Effects of grain size on subaerial granular landslides and resulting impulse waves: experiment and multi-phase flow simulation

Subaerial landslides falling into a large body of water can generate large impulse waves (tsunamis). The wave generation by subaerial landslides involves sediment, water and air, and thus multi-phase flow models are most suitable for simulating the processes involved. This paper reports a laboratory and numerical study of impulse waves generated by subaerial landslides, with a focus on grain size effects. Four different grain sizes were examined in this study, ranging from fine sand to very coarse sand. A multi-phase flow model was used to perform the numerical simulations of the laboratory experiment. Both measured and simulated results have shown that the speed of the granular front and the height of the impulse wave increase with decreasing grains size. Possible explanations for the effects of grain size on the landslide process and the resulting waves are discussed.