Negatively Buoyant Debris Impact under Tsunami-Like Flows

Debris impact on critical infrastructure is a major cause of destruction during tsunami events. While the loading of positively buoyant debris (debris with a density lower than water) has been well researched, to the author’s knowledge, few studies have focused on the impact of negatively buoyant debris (debris with a density higher than water). To address this knowledge gap, this paper presents the results of an experimental program investigating the impact of negatively buoyant debris on a structure using a dam-break wave. Spherical debris scaled down to a 1:60 ratio was entrained by a bore wave to impact a cylindrical structure. The final velocity of negatively buoyant debris was shown to be lower than the bore front velocity, with a relative velocity decreasing with increasing density. The Stokes number of the debris was found to be a good parameter to approximate this relative speed. For the calculation of the impact force, a single-degree-of-freedom equation based on the contact stiffness model was found to be a good fit for the experimental data. However, this fit can be improved by incorporating an extra parameter dependent on the density and diameter of the debris.