Influence of toe berm geometry on stability of reshaping berm breakwaters

Mehdi Shafieefar, Mohammad Reza Shekari, Bas Hofland

Research output: Contribution to journalArticleScientificpeer-review

2 Citations (Scopus)

Abstract

Reshaping berm breakwaters have been mainly designed and built for water depth less than 20 m. In such conditions, a toe structure may be needed to reduce bottom settlements and increase geotechnical stability in the loose subsoil condition. Also, a toe berm can be deployed to reduce the berm recession and increase the stability of the Reshaping berm breakwater, especially in deep water. Although many studies have been conducted to study the effects of toe berms on stability of conventional breakwaters, investigations on the influence of a toe berm on stability of reshaping berm breakwaters are rare. This paper presents results of an experimental work that has been carried out to investigate the influence of a toe berm on the hydraulic stability of reshaping berm breakwaters. In a 2D physical test setup in a wave flume, a total of 207 tests were conducted to systematically examine the effects of toe berm configuration on the reshaping of berm breakwaters with three types of armor stones. The experimental program covers the influence of different geometrical parameters of the toe berm on the berm recession under various sea state conditions. Comparing results of berm recession of the cases having a toe structure with the cases without a toe berm shows that the amount of berm recession with toe berm is considerably less than the analogous amount for without toe structure. It is observed that an increasing toe berm width and thickness both have considerable influence on recession reduction. However, the toe depth has a relatively larger influence on recession than the toe width, and the influence is larger for higher stability numbers. It is concluded that a toe berm in front of reshaping berm breakwater not only does have influence on recession due to the depth influence and the changing wave conditions, but also the toe depth has a direct influence on the reshaped profile by preventing the displaced rocks to fall down to deeper parts. Using the test results, a new formula is developed for estimation of berm recession by taking into account the influence of the toe berm configuration. Given an acceptable stability number (Ho) as a design criterion for reshaping berm breakwaters, the present method predicts that the recession can be reduced up to 35% by the application of a toe berm. Thus, the main berm width can be shortened, resulting in reduction of the required armor stones volume. So, by using a smaller stone size for the toe berm, the stability of the structure is secured and also the total cost of the breakwater can be reduced.

Original languageEnglish
Article number103636
Number of pages13
JournalCoastal Engineering
Volume157
DOIs
Publication statusPublished - 2020

Keywords

  • Armor stone
  • Design formula
  • Physical modelling
  • Recession
  • Reshaping berm breakwater
  • Toe berm

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