export cables immediately, or ducts would be left within the sea bed until the cables are installed within them and connected to offshore export cables.
275. The short HDD method of installing the export cables is similar to that for the long HDD method with the exception of a shorter offshore set back distance. Offshore, a trench would be excavated using a barge based excavator or suction dredger from the duct end towards deeper water and softer sediments whereby a plough or jetting tool could be used to install the export cable further offshore.
276. In the short HDD option the HDD exit point would require temporary access from the cliff top to the beach area. It is proposed that any temporary works access would be constructed to the northeast of the proposed HDD site, in order to minimise disturbance to the SSSI at Bawdsey Cliffs and to avoid vegetated shingle at landfall. A site investigation has demonstrated that although the Red Crag is present inland it is absent along this section of the coast. Temporary access would most likely comprise a ramp constructed over the cliff. The temporary access would be required for a tracked excavator, which would be used to prepare the exit point and make the connection with the duct. The excavator and site personnel must have a safe exit from the beach at all times.
277. The beach access will remain in position for the duration of the drilling programme and for the cable landing, but actual access to the beach will only be required for a few hours to excavate and rebury the exit pit each time a duct is pulled into the drill bore, or when the cable is installed into each duct. During duct and cable pulling operations access to the beach may need to be restricted or sections of beach may need to be temporarily closed for the day to protect members of the public from construction hazards. At all other times the beach will remain open and no plant or equipment will be present.
5.5.2.1 Horizontal directional drilling (HDD) 278. The method comprises a three stage process wherein:
The first stage drills a pilot hole along the designated route;
The second stage enlarges the hole by passing a larger cutting tool known as the back reamer; and
The third stage places the product, casing pipe or duct in the enlarged hole.
279. HDD is undertaken with the help of a viscous fluid known as drilling fluid. It is a usually mixture of water and bentonite or polymer continuously pumped to the
Preliminary Environmental Information May 2014
East Anglia THREE Offshore Windfarm
Chapter 5 Description of the Development Page 61
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