Review of Cabling Techniques and Environmental Effects Applicable
Review of Cabling Techniques and Environmental Effects Applicable
Review of Cabling Techniques and Environmental Effects Applicable
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<strong>Review</strong> <strong>of</strong> <strong>Cabling</strong> <strong>Techniques</strong> <strong>and</strong> <strong>Environmental</strong> <strong>Effects</strong> <strong>Applicable</strong> to the Offshore Wind<br />
Farm Industry – Technical Report<br />
for the planning <strong>of</strong> the <strong>of</strong>fshore cable installation works rather than to assess the<br />
fate <strong>of</strong> disturbed sediment.<br />
4.3 Level <strong>of</strong> Sediment Disturbance<br />
The level to which the seabed is disturbed is primarily related to the nature <strong>of</strong> the<br />
ground <strong>and</strong> the type <strong>of</strong> tool selected to bury the cable. The type <strong>of</strong> device used<br />
to support the tool is likely to have a secondary influence.<br />
This section discusses the application <strong>of</strong> the cable burial tools described in<br />
Section 3 in the range <strong>of</strong> ground conditions described in Section 4.2. The<br />
following cable burial tools have been considered:<br />
●<br />
●<br />
●<br />
●<br />
●<br />
82<br />
Ploughs Simple<br />
Advanced Jetting<br />
Deep Burial<br />
Rock Ripping<br />
Vibrating<br />
Jetting Fluidisation<br />
Erosion<br />
Dredging<br />
Rock Wheel Cutter<br />
Mechanical Chain Excavator<br />
The section covers the likely effect <strong>of</strong> these systems in terms <strong>of</strong> the level <strong>of</strong><br />
disturbance to the seabed. Section 4.3.5 attempts to quantify this disturbance by<br />
ranking the effects <strong>of</strong> the cable burial systems <strong>and</strong> provides limited advice on the<br />
calculation <strong>of</strong> the volume <strong>of</strong> sediment disturbed <strong>and</strong> brought into suspension.<br />
4.3.1 PLOUGHING<br />
Cable ploughs (Section 3.8.2) are generally used in s<strong>and</strong>, silt, all types <strong>of</strong> clay<br />
<strong>and</strong> weak rock such as structureless chalk, which generally consists <strong>of</strong> s<strong>and</strong> to<br />
cobble-sized fragments in a matrix <strong>of</strong> silt. They can also be used in harder rock<br />
if the plough is fitted with a rock penetrating tooth, or in chalk <strong>and</strong> gravel beds<br />
if a vibrating plough share is used.<br />
The controlled operation by which cable ploughs work, “displacing” the<br />
sediment into which the cable is lowered, followed by the natural backfilling<br />
<strong>of</strong> the trench ensures that soil disturbance is kept to a minimum, <strong>and</strong> also<br />
minimises mixing between soil particles <strong>and</strong> the surrounding water. The type <strong>of</strong><br />
soil most susceptible to mixing with water during ploughing is silt, because silt<br />
possesses no internal cohesion <strong>and</strong> the particles are small enough to be eroded<br />
by gentle water turbulence. Silt may remain in suspension for days giving the<br />
current chance to transport the sediment some distance away from the trench.