breaking might prevent the 1 percent wave from reaching the structure; if so, 

 the maximum wave that could reach the structure should be taken for the design 

 value of H . ) 



(2) For less critical structures, where some risk of exceeding design 

 assumptions is allowable, wave heights between Hiq and Hi are acceptable. 



The design wave for rubble toe protection is also between H,q and Hj^ . 



b. Stability Number . The stability number (Ng) is primarily affected 



by the depth of the rubble foundation and toe protection below the still-water 



level d, and by the water depth at the structure site, dg . The relation 



3 

 between the depth ratio d /d and N is indicated in Figure 7-120. The 



J. O O 



cube value of the stability number has been used in the figure to facilitate 

 its substitution in equation (7-125). 



c. Armor Stone . The equation used to determine the armor stone weight is 

 a form of equation (7-116): 



w H^ 

 W=-r— ^^ ^ (7-125) 



N^ (S - ll^ 



where 



W = mean weight of individual armor unit, newtons or pounds. 



w = unit weight of rock (saturated surface dry), newtons per cubic meter 



or pounds per cubic foot (Note: substitution of pr , the mass 



density of the armor material in kilograms per cubic meter or slugs 



per cubic foot, will yield W in units of mass (kilograms or slugs) 



H = design wave height (i.e., the incident wave height causing no damage 

 to the structure) 



S^ = specific gravity of rubble or armor stone relative to the water on 

 which the structure is situated (S„ = w /w,,) 



V r W 



V 



Wy = unit weight of water, fresh water = 9,800 newtons per cubic meter 



(62.4 pounds per cubic foot), seawater = 10,047 newtons per cubic 



meter (64.0 pounds per cubic foot). (Note: subsitution of 

 \7> 



, where pw is the mass density of the water at the 



/pr - pw \ 

 \ pw / 



structure, for (S„-l) yields the same result.) 



N = design stability number for rubble foundations and toe protection (see 

 Fig. 7-120). 



7-243 



