Chapter 7: Lateral cyclic pile–soil interaction studies on a rigid model monopile

Currently, monopiles with a diameter of 3–8 m are widely used in European and Chinese offshore wind farms owing to their relatively easier installation and lower cost. The monopile foundations of offshore wind turbines are generally short and rigid and are becoming an ideal type of foundation for offshore wind turbines located on a seabed with silt or silty sand, which is the case across much of the coastal region of China.

During its lifetime, the monopile foundation of an offshore wind turbine is unavoidably subject to long-term cyclic loads, originating from waves and wind. This leads to accumulated rotation and changes in the stiffness of the monopile, and has a serious impact on the normal operation of an offshore wind turbine. Therefore, it is important to predict the deformation behaviours of the monopile under such conditions. Numerical analysis and model or field tests are generally the two most favoured ways used to solve the problem. Achmus et al. (2009) and Lesny and Hinz (2007) proposed new approaches to calculate the long-term cyclic behaviours of a monopile in sand, while also considering the cyclic responses of the soil. They also combined triaxial test results of the soil with numerical calculations. These numerical analyses still need further verification using model or field tests.