Position HDD rig adjacent to joining pit and drill a pilot hole up to 1,100m from the base of the cliff;
Enlarge the pilot hole;
Install the casing pipe or duct in the enlarged hole, and install messenger wire and winch for future cable installation within the duct;
If required, drawback of the offshore duct end and natural burial by sandy sediments until required to be jointed to the export cable; and
Demobilise construction equipment and re-instate the site to its previous condition.
287. Once the export cable is ready for jointing to the cables within the cable ducts at the landfall, the following steps would be required:
On arrival of the export cable installation vessel, the duct exit would require de- burial. This would most likely be achieved using a mass flow excavator.
The export cable installation vessel would be positioned by anchors prior to undertaking the cable pull in operations, facilitated by a pre-installed messenger wire within the HDD duct and a pre-mobilised pull-in winch located in the onshore transition pit.
Following completion of the pull in operation (and subsequent termination and cable testing) the export cable installation vessel would commence cable lay operations. If the cable is installed as bundled pairs, then trenching is the most likely means of cable protection in this area, whilst for single cables, ploughing would be the preferable means of burial due to the nature of the sea bed in this area (out-cropping London Clay).
Subsequent to the cable lay operations, the cable in the transition zone between the HDD duct and full depth of cable trench would be lowered utilising diver based jet lancing and dredging operations, most likely supported from a small anchored or spudded barge.
5.5.2.2 Transition Pits 288. Transition pits would be required at an appropriate distance behind the shore to house the offshore to onshore cable joints. Each transition pit would comprise a buried concrete-lined structure. The purpose of the transition pit at the landfall would be to provide housing for the joint between the heavily armoured marine cables and the onshore cables.
Preliminary Environmental Information May 2014
East Anglia THREE Offshore Windfarm
Chapter 5 Description of the Development Page 64
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