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 would be up to 50m wide per cable and this section of the channel would be the only area subject to local excavation. Excavation would either be achieved by use of conventional grab dredging equipment or by using specialised remotely controlled underwater excavation machines which are used for localised excavation. Figure 3.31 (Option 1) shows the profile of the anticipated locally excavated section. In the example provided, the local excavation would have the objective of lowering the seabed level from reference Elevation +8.5m down to reference Elevation -10.5m. Following the completion of the local excavation, a subsea cable plough or trenching vehicle would then traverse across the locally excavated section cutting the 1m depth of trench and simultaneously burying the cable to this target depth during the cable lay procedure. This will then ensure a target cable installation to reference Elevation -11.5m. Option 2 – deep burial with plough or trenching machine In order to avoid any pre-excavation across the navigable channel it may be possible to utilise a subsea plough or trenching vehicle fitted with either a deep burial plough share or cutting tool. The burial machine would be deployed to the full penetration depth of 3m when the plough or trenching unit traverses across the navigable channel. The same burial machine would then revert to the standard target depth of burial for the remainder of the export cable route. Figure 3.31 (Option 2) shows the concept of deeper burial either using a subsea plough or the trenching vehicle. The likelihood of success of this methodology would be dependent upon the local geotechnical conditions which exist at the point of the crossing of the navigable channel. These conditions would be verified by local site investigation prior to any installation activities commencing. 68
Cable types and installation techniques Figure 3.31: Methods to Achieve Cable Installation to Reference Elevation -11.5m across the Navigable Channel 3.8.9 BLASTING THROUGH ROCK Blasting through rock has not been included in this review as an alternative cable protection methodology as it would be discounted on the grounds of high cost and significant impact to the environment. Where rock was encountered at a cable landing zone, horizontal directional drilling would be the preferred cable protection method. Further offshore, either a rock ripping plough, rock wheel cutter or a vibratory share plough would be used. 69
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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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Page 20 and 21: 3 Cable types and 18 installation t
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Page 82 and 83: 4 Physical change 4.1 Introduction
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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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