Wind energy refers to the process of creating electricity using the wind. The number of wind power projects around the world has grown exponentially in the last decades. Modern and efficient turbines are used to capture kinetic energy from the wind and generate electricity.
The wind turbine (and the blades, rotor shaft, nacelle, gear box, generator, and pitch control unit) stands on a tower that usually has got the form of a hollow truncated cone and is made of high–quality steel or concrete. The wide tower base connects, the prefabricated tower, to the in situ made foundation via an interface.
The foundation’s only task is to ensure the stability for the wind turbine, and to do so over its lifetime. This is done by transferring and spreading the loads acting on the foundation to the ground.
The vertical force acting on the foundation is mainly dead load from the tower, the nacelle and the rotor blades, but the wind may also give arise to some vertical force. The most significant loads on the foundation origins from the wind. Due to the big height of the tower, a horizontal force from the wind is giving a considerably big bending moment at the foundation (several hundred GigaNewton-meter/radian).
For this reason, soil investigations should carefully be carried out for the wind energy system. Otherwise, unstable operations, degrading the performance of the wind turbine shall be expected.
In this regard, geophysics plays a fundamental role. Seismic surveys such as seismic refraction, MASW, down-hole or cross-hole provide the fundamental dynamic elastic properties needed for the proper design of the foundations. Substituting these field surveys with standard geotechnical tests have led to erroneous results with profound consequences.