Application of Model Test Results . 



The original riprap slope was damaged by storms which had an esti- 

 mated significant wave height of 3.3 feet. The original 1 on 3 slope 

 riprap gradation, as sampled on the constructed slope, was: 



Large quarrystone area Small quarrystone area 

 (lb) (lb) 



w 



max 



= 



1; 



,200 



\o 



= 





75 



w . 



rmn 



= 





4 



W 

 max 



= 



180 



\o 



= 



10 



w . 



mvn 



= 



< 1 



The stability of these existing rock gradations for zero damage is com- 

 puted using the definition of the stability number (eq. 2) rearranged 

 to yield: 



W, 



Wv, h3 



50 



N3 (S - 1)3 

 ST 



where 



WjQ = median stone weight (pounds) 



Wjo = unit weight of stone (165 pounds per cubic foot) 



H = significant wave height (feet) 



Ng =1.46 (cot e) ' =1.86 CAhrens and McCartney, 1975). 



6 = angle of structure slope with the horizontal (cot 0=3) 



Sp - armor specific gravity, = , , . = 2.64 



62 . 4 



Using this equation, the zero-damage wave heights for the damaged 

 railroad embankment slope follow: 



Area Wgg Zero-damage wave height 



(lb) (ft) 



Small stone (riprap) 10 1.2 



Large stone (riprap) 75 2.4 



This analysis of the original riprap shows it was considerably smaller 

 than the size required to be stable against the design waves. Using this 

 same equation for the design significant wave height of 3.3 feet, W^q = 209 

 pounds is required for stability. This computed stable stone overlay 

 weight of 209 pounds was increased arbitrarily to 600 pounds (272 kilo- 

 grams) to incorporate a factor of safety into the repair design and 

 because stone up to this weight was available at about the same unit 



30 



