Monopile installation in clay and subsequent response to millions of lateral load cycles

Abstract

The installation-induced changes in the state of clayey soils caused by pile driving processes are investigated numerically. Hydro-mechanically coupled Coupled-Eulerian–Lagrangian analyses are carried out for this purpose. After installation, the piles are subjected to one million lateral loading cycles using a novel high-cycle accumulation (HCA) model for clay implemented in an in-house code, modelling loading conditions to which piles are subjected in the offshore environment. Consistent with the results of field tests, it is found that higher values of initial overconsolidation ratio result in a greater increase in radial effective stress during the installation process. Compared to simulations neglecting the installation process, jacked piles show less accumulation of deformations when subjected to lateral cyclic loading, especially for a larger number of load cycles and for initially overconsolidated soil. It is concluded that the assumption of wished-in-place conditions is conservative in terms of pile rotation in most cases, while the stiffness of the soil–pile system at small rotations is comparable for jacked and wished-in-place piles.