PART V: DISCUSSION 



34. Both the toe berm stone and buttressing stone addressed herein are 

 required when designing for a high-energy wave environment. When either toe 

 buttressing stone or toe berm stone is used on a structure being constructed 

 on erodible bottom material, adequate thicknesses and gradations of filter or 

 bedding layers need to be incorporated into the design to prevent the leaching 

 of foundation material. Failure to prevent leaching could result in the 

 ultimate failure of the entire structure. 



35. During conduct of the 2-D toe berm stone tests, damage measurements 

 were made by observation for a range of H/H D . During some tests, the toe 

 berm stone design wave would be reached prior to reaching the maximum wave 

 that could be created in the test flume with the IV on 10H foreslope and at 

 the selected wave period and water depth. By extending the tests to condi- 

 tions which exceeded the design level, general data on damage related to 

 extreme wave heights (wave heights which exceed the design height) were 

 obtained. These data are presented in Figures 18-20. Figure 18 presents 

 percentage of berm armor stone showing in-place rocking as a function of 



H/H D . The percentage of toe berm armor stone displaced from its original 

 position is plotted against H/H D in Figure 19. The percentages of berm 

 armor stone rocking in place and displaced at a given value of H/H D were 

 summed for each test and are presented in Figure 20. 



36. Although it is not recommended, it is understood that there are 

 occasions when a designer is forced by economic constraints or other consid- 

 erations to design for a lower wave environment and accept the damage and 

 resulting maintenance costs that will occur due to damage accrued at larger 

 wave conditions. Figures 18-20 have been included to provide some insight 

 into what has become known as "designing for damage" . The "upper limit damage 

 line" in Figure 20 could be used for making rough predictions of possible 

 damage that could occur for H/H D range of 1.0 to 1.3. The upper limit 

 damage line is essential due to the large scatter associated with data points 

 over this range of H/H D . An example of how to use this upper limit damage 

 line is in the following paragraph. 



37. Maximum depth- limited breaking wave height that could occur at the 

 structure toe equals 13 ft, but economics requires a design wave height of 



10 ft be used. Thus, it is possible to get a wave condition at the site which 



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