Numerical simulation of soil-pile interaction in offshore jacket piles under axial loads

In jacket foundations, the overturning moments caused by winds/waves are transferred to the piles mostly in the form of axial loads; understanding the complex mechanics of soil-pile interaction under axial loads has been a key subject in offshore wind turbines (OWT) design. In this paper, the application of a numerical modelling approach called 'Hybrid-Winkler-Interface' (HWI) in predicting the behavior of axially loaded piles in granular soils is described. The HWI approach is a hybrid formulation comprising beam elements, Winkler springs and 'thin-layer' solid interface elements. This approach, employing a constitutive model in the framework of bounding surface plasticity and critical state soil mechanics, is capable of simulating complex behavior in soil-pile systems under axial loading including hardening/softening, compaction/dilation, and stress degradation. In this study, the detailed load-displacement behavior of piles under monotonic and cyclic axial loads are numerically predicted. Model predictions are verified against available centrifuge and equivalent shear test observations.