Equation 7-105 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: 



w. H^ 



W„ = 



KRi?(S,-l)' cot 



(7-106) 



Tlie symbols are the same as defined for Equation 7-105 except that W50 

 is the weight of the 50-percent size in the gradation. The maximum 

 weight of graded rock is 3.6 Wjg; the minimum is 0.22 Wgg. K^j^ is a 

 stability coefficient for angular graded riprap, similar to K^j. Values 

 of Kj^j^ are shown in Table 7-6. These values allow for 5 percent damage. 

 (Hudson and Jackson, 1962.) 



Use of graded riprap cover layers is generally more applicable to 

 revetments than to breakwaters or jetties. A limitation for the use of 

 graded riprap is that the design wave height should be less than about 

 5 feet. For waves higher than 5 feet, it is usually more economical to 

 use the more uniform-size armor units as indicated in Equation 7-105. 



7.374 Selection of Stability Coefficient . The dimensionless stability 

 coefficient K^ in Equation 7-105 accounts for all variables other than 

 structure slope, wave height, unit weight of armor units, and the specific 

 gravity of water at the site (i.e., fresh or salt water). These variables 

 include: 



(1 

 (2 

 (3 

 (4 



(5 

 (6 

 (7 

 (8 



(9 

 (10 



(11 



Shape of armor units, 



number of layers of armor units, 



manner of placing armor units, 



surface roughness and sharpness of edges of armor units 

 (degree of interlocking of armor units), 



type of wave attacking structure (breaking or nonbreaking), 



part of structure (trunk or head) , 



angle of incidence of wave attack, 



model scale (Reynolds number) , 



unit weight of armor units, 



distance below Stillwater level that the armor units extend 

 down the face slope, 



size and porosity of underlayer material. 



7-175 



