Experimental study of debris transport driven by a tsunami-like wave: Application for non-uniform density groups and obstacles

Abstract

Water-borne disaster debris can exacerbate the damage on the built-environment through debris impact and debris damming loads and by decreasing the functionality of infrastructure systems after these events. Therefore, an understanding of disaster debris transport is essential for disaster management. In this paper, an experimental study of tsunami-driven debris spreading over a flat testbed was conducted considering different density conditions of debris elements. Debris elements of two different materials (densities) were considered various debris groups and starting orientation. The final dislocations and local velocity of debris elements were measured optically and compared to flow velocity. Among two debris elements in a debris group, it was found that debris elements of higher density affected the mean longitudinal displacement of the less dense debris, but the less dense debris did not affect the displacement of higher density debris. Also, it was found that the initial orientations of the debris groups had no measurable impact on the final displacement. The effects of obstacles on the passage of debris and the probability of collision to obstacles were examined and the process of debris-debris and debris-obstacle interactions from debris entrainment to final dislocation was studied. It was found that the less dense debris had a higher probability of collision with the obstacles compared to the more dense debris case. However, when the debris types were mixed, the less dense debris had a lower probability of collision. Finally, the characteristics of debris dislocation and velocity fields under various density conditions as a group were also evaluated. The reflected wave and interaction among different debris play a role in the probability of collision. However, the density of each debris element was a dominant factor in determining the collision probability.