structure. Once the core material was in place, it was sprayed with a 

 low-velocity water hose to ensure adequate compaction of the material. The 

 underlayer stone was then added by shovel and smoothed to grade by hand or 

 with trowels. No excessive pressure or compaction was applied during place- 

 ment of the underlayer stone. Armor units used in the cover layers were 

 placed in a random manner corresponding to work performed by a general coastal 

 contractor; i.e., they were individually placed but were laid down without 

 special orientation or fitting. After each test series the armor units were 

 removed from the breakwater, all of the underlayer stones were replaced to the 

 grade of the original test section, and the armor was replaced. 

 Selection of critically breaking waves 



7. For the given wave period and water depth, the most detrimental 

 breaking wave (i.e., the most damaging wave) was determined by increasing the 

 stroke adjustment on the wave generator in small increments and observing 

 which wave produced the most severe breaking wave condition on the experimen- 

 tal structures. Wave heights of lower amplitude did not form the critical 

 breaking wave and wave heights of larger amplitude would break seaward of the 

 test structures and dissipate their energy so that they were less damaging 

 than the critically tuned wave. 



8. A typical stability test series consisted of subjecting the test 

 sections to attack by waves of given heights and periods until all damage had 

 abated or the structures failed. Test sections were subjected to wave attack 

 in approximately 30-sec intervals between which the wave generator was stopped 

 and the waves were allowed to decay to zero height. This procedure was neces- 

 sary to prevent the structures from being subjected to an undefined wave sys- 

 tem created by reflections from the experimental breakwater and wave genera- 

 tor. Newly built test sections were subjected to a short duration (five or 

 six 30-sec intervals) of shakedown by using a wave equal in height to about 

 one-half of the design wave. This procedure provided a means of allowing con- 

 solidation and armor unit seating that would normally occur during prototype 

 construction. 



Method of determining damage 



9. In order to evaluate and compare breakwater stability test results, 

 it is necessary to quantify the changes that have taken place in a given 

 structure during attack by waves of specified characteristics. The US Army 

 Engineer Waterways Experiment Station (WES) developed a method of measuring 



