The equation relating the moments is, 



K = (l-^m) M (7-74) 



where MV is the moment about the bottom (point A on Figure 7-73). 

 Usually, the moment desired is that about point B which may be found 

 from 



m; 



1-r^) M-b (l-ryr)F 



(7-75) 



K = K~ bF" 



The values of (1 - r ) and (1 - rj may be obtained directly from 

 Figure 7-72. 



Crest of Clapotis 



Figure 7-73. Wall on Rubble Foundation - Pressure Distribution 

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

 GIVEN : 



(a) A smooth-faced vertical wall on a rubble base. 



(b) Height of rubble foundation, b = 9 ft. 



(c) Incident wave height. Hi = 5 ft. 



(d) Design depth at the structure, d = 10 ft. 



(e) Wave period, 



T = 6 sec. (minimum), T = 10 sec. (maximum) 



7-143 



