ebc/eea - offshore wind energy seminar series session 2 -...

EBC/EEA - Offshore Wind Energy Seminar SeriesSession 2 - Logistics: Garnering Wind Power Offshore

Foundation Design Options

Presented by: Scott Key, AMEC Paragon, Houston, Texas (November 2007)

Onshore Wind Farm Development

� Foundations:

� Spread footings (bearing)

� Piled foundations

� Materials:

� Reinforced concrete

� Construction:

� Typical onshore

construction techniques

Offshore Wind Farm Development

� Offshore Foundation Concepts:

� Steel mono-pile (caissons)

� Gravity based structures

� Open frame steel structure(jacket and piles)

� Floating structures

Steel Mono-Pile (Caisson)

� Shallow water (<30')

� Very dependent on

geotechnical data

� Large diameter

� Pile driving equipment

� Penetration below mudline ≃ 150'

� Dynamics

� No structural redundancy

Gravity Based Structure

� Concrete box (normally concrete, but may be steel)

� Float into position; ballast into place

� Prepared sea bottom; uniform bearing

� Shallow water (30' to 40')

� May require piles

� Dynamics

� No structural redundancy

Jacket and Piles

� Open frame steel structure

� Main or skirt piles

� Water depth (probably <150';

economic decisions; shallow

to very deep)

� Dynamics (much more rigidity)

� Structural redundancy (multiple

piles; redundant framing)

� Normally no mud-line

preparation

Jacket and Piles (continued)

Jacket and Piles (continued)

Floating Structures

� Spread mooring

� Piles for mooring system

� Deeper water

� Dynamics

� Redundant mooring and buoyancy

Foundation Options

� Steel Mono-pile (Caisson)

� Gravity Based Structure (GBS)

� Jacket and Piles

� Floating

Foundation Rankings

344444Floating

111222Jacket

321133GBS

111211Mono-pile

ConstructabilityStormRisk

Distance from shore

MaintenanceInstallation

CostFabrication

CostOPTIONS

ASSESSMENT CATEGORIES