09.02.2021 | Commissioning of second wind turbine in Freimann - EDR designs custom foundation on difficult subsoil
A second wind turbine has been commissioned by the Urban Utilities of Munich (SWM) in January 2021. The turbine is located in the north of Munich on the slopes of the north-west landfill site in Freimann, close to the world famous Alianz Arena. The wind turbine is another component of SWM's "Renewable Energies Expansion Offensive". EDR had significant involvement in the development of the wind turbine.
Between 2015 and 2019, Prof. Christian Kellner (Munich University of Applied Sciences) in cooperation with EDR has developed an innovative and unique special foundation for this project. The final design and structural engineering of the foundation was implemented by EDR since 2019 and has been successfully completed by the end of 2020.
The former landfill site constitutes a very inhomogeneous subsoil. Therefore, it is much harder to predict subsoil deformations caused by the loads from the structure with the precision required for the safe operation of the wind turbine. The acceptable tolerances for a possible inclination of the wind turbine are very tight.
Due to the material composition of the existing landfill, standard solutions like a deep foundation or subsoil improvements had to be discarded. The only remaining option was a shallow foundation. For the necessary distribution of the load over as large an area as possible, a foundation diameter of 26 m has been chosen. In addition, in the centre of the foundation an area with the diameter of 10 m has been completely decoupled from the subsoil and kept load-free.
For the compensation for a tilted position during operation, which cannot be completely ruled out, the foundation can be stabilised in its position or restored to the original position by a two-stage concept:
1) Eight chambers with a volume of approx. 150 m³ each are placed on the foundation plate. These can be filled individually with water or soil. In the event of unplanned tilting, counter ballasting can be used to relieve the subsoil in specific areas.
2) An injection layer is placed below the foundation: Injection pipes are installed in 2 levels like a fan. With this, the foundation can be lifted if necessary and deformations that have occurred can be compensated repeatedly.
For the years ahead we would like to wish best of luck and a smooth operation to the wind turbine and SWM. We also take pride in the reference as an “engineering masterpiece” by SWM's technical managing director Helge-Uve Braun (https://www.youtube.com/watch?v=OtH5yCNrKlE&feature=youtu.be).