The recent growth of the offshore wind energy industry in Northern Europe presents a significant challenge and opportunity to the offshore site investigation industry Potential sites, by definition, are situated in areas of dynamic and sensitive environmental conditions, which present a unique challenge for all aspects of data acquisition. Recent experience has highlighted the critical nature of the planning process to achieve fully integrated and cost effective geophysical, geotechnical and environmental investigations. High quality geotechnical data are requlred for effective foundation design and to minimise development and construction risks. It is therefore necessary that all parties are focussed on the objectives of data acquisition. This paper examines the issues involved when planning offshore site investigations for offshore wind farm projects
A variety of natural and man-made environmental and geological conditions impact an offshore wind farm throughout its life cycle, from feasibility through to decommissioning An offshore developer will want to minimise the commercial and technical risks resulting from impacts by the environment on a development, and impacts by the development on the environment.
The oil and gas industry has been one of the main drivers in the development of offshore and nearshore site investigation techniques. The lessons learned have subsequently been transferred with varying degrees of success to the offshore aggregates, submarine cables and more recently offshore renewable industries. However, by comparison with typical oil and gas applications, the offshore wind turbine developments differ in several key aspects, notably
Offshore wind farm sites typically cover a relatively large offshore area Spacing between adjacent turbines varies but 300 to 5OOm is common. With developments of up to 100 turbines being planned, areas of up to 5km2 are possible.
The vertical loadings are much smaller (by a factor of say 5 to 200).
As a proportion of the vertical loading the horizontal loads and overturning moments are significantly greater
Water depths are typically much shallower
Multiple installations (say 10 to 100) of relatively economical designs are required, rather than one-off foundations for large high-cost structures [l]
The experiences of offshore wind farm projects completed to date have been well documented, but it is still early days in the operational lives of these projects. Typical projected life spans are m the order of 20 years, but to date no project has been operational for this length of time.
Relative costs of foundation technology and grid connection issues are just some of the factors limiting the practical location of offshore wind farms to nearshore environments in water depths typically of Om to 30m. The dynamic nature of these nearshore environments brings a range of unique environmental and geological challenges that need to be addressed in order to minimise the risks associated with installing, operating and decommissioning offshore wind farms.
Due to the size and nature of offshore wind turbines, dynamic behaviour and interactions tend to be more significant than for traditional offshore structures [2].
