1.3 23
Project description / groundworks methodology
The proposed East Anglia ONE Onshore Cable Route is approximately 37km long and is shown on Figures 25.6.1 - 4. An indicative working width layout is shown in Diagram 1. See the Environmental Statement (ES) Volume 1, Chapter 4 Description of Development (November 2012) for detail.
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The cables for East Anglia ONE would be installed in two parallel trenches. In addition four further trenches each containing two ducts would be installed for future projects. Construction activities would be undertaken within a temporarily fenced strip of land (the Preferred Onshore Cable Corridor) which would generally be no wider than 55m.
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The Preferred Onshore Cable Corridor would be widened in certain locations in order to apply other special engineering techniques. In particular, this would be the case where cables would be required to be buried at greater than the normal trench depth, for example, where the route crosses a major watercourse using horizontal direct drill (HDD) techniques; this would also include construction consolidation sites (CCS).
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The 55m Preferred Onshore Cable Corridor incorporates sufficient spacing between cable trenches to prevent cable overheating, plus room for temporary construction works. The latter incorporates storage space for excavated material (a 9m wide subsoil storage area and a 11m wide topsoil storage area) and a haul road (5.5m wide) for the safe passage of construction personnel and machinery alongside the cable trench.
27 Where necessary, the working width would be reduced in certain locations by applying a range of special engineering techniques that could include:
• •
• •
28 Using lower thermal resistivity backfill in the cable trench
Removing the spoil to a remote storage area, thereby negating the need to store spoil adjacent to the trenches Routing the haul road elsewhere
Moving the haul road onto the top of backfilled trenches
Thus the area of impact requiring pre-construction assessments and covered by this WSI includes 35m of the (55m total) Preferred Onshore Cable Corridor that would be subject to topsoil stripping (i.e. less the topsoil and subsoil bund locations), plus the wider areas required for HDD and CCS (hereafter ‘the 35m working width/HDD/CCS areas’).
Outline Written Scheme of Investigation: Archaeology and Cultural Heritage (Onshore) Rev 01
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