between the two extremes of solid blocks and slender-legged units. Examples 

 of very slender- legged units include the dolos and the tribar, while the 

 tetrapod and accropode could be described as stout-legged units. Concrete 

 armor can also be categorized according to the placement strategy: regular or 

 random. The discussion in this report is restricted to randomly placed armor. 



4. For stone armor, poor performance is generally due to hydrodynamic 

 instability, with stones being dislodged by waves. Breakage of stone armor is 

 not a problem if care is taken in choosing a quarry site and quarrying the 

 stone. On the other hand, poor performance of concrete armor is due to com- 

 bined hydrodynamic instability and armor breakage or severe abrasion. For 

 CAUs , the breakage and abrasion can be a function of the units rocking, but 

 need not be. The units can fail statically due to their own weight, or due to 

 the weight of surrounding units, when subjected to unfavorable boundary con- 

 ditions (Melby and Howell 1989). Concrete units can be abraded by unit-to- 

 unit contact or by small sand particles and pebbles , entrained by highly 

 turbulent breaking waves. Abrasion generally reduces the ability of the 

 section to resist loads or reduces cover over steel-reinforced sections, 

 accelerating corrosion of the steel. 



5. Instability- induced impact loads generally result in accelerated 

 breakage which produces more instability. Therefore, the armor unit-to-unit 

 interlocking characteristics, which resist armor movement, are of primary 

 importance to the performance of concrete armor. But increasing interlocking 

 requires slender appendages, which are less able than stout appendages to 

 resist forces due to self weight, adjacent units, waves, and rocking or pro- 

 jectile impacts. Thus, stout- legged units may produce less interlocking and 

 hence, less residual stability, but they are also less susceptible to 



structural failure. 



Table 1 

 CAU Loadings 



Load Category Load 



Static Self Weight 



Wedging 

 Buoyancy 



Dynamic Pulsating 



Impact 

 Abrasion 



Material Thermal 



Chemical 



