Tsunamis have long been recognized to destabilize the seabed by causing severe erosion and potential liquefaction. However, the effect of the dynamic seepage response induced by tsunami loading on sediment transport remains elusive. Here, we conduct computational fluid dynamics (CFD) simulations to investigate the role of seepage response in the full-scale tsunami-induced scour. It is shown that the increased hydraulic gradient can lower the onset threshold of the sediment motion, thus facilitating sediment transport. In the meantime, it can also curtail the fluid-sediment momentum transfer, consequently weakening sediment transport. The competing effects of seepage response on the onset threshold and fluid agitation are such that the seepage response during the depression wave does not necessarily increase bed mobility. Seepage responses influence sediment transport and scour patterns around the pipeline. Notably, seabed injection during depression waves exacerbates scour beneath the pipeline, while suction during elevation waves mitigates scour. The outcomes significantly update the knowledge about the role of seepage in the progress of tsunami-induced sediment transport and scour.

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