The soil response under the inherent cyclic loading conditions when dealing with offshore foundations can be considered by using contour plots. These plots are derived from several cyclic laboratory tests and characterize the general cyclic soil behaviour. In the design process with explicit numerical methods, such plots are needed in order to assess the soil behaviour under arbitrary loading conditions and hence estimate the cyclic foundation response. In the paper, excess pore pressure contour plots for a poorly graded medium sand are derived from numerous constant volume (CV) cyclic direct simple shear (DSS) tests and a new approach for parametrization of the plots is presented. Subsequently, the data are assessed regarding scaling for other sand soils, i.e., construction of contour plots with only a small number of test results by using the general trends observed.

The current design practice for offshore monopiles applies widely accepted simplifications of complex irregular loading scenarios. Highly cyclic loads from varying directions offshore are simplified by means of classification methods. This procedure involves reordering individual cycles in irregular loading scenarios by frequency, mean load, and amplitude. This approach is based on the assumption that the resulting accumulated deformation in the soil is independent of the ordering of the cycle packages, i.e. the validity of Miner's rule. Different contributions in literature investigate the validity of Miner's rule by evaluating the effect of the ordering of cycle packages on the resulting damage in the soil, i.e. the accumulated volumetric strain. This paper addresses the question of the validity of Miner's rule from a different perspective. It investigates the load-displacement behaviour of sand in direct simple shear tests due to dynamic load scenarios. Hence, the load sequences during testing vary while the energy spectrum being employed to generate the irregular load signals remains constant. This method enables capturing natural conditions offshore during testing and allows for comparing individual loading scenarios as the wave spectrum in the frequency domain defines the distribution of wave amplitudes. The test program is carried out on medium dense fine silica sand. The test results are evaluated regarding the accumulated volumetric strain and relate to previous studies on the validity of Miner's rule in sand.