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.

水源性灾害碎片会通过碎片撞击和碎片填塞负荷，并在这些事件发生后降低基础设施系统的功能，加剧对建筑环境的破坏。因此，对灾害碎片运输的了解对于灾难管理至关重要。在本文中，考虑了碎片元素的不同密度条件，进行了海啸驱动的碎片在平坦测试台上扩散的实验研究。两种不同材料（密度）的碎片元素被认为是各种碎片组和起始方向。最终测量碎片元素的最终位错和局部速度，并将其与流速进行比较。在一个碎片组中的两个碎片元素中，已经发现，密度较高的碎片元素会影响密度较小的碎片的平均纵向位移，但密度较小的碎片不会影响密度较高的碎片的位移。此外，还发现碎片组的初始方向对最终位移没有可测量的影响。研究了障碍物对碎片通过的影响以及与障碍物碰撞的可能性，并研究了从碎片夹带到最终脱位的碎片-碎片和碎片-障碍物相互作用的过程。已发现，与密度较大的碎屑相比，密度较小的碎屑与障碍物碰撞的可能性更高。但是，当混合碎片类型时，密度较小的碎片发生碰撞的可能性较低。最后，还评估了在各种密度条件下作为一组的碎片位错和速度场的特征。反射波和不同碎片之间的相互作用在发生碰撞的可能性中起作用。但是，每个碎片元素的密度是确定碰撞概率的主要因素。