Mechanisms of soil flow during submarine slide-pipe impact

This paper investigates submarine slide-pipe interaction through centrifuge tests and computational fluid dynamics (CFD), with particular focus on the soil flow mechanisms that occur around a suspended pipe at non-Newtonian Reynolds numbers (Re_{non-Newtonian}) between 0.5 and 40. The centrifuge tests involve horizontal translation of a model pipe in samples of kaolin at different densities and undrained strengths whilst measuring pore pressures at the model pipe front and rear. These measurements provide insights into the pressure evolution at these pipe locations with increasing Re_{non-Newtonian}. In the CFD simulations, the submarine slide is idealised as a single phase non-Newtonian, power law fluid that flows around a two-dimensional pipe (fully engulfed). CFD modelling demonstrates that the drag coefficient depends on both Re_{non-Newtonian} and the power law index controlling the slide material viscous behaviour. Examination of the observed CFD flow features reveals that slide flow can separate from the pipe surface when Re_{non-Newtonian} > ∼10. It is shown that the Re_{non-Newtonian} at which soil flow separation occurs approximately coincides with increases in the: 1) differences in front and rear pore pressures measured in the experiments; and 2) the measured net horizontal drag pressure acting on the model pipe.