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 under- 

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

 trowels. No excessive pressure or compaction was applied during placement 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 orien- 

 tation 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 a given wave period and water depth, the most detrimental break- 

 ing 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 experimental struc- 

 tures. 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 allowed to decay to zero height. This procedure was necessary 

 to prevent the structures from being subjected to an undefined wave system 

 created by reflections from the experimental breakwater and wave generator. 

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

 30-sec intervals) of shakedown using a wave equal in height to about one-half 

 of the design wave. This procedure provided a means of allowing consolidation 

 and armor unit seating simulating that which would normally occur during pro- 

 totype construction. 



Method of determining damage 



9. 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 the 



