Windplanblauw is located on the north-east side of Flevoland in the area of Swifterbant and Dronten. This is where Vattenfall, in cooperation with SwifterwinT and Molenrak B.V. is realizing Windplanblauw. The plan involves the replacement of 74 old wind turbines for 61 new ones, which are larger and more powerful. The project consists of two parts, namely the onshore part consisting of 37 wind turbines supplied by Vestas type EnVentus 5.6MW, and 24 wind turbines located in the IJsselmeer (Nearshore) supplied by GE, type Cypress 5.5MW. Operationally, the entire wind farm will have a capacity of about 340MW, enough yield the electricity consumption of 450,000 households (about 1.0mln people).WindplanBlauw consist out of 5 contracts namely:1. Contract WTG supplier Onshore2. BOP Onshore3. WTG Supplier Nearshore4. BOP Nearshore5. SubstationWindBase was involved in all the contracts, which included:1. Contract WTG supplier Onshore, Qa/Qc of the coatings, Welding of the tower, and the stairs but also problems which occurred during the lifting process..2. BOP Onshore, Active assessment of the design, risk controlled design review but also on the work method plans, maintenance plans and inspection plans3. WTG Supplier Nearshore, visiting tower fabrication process, QA/Qc steel towers and coating inspections4. BOP Nearshore, Engineering Bases of design, Active assessment of the design and risk controlled design review en inspections during construction.5. Substation Active assessment of the design, risk controlled design review but also on the work method plans, maintenance plans and inspection plans

Combination of technical and procedural expertise In the northwestern corner of Flevoland, the construction of 61 wind turbines, 37 on land (onshore) and 24 on the IJsselmeer (nearshore), is in full swing. The turbines are being built at the Windplanblauw wind farm near the village of Swifterbant. The construction of a substation, crane emplacements and other infrastructure are also part of the project. ABT subsidiary Windbase is advising client SwifterwinT about all the civil engineering contracts of the project. The new wind turbines will be replacing smaller models which were at the end of the their lifespan. With a total capacity of 335 MW, Windplanblauw will generate enough green electricity to power around 400,000 households. Other side of the table “We're now sitting on the other side of the table", says civil engineering package manager Paul Schraven of Windbase. “We were hired for this technically challenging project to check all the documents supplied by the contractors. The client doesn't only want to use our knowledge about the design of foundations, but is also calling upon our broader expertise, both technical and procedural. We are participating in the project organization for Windplanblauw, with our technical team available in the background. We think that this particular combination of technology and process is a strength. As a firm, we have a lot of experience with this in other areas, which we are now using for a wind project for the first time.” Windplanblauw is a partnership between energy company Vattenfall and SwifterwinT, a unique local initiative. SwifterwinT is a cooperative partnership between 170 (agricultural) entrepreneurs, residents, and turbine owners in the project area. They share the returns individually and every year, part of these go to projects that improve livability in Swifterbant and its environment. Integral approach Paul: “As civil engineering package manager, I stand for an integral approach and operate as a kind of playmaker. One of my tasks is getting the documents to be checked to the right colleagues in the Windbase organization. These concern construction work on the foundations, roads, crane emplacements, bridges, and temporary constructions. Additionally, I'm involved in all technical discussions regarding the various contracts. Together or in consultation with concrete specialist and quality engineer Casper Meijer, we also regularly make inspection rounds outside. Land foundation in the water For the nearshore contract, the wind turbines on the water, Windbase drew up a proof of concept for realising a land foundation in the IJsselmeer. The design provides for a construction with a combi wall. Paul Schraven: “Placing a land foundation in the IJsselmeer is a special project, considering it will have to deal with forces that are typical for water, such as wave load, ice load, and collision load from vessels. The method of laying a foundation is also different. Offshore turbines are normally built on a monopile foundation. Partly due to the shallowness of the IJsselmeer, this is not possible at this location. “The process and cooperation with all parties involved is going according to plan", says Paul. The dynamics feel familiar to Windbase. At the same time, the company is also learning from the relatively new role which it is now playing on behalf on the client. The company will remain committed to this until the completion and commissioning of the new wind turbines. It is expected that Windplanblauw will be commissioned in the final quarter of 2023. Project partners Client Windbase: SwifterwinT, Aratis Contractor for foundations, roads, and onshore crane emplacements: Dura Vermeer Contractor nearshore foundations: Ballast Nedam Contractor substation: Hitachi Energy Transport and installation of turbines nearshore: Mammoet Turbines suppliers: Vestas (onshore) en GE Renewable Energy (nearshore)   For more information: p.schraven@abt.eu | telnr: +31 6 309 946 64 Header © Windplanblauw Back to news

Land foundation for wind turbines in the IJsselmeer? This requires a fundamentally different design approach. How did we at ABT and WINDBASE, in collaboration with SwifterwinT, TU Delft, Vattenfall, Aratis, GEvernova and Ballast Nedam, arrive at this solution? Read the English version of the article by colleagues Paul Schraven, Thomas Lankreijer, and Casper Meijer that was published in the latest edition of Land+Water. Land foundation for wind turbines in the IJsselmeer   For the design of the 24 foundations of wind turbines in the IJsselmeer near Lelystad, a different approach instead of a traditional monopile was made. After extensive research, a Cofferdam construction was chosen. The stiffness requirements from the turbine supplier and the collision load were among the design determinants.  Along the dike between Lelystad and Swifterbant, the view has changed remarkably in recent years: the iconic Irene Vorrink wind farm has been replaced by 24 imposing wind turbines on the IJsselmeer. These nearshore foundations are part of the larger project Windplanblauw, which involves replacing 74 old wind turbines: 37 onshore and 24 nearshore. When operational, the entire wind park will have a capacity of approximately 340 MW, providing enough electricity for the consumption of 450,000 households (about 1 million Dutch residents).  Dolphin or Cofferdam  Given the size of the turbine and the relatively shallow IJsselmeer, placing a land-based turbine in the IJsselmeer proved to be the best solution. Two promising foundation solutions were considered: the Dolphin construction and the Cofferdam constructions. The Dolphin construction consists of a system of vertical steel foundation piles with a concrete pedestal placed on top. The turbine can then be tensioned using prestressed anchors, similar to the practice with onshore turbines. The Cofferdam is a circular combined wall construction made of steel foundation piles with double Z-sheetpiles in between. The foundation is filled with sand to provide additional stiffness and strength, allowing it to better withstand various loading scenarios. On top of the foundation piles, a concrete pedestal is placed to support the turbine.  Basis of Design  In order to apply a land foundation in a near shore environment, it is necessary to adopt a fundamentally different design approach. A variety of factors that are typically applicable in either on-shore or marine environments must be integrated. These factors include the need to address ice loads, collision loads, scour, hydraulic conditions, and to translate typical land turbine-related requirements, such as "no-gapping" and "dynamic stiffness," to nearshore conditions. In order to translate these effects into design constraints, a Basis of Design (BoD) was established, outlining the practical design conditions. Some of the most significant conditions within this Basis of Design (BoD) pertain to the practical handling of ice and collision loads. In order to determine the requisite ice loads, recent measurements and an extrapolation of ice thicknesses from the IJsselmeer were employed by Deltares. Furthermore, in cooperation with TU Delft, a straightforward calculation model was devised to ascertain the maximum ice load on a range of structural components, including continuous walls and slender steel foundation piles. Although an ice load scenario is highly improbable, it could potentially affect the entire wind park. Consequently, special load cases – ULS & SLS ice (ultimate limit state & serviceability limit state) – were considered, ensuring that the turbine park remains fully operational even after such an event.   Deformed mesh of the turbine foundation after a collision load   Maritime research  A maritime study was conducted by Marin to assess the collision probabilities of different turbines with shipping vessels, given that the new turbines are positioned on both sides of the fairway. While the individual collision probabilities at each turbine location are relatively small, the cumulative chance of a random collision with a CEMT Class Va inland vessel (a large Rhine ship) was significant when considering all turbines. This cumulative risk was taken into account during the Basis of Design (BoD) phase.  After consultation with the wind park operator, an AL (Accidental Limit State) approach was selected in the event of a head-on collision. This approach allows for the structure to be written off, after which the turbine must be dismantled in a safe manner. The BoD involved a pushover analysis of the foundation. An energy balance was established, converting the ship’s kinetic energy during a collision into crumpling of the ship’s hull and plastic deformations of the foundation structure. The crumpling of the ship’s hull was calculated according to both the ROK (Guidelines for Structural Design) and the DNV standard (Det Norske Veritas).  Proof of concept & design  Following the completion of the BoD and prior to the tendering process and drafting the contract based on UAV-gc (Uniform Administrative Conditions for Integrated Contracts), the two promising foundation variants (Dolphin and Cofferdam) were investigated and developed up to preliminary design (PD) level. This step demonstrated the feasibility of the design principles.  Key dimensions, such as the concrete diameter and indicative lengths/dimensions of the foundation piles, were determined. These dimensions remained relatively unchanged in the subsequent Detailed Design (DD) phase carried out by the contractor. For the design, advanced PLAXIS 3D analyses were conducted to calculate stresses in the foundation piles. The sheet piles and foundation piles were modeled as shell elements, with Z-profiles accurately connected to the steel foundation piles using predefined degrees of freedom to correctly represent the system’s stiffness.  Innovative construction principles  The analyses confirmed the feasibility of both design principles. A trade-off led to the selection of the Cofferdam as the optimal solution, which was then further developed in the DO phase. Ballast Nedam worked on the DO, including reinforcement design, with Windbase serving as an advisor to Windplan Blauw in the reviewing role within the SCB contract (System-Oriented Contract Management).  The contractor subsequently refined innovative construction principles, such as the installing frame for the steel foundation piles, the prefabricated lost formwork and reinforcement elements. Optimization was also carried out regarding the collision load to be considered. An interesting yet crucial detail was the cable routing to the turbine. The contractor opted for J-tubes attached to the sheet pile walls.  Execution  The use of prefabricated elements simplified the construction of the foundations and allowed for multiple operations. Construction began with the placement of four auxiliary piles with an H-frame. From this H-frame, the 22 steel foundation piles were accurately driven in a circular pattern to the required depth. After installing the steel foundation piles, sheet pile, the ring beams and the J-tubes were added. The foundations were then filled with moderately compacted sand. Prefabricated L-walls formed a large formwork into which the concrete base was poured. The exterior of the L-walls features an aesthetically which serves as a visual signal for future navigation in the waterway. Once the formwork was in place, the anchor cage as the core reinforcement was installed followed by the lifting of seven large reinforcement cages. The final step involved manual tying of the rebar to close the reinforcement cage. Using a floating concrete pouring plant, approximately 900 m³ of concrete was poured for each foundation. This base ring serves as the starting point for the tower and acts as the interface between the foundation work and the turbine structure. Once the grout had been applied and allowed to set, the 152 anchors securing the tower base ring to the foundation were pre-tensioned and safety features such as fencing, stairs and a davit crane were installed.  The pouring of the concrete in the foundation   Once the foundation contractor had completed the work, the various turbine components were lifted into place. For this purpose, a 1350-tonne crane was mounted on a special barge (a small ship) equipped with spud piles (which extend through the ship to the bottom of the lake). Mammoet designed this installation. To ensure the stability of the barge, third parties conducted dynamic interaction calculations based on standard soil profiles, wind directions and wave heights occurring in the IJsselmeer. At each turbine location, at least three spud pile positions were defined based on cable positions and in the subsoils, to allow for safe lifting operations.  Conclusion  The installation of the final wind turbine was completed on 20 March. We can reflect on a period of learning, during which complex calculations were carried out using Plaxis 3D and DIANA. These demonstrated that a land-based turbine on a nearshore foundation in the IJsselmeer meets the specified requirements and can be certified and installed.  Authors:  Paul Schraven: Design Lead Thomas Lankreijer: Geotechnical Advisor Casper Meijer: Senior Quality Inspector (all working at ABT and its subsidiary, WINDBASE)