An experimental study of pipe-soil interaction for free-spanning pipelines subjected to cross-flow VIV in carbonate silty sand

This paper presents findings from a series of geotechnical centrifuge tests investigating the vertical cyclic response of a pipeline ‘element’, and form part of a broader study into pipe-soil interaction (PSI) of pipeline segments at a free-span ‘shoulder’. The tests were performed on natural carbonate silty sand from the North West Shelf of Australia. A total of five tests were conducted, examining the influence of cyclic displacement amplitude, static vertical load, initial embedment, and pipe installation method on soil stiffness, soil material damping and embedment under cross-flow Vortex-Induced Vibration (VIV). The results show nonlinearity and dependence on both cyclic amplitude and vertical load, with progressive soil densification and embedment leading to increasing stiffness and reducing damping – but with trends that appear to converge with continued cycling. Comparison with current design guidance DNV-RP-F114 ‘Pipe-Soil Interaction’ (DNV, 2021a) shows broad agreement between these tests and industry practice, although some uncertainty remains over the selection of appropriate soil inputs when undertaking code-based assessments. Experimentally derived damping ratios provide new data for modelling hysteretic soil energy dissipation. Overall, the presented data improve the basis for selecting soil springs and dashpots in free-spanning pipeline assessments.