399. Rubble-Stone Preakvjaters . - The design of a rubble-stone break- 

 water is best illustrated by numerical examole. It is assumed that a 

 breaktrater is to be constructed in sea water in a depth of 30 feet. The 

 stone available locally has a soecific gravity of 2.65. The quarry is 

 capable of producing adequate quantities of stone weighing as much as 15 

 tons, 



UOO. Referring to the methods of paragraphs 222 . , the wave height 

 at the structure's location, will be given by 



H = H^ (S ) ^^7T- (1U9) 







AssuiTie H = 17 , L = I8I4, (T = 6), V b /b = O.8I1 and d = 30, d/L = O.I63, 



and from Table 1, Appendix D, d/L = 0,19U and H/H'^ = 0.913. Therefore, 

 from equation (li49), H = 13 feet. From Plates 7a and 12, Appendix D, stable 

 slopes for various stone weights may be fixed in the following manner. 



T/ 



voL 



E 30 - Computations for Stable 



Ab 



3ve Surface Sic 



3pes 















Slope 



1 on 3 

 1 on 2 

 1 on 1, 



5 



W/K' (Fig. 7a) 



3.3 X lo5 

 8.2 X 10? 

 2.7 X 10 



K' (Fig. 12) 



0.033 

 0.019 



0,015 





W (pounds ) 



11,000 

 15,600 

 UO, [iOO 



W (tons) 



5.5 

 7.8 



20,2 



Since l5-ton stone would be stable on a slooe somewhere betx^een 1 on 1.5 

 and 1 on 2, the slope of 1 on 1,75 will be chosen for this desipn. 

 (Further refinements may be calculated by use of the equation 



i.= 23hiul — . a^o) 



ri.09 cos Of - sin Of r (1.62)-^ 



and reference to Table l5) 



liOl, Sub-surface slopes m.ay be determined by substituting, for H 

 in equation (l50) for any depth, an hyoothetical wave height H' given by 



^ H ^ 



H' = r~^r^ — 



h ^^^ -IT (151) 



in which H is deterrflined by extending equation (II4.9) to points over the 

 breakinrater slope. Starting at depth 13 (one wave height below the surface) 



19h 



