Abstract
It is common to construct a rock toe berm of three to four rocks wide when concrete armor units are placed in the armor layer. This toe berm is a relevant element, especially in very shallow waters combined with steep sea bottoms, where waves directly attack the toe berm and the lowest part of the armor. Several formulas are available to estimate the damage to rock toe berms. In this paper, these formulas are compared for different design conditions within their range of application. Most of these formulas use the damage parameter Nod. However, there are often situations in which wider toe berms are required for a safe design, and the damage parameter Nod is not recommended. A methodology is thus proposed to design wider toe berms based on the damage to the nominal toe berm of three rocks wide (Nod*), considered as the most shoreward part of the toe berm which effectively supports the armor layer.
Highlights
When concrete armor units are used, a toe berm of three or four rocks wide (Bt=3-4Dn50) is usually placed on the seafloor to provide support to the armor layer
This paper focuses attention on the design of rock toe berms, the relevance of the sea bottom slope on the hydraulic stability of toe berms, and the use of wider than conventional rock toe berms to reduce the size of the required rocks
Estimations given by existing formulas are compared, considering standard toe berms with berm width (Bt)=3Dn50 and tt=2Dn50
Summary
When concrete armor units are used, a toe berm of three or four rocks wide (Bt=3-4Dn50) is usually placed on the seafloor to provide support to the armor layer. USACE (1984) proposed estimating the mass of the toe berm rocks as one order of magnitude lower than the mass of the armor units. This design criterion is not valid for depth-limited breaking wave conditions, especially, when breakwaters are placed on rocky coastlines with steep seafloors and shallow waters. In these conditions, mound breakwaters may require emerged toe berms, and the rock size may exceed the armor unit size (see Herrera and Medina, 2015)
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