87.
If this foundation type is adopted, detailed work would be required to design suitable scour protection in the post-consent period. Table 5.7 shows the maximum area of scour protection material required for foundations for gravity based structures, this also equates to the worst case scenario for scour protection regardless of the foundation type used.
Table 5.7 Estimatedmaximum area of scour protectionmaterial required for gravity base structures Item
Max area (m2)
60m GBS for wind turbines and collector and converter stations (106 in total)
2 Met masts Note: these areas exclude the area taken up by the footprint of the gravity base structures
5.4.4.2.6 Decommissioning of gravity base structures 88.
The removal methodology for gravity base structures would typically be as follows:
Removal of wind turbine, met mast, switchgear and ancillaries, and cutting of cables (leaving buried inter-array cables in-situ).
Mobilisation of heavy lift DP vessel or fleet of tugs (dependent on whether foundation design is buoyant or requires heavy lift).
Removal of marine growth and sediment from base and jetting under base plate to remove adhesive effects of grout (if present) or cohesive bearing material. If a deep skirt has been used, the skirt may require cutting.
It may also be necessary to locally remove scour protection via dredging.
For buoyant design: controlled de-ballasting of foundation using remote pumping equipment and / or installation of buoyancy aids. Disposal of the ballasting material (i.e. whether it is disposed of locally or requires to be transported to a particular offshore disposal area) would be agreed with the regulators as part of the decommissioning plan.
For design requiring heavy lift: lifting of foundation from sea bed onto barge (as per installation, a bespoke transportation barge may be required dependent on the design).
For buoyant design: foundation would become buoyant on de-ballasting. 2,403,253 5030
Preliminary Environmental Information May 2014
East Anglia THREE Offshore Windfarm
Chapter 5 Description of the Development Page 20
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