Offshore Foundations: Mono Pile
The mono pile foundation is a simple construction. The foundation consists of a steel pile with a diameter of between 3.5 and 4.5 metres. The pile is driven some 10 to 20 metres into the seabed depending on the type of underground. The mono pile foundation is effectively extending the turbine tower under water and into the seabed.
An important advantage of this foundation is that no preparations of the seabed are necessary. On the other hand, it requires heavy duty piling equipment, and the foundation type is not suitable for locations with many large boulders in the seabed. If a large boulder is encountered during piling, it is possible to drill down to the boulder and blast it with explosives.
Costs by Water Depth for Mono Pile Foundations
The dimensioning factor of the foundation varies from the North Sea to the Baltic Sea. In the North Sea it is the wave size that determines the dimension of the mono pile. In the Baltic Sea the pack ice pressure decides the size of the foundation. This is the reason why the mono pile foundation cost increases more rapidly in the Baltic Sea than in the North Sea. The costs include installation (1997 prices).
Erosion will normally not be a problem with this type of foundation.
Swedish Offshore Project
A 2.5 MW pilot project with five Danish wind turbines using the mono pile technology has been installed in the Baltic sea south of the Swedish island of Gotland.
Using the mono pile foundation technique at Gotland involved drilling a hole of 8 to 10 metres depth for each of the turbines (Wind World 500 kW). Each steel pile is slotted into the the solid rock. When the foundations are in place the turbines can be bolted on top of the mono piles.
The whole operation takes about 35 days under average Baltic weather conditions.
© Copyright 1997-2003 Danish Wind Industry Association
Updated 10 May 2003