 Transportation of foundation to port and dry dock (via towing or on barge dependent on foundation type) for deconstruction and reuse and recycling of materials where possible.


5.4.4.3 Suction caisson foundations 89.


The suction caisson has only previously been used as a prototype for offshore wind turbines or a met mast, although in the oil and gas industry suction buckets have been used as alternatives to piles at the base of jackets.


90.


Existing suction caissons comprise a steel cylindrical tower (the shaft) with a diameter of approximately 5 to 9m, a transition structure (the lid) and a large diameter cylindrical skirt, which penetrates into the sea bed.


91. Footprint sizes for the base are outlined in Table 5.8 below.


Table 5.8 suction caisson dimensions Water Depth (m)


Up to 49


Minimum diameter (m)


25


Minimum Footprint (m2)


491


Maximum diameter (m)


30


Maximum Footprint (m2)


707


92.


93. 94.


The base height of the skirt above sea bed is typically 5m, although it may be possible to install it below sea bed to reduce scour effects.


The skirt penetration could vary from 10 to 20m below sea bed.


There are other foundation concepts comprising a cluster of smaller diameter suction piles, instead of a single larger diameter caisson. However, the overall maximum footprint and penetration is expected to be of a similar magnitude.


5.4.4.3.1 Material requirement for suction caisson foundations Suction caisson foundations usually comprise mainly steel. However, it is possible that some secondary structures, such as handrails, gratings and ladders, could be produced using other metals, such as aluminium, or composites. Also, concrete could be used to form the working platform.


5.4.4.3.2 Sea bed preparation and penetration for suction caisson foundations 95.


In areas where the sea bed is level, the suction caisson foundation may not require significant sea bed preparation. However, measures may be required in areas in which sand waves are present to provide a level formation for the installation and to allow scour protection to be later placed around the foundation. It is possible that excavation to the trough of the sand wave would be necessary before installing the


Preliminary Environmental Information May 2014


East Anglia THREE Offshore Windfarm


Chapter 5 Description of the Development Page 21


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