East Anglia ONE Offshore Windfarm Construction Artificial Lighting Emissions Plan


September, 2016


working width shall not exceed 55m, except at the HDD locations identified in DCO Requirement 10 (6), where the working width is permitted to be increased to allow for the installation and use of the specialist equipment to undertake the HDD.


17.


There are two basic techniques to be used for the installation of the cable ducts during the construction of the onshore cable route. These are:


 Open Cut techniques; where a trench is excavated and the cable ducts laid in the trench before reinstatement, using the excavated material; and


 Trenchless Technique; typically HDD, where a pit is excavated to access the crossing and from which a drill is passed through the ground on one side of the obstacle to a receiving pit created on the opposite side. The bore is then gradually enlarged to receive the duct, which is the technique that will be used to pass under roads, main rivers and other sensitive sites.


18.


For the open cut technique two trenches will be excavated for the EA ONE ducts and cables and an additional trench will be excavated in parallel for the cable ducts that will be installed to serve EA THREE in the future. An indicative cross section showing the open trench working width layout is included in Appendix 2. As the trench excavation progresses, subsoil will be removed to create the trenches to working depth for duct installation, the subsoil will be temporarily stored separately from the topsoil, and then reused to backfill the trenches.


19.


Particular care will be taken when backfilling the trenches with the excavated material (subsoil) to reinstate it in the order in which it was excavated, again to minimise any disruption to the existing ground drainage pattern. The ducts will be installed in the trench, where they will be bedded on and then surrounded and topped by Cement Bound Sand (CBS) or equivalent which will gradually set and harden in situ as water is absorbed. Above this, the subsoil will then be used to reinstate the trench to the previous level.


20.


Where, due to the existence of obstacles, it is not possible to install the cable ducts using the open trench method, trenchless installation techniques shall be used. The onshore cable route traverses a number of major transport networks and natural obstacles, to enable the installation of the cable across these features specialist techniques are required, namely the use of HDD. These key locations are referred to a ‘Category 1’ HDD sites as identified in Table 3-1.


21.


These HDD sites will require additional equipment, storage and ancillary facilities to that required for the conventional open trench installation methods in order to accommodate the drilling activities. As such, a specialist HDD compound will be set up at each side of the HDD location to enable the specialist plant and materials to be delivered directly.


22.


In addition to the above major features, a number of other features have been identified where the conventional open cut trenching technique are not appropriate. At these locations ‘trenchless’ methods will also to be implemented, which will comprise of a smaller HDD or auger bore. These sites are referred to as ‘Category 2’ HDD/trenchless. As the features to be crossed are less significant, they will not require any additional compounds and works will take place within the standard working width. Table 3-1 provides a list all the HDD / trenchless locations.


Table 3-1 HDD / Trenchless Locations Reference Category


HDD-01 HDD-02 HDD-03 HDD-04


HDD-05


HDD-06 HDD-07


Cat 1 Cat 2 Cat 2 Cat 1


Cat 1


Cat 2 Cat 2


Location/ Feature


MillersWood off Bullen Lane SomershamWatercourse Pound Lane


River Gipping and Network Rail track west of A14


A14 Trunk Road and Old Ipswich Road


River Fynn Lodge Road


Approximate Length (m)


200 70 60


385 200


30 60


MaxWidth (m)


130 55 55


130 160


55 25


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