CFD investigations of tsunami-induced scour around bridge piers

Abstract

Tsunamis impacting on the coastal bridges could cause severe scour around piers, which subsequently threatens the stability of bridge foundations. This paper presents a numerical investigation on tsunami-induced scour around bridge piers based on a CFD model coupling hydrodynamic, sediment transport, and morphological models. The tsunami generation is numerically realized by prescribing a time-varying soliton flow in the inlet boundary. The model is first validated by comparing with available experimental results, which shows that it can accurately simulate the tsunami-induced velocity field, as well as the time development of the scour and the final scour depth. Based on the reliable CFD model, a total of 14 numerical experiments of tsunami-induced pier scour are then performed. The temporal development of scour indicates that substantial scour is occurred during the 0.4 to 0.6 times of the tsunami period. The scour rate highly depends on the tsunami period T and peak velocity Um, and the scour rate is enhanced significantly with the increase of either T or Um. The relative scour depth (normalized by the final scour depth) S/Sf over normalized time t/T for all the cases are generally collapsed to one curve that can be represented by a tanh function, and a simple equation is proposed to predict the final scour depth. Finally, a practical engineering methodology is established to predict the tsunami-induced pier scour, including the temporal scour development and the final scour depth. It demonstrates that this method is capable of reasonably predicting all the cases considered in this study.