Development of a real-time hybrid testing method in a centrifuge

This paper presents a pioneering real-time hybrid testing method for geotechnical centrifuges. The method was used to investigate the behaviour of a jack-up leg reinstalled near an existing footprint, a problem that is highly non-linear, stress dependent and involves complex soil–structure interactions. By physically modelling only the footprint–leg interaction and numerically modelling the rest of the jack-up structure, the method enables a realistic account of all the parameters involved in the interaction, including the footprint geometry, soil heterogeneity and structural properties of the jack-up unit. The paper also details the three-degree-of-freedom actuators developed to model the interaction, which features controlled loads and motions along the vertical, horizontal and moment directions, and the real-time algorithm that bridges the physical and numerical models. The algorithm allows the stiffness on each axis to be varied. Testing performed at 1g and in the centrifuge, modelling jack-ups with different stiffness on the horizontal and moment axes, is presented to validate the apparatus and methodology. The hybrid apparatus and real-time testing method were found to produce much more realistic boundary constraints than previous fixed-system apparatuses, and this allowed the test results to be considerably more informative, accurate and useful.