial Capability; and Burial Sleds. All of the cable burial methods and cable protection methodologies which are described are used on a worldwide basis and on all different types of subsea cable systems. Table 3.5 sets out the various burial method options associated with each cable burial methodology and also provides a summary of the mode of operation. 35
Page 1: REVIEW OF CABLING TECHNIQUES AND EN
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Page 9 and 10: Abbreviations AIS Automatic Identif
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Review of Cabling Techniques and En
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6 Good practice measures This secti
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7 Gaps in understanding Research fo
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References Introduction Sinden, G.
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Appendix A: Standards and codes of
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Printed in UK on recycled paper. De
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