Review of Cabling Techniques and Environmental Effects Applicable

Wind Farm Cable Route Soil Conditions Burial Depth and
Method
North Hoyle Export Cables Close to the
wind farm there
were stiff clays
associated
with glacial till.
However, the
vast majority
of the route
consisted of
sands and
gravels.
Inter-Array
Cables
The array on
the east side of
the wind farm
had stiff clays
associated with
glacial till. The
remainder of the
site consisted
of sands and
gravels.
A Sea Stallion subsea
cable plough with a 2m
burial depth capability
was employed to achieve
a target burial depth of
1.5m.
The LBT1 trencher was
used which simultaneously
laid and buried the interarray
sections of cable to a
target burial depth of 1m.
Cable types and installation techniques
Feedback Information
(where available)
The installation work
proceeded well without any
problems. One of cables was
installed from the shore to the
wind farm and the other cable
installed from the wind farm to
the shore. Both cables crossed
the BHP owned pipeline to
the Hamilton offshore facility.
Concrete mattresses were
used to separate and protect
the cables at the crossing
and diver intervention was
required to bury the sections
of cable from the edge of the
mattresses to the termination
points of ploughing
operations.
The LBT1 is equipped with a
forward mechanical cutting
tool which sits in front of the
main jetting unit for cable
burial. It achieved good burial
across the majority of the site
apart from when working in
the stiff clays on the eastern
array where burial was
only possible in the softer
sediments. The LBT1 also has
to overrun the cable line to
allow the final cable end to
be pulled in the J-tube. This
typically leaves a 50m section
of cable unburied close to
the second WTG structure.
Diver techniques were used to
bury these sections of cable
and this resulted in the burial
works being carried over into
a second season following
the main installation of the
offshore wind farm.
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