ways to reflect both irregularity and groupiness, was found to be minimal. 

 This result differs from the conclusions of other tests relative to the 

 influence of wave groupiness on stability (Burcharth 1979). A major influ- 

 ence by core permeability was found. The stability formulae proposed for 

 rubble-mound (quarrystone) structures with permeable cores (D^q armor /D^q core 

 = 3.2 , as tested) for breaking waves {e, < 2.5 - 3.5) was 



0.22 



H 

 " = 5. 



n50 



^2 



N^/2 



C'-^' ,. (5) 



or, equivalently , 



/ s V/3 



n50 \ n50/ \N / 



The formula proposed for nonbreaking waves {E, > 2.5 - 3.5)* with cot 9 < 3 

 was 



"^ 1.65 (cot 9)^/2(^) ^0.1 (^) 



n50 \N / 



whereas for nonbreaking waves {e, > 2,5 - 3.5) with cot 9 > 3 the formula 

 was 



where 



H = the significant wave height of the incident spectrum 



^n50 ~ ^^^ nominal diameter, based on the mass of the 50th percentile 

 WcQ from the armor material mass distribution curve 



= (W5o/p,)i/5 



Sp = a dimensionless damage level, defined as the number of 

 equivalent Dj^cq cubes eroded over a width of 0^50 



= 2-3 for incipient damage (as with the Hudson formula) 



= 8 to 17 for armor layer "failure" (significant exposure or 

 underlayers) 



N = number of incident waves 

 The range of E, values from 2.5 to 3.5 for the transition from breaking 

 to nonbreaking wave conditions apparently represents the difficulty in de- 

 scribing an irregular sea state as either breaking or nonbreaking, since both 



17 



