Pipe-soil interaction for free-spanning pipelines subjected to in-line VIV: Geotechnical centrifuge testing on natural carbonate silty sand

This paper presents an experimental investigation of pipe–soil interaction using geotechnical centrifuge modelling. The tests simulated the response of rigid pipe ‘elements’ at free-span ‘shoulders’ subjected to horizontal cyclic loading representative of pipeline movements during in-line Vortex-Induced Vibration (VIV). A natural carbonate silty sand from the North West Shelf of Australia was used, and the effects of vertical load, cyclic displacement amplitude, installation method, and loading history were investigated. The response was assessed in terms of changes in pipe embedment (or load), horizontal cyclic stiffness and soil material damping. The results show that the mobilised stiffness decreases with increasing displacement amplitude and increases with increasing vertical load as expected, but that stiffness values are substantially lower than those predicted with state-of-practice calculations. Soil damping increases nonlinearly with cyclic amplitude and is strongly load-dependent, with lower vertical loads producing more damping. The findings demonstrate that strain and load dependent soil behaviour governs pipe-soil interaction during in-line VIV and should be explicitly accounted for in pipeline free-span assessment.