Procedure for Site Assessment of the Potential for Tsunami Debris Impact

Abstract

Tsunami debris can place large demands on the structures it impacts. The types of potential debris and impact forces they generate are not well understood, and relatively little consideration is taken for the risk of tsunami debris strikes during structural design. A procedure is outlined to assess the site-specific potential for debris impact and its significance to structures. The procedure involves a categorization of potential debris based on fundamental characteristics. It includes an assessment of the ability and likelihood of debris transport, as constrained by the topography and the constructed environment. Data from aerial surveys and on-ground surveys after the March 2011 Tohoku tsunami are used to demonstrate and validate the considerations proposed for an assessment of debris and its transport. Instances of structural damage found during the site survey and that potentially resulted from debris strikes are reported. These cases are evaluated to correlate the proposed debris categories and impact demands with the observed structural damage. The velocities needed to cause the observed damage were determined using existing guidelines for debris impact forces. The procedure proposed here can be considered as a preliminary effort toward the development of a framework for risk assessment, including estimates of probable damage levels. Applications include both structural design and tsunami disaster planning.