Upper-bound analysis of laterally loaded rigid monopiles in clay with linearly increasing strength

Abstract

Monopiles supporting offshore wind farms are often subject to severe lateral environmental loads due to wind, waves, and currents. Previous studies have reported various failure patterns for such rigid monopiles in clay; hence predicting lateral pile capacity of widely different magnitudes. In this study, both a single-sided wedge failure mechanism involving passive soil failure only and a two-sided wedge failure mechanism with simultaneous active and passive soil failures are proposed. The single wedge mechanism is found to be applicable if the soil behind the pile does not move together with the pile, resulting in a gap between the soil and the pile upon loading. In contrast, the two-sided wedge is found appropriate for the soil behind the pile that moves together with the pile upon loading. Two formulations are then derived from the two upper-bound failure mechanisms. The lateral pile capacity can be determined and the corresponding failure mechanism identified based on the formulation that yields the lower capacity magnitude. In addition, the reliability of the formulations is verified against reported finite element methods as well as existing experimental and field test results.