Design of a full scale prototype concrete monopile, including the design for (pre)fabrication, handling and drilled installation offshore and including certification

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Public summary

Almost 75% of the support structures for offshore wind turbines are (steel) monopiles. In 2012 only this represented a total market of approximately one billion Euros for fabrication and installation. Earlier studies and experience of Ballast Nedam indicate that the use of (prefabricated) concrete instead of steel monopiles for piles with lager diameters can save considerable costs.

The CDM research project investigates all issues related to the design, the fabrication and handling of a full scale concrete monopile and the handling and use of the drilling equipment in an offshore environment. This is done by means of feasibility studies for actual projects in design, with specific site and soil data and specific onshore sites and harbours, rather than theoretic ‘virtual’ sites.
The initial result of the CDM project will be a design of a concrete offshore monopile and a work out of the industrial multiple (mass) fabrication, assembly, launching, handling, transport, upending and installation of a concrete monopile.
Installing a prototype, which was also an initial aim of the project, is an expensive operation – considerably more expensive than originally estimated – and is only possible with dedicated drilling equipment, which is in design by several recognized professional companies, but not yet in production, as it is a major investment.
The interest by drilling equipment suppliers has been increased for reason that drilling might also be a suitable alternative installation technique (instead of hammering and next to vibrating) meeting sound restriction requirements as applicable in recent years. Drilling as such is already used for relief in hard soil and rock.

This FLOW project concludes with the design for the concrete pile and the result of multiple feasibility studies, mainly for projects in the Baltic Sea.
As a follow up, the aim is to install in the future a near shore prototype of a concrete drilled monopile, in close cooperation with one of the drilling equipment suppliers. Serious contacts are ongoing, and a proposal within the Horizon 2020 programme has been issued by one of these suppliers in cooperation with BNO. After the acquisition of BNO by Van Oord the contacts have been followed up by the latter. Although these developments are a very positive spin off of this project - and will take several years to mature – they are not part of the final scope of this project.

During the project the scenario for the completion of the project, has been adapted as such that the project is completed with an overarching final Engineering Report in which the results of the multiple designs of concrete monopiles and related feasibility studies are bundled. The aim of installing a prototype has been abandoned for reasons mentioned above.
This overarching report “Alternative Foundation Installation of a Concrete Drilled Monopile” has been issued on 18^th December 2014 and main topics are mentioned in this summary.

Results obtained
The main result of this project is the proof of feasibility and multiple designs of concrete offshore monopiles and designs and work outs of the launching, handling, transport, upending and installation of these concrete monopiles.

Contribution to cost and risk reduction of far offshore wind energy
At present the concrete drilled monopile will be competitive in the Baltic Sea area where wave conditions are more favourable for this type of foundation than in the North Sea. For this reason many designs have been made, for specific projects and compared with conventional solutions. Meanwhile the development of making the drilling technique suitable for (concrete) monopiles is ongoing in close cooperation with respected drill manufacturers. This is a process which will take several years. With the trend of increasing size of turbines and fluctuating steel prices, the CDM might well become also competitive in regions other than the Baltic Sea.

So in principle the use and fabrication of a Concrete Monopile is feasible and cost effective for certain projects as is the drilling technique as such. The main constraint is the certification of the soil-pile-interaction of a once drilled monopile (either steel or concrete) as foundation for offshore wind turbines in sandy soil. This aspect is dealt with in the FLOW Alternative Foundation Installation project and is followed up as described in that project report.
The introduction of the Concrete Monopile will, next to the ‘noise-friendly’ installation method, stimulate competition and will eliminate the still limited capacity for (the fabrication of) steel monopiles. As this project has proven the feasibility the CDM as such, it will contribute to the acceleration of offshore wind developments.

Link

Ballast Nedam Offshore - Drilled Concrete Monopile