Review of Cabling Techniques and Environmental Effects Applicable

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.
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