concrete as well as its stability and resistance to the environment make 

 it an ideal coastal zone construction material. However, concrete being a 

 relatively heavy material is limited in its use where its heavy weight may 

 be a deterrent . 



In addition to structures constructed totally of concrete, many concrete 

 structural elements are used in a variety of coastal projects, such as 

 armor units of various shapes and size, concrete caissons, solid and 

 perforated blocks, sheet and bearing piles, and beams and slabs. Floating 

 structures such as caissons, barges, and pontoons have been successfully 

 built and used. Concrete is also used unreinforced in mass structures. 

 Reinforced and prestressed units are usually precast structure elements. 



b. Seawalls, Bulkheads, and Revetments . Seawalls, bulkheads and 

 revetments are distinguished by purpose. In general, seawalls are the most 

 massive of the three structures, because they resist the force of the 

 waves. Bulkheads are next in size. Their function is to retain fill; they 

 are generally not exposed to severe wave action. Revetments are the 

 lightest, because they are designed to protect shorelines against erosion 

 by currents or light wave action. 



(1) Seawalls . A curved-face seawall and a combination stepped and 

 curved-face seawall are usually massive structures which are built to 

 resist high wave action and reduce scour. Figure 24 shows an example of 

 reinforced concrete curved surface seawall. The stepped seawall was 

 designed for stability against moderate waves. 



(2) Bulkheads . Concrete bulkheads can take virtually- any form or 

 configuration required for the intended use and location. 



(3) Revetments . Structural types of revetments used for coastal 

 protection in exposed and sheltered areas are illustrated in Figures 25, 

 26, and 27. There are two types of revetments: the rigid, cast-in-place 

 concrete type (Fig. 25) and the flexible or articulated armor unit type 

 (Figs. 26 and 27). A rigid concrete revetment provides excellent bank 

 protection, but the site must be dewatered during construction to pour the 

 concrete. A flexible structure also provides excellent bank protection, 

 and can tolerate minor consolidation or settlement without structural 

 failure. The articulated block structure in Figure 27 allows for the 

 relief of hydrostatic uplift pressure generated by wave action. 



Interlocking concrete blocks have been used extensively for shore pro- 

 tection in the Netherlands and England, and have become popular in the 

 United States. Typical blocks are generally square slabs with shiplap-type 

 interlocking joints (Fig. 27). The joint of the shiplap type provides a 

 mechanical interlock with adjacent blocks. Stability of an interlocking 

 concrete block depends largely on the type of mechanical interlock. Concrete 

 piles are sometimes used as cutoff walls for revetments and seawalls. 

 Concrete foundation piles are sometimes used to support seawalls and other 

 massive concrete structures, such as caisson breakwaters. 



c. Groins . Concrete groins are built of concrete sheet piles or king 

 piles and panels if they are impermeable. The piles are usually prestressed 

 units and tied together with a cast-in-place concrete cap. If greater pile 



148 



