Offshore monopiles accumulate permanent tilt under long-lasting cyclic environmental loads. Accurate prediction of monopile tilt is key to assessing their serviceability, and requires a fundamental understanding of loading history effects. While both experimental and numerical studies are shedding light on this matter, this work uses step-by-step implicit 3D FE modelling to investigate loading history effects in the response to cyclic lateral loading of monopiles in sand and to identify links between local soil behaviour and relevant features of global pile behaviour. For this purpose, the recently developed SANISAND-MS model is adopted to achieve a reliable simulation of sand's cyclic ratcheting. In particular, the validity of an up-scaled Miner's rule for monopile tilting under multi-amplitude cyclic loading is assessed based on the results of 3D FE parametric analyses, with emphasis on the role played by the engineering idealisation of random environmental loading. The validity of such a rule has been numerically investigated both in terms of local soil element response and global foundation behaviour — for the particular case of a large-diameter monopile. In respect, the effect of the loading history idealisation is presented, and it is concluded that Miner's rule does not always rigorously apply to all the cases considered herein. The translation of irregular loading histories into a regular version with loading packages sorted in ascending amplitude order is shown to be a reasonable approach, at least when the possibility of cyclic pore pressure build-up is disregarded.

This paper shows the comparison of two anisotropic models: an advanced rotational hardening model that accounts for both inherent and plastic strain induced anisotropy (S-CLAY1) and the Sekiguchi-Ohta model which accounts for inherent anisotropy only. In the paper, two-dimensional behaviour of a benchmark embankment on soft soils is modelled with the PLAXIS fi nite element program using user-defi ned implementations of the S-CLAY1 and Sekiguchi-Ohta models. The same problem is then reanalysed by switching off the evolution in anisotropy in the S-CLAY1 model.