Wind farm, Stemwede

In autumn 2023, a 45-megawatt wind farm of the municipal energy service provider enercity with ten 125-metre-high Nordex turbines will be connected to the grid in Stemwede. In the expansion of renewable energies, enercity is setting a high pace. By 2025, the company's own turbines are to generate 1 gigawatt of wind energy output. The Oldenburg team of PORR Spezialtiefbau Region Nord was therefore challenged with both the reliable and on-time execution of the deep foundations. Exactly according to plan, 380 Frankipile NG® piles were constructed in five months. 

Extremely high loads must be carried

The total mass of each individual wind turbine is well over 2,000 tonnes. Due to these extremely high loads, they fall within the typical application range of full displacement piles such as the Frankipile NG®. In Stemwede, 30 piles of this type with d = 51 cm and up to around 11 m in length were produced for each foundation; 8 more were required for the crane foundation. The upper 5 to 6 m of the subsoil consists of humic topsoil, loose sands, humic silts as well as silty sands, which are predominantly underlain by medium dense sands.

These alternating layers made it necessary to partially pre-compact the gravel above and below the pile setting depth in order to increase the bearing capacity. Due to the soil improvement, the piles could be dimensioned shorter and more economically.

Economical francipiles reduce CO₂ emissions

Since concrete of monitoring class 2 was used, external monitoring by an appreciation monitoring agency was carried out as part of the quality assurance in addition to the self-monitoring of the concrete quality. The measurements for the verification of the external pile load-bearing capacity were carried out by PORR Spezialtiefbau Planung. PORR branch manager Thomas Cramer explains how choosing the right foundation method minimises resources and reduces CO₂ emissions: "With our slender full displacement piles, we make a significant contribution to sustainability and economic efficiency in the construction of wind turbines. Significantly less in-situ concrete is required than with comparable pile types and, in addition, there is no need to dispose of the drilled material."