Chapter 8 

 SUMMARY AND CONCLUSIONS 



This thesis addresses depth-limited breaking wave damage on rubble mound 

 breakwaters. Chapters 1-3 are introductory. Chapter 1 introduces the topic of rubble 

 mound structures and their failure modes. It is noted that deterioration models are 

 required for risk and reliability analyses as part of rehabilitation studies for these 

 structures. 



Chapter 2 discusses a new experiment conducted to investigate incipient 

 motion of stone armor units in depth-limited breaking waves. Observations were made 

 of incipient motion on both stone and sphere armor layers. Velocity measurements were 

 made during these experiments both inside and just outside the armor layer using a laser 

 Doppler velocimeter. It is shown that the maximum vertical convective acceleration 

 across the armor layer is proportional to the square of the maximum vertical velocity. 

 Equation 2.1 1, an incipient motion criterion similar to the Shields criterion for sediment 

 motion, is derived based on Morison forcing for the dominant mode of motion: vertical 

 lift under the steep breaking-wave face. Equation 2. 1 1 is restated in terms of the 

 stability number as Equation 2.12 as follows 



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