Model pile response to multi-amplitude cyclic lateral loading in cohesionless soils

Abstract

Monopile foundations for offshore wind turbines are subjected to many cycles of loading during their lifetime. This loading consists of a range of amplitudes, applied in various sequences, of many different cycle numbers. Calculation of the accumulated rotation experienced by the monopile as a result of this cyclic loading, and whether this exceeds allowable limits, is an important part of the design process. This paper provides an overview of recent research exploring laterally loaded pile response relevant to the design of offshore wind turbine monopiles. Experimental equipment for carrying out cyclic lateral loading tests is introduced, along with considerations of scaling for model testing. Results from a series of small scale model tests covering realistic multi-amplitude testing are then presented, providing new insight into the behaviour of rigid piles subjected to cyclic loading. The results are interpreted using a linear superposition method, as typically used for structural fatigue calculations, and this shows a good fit to the experimental results.