Offshore wind power structures are subjected to cyclic loading. Several loads like wind and wave loading are acting on the structure and therefore its foundation. It is important to involve the impact of this cyclic loading into the design of the structure. A cyclic load influences the strength and deformation characteristics of the soil. Due to this the cyclic loading the cyclic shear strength will decrease. This cyclic shear strength depends on several factors which can be influenced by soil properties and shear mechanisms. The aim of this Master thesis is to provide correlations between index parameters and the cyclic simple shear strength to observe how and which parameters influence the shear strength behaviour due to cyclic loading. This research focuses on the results from cyclic simple shear tests and only for cohesionless soil from North Sea sand. The project material was obtained from several offshore windfarm projects by Fugro, namely The Hollandse Kust West ,The Hollandse Kust Noord and The Hollandse Kust Zuid. Available data from these project locations is analysed and translated to cyclic resistance curves. In these curves the number of cycles to reach a nominal strain failure is plotted against a normalised cyclic shear strength, also called a cyclic stress ratio. The strain failure criterion was chosen at 3.75\% and a commonly equivalent number of cycles of 10. The soil parameters that are elaborated for this research are based on characteristics compared to density of the soil, grain structure and in-situ characteristics. These parameters are the relative density, fines content, mean particle size and the normalised cone penetration resistance. The relative density is an unknown parameter in this research and is determined in two ways. First, by considering in-situ data where it was measured along depth and an assumption was made about the real value based on the known depth range of the borehole sample. The second method was based on the initial void ratio measured in the laboratory to obtain a relation between the in-situ measured relative density and the initial void ratio, which is called the theoretical value of the relative density. From this thesis, it was concluded that due to the small range of data it was not possible to provide clear correlations and to observe trends of soil index parameters with the cyclic shear strength. By looking at the total range of the cyclic response of the data in the cyclic resistance curves and the elaborated soil parameters, the relative density and the fines content influence the shape of the power failure lines. A relatively high value of the relative density results in a larger range of different cyclic stress ratio values, i.e. a failure line with a higher gradient. An increment in fines content results in a relatively lower values for cyclic stress ratio and do not differ much by an increment of load cycles. This observation is based on the available results from this research with a relatively low amount of data and a small range of fines content.