FIND: Determine the force and overturning moment on the given wall on 

 a rubble foundation. 



SOLUTION : For this example problem Figures 7-65 through 7-67 are used 

 to evaluate h , F and M even though a rubble base will reduce the 

 wave reflection coefficient of a structure by dissipating some incident 

 wave energy. Values of h , F, and M used in this example, have beei 

 determined in the example problem of Section 7.323, 



y^ = 18.5 ft. 



(T = 6 sec.) 

 y^ = 8.5 ft. 



Compute b/y for each case, remembering that b now represents the 

 height of the foundation. 



b 9.0 



— = = 0.486 



y^ 18.50 



(T = 6 sec.) 



b 9.0 



— = = 1.058 > 1.0 



y^ 8.50 



Enter Figure 7-72 with the computed values of b/y and determine 

 corresponding values of (1 - r^.) and (1 - r ) . For the 6-second 

 wave, 



b 



— = 0.486; (l-tyr) = 0.264 ;(l-r^) = 0.521 



and 



^>1.0; (1-r^) =0.0; (1 - r^ 



From Equation 7-73, 



F'' = 0.264 (8,000) = 2,100 Ibs./ft. 



0.0 



F" = 0.0 (1,860) = Ibs./ft. 

 For the 10-second wave, a similar analysis gives, 

 F" = 2,620 Ibs./ft. 



F;' ^ Ibs./ft. 

 The overturning moments about point A are, from Equation 7-74, 



(T = 6 sec.) 



(T = 10 sec.) 



, ,M Ib.-ft. 



M)c " ^-521 (45,900) = 23,900 — — 



(T - 6 sec.) 



, „, Ib.-ft. 



(M;;)^ = 0.0 (5,120) = — - 



7-144 



