Development of a rig to study model pile behaviour under repeating lateral loads

This paper deals with an important problem of the effect of repeating lateral loads on large-diameter monopile foundations for offshore wind turbine (OWT) structures. The cycles of typically low-amplitude repeating lateral loads and moments generated by various environmental factors are resisted by horizontal earth pressures mobilised in the soil surrounding the pile. Laboratory testing on reduced-scale piles is an efficient and economical way to investigate such pile–soil behaviour. This paper presents the development of a new mechanical loading system to apply many thousands of repeating cycles of lateral load in different forms to a 1g model, with full control provided over the loading direction (i.e. one-way or two-way lateral loading), amplitude, frequency and waveform shape (e.g. sinusoidal, square or haversine). Compared with equivalent setups employing pneumatic or hydraulic actuators, the new loading system is able to produce similar performance at lower cost and also provides more control over the waveform shape. A programme of lateral load tests, each involving many thousands of load cycles, was performed on a rigid model pile installed in dry sand beds to demonstrate some of the main capabilities of the new system.