Centrifuge and Numerical Investigation of Fault Rupture Interaction with a Three-legged Jack-up Rig Founded on Spudcan Foundations

This paper presents findings from finite element (FE) and geotechnical centrifuge testing on the interaction of a seismic fault rupture with a three-legged jack-up rig founded on spudcan foundations. A normal fault is modelled experimentally and numerically, exploring the interaction mechanisms of the spudcan and the associated structural response. The instrumentation of the physical model consists of an accelerometer recording hull pitch, strain gauges measuring leg axial loads and bending moments, and a linear variable differential transducer (LVDT) tracking fault throw (vertical displacement). The experiments improve the understanding of structural performance and the threat posed to the jack-up rig from earthquake faults. Understanding Fault Rupture-Soil-Foundation-Structure Interaction (FRSFSI) is of paramount importance for jack-ups in seismically active environments across the globe, and the findings of the current study may be used alongside other hazard and risk mitigation strategies deployed during site investigation and assessment of rig operations. This research forms part of a wider study, where a numerical analysis methodology was developed to simulate the jack-up-fault rupture interaction, using the centrifuge experiments for validation. The study reveals the interaction mechanisms and the minimum distance between the rig and outcropping fault rupture, where the structural distress starts to become significant. When considering a known fault rupture outcrop, or with the assumption that the outcrop can be predicted (which is problematic, given the uncertainties regarding bedrock location and propagation through soil) non-operation envelopes/zones could be developed, within which significant structural distress would be expected.