Abstract
This paper presents a stability estimation method for armor units to cover a rubble mound on the rear side of a caisson breakwater against tsunami overflow while taking into account the influence of the shape of the superstructures of the caisson. In this method, the required mass of the armor units is obtained from the impinging velocity onto the rear side mound. This is calculated by using the overflow depth. Accordingly, the influence of the shape of the superstructure is taken into account directly. This method also takes the influence of the slope angle into account properly by using the formula by Isbash. In addition, the influence of the impingement position of the overflow nappe and the influence of the thickness of the water jet are considered. The validity of this method is confirmed by comparing with the results of hydraulic model experiments conducted in a wide range of conditions.
Highlights
The huge tsunami generated by the 2011 off the Pacific coast of Tohoku Earthquake brought severe damage to caisson breakwaters in Japan
We propose a new stability estimation method applicable to the caisson with various sizes of parapet
The caisson model was fixed with a weight so that it would not be moved by tsunami action since this study was focused on the stability of armor units
Summary
The huge tsunami generated by the 2011 off the Pacific coast of Tohoku Earthquake brought severe damage to caisson breakwaters in Japan. One of the failure mechanisms of breakwaters was scouring of the rear side rubble mound and subsoil behind the caisson due to overflow. One possible method is the placement of a widened protection mound using additional rubble stones behind the caisson to increase the resistance against sliding. Installing armor units on the rubble mounds on the rear side would be required to prevent scouring of the rubble mound. Installing a parapet on the caisson would be effective because the parapet would redirect the overtopped water flow in the horizontal direction (Satoh et al 2012, Higashiyama et al 2013)
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