33. Recently, laboratory scaled model studies were conducted by Markle 

 (1989) to address the sizing of toe berra and toe buttressing stone in breaking 

 wave environments. These tests resulted in the most recent guidance for 

 sizing toe berm armor stone and toe buttressing stone. Basically, guidance is 

 given in terms of the stability number N s defined by 



N„ = 





1/3 



H r 



(S r - 1) 



(44) 



with W 50 , the median weight of individual berm stone in lb f , as defined 

 previously in Equation 39. In addition, 



7 rb = specific weight of berm stone, lb f /ft 3 



S r = specific gravity of berm stone relative to the water in which 

 the structure resides, i.e., S r = 7 r b/7 



H D = design wave height, ft 



7 = specific weight of water in which structure resides, lb f /ft 3 



Basically, the guidance for toe berm stone states that "unless site-specific 

 model tests are conducted to justify higher values of N s , stability number 

 should be selected based on the lower limit curve presented in Figures 11 and 

 12, and the individual toe berm armor stone weights should range from a 

 maximum of 1.3 W 50 to a mimimum of 0.7 W 50 . " For toe buttressing stone, 

 limited 2-D stability tests for toe buttressing a one-layer uniformly placed 

 tri-bar structure, a stability number N s equal to 1.5 should be used in a 

 wave -breaking environment. 



Ns 3 VS dl/da 



ALL TESTS 



TESTS: 5- & 6.75-JT FUUUES 



08UQUE WAVES ON TRUNKS 

 90 OECREE WAVES OH TRUNK! 

 06UOUE WAVES OH MEADS 

 90 OECREE WAVES OH HEAOS 

 I TESTS: T-SHAPED WAVE BASW 



RELATIVE BERM DEPTH, dl/da 



Figure 11. Stability number cubed versus relative berm depth from 

 Markle (1989). (See Figure 12 for definition of d x and d s ) 



31 



