5.4.4.3.5 Decommissioning of suction caisson foundations 100. The overall removal methodology for suction caisson foundations would typically be as follows and would be agreed with regulators in the decommissioning plan:


 Removal of wind turbine, met mast, switchgear and ancillaries, and cutting of cables (leaving buried inter array cables in-situ);


 Mobilisation of service vessel with pumping equipment and ROV, and mobilisation of tugs. It may also be necessary to mobilise a DP vessel with craneage to facilitate with the refloating and subsequent manipulation of the foundation;


 Removal of sediment and marine growth from suction caisson lid, and jetting of pump connections on lid. It may also be necessary to locally remove scour protection via dredging;


 De-ballasting or adding of buoyancy aids to foundation as required by design;  Connection of pumping equipment to suction caisson valves;


 Controlled pumping of water into caisson chambers. The caisson would rise from its installed position to the surface as the internal pressure overcomes the side wall friction. Some manipulation from craneage on a DP vessel may also be required; and


 Towing of foundation to port and dry dock for dismantling and reuse and recycling where possible.


5.4.4.4 Monopile foundations 101. Monopile foundations are the most common wind turbine foundation type used to date. They comprise a steel cylindrical pile and a steel cylindrical transition piece. Conical transitions are sometimes used to reduce the diameter of the structure at the top of the foundation. Site specific analysis is required to assess whether this foundation type is an economic option for East Anglia THREE. Footprint sizes for the base are outlined in Table 5.9.


Table 5.9 Monopile dimensions Wind turbine size (MW) Maximumdiameter (m) Maximum Footprint (m2)


7 12


10 12


79 113


Preliminary Environmental Information May 2014


East Anglia THREE Offshore Windfarm


Chapter 5 Description of the Development Page 23


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