Il86o structure Design . - The ru.bble-stone groin is designed without 

 regard to differential ground lines except to be certain that the shore 

 end is carried far enough inshore to insure that the structure will not 

 be flanked. Should one side scour, the stones in the groin will settle 

 and readjust themselves » Should settlement prove excessive, s csne mainten- 

 ance may be ret^ired. In some instances the width of the groin may be 

 determined by construction methods, and in other instances may be determined 

 by the size of capstone required. 



USYq Stone Sizes On Side and End Slopes. - Assume, in this case, 

 that the specific gravity of the stone is 2,70. A 10-second wave has a 

 deep water wave length of 5l2 feet. At a depth d of 9 feet, d/L = 9/512 » 

 0,0176 and from Table 1, Appendix D, d/l ^O.O^li, Referring to p?ate 12 

 of Appendix D, with d/L = O.O^li and a slope of 1 on 1,5> an ext ranolated 1 

 on l«5i slone curve gives for K' approximately K' = 0.03. Blate 9b Appendix 

 D gives for ¥/K' under a 7 foot wave attack, w/K' = li x 10^, aid under 

 a 3.2 foot wave attack ¥/K» = 3.7 x 10^, With K' = 0.03 the stable stone 

 weights for the 7 and 3.2 fiSot wave heights are approximately 6 tons and 

 0.55 tons respectively, 



Il88, The stone dimensions determined for a slope of 1 on 1,5 would 

 seem reasonable to obtain from most quarries. However, should stone as 

 large as 6 tons not be available, a flatter end slope could be tried. 

 To allow for ravelling and settlement at the end of the groin, the sea- 

 ward 25 feet (minimum) should be constructed with stone of 6 tons minimum 

 size on side slopes and top. Smaller stone, well graded to form sand 

 tight core should be used inside the armor or capstone. Landward of this 

 end section, the stone cao and slooe stone should b e as large as the (tjuarry 

 will economically produce with a minimum size of 0.55 ton. A typical groin 

 of this type is shov^m in Figure ll|.3« 



230 



