Tradeoffs between stout and slender armor 



6. The perfect CAU shape would depend on the specific environmental 

 conditions and would therefore be unique to each site. But development of 

 armor units must be restricted to a few shape groups because of the high cost 

 of developing general design guidance for the complex coastal structure 

 environment. The optimal armor unit shapes will be hybrids between the strong 

 stout units and the weaker, but hydrodynamically stable, slender units. Even 

 restricting the CAU selection to a few select shapes, the choice of armor 

 requires consideration of a great many complicated and inter-related factors. 



7. Because stout armor units such as the accropode and modified block 

 have no thin sections, sophisticated structural design methods are generally 

 not required for these units. Stout CAUs require a steep slope to maintain 

 stability because of the low degree of interlocking. And while these steep 

 slopes are less expensive because they require less material than flatter 

 slopes, they can fail in a very abrupt and catastrophic manner, should 

 instability occur. 



8. On the other hand, slender armor units, such as the dolos, tetra- 

 pod, and tribar can be built on either flat or steep slopes. But if the 

 slender units fail structurally, a steep slope can promote abrupt failure. 

 Excessive breakage of slender units on coastal structures worldwide simply 

 shows that these units are not being designed with adequate strength or 

 appropriate geometry. Therefore, in order to compare slender and stout units, 

 one must assure that both will remain structurally intact. Holzhauzen and 

 Zwamborn (1991) showed that accropodes and dolosse have about the same stabil- 

 ity on the steep slope of 1V:1.5H. They showed that dolosse have more reserve 

 stability than the accropodes, provided they have enough strength in the 

 slender appendages to resist static, wave-induced, and impact loads. 



Why use dolosse? 



9. As stated previously, the dolos armor unit (Merryfield and Zwamborn 

 1966), shown in Figure 2 , is a good example of a slender armor unit because it 

 exhibits very high hydrodynamic stability due to the interlocking slender 

 flukes. But the slenderness of the dolos makes it susceptible to structural 

 failure. The Sines breakwater failure, for example, is believed to be partly 

 due to the structural failure of slender unreinforced dolosse (Baird et al . 

 1980) . 



