and concrete caissons have been used. Figures 6-67 through 6-70 illus- 

 trate stXTictural types of shore-connected breakwaters used for harbor 

 protection. 



6.811 Rubble-Mound Breakwaters . The rubble-mound breakwaters in Figures 

 6-67 and 6-68 are adaptable to almost any depth, and can be designed to 

 withstand severe waves. 



Figure 6-67 illustrates the first use in the U.S. of tetrapod armor 

 units. The Crescent City, California, Breakwater was extended in 1957 

 using two layers of 25-ton tetrapods. (Deignan, 1959.) 



Figure 6-68 illustrates the use of tribar armor units on a rubble- 

 mound structure. The 18-ton tribars were used to rehabilitate the 2,150- 

 foot Nawiliwili breakwater in 1959. (Palmer, 1960.) In 1965, 35- and 

 50-ton tribars were used in the repair of the East Breakwater at Kahului, 

 Hawaii. 



6.812 Stone-Asphalt Breakwaters . (Kerkhoven, 1965 and Asphalt Institute, 

 1969). At Ijmuiden, the entrance to the port of Amsterdam, The Netherlands, 

 the existing breakwaters were extended in 1964 to provide better protection 

 and enable larger ships to enter the port. (See Figure 6-69.) The southern 

 breakwater was extended 6,890 feet, and now projects 8,340 feet into the 

 open sea to a depth of about 60 feet. These breakwaters had to be heavily 

 protected to withstand wave attack. The Rijkswaterstaat (a government 

 agency of The Netherlands) decided to construct rubble breakwaters in the 

 open sea with a core of heavy stone blocks weighing 660 to 2,200 pounds. 

 Since such blocks were not heavy enough to be stable against prevailing 

 wave attack, a protective cover was needed. Application of a normal sand 

 mastic grouting of the stone core was not possible because the dimensions 



of the stones and consequently the interstices were too large. A new 

 material called stone-asphalt was developed to protect the stone core. 



The stone-asphalt contained 60 to 80 percent by weight stones 2 to 

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

 with a maximum stone size of 2 inches. The stone-asphalt mix was pourable 

 and required no compaction. 



During construction the stone core was protected with about 1 ton of 

 stone-asphalt grout per square yard of surface area. For this application 

 the composition was modified, so that it was possible to obtain some pene- 

 tration into the surface layer of the stone core. This stone-asphalt grout 

 was effective and demonstrated the outstanding properties of this material 

 for protection against wave attack. 



The final protection of the stone core was a layer or revetment of 

 stone asphalt about 7 feet thick. The structure side slopes are 1 on 2 

 above water and 1 on 1.75 under water. (See Figure 6-69.) 



The stone-asphalt was manufactured by a double mixing procedure. An 

 asphaltic concrete type of mix was made in a normal hot mix plant and then 



6-89 



