One of the challenges in offshore geotechnical en- gineering, is how to account for cyclic loading. This has lead to several research projects regarding cyclic loading. However, due to the complexity of the loading and the effects hereof, no standardized method for taking cyclic loading into consideration has yet been made. Therefore the topic of cyclic loading still needs more investigation.
Through this Master Thesis the effects that cyclic loading will have on cohesionless soils have been investigated. The soil in question is a marine sand taken from an offshore site in Frederikshavn, Den- mark, where a prototype of a suction bucket founda- tion has been installed supporting a Vestas V90-3.0 MW wind turbine.
Cyclic triaxial tests have been conducted in order to construct design diagrams that can be used in the design of new offshore wind turbine foundations. During these tests it was found that the cyclic and average load ratios, along with the pore pressure, had a significant impact on the cyclic load bearing capacity.
An advanced constitutive model in form of the Modified Critical State Two-Surface Plasticity Mo- del for Sand with an explicit integration scheme was also coded in Matlab. This was done in order to cre- ate a model, which could accurately simulate cyclic soil behaviour. However, the explicit integration scheme was found to be inefficient and could there- fore not be recommended for a constitutive model of this advanced level.