blended with dried and preheated stones. Because of the special mixing 

 plant and equipment necessary, this material can be used only on large 

 projects. At Ijmuiden, specially designed 22-ton vehicles transported 

 the stone-asphalt mix to buckets of the same capacity. These buckets were 

 lifted by crane for placing the mix either above or under water. (See 

 Figure 6-69.) A specially designed plot system was used to ensure accurate 

 placement of the mix. Because large amounts were dumped at one time, cool- 

 ing was slow, and successive batches flowed together to form one monolithic 

 revetment . 



Extension of the breakwaters started in 1964. By the completion of 

 the project in 1967, about 1 million tons of stone asphalt had been used. 



To date regular maintenance has been required to deal with settle- 

 ments in the stone-asphalt revetment, especially during the summer, but 

 it is expected that a steadily decreasing amount of maintenance will be 

 required. 



6.813 Cellular Steel Sheet-Pile Breakwaters . These breakwaters have 

 been used where storm waves are not too severe. The shores of the Great 

 Lakes have moderately high wave exposure. A cellar steel sheet-pile and 

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

 illustrated in Figure 6-70. 



Cellular steel sheet-pile structures require little maintenance and 

 are suitable for construction in depths up to about 40 feet and into 

 various types of sedimentary foundations. Steel sheet-pile structures 

 have advantages of economy and speed of construction, but are vulnerable 

 to storm damage during construction. Corrosion is the principal dis- 

 advantage of steel in sea water. 



6.814 Concrete Caisson Breakwaters . Breakwaters of this type are built 

 of reinforced concrete shells, that are floate4 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 6-71 illustrates the patented perforated type of caisson break- 

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

 1963), utilizes the caisson as a wharf on the harbor side. The holes or 

 perforations on the seaward side reduce the undesirable conditions of a 

 smooth vertical face wall (wave overtopping and wave reflection) by partly 

 dissipating the wave energy within the wave chamber (Marks, 1967), (Marks 

 and Jarlan, 1969), (Terrett, et al., 1969), (Richey and Sollitt, 1969.) 



6-93 



