EXPERIMENTAL STUDY OF HYDRODYNAMIC FORCE- AND STABILITY-CHARACTERISTICS OF ARMOR BLOCKS COVERING THE RUBBLE MOUND AGAINST TSUNAMI FLOW

Abstract

 A hydraulic model experiment was performed on tsunami-induced hydrodynamic forces acting on armor blocks covering a rubble mound to validate the assumption in the derivation process of the Isbash formula, which is a method used to calculate the required mass of an armor block. The result of pressure distribution around the blocks demonstrated that the hydrodynamic force works on the plane of the armor block locally. Based on the assumptions of the local distribution of lift force, we modified the formula for calculating the required mass of an armor block, which refers to the velocity value to the sixth power or that to the third power. On the other hand, it was unclear whether the action length of the lift force varies with the size of the armor block. This issue is strongly related with the rationality of the modified formula. Furthermore, the relationship of the near-bottom velocity and cross-sectional average velocity (the former is related with the stability of armor blocks more directly, whereas the latter is supposed to be used in the design practice) remains to be investigated in future research.