a. Rubble-Mound Breakwate rs . The rubble-mound breakwaters in Figures 

 6-63 and 6-64 are adaptable to almost any depth and can be designed to with- 

 stand severe waves. 



Figure 6-63 illustrates the first use in the United States of tetrapod 

 armor units. The Crescent City, California, breakwater was extended in 1957 

 using two layers of 22.6-metric ton (25-short ton) tetrapods (Deignan, 

 1959). In 1965, 31.7- and 45.4-metric ton (35- and 50-short ton) tribars were 

 used to repair the east breakwater at Kahului , Hawaii (Fig. 6-64). 



b. Stone-A sphalt Breakwaters. In 1964 at Ijmuiden, the entrance to the 

 Port of Amsterdam, The Netherlands, the existing breakwaters were extended to 

 provide better protection and enable passage for larger ships. The southern 

 breakwater was extended 2100 meters (6,890 feet) to project 2540 meters (8,340 

 feet) into the sea at a depth of about 18 meters. Then rubble breakwaters 

 were constructed in the sea with a core of heavy stone blocks, weighing 300 to 

 900 kilograms (660 to 2,000 pounds), using the newly developed material at 

 that time, stone asphalt, to protect against wave attack. 



The stone asphalt contained 60 to 80 percent by weight stones 5 to 50 



centimeters in size, and 20 to 40 percent by weight asphaltic-concrete mix 



with a maximum stone size of 5 centimeters. The stone-asphalt mix was 

 pourable and required no compaction. 



During construction the stone core was protected with about 1.1 metric 

 tons of stone-asphalt grout per square meter (1 short ton per square yard) of 

 surface area. To accomplish this, the composition was modified to allow some 

 penetration into the surface layer of the stone core. The final protective 

 application was a layer or revetment of stone asphalt about 2 meters thick. 

 The structure side slopes are 1 on 2 above the water and 1 on 1.75 under the 

 water. Because large amounts were dumped at one time, cooling was slow, and 

 successive batches flowed together to form one monolithic armor layer. By the 

 completion of the project in 1967, about 0.9 million metric tons (1 million 

 short tons) of stone asphalt had been used. 



The requirements for a special mixing plant and special equipment will 

 limit the use of this material to large projects. In addition, this partic- 

 ular project has required regular maintenance to deal with the plastic-flow 

 problems of the stone asphalt caused by solar heating. 



c. Cel lular-Steel Sheet-Pile Breakwaters . These breakwaters are used 

 where storm waves are not too severe. A cellular-steel sheet-pile and steel 

 sheet-pile breakwater installation at Port Sanilac, Michigan, is illustrated 

 in Figure 6-65. Cellular structures provide a vertical wall and adjacent deep 

 water, which is usable for port activities if fendered. 



Cellular-steel sheet-pile structures require little maintenance and are 

 suitable for construction on various types of sedimentary foundations in 

 depths to 12 meters. Steel sheet-pile structures have advantages of economy 

 and speed of construction, but are vulnerable to storm damage during construc- 

 tion. Retention of cellular fill is absolutely critical to their stability. 

 Corrosion is the principal disadvantage of steel in seawater; however, new 

 corrosion-resistant steel sheet piles have overcome much of this problem. 

 Corrosion in the Great Lakes (freshwater) is not as severe a problem as in the 

 ocean coastal areas. 



6-92 



