



Table 



6. Example problem 5 comparison 



data. 







Slope 



N sz 



Zero 



damage 



"50 

 kg(lb) 



r min 

 'm(ft) 



Hin. w 85 

 filter 



kg(lb) 



(Stoa 1978 

 method) 

 m(ft) 



"max 

 (this report 

 method) 

 m(£t) 



"max 



(ETL 1110-2- 



221 method 



m(ft) 



Length of 

 revetment 



m(ft) 



Armor 

 weight 2 



kg/m(lb/ft) 



Reserve 



stability 



factor 3 



(H/H z ) 



1 on 1.5 



1.55 



201 

 (443) 



0.85 

 (2.79) 



1.25 

 (2.76) 



2.91 

 (9.55) 



2.00 

 (6.56) 



2.49 

 (8.17) 



6.90 

 (22.64) 



9,304 

 (6,253) 



1.12 



1 on 2 



1.63 



173 

 (381) 



0.81 

 (2.66) 



1.08 

 (2.38) 



2.72 

 (8.92) 



1.77 

 (5.81) 



2.20 

 (7.22) 



8.05 

 (26.41) 



10,344 

 (6,952) 



1.18 



1 on 3 



1.74 



142 

 (313) 



0.75 

 (2.46) 



0.89 

 (1.96) 



2.02 

 (6.63) 



1.44 

 (*.72) 



1.80 

 (5.91) 



10.34 

 (33.92) 



12,303 

 (8,269) 



1.31 



1 on 5 



1.90 



109 

 (240) 



0.69 



(2.26) 



0.69 



(1.52) 



1.15 

 (3.77) 



1.05 

 (3.44) 



1.31 

 (4.30) 



14.69 

 (48.20) 



16,080 

 (10,807) 



1.59 



!Used to compute length of revetment. 



2 Void space in the riprap armor Is assumed to be 40 percent of the total volume. 



3 From Figure 3. 



lack of riprap stability and runup data for this condition, and its antic- 

 ipated low reserve stability. These factors indicate that a 1 on 1.5 

 slope is useful to consider as an example, but it would not be the most 

 acceptable design. 



In Table 6 the height of the revetment was chosen to be the value of 

 Kmax calculated by the method developed in this report. If overtopping 

 might cause a life-threatening situation, then a more conservative estimate 

 °f Rmax should be used due to the uncertainty in predicting extreme values 

 of runup and model studies to determine Rmax should be considered. Addi- 

 tional conservatism could also be used in the riprap weight and armor layer 

 thickness. Since the riprap weight is proportional to the cube of the wave 

 height, an uncertainty of ±15 percent in the wave height becomes ±52 per- 

 cent in the riprap weight. It may be assumed that the uncertainty about 

 the incident wave height is compensated for by the reserve stability; how- 

 ever, for steep slopes there may not really be enough compensation so that 

 use of a larger W50 might have to be considered. 



A complete analysis would have to weigh the first costs against mainte- 

 nance costs and the possibility of other losses if the design conditions 

 were exceeded. These considerations are beyond the scope of this report. 



Since the weight of overlay stone required to upgrade an existing revet- 

 ment is the same as the weight of armor stone required for stability (eq. 

 5), the overlay stone weight is the same as given in Table 6. Using the 

 slope of 1 on 3 and blocky-shaped stone as an example, the average overlay 

 stone weight and weight of overlay per square meter can be calculated using 

 equation (10) and (9) , respectively 



W = 0.87 W 50 = 0.87(142) - 124 kilograms (273 pounds) 



and 



5 \l/3 



1/3 



CC. F .(^)' 3 („ r , = 0.4 2 (^)' 3 C2, 644 > 



= 400 kilograms per square meter (82 pounds per square foot) 



28 



