Since the bearing capacity of the foundation is 2=000 pounds per square 

 foot J no piling woxild be required under these force conditions. 



29i;, Steel Sheet Pile Cellular Seawall.- A wall is to be placed in 

 a low bluff areaj to protect the bluff line from the action of storra 

 waveso The water depth at the toe of the wall is to be 3 feet below low 

 water datum. There is a maximum expected wind set-up of 2 feet. The 

 slope of the bottom seaward of the site of the wall is approximately 

 1 on iiO. The elevation of the top of 'the bluffs is about 10 feet above 

 low water datura. This would also be the elevation of the top of the 

 backfill. Wave analysis indicates that the maximum deep water wave height 

 expected is 10 feet, and that a wave this high will have a period of 

 12 seconds. The maximum refraction coefficient is 0,5v at a depth of 

 $0 feet, 



295 o The bottom is composed of a 2-foot thickness of gravel and 

 shale overlying bedrock. Because of poor penetration pOuS'sibilities^ 

 a sheet pile^ cellular type structure was chosen for design, 



296. The backfill material has a natural drained unit weight of 

 130 pounds per cubic foot and an internal friction angle of 25°, The 

 cell fill material (gravel) has a natural drained unit weight of 120 

 pounds per cubic foot and an internal friction angle of 14.5°.. The 

 coefficient of friction between the cell fi].l and the bottom is 0o5 = 



297, Wave Forces. - The deep water wave length of a 12=second 

 wave is Lq » SJTJl^ s 737 feet. At a depth of 50 feet d/Lo s 

 50/737 s 0«068, From Table 1 of Appendix D the corresponding d/L s 

 0.112 and H/H^ s 0.98. Therefore, the wave height in this depth of 

 water where the refraction coefficient is 0.5 for a wave 10 feet high 

 in deep water is 



H s Hq X k X (H/H«q) - 10 X 0.5 X 0,98 f 5 feet (70) 



From this equation,, k must be equal to (H'q/Hq) whtre H'q is the deep 

 water w^ave height which^ in the absence of refraction^, would give a 

 wave heights of H in a depth of 50 feet. This equivalent deep water wave 

 height H»o is 5 feet. 



298, A wave with deep water length of 737 feet and deep water 

 height of 5 feet will have a steepness of H«o/Lq =s 5/737 ^ 0,0O68. 

 From Plate 5^5, Appendix Dj the ratio d^/HQ s 2,0^ from which d^,, the 

 breaking depth^ is d)-, s 2,0 x 5 ^ 10 feet. The maximum anticipated 

 depth at the viall including tidal rise is 5 feetj which indicates that 

 waves will break before reaching the structure, and ihat the wave force 

 criteria for broken waves must be used for this deep water design wave, 



299. Forces Due to Broken Waves. - Referring to Plate Sh^„ Appendix 

 Dj H-b/Ho for a wave whose deep water steepness (Hq/Lq) =5 0,0068, moving 

 up a l^UO slope is Hi-,/Ho ==. 1.5. Therefore the breaking wave height 



is 7,5 feet, 



IL16 



