also allowed the generation of 14 to 15 well -formed waves at a test per- 

 iod of 1.16 seconds. 



The wave heights referred to in this report are the significant wave 

 heights of the 14 or 15 well-formed waves in each burst. The significant 

 wave height is the average of the highest one-third of the waves in the 

 burst. This does not necessarily correspond to the significant height 

 in an ocean wave spectrum. Although the wave height was spot checked 

 during the stability tests, the actual wave heights used were obtained 

 from a previous calibration of the wave generator. Both the small and 

 large wave tanks were calibrated for wave heights using absorber beaches 

 at the location of the embankment toe. Therefore, the wave heights used 

 in this report represent the actual incident height at the embankment toe. 

 The wave height for each condition tested was predetermined by calibra- 

 ting the wave tank and running-in bursts. The location of the wave gages 

 used to spot check the wave height in the small tank is shown in Figure 1. 



The basic data in this study consisted of surveys of the embankment 

 taken after each run was completed. A run (series of bursts) continued 

 until the embankment slope had reached equilibrium at a particular wave 

 height; however, never less than 50 waves bursts (about 750 well-formed 

 waves) were considered sufficient to constitute a run. Normally, after 

 50 bursts the slope became stable, the run was terminated, and a survey 

 was taken. In the small wave tank the wave height was increased in incre- 

 ments of from 0.015 to 0.030 foot (4.6 to 9.1 millimeters) between runs. 



Tests S-1, S-2, and S-3 (Table 1) were used to establish the zero- 

 damage stability of the crushed bluestone which constituted the model 

 riprap layer without overlay, i.e., base condition. 



Tests S-4 to S-13 (Table 1) determined the stability characteristics 

 of armor stone overlay. The overlay stones were of two general types, 

 rounded boulders and angular Sioux quartzite quarrystone. Three sizes of 

 boulders were tested and designated 0.75 to 1 inch (19 to 25.4 millimeters) 

 1 to 1.5 inches (25.4 to 38.1 millimeters), and 1.5 to 2 inches (38.1 to 

 50.8 millimeters). Both the boulders and the quarrystone had a specific 

 gravity of 2.65. Details on the type of stone, stone size, and weight and 

 coverage fractions for the various tests are given in Table 1 . 



In test S-7 the wave generator was run continuously, as opposed to 

 wave bursts, for a fixed number of waves to see if continuous wave action 

 of less than design height could displace the riprap through the voids in 

 the armor overlay. 



Test S-14 was considered to be a conventional overlay test, in that 

 the overlay constituted a layer about two stones in diameter thick, rather 

 than 100- or 67-percent coverage of a single layer of stone on top of the 

 riprap. Kimmswick limestone quarrystone at a designated size of 1 to 1.5 

 inches was used for this test. The test was used as a reference for com- 

 parison with the overlay tests using considerably smaller coverage frac- 

 tions . 



Small tank tests photos of quarrystone and boulders having 100-percent 

 overlay and the boulders having 67-percent overlay are shown in Figures 

 2, 3, and 4. 



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