Figure 28. Fabric tubes filled with concrete form a jetty 

 (photo courtesy of Fabriform) . 



used to rehabilitate the seaward end of the Humboldt Bay jetties against 

 12-meter (40 foot) breaking waves (Magoon and Shimizu, 1971) . 



(1) Concrete Caisson Breakwater. Breakwaters of this type are 

 built of reinforced concrete shells that are floated into position, settled 

 on a prepared foundation, filled with stone or sand for stability, and then 

 capped with concrete or stones. These structures may be constructed with 

 or without parapet walls for protection against wave overtopping. In 

 general, concrete caissons have a reinforced concrete bottom, although 

 open-bottom concrete caissons have been used. The open-bottom type is 

 closed with a temporary wooden bottom that is removed after the caisson is 

 placed on the foundation. The stone used to fill the compartments combines 

 with the foundation material to provide additional resistance against 

 horizontal movement. 



Figure 31 illustrates a patented perforated type of caisson breakwater 

 (Jarlan, 1961). The installation at Baie Comeau, Quebec (Stevenston, 

 1963), utilized the caisson as a wharf on the harborside. The holes or 

 perforations on the seaward side reduce the undesirable conditions of a 

 smooth vertical face wall and are an illustration of complex structural 

 shapes possible because of the way concrete is cast. 



(2) Concrete Armor Units. Many different concrete shapes have 

 been developed as armor units for rubble structures. The major advantage 

 of concrete armor units is that they usually have a higher stability 

 coefficient value, thus permitting the use of steeper structure side 

 slopes or a lighter weight of armor unit. This property is especially 

 valuable when quarrystone of the required size is not available. 



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