Soil-Structure Interaction and Damping

  • Roesen, Hanne Ravn (Projektdeltager)
  • Andersen, Lars Vabbersgaard (Projektdeltager)
  • Ibsen, Lars Bo (Projektdeltager)



In recent years, the interest in offshore wind turbines compared to the onshore ones has increased. This preference is among other factors due to less turbulent wind and higher wind intensity and, thus, a higher power output. However, going offshore doubles the cost per kWh. One of the major expenses for these offshore wind turbines is the foundation which is responsible for approximately one third of the total costs. Therefore, much attention is dedicated to reducing the cost of the foundations.

Today, the majority of offshore wind turbines are installed on monopiles which are single cylindrical steel pipe piles which extend into the soil. During the lifetime of the wind turbine, the monopile foundation is exposed to millions of lateral load cycles due to the wind and wave loading. In the design standards, today, the effect of this long-term loading is not taken into account which results in imprecise calculations of the deformation of the wind turbine. In this study, the correct behaviour of monopiles subjected to long-term lateral loading is analysed by means of both experimental small-scale tests in the laboratory and by numerical modelling.

Another aspect for the offshore wind turbines is the damping of the entire structure. Measurements have shown that the real damping on the site is larger than indicated by theoretical calculations. This extra damping is believed to originate from the pore water dissipation and pore pressure build up in the soil which may occur because the loading rate is shorter than the drainage time for the soil. Therefore, in order to get a better understanding of this damping, experimental laboratory tests are performed to find the correlation between the loading rate, permeability of the soil, and damping effect.

To summarise, the primary objective in this study is therefore, through investigation of the long-term and damping effects, to assess and improve the recommendations for the design of laterally loaded monopiles in sand and thereby, obtaining more cost effective designs.
Effektiv start/slut dato01/05/201130/04/2014