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Vibratory piling a possible installation methodology for offshore foundations

Joint project by RWE Innogy, Bilfinger Offshore, DONG Energy, EnBW, E.ON and Vattenfall as part of the Carbon Trust Offshore Wind Accelerator and the offshore supply industry

On the test site the vibratory pile installation method has shown significantly reduced peak noise emissions as well as installation time compared to a hammered installation and can be controlled to produce a similar bearing capacity to impact hammered piles

Additional research activities planned to develop the technology further

In the dynamic offshore wind industry, new methods of constructing wind farms at sea are playing a major role in reducing costs and shortening building times. That is why a group of developers and operators of offshore wind farms – RWE Innogy, Bilfinger Offshore, DONG Energy, EnBW, E.ON and Vattenfall joined forces last year and launched a pilot project to test the pile behaviour as a consequence of an alternative installation method for offshore foundations. The project was part of the Carbon Trust Offshore Wind Accelerator, a world-leading research and development programme for reducing the costs of offshore wind energy.

The tests involved a comparison of the conventional method of impact hammering with the vibration of steel piles in a test environment on land. It aimed to prove whether vibratory piling can offer a faster and more environmentally friendly method of installing steel foundations for offshore wind farms and to evaluate the method with regard to stability. 

The results have been positive: the test on land are highlighting the vibratory method generates lower peak noise emissions and is up to ten times faster. Continuously present noise emissions will need to be determined on a project specific basis. The lateral bearing capacity of large diameter piles has been measured allowing an initial methodology for the prediction of vibrated pile bearing capacity to be developed. 

In Summer 2014, three steel piles were vibrated and another three piles were hammered conventionally into saturated, sandy soil on a test area near Cuxhaven. The 4.3 m diameter monopiles were the very first produced from the new Steelwind Nordenham fabrication facility, the hammer was supplied by IHC Hydrohammer and the vibrator was supplied by PVE Dieseko. Technical University Braunschweig ran the data capture, such as installation times and noise emissions, in collaboration with various other institutions and technical experts alongside certification and regulatory authorities. It was also possible to gain important insights into the installation methods themselves. The piles were then left in the ground for a period of four month before they underwent static load testing, which examined how the piles behave when subjected to the kind of lateral load that is typical in offshore conditions. RWE Innogy was the project lead and contracted Bilfinger Offshore, who also sponsored parts of the project, to execute the major test works.

Jan Matthiesen, Director of Innovation at the Carbon Trust commenting on the positive results: “Finding innovative methods to reduce the cost of installation will help to bring down the cost of offshore wind, making it competitive with conventional energy sources. The project results not only demonstrate that vibro techniques could be a viable method for piling, but also evidence of what can be achieved through industry collaboration.” 

Noise emissions will need to be investigated on a project specific basis to determine if the significantly reduced, but continuously present noise will have an impact on the environment under water. In the course of the tests it was discovered that the vibratory installation method has a major impact on the lateral load-bearing capacity of the piles. If during the installation process various parameters, such as vibratory frequencies or pile design, are controlled, similar lateral load-bearing capacities to hammered piles could be achieved. The consortium devised a methodology that made it possible to pre-determine the load-bearing capacity of vibrated piles. RWE Innogy now plans to build on these tests and launch an additional subproject intended to investigate ways of optimising the installation methodology itself. 

“Throughout the project we have collected a lot of important data, that can now be used to further develop the technology to bring it offshore”, explains Ben Matlock from RWE Innogy.

The findings of the research project have been made available to all project partners and the Carbon Trust Offshore Wind Accelerator. 

The vibratory piling project is one of many research activities by RWE Innogy. The company invests roughly €4.5 million a year in research projects that could reduce the costs of building and operating offshore and onshore wind farms as well as hydro power plants.