systems could be employed and could comprise motorised rollers or tracked caterpillar drives.
372. The cable drum would be placed on a raised spindle mounted on hydraulic jacks. The cable would then be pulled from the drum into the trench on the pre-installed rollers, with sufficient cable pulled through to the far jointing pit to allow for jointing onto the next section.
373. This process would be repeated for the second cable to be installed in the trench. The two cables would then be spaced in the trench in accordance with the design specification, separated by a spacer board to ensure the spacing is maintained during the backfilling process.
374. Once the cables are laid sand or Cement Bound Sand (CBS) would be laid around and over the cables, providing a typical depth of cover above the cable of around 150mm. The cover tiles and warning tape would then be placed above the cables. At this point the supporting materials would be removed and backfilling would be carried out using the previously excavated material.
5.6.4.7 Export cables: estimated volume of material displaced by cable installation 375. For the onshore export cable installation, removed soil would be temporarily stored at the side of each trench and would be used to backfilled the trenches after the cables or ducts have been installed. There would be some soil that would not be placed back into the trenches. The approximate volumes of soil to be temporarily stored at the side of each trench and residual amounts to be removed from site are outlined in Table 5.28.
Table 5.28 Volumes of soil to be temporarily stored at the site of each trench Volume (m3)
Approximate volume of soil to be excavated over the onshore cable route under Scenario 2
Approximate volume of soil to be removed from site under Scenario 2 154,416 36, 034
5.6.4.8 Special Crossings 376. Where it is impractical to trench through major obstacles, it may be necessary to use a trenchless cable-laying technique, such as HDD. In order that the target depth under the obstacle is achieved using HDD, the entry and exit points would be located some distance from either side of the obstacle. The distance at which the points would be located would be dependent on the target depth at which the conduit must pass under the obstacle.
Preliminary Environmental Information May 2014
East Anglia THREE Offshore Windfarm
Chapter 5 Description of the Development Page 81
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