effects of the wave are felt, resulting in decreasing berm stone stability. 



23. The stability number exhibits a well defined trend of increasing 

 with increasing values of d x /d s (Plate 3) . This is an expected trend 

 because as the water depth over the berm decreases the berm stone becomes more 

 exposed to incident wave energy requiring larger stone weights to ensure wave 

 stability. This is the same trend shown by Brebner and Donnelly (1962). 



3-D Toe Berm Stone Tests 



24. Twenty-seven tests were conducted using four different head and 

 trunk designs exposed to 90-deg and oblique wave attack in the L-shaped wave 

 basin. Ten tests were conducted on one head and trunk design constructed in 

 the T-shaped wave basin. As mentioned earlier, the slope fronting the test 

 sections was steeper in the T-shaped wave basin than in the L-shaped test 

 facility. The toe berm on each test section was constructed using stones of 

 various weights in several areas (Figure 10) . The selection of stone weights 

 for testing was based on both incident wave and water level conditions and 

 placement location on the structure. For example, two to three larger stone 

 sizes might be used on the trunk which is exposed to 90-deg wave attack, while 

 berm areas on the head, which experienced less severe wave conditions, were 

 constructed with several smaller stone sizes. When a test section built in 

 this manner was exposed to one fixed wave and water level, it was probable 

 that some stone sizes would be large enough that no movement or in-place 

 rocking would be observed (oversized for the test condition) , while areas with 

 smaller stone would exhibit large amounts of displacement (undersized, for the 

 test condition) ; and an intermediate stone size would sustain little or no 

 displacement but would show some minor movement (correct stone size for the 

 test condition). By conducting tests in this manner, design data could be 

 obtained from a larger percentage of tests than would have been possible if 

 each test section were constructed with only one weight of berm stone. 

 Tables 4-6 list test conditions, nondimensional parameters, design wave height 

 and toe berm stone N s associated with trunk tests in the L-shaped wave 

 basin, head tests in the L-shaped wave basin, and trunk and head tests in the 

 T-shaped wave basin, respectively, from which toe berm design data were 

 gathered. 



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