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Proceedings of the Thirty-second (2022) International Ocean and Polar Engineering Conference
Shanghai, China, June 5–10, 2022
Copyright © 2022 by the International Society of Offshore and Polar Engineers (ISOPE)
ISBN 978-1-880653-81-4; ISSN 1098-6189

Analysis of wave-induced abrasion on a slit-type seawall along a rocky coastline
Shota Abe
Yachiyo Engineering Co., LtdTaito, Tokyo Japan

Katsutoshi Kimura
Department of Architecture and Infrastructure, Muroran Institute of Technology
Muroran, Hokkaido, Japan

Takao Nakoshi
Hokkaido Road Management Engineering Center
Sapporo, Hokkaido Japan

Yasuji YamamotoDepartment of Civil and Environment Engineering, Hokkaido University of ScienceSapporo, Hokkaido JapanYoshihiro Murata
Civil Engineering Consultant Sapporo BranchSapporo, Hokkaido Japanof Shizuoka Prefecture, reporting larger abrasion volumes around anelevation of still water level (T.P. 0.0 m). Abrasion research conductedby Matsuda et al. (2007) regarding coastal bridge piers on the Hokuriku
Expressway in Ishikawa Prefecture also revealed an abrasion rate ofapproximately 10 mm/year. Oide et al. (2018) further reported a risk oftunnel collapse along the Ogon route in the Hiroo area of Hokkaido due
to ongoing abrasion to the lower levels of block masonry.
The study reported here was conducted to investigate abrasion of a slittype seawall (Fig. 1) along a rocky Sea of Japan coastline in Hokkaido,
and elucidated the movement characteristics of stones based on hydraulicmodel experiments. The seawall abrasion rate was estimated using datacollected at the local NOWPHAS station using an experimental formula,and a wave overtopping test was conducted to establish a repair
technique for such damage.

ABSTRACTThe research reported here involved clarification of the process of waverelated abrasion on a slit-type seawall along a rocky coastline, withinvestigation of the movement characteristics of 100 kg of stones via
hydraulic experiments with a model scale of 1/20. Abrasion damage was
generally observed near the still water level with correspondence to theposition with the highest collision ratio, which was higher for longer
wave periods. The relationship between wave height and collision speed
was clarified from analysis of video on stone movement patterns relating
to wave action. The characteristics of flow patterns and overtopping
waves were investigated up to design wave conditions via hydraulicexperiments with a model scale of 1/40, and seawall abrasion wasestimated as 10 mm/year (similar to the observation value) using anexperimental formula based on local wave data. Damage repair was also
proposed from the wave overtopping test results, with concrete filling ofworn parts and placement of wave-dissipating blocks found to be anoptimal approach.

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field observation; hydraulic experiment

INTRODUCTION60037007005500

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KEY WORDS: rocky coast; slit-type seawall; abrasion; stones; repair;

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Deformation of concrete structures along rocky coastlines due to stone
motion caused by wave action often progresses rapidly, seriously
affecting seawall safety and the anti-wave performance of related
background facilities. To elucidate the status of such abrasion, Watanabe,
et al.(2013) researched concrete-block erosion along the Shimoniikawa
coast of Japan’s Toyama Prefecture and the Suruga and Numazu coasts

Fig. 1 Slit-type seawall

2720

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EL=0.00

800H.H.W.L
単位：mm
Unit: mm500700