w H 



r 



W = 



(7-116) 



K (S - 1) cot 



D r 



where 



W = 



weight in newtons or pounds of an individual armor unit in the primary 

 cover layer. (When the cover layer is two quarrystones in thickness, 

 the stones comprising the primary cover layer can range from about 

 0.75 W to 1.25 W, with about 50 percent of the individual stones 

 weighing more than W . The gradation should be uniform across the 

 face of the structure, with no pockets of smaller stone. The maximum 

 weight of individual stones depends on the size or shape of the 

 unit. The unit should not be of such a size as to extend an 

 appreciable distance above the average level of the slope) 



w 



unit weight (saturated surface dry) of armor unit in N/m or lb/ft . 



density of the armor material in 



in units of mass (kilograms or 



Note: Substitution of p , the mass density of the armor material in 



kg/m-^ or slugs/ft , will yield W 

 slugs) 



H = design wave height at the structure site in meters or feet (see Sec. 

 III,7,b) 



S = specific gravity of armor unit, relative to the water at the structure 



^ (S = w /w ) 



r r w 



w 



w 



unit weight of water: fresh water = 9,800 N/m^ (62.4 Ib/ft^) 

 seawater = 10,047 N/m^ (64.0 Ib/ft"^) Note: Substitution of 



Pr - P 



w 



pw 



where 



w 



is the mass density of water at the 



structure for (Sr - 1) , yields the same result 



9 = angle of structure slope measured from horizontal in degrees 



K = stability coefficient that varies primarily with the shape of the 

 armor units, roughness of the armor unit surface, sharpness of edges, 

 and degree of interlocking obtained in placement (see Table 7-8). 



Equation 7-116 is intended for conditions when the crest of the structure is 

 high enough to prevent major overtopping. Also the slope of the cover layer 

 will be partly determined on the basis of stone sizes economically avail- 

 able. Cover layer slopes steeper than 1 on 1.5 are not recommended by the 

 Corps of Engineers. 



Equation 7-116 determines the weight of an armor unit of nearly uniform 

 size. For a graded riprap armor stone, Hudson and Jackson (1962) have 

 modified the equation to: 



7-205 



