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



*************** 



GIVEN: The elevation at the toe of a vertical wall is 2 feet above the 

 mean lower low water (MLLW) datum. Mean higher high water (MHHW) is 

 4.3 feet above MLLW and the beach slope is 1:20. Breaker height is 

 H, = 9.0 ft., wave period is T = 6 sec. 



FIND : 



(a) The total force and moment if the SWL is at MHHW. 

 (Wall seaward of Stillwater line.) 



(b) The total force and moment if the SWL is at MLLW. 

 (Wall landward of Stillwater line.) 



SOLUTION : 



(a) The breaking depth d, can be found from Figure 7-2. Calculate, 



H, 



9.0 



, = 0.0078 , 

 gT^ 32.2 (6)2 



and the beach slope, 



1 

 m = tan |3 = — = 0.05 . 

 20 



Enter Figure 7-2 with Hj^/gT'^ = 0.0078 and using the curve for 

 ra = 0.05, read. 



= 1.10 , 



Therefore, 



dy = 1.10 Hj, = 1.10(9.0) = 9.9 ft. 



From Equation 7-86, 



h^ = 0.78 Hj, = 0.78(9.0) =7.02 ft. 



The dynamic force component from Equation 7-87 is 



wdfeh 64 (9.9) (7.02) „ . 



R = = — ^^ — = 2,200 Ibs./ft. 



'"2 2 



and the moment from Equation 7-88 is 



L \\ I 7.02\ lb .-ft. 



Mn. = Rm \^s+^) = 2.200 ^2.3 + —j = 12,900 -^ 



7-162 



