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 Wind Farm Cable Route Soil Conditions Burial Depth and Method Scroby Sands 76 Export Cables Mostly sands along the export cable route. Inter-Array Cables Mostly sands along the interarray cable route. Burial was undertaken using a Sea Stallion plough which had been modified to achieve a target depth of burial of 3m. Burial was undertaken using a Sea Stallion plough which had been modified to achieve a target depth of burial of 3m. Kentish Flats Export Cables - The export cables were buried using the Global Marine owned Hi-Plough. Inter-Array Cables - The inter-array cables were buried using the Global Marine Otter tracked vehicle in jetting mode. Feedback Information (where available) It is understood that all three export cables were generally buried to the target depth of burial of 3m and this deep burial requirement was a permit requirement based on EMF and its effect on migratory fish as well as concerns with mobile sands. The second export cable had to be cut during the installation due to adverse weather, an offshore joint was subsequently introduced and the repair splice buried with post lay burial techniques. It is understood that some inter-array cables have become exposed as a consequence of scour around the base of the offshore structures. It is also believed that remedial rock dumping has been undertaken but the results of this subsequent intervention are unknown. The Hi-Plough was fitted with jetting equipment to reduce tow forces during installation. However, the jetting system was not utilised, partly owing to concerns with respect to suspended sediments affecting local shell fish beds and fish spawning grounds. Sediment load downstream of plough operations was monitored and the limits imposed by CEFAS for increase in sediment load over background levels were not breached at any time during operations. Difficulties in burial operation were encountered where the cable installation had crossed spud depressions from the main installation vessel – Mayflower Resolution. Generally the work appears to have been successfully completed without any major incidents.
Wind Farm Cable Route Soil Conditions Burial Depth and Method Barrow Wind Farm Export Cables Gravels and glacial tills. Cable types and installation techniques Feedback Information (where available) Subsea cable plough. A subsea cable plough was used to bury both the export cables. During the installation of one of the cables an operational incident occurred in which the plough overran and damaged the cable which resulted in the need for an offshore joint. 3.10 Burial Assessment and General Survey Techniques Burial assessment survey (BAS) techniques are commonly employed by the subsea telecommunications industry. A BAS survey is conducted along the proposed corridor for the installation of the subsea cable to provide an advance indication of the likely seabed conditions which will be encountered during cable burial operations. The survey will also give further confirmation of the seabed topography. The BAS survey will be complementary to the other surveys which are commonly employed along the potential planned cable route. These surveys would comprise: ● ● Geophysical survey – to establish the bathymetry and seabed profile and also identify any potential hazards along the proposed cable route. Geotechnical survey – this will usually consist of vibrocores and cone penetration tests (CPT) along the cable route to establish the viability of cable burial. Boreholes are not usually undertaken as they are expensive and the cable installer is only interested in data for the top 2m to 3m of seabed and the CPT and vibrocore data adequately provides this data. The BAS survey is usually undertaken using a burial assessment survey tool which is normally a scaled down simplified version of a narrow share cable plough. The BAS tool is pulled along the route of the proposed cable well in advance of the scheduled cable installation work as part of the pre-survey operations. The BAS tool provides real time data obtained for the penetration of the tool into the seabed. This includes the towing resistance of the tool, pitch and roll data, plus sonar and visual data if camera systems are fitted to the tool. In certain cases the burial assessment tool can be a simple grappling hook, although the feedback results are not as precise as those obtained from the plough-like BAS tool. The data is still meaningful in that it provides an indication of the potential difficulties in cutting a trench into the seabed. All BAS tools have the added advantage of clearing the route of any unchartered debris such as disused or out of service cables or discarded anchor chain or wire. This creates 77
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REVIEW OF CABLING TECHNIQUES AND EN
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Review of Cabling Techniques and En
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Abbreviations AIS Automatic Identif
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TTS Temporary Threshold Shift TWA T
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3 Cable types and 18 installation t
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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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