and 



R = 236 kN/m (16,164 lb/ft) 

 m ' \ » 



The resulting maximum pressure is about the same as for the wall on a 1:20 

 sloping beach (p^ = 336 kN/m); however, the dynamic force is less against 

 the wall on a 1:100 slope than against the wall on a 1:20 slope, because the 

 maximum possible breaker height reaching the wall is lower on a flatter 

 slope. 



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



b. Wall On a Rubble Foundation . The dynamic component of breaking wave 

 force on a vertical wall built on a rubble substructure can be estimated with 

 either equation (7-85) or Figure 7-101. The procedure for calculating forces 

 and moments is similar to that outlined in the Example Problem 34, except that 

 the ratio ^ /D is used instead of the nearshore slope when using Figure 

 7-101. Minikin's equation was originally derived for breakwaters of this 

 type. For expensive structures, hydraulic models should be used to evaluate 

 forces . 



c. Wall of Low Height . When the top of a structure is lower than the 

 crest of the design breaker, the dynamic and hydrostatic components of wave 

 force and overturning moment can be corrected by using Figures 7-102 and 

 7-103. Figure 7-102 is a Minikin force reduction factor to be applied to the 

 dynamic component of the breaking wave force equation 



R' = r R 



m mm 



(7-91) 



Figure 7-103 gives a moment reduction factor a for use in the equation 



M' = d R - [d + a] fl - r 1 R (7-92) 



m 6 m ^ s ^ ^ rrf' m 



or 



M' = R fr (d + a) - al 

 m m \m s \ 



(7-93) 



*************** EXAMPLE PROBLEM 35 ************** 

 GIVEN: 



(a) A vertical wall 3 m (10 ft) high in a water depth of d = 2.5 m (8.2 

 ft) on a nearshore slope of 1:20 (m = 0.05); 



(b) Design wave periods of T = 6 s and = 10 s . 



FIND : The reduced force and overturning moment because of the reduced wall 

 height. 



SOLUTION : Calculations of the breaker heights, unreduced forces, and moments 

 are given in preceding example problems. From the preceding problems, 



IL = 2.8 m (9.2 ft) (d = 3.0 m > d ] 



7-187 



