APPENDIX B 



EXAMPLE PROBLEM 



This appendix illustrates how the findings of this study can be used 

 to calculate the weight of stone and amount of stone required for a 

 stable overlay-type revetment. Guidance is provided on how this infor- 

 mation can be used to develop a cost-effective design. 



******************** *********EXAMPLE PROBLEM**************************** 



GIVEN: 



(a) 1 on 3 slope existing riprap revetment damaged by 

 Hg = 5 feet, T = 4 seconds. 



(b) Stability number is Ng = 1.86 [Ng =1.46 (cot 6)^'^] for 

 a 1 on 3 slope riprap revetment. 



FIND: 



(a) A 100-percent stone overlay size (W50) necessary to sta- 

 bilize slope against wave Hg = 5 feet, T = 4 seconds. 



(b) Stone weight per unit area for overlay of (1) boulders, 

 (2) overlay of conventional riprap- shaped quarrystone, 

 and (3) conventional two-layer overlay. 



Stable quarrystone weight for: 



Hg = 5 feet 



165 ^ ^^ 



\i-p = 165 pounds per cubic foot 

 W50 = H3 w^/ [(N^3 (s^^_ -jpj 

 W50 = (53) (165)7(1.863) (2.64 - 1)3 

 W5Q =727 pounds. 

 Use W5Q = 730 pounds. 

 From Figure 7, stone coverage fraction (C.F.) for boulders and riprap: 



(a) C.F. = 0.55 for boulders (100-percent coverage). 



(b) C.F. = 0.43 for riprap (100-percent coverage, "E" stone 

 shape) . 



33 



