Wilstedt-Süd wind farm, Wilstedt

Wilstedt is around 30 kilometres north-east of Bremen, and this idyllic locality in the heart of the Teufelsmoor region has been the site of nine wind turbines operated by wpd onshore GmbH since 2008. Construction works for the second gambit by this Bremen-based wind farm developer began in May 2021 – the new Wilstedt-Süd wind farm will contribute a further six wind turbines to the successful progress of the energy transformation. The Oldenburg branch installed 336 Frankipfahl NG® piles with diameters of 51cm and pile lengths of up to 16m to create deep foundations for the new turbines. Our colleagues at PORR Spezialtiefbau Planung were responsible for the pile statics.

Gravel precompaction improved the load bearing capacity of the soil

Laying the foundations for a wind turbine is a complex undertaking. Many thousands of tonnes of dead load will be generated by the plant, while soil conditions and dynamic strain resulting from wind and fluctuating groundwater levels also affect the foundation concept. The Wilstedt-Süd wind park is located on a moorland area.

The extremely settlement-prone soil of the site is chiefly composed of peat, organic silt and slush, but load bearing sands were found between 6 and 12m below the site of the proposed foundations. As a result, a deep pile foundation was the only possible option. For a variety of reasons, the well-proven Frankipfahl NG® pile system with an expanded pile foot was chosen for this project. This system is ideally suited for transferring high loads, and the ability to flexibly adapt the pile number, length and foot volume to suit site conditions represents a significant advantage. In some areas, the site soil at the planned casing depth still did not have sufficient load bearing capacity, and so the soil was rammed to compact the earth both above and below the pile casing depth before the actual pile ramming process began.

Once the installation is complete, the state-of-the-art Nordex N149 wind turbines will supply the electricity needs of 24,000 four-person homes each year. The employer for these foundation works was the wind power division of the Max Bögl Group.