formulae, presented as Equations 1 through 8, apply only to the resistance 

 to displacement of individual armor units. The use of concrete armor units 

 also requires the investigation of mechanical strength related to the 

 interaction betw^ :n the units in the armor layer and the associated impacts, 

 fatigue, and creep (static) effects that occur. Quarrystone can be subject 

 also to fracturing without displacement, but experience shows rock and the 

 bulkier concrete units (such as plain or modified cubes) develop less of this 

 sort of damage than do more slender concrete units (such as dolosse). A num- 

 ber of proof tests and other quality control procedures have been proposed to 

 account for mechanical strength limitations in concrete armor units (Burcharth 

 1981 and Price 1979) which should be considered for application in any project 

 involving these units. Large concrete armor units should be designed with the 

 advice of a specialist in concrete engineering, particularly where fiber re- 

 inforcement is contemplated. The availability of existing forms should be 

 investigated before fabrication of expensive specialized concrete forms is 

 undertaken (Owen 1985). Design formulae indicate a minimum size armor unit, 

 but the availability of existing forms and other practical factors may make 

 slightly larger units more economical. 



32. Design considerations related to the geometry of the armor layer 

 are of particular interest in discussions of optimization since armor units 

 are typically the most expensive materials used in a rubble-mound breakwater. 

 The extent to which primary armor extends below the still-water level on the 

 seaward face is typically set subjectively at 1.5 to 2.0 design wave heights 

 (Figure 1). A berm of secondary armor or underlayer material at the toe of 

 the primary armor is considered good practice, enhancing both the accuracy of 

 underwater placement of the primary armor units and their resistance to slid- 

 ing failure near the toe. The primary armor is usually extended below the 

 waterline on the leeward side by 0.5 to 1.5 wave heights, depending on the de- 

 gree of overtopping anticipated. If a monolithic wave screen is planned for 

 construction on the crest (as illustrated in Figure 6) and virtually no over- 

 topping is to be allowed, armor on the lee side need only be sized to remain 

 stable in the ambient wave climate on that side of the breakwater. Wave 

 screens and monolithic crest structures are sensitive and highly specialized 

 features (Jensen 1983) and will not be dealt with in this paper. 



33. The allowances above, along with the crest width, crest height, 

 and number of armor units comprising the thickness of the primary armor layer. 



22 



