AN EXPERIMENTAL STUDY ON ESTIMATION OF CRITICAL YIELD AND THICKNESS FOR MUD EROSION UNDER TSUNAMI FLOW

Abstract

 In the 2011 Great East Japan Earthquake, the so-called “black tsunami”, which involved bottom mud and sludge, were observed. It is required to reveal generation mechanism of black tsunamis, in order to examine their effects on tsunami loads. In this study, moving bed experiments using a mud model with a grain size of a few μm were performed and summarized the erosion thickness based on the pressure gradient in the downstream direction and the vertical distribution of water content ratio of the bottom mud. The failure limit of the bottom mud due to Tsunami flow was estimated by comparing the yield shear stress of the bottom mud model. As a result, the failure limit of bottom mud can be estimated from the relationship between the bottom shear stress of the Tsunami flow and the yield shear stress of bottom mud. Furthermore, the erosion depth of mud becomes significantly larger when the bottom shear stress of the flow becomes larger. An estimation equation for mud erosion under tsunami flow was proposed.