102. Penetration could be up to 40m depth below the surface of the sea bed.
5.4.4.4.1 Material requirement for monopiles 103. Monopile 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. Sea bed preparation and penetration for monopiles
104. Scour protection would be provided around the monopiles. The requirements would be similar to those listed for gravity base structures above. The quantities and extent of scour protection would be dependent on current speed, sediment type and the foundation details.
105. As for gravity base structures, if this foundation type is adopted, detailed pre- construction work would be required to design the scour protection for each foundation.
5.4.4.4.2 Installation method for monopiles 106. The installation of steel monopile foundations would typically consist of the following key stages:
Confirmation investigation of sea bed to ensure no obstructions are present (this would be ongoing throughout the installation process);
Prepare sea bed (if necessary) prior to installation; delivery of steel monopiles and transition pieces to site via barge or by installation vessel. It may also be possible to tow floated piles to site using tugs;
Mobilisation of jack-up rig (alternatively floating vessel) with heavy craneage at installation location. It may also be necessary to mobilise a support vessel;
Monopile upended by crane to vertical position; Monopile lowered to sea bed;
Locating of driving hammer onto top of pile using craneage, and monopile driven to required depth. Where ground conditions are difficult, it may also be necessary to carry out drilling using drilling equipment operated from the installation vessel before completing the driving;
Lifting of transition piece on to top of monopile using craneage from installation vessel, levelling of transition piece and grouting of connection; and
Preliminary Environmental Information May 2014
East Anglia THREE Offshore Windfarm
Chapter 5 Description of the Development Page 24
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