3. Other Forms of Plastics Used in Coastal Structures . 



a. Flexible Forms for Concrete . High strength fabric such as nylon may- 

 be used in conjunction with concrete to control erosion. To form slabs, the 

 fabric is put down as a double layer along a bank or shoreline and acts as a 

 mold form for concrete that is injected into it. Figure 83 shows two types 

 of double layer fabric forms. Figure 84 shows installation of a concrete 

 filled form. 



FILTER POINTS 



CONCRETE FILLER 



Figure 83. Two types of double layer fabric forms 

 (courtesy of Fabriform) . 



Grout-filled fabric tubes may be arranged in various configurations 

 along the shoreline. They are useful as groins, dikes, breakwaters or 

 weirs. Figure 85 shows an arrangement of tubes and a filling point. 

 Figure 86 shows the use of fabric pillows as concrete forms for erosion 

 control. Koerner and Welsh (1980) give examples of slab and tube forms. 



b. Sheet Forms . Synthetic sheet materials made of polyethylene, vinyl 

 or rubber are used as linings and as covers for controlling water seepage 

 and preventing pollution. These liner-type materials may be bonded together 

 to form a large continuous sheet. As such it is useful in lining storage 

 ponds or pits where coastal pollution is a problem. Synthetic sheet materials 

 are also utilized in harbors to control and to clean up oil spills. Flexible 

 plastic sheeting is held between floats so that it passes through the surface 

 layer as a pollution dike (Fig. 87). The polluting material is retained 

 within the flexible floating dike. Such diked areas can be set up in advance 

 of operations that might result in a spill. For example, the regular off- 

 loading of oil at a cargo terminal would require that a containment boom be 

 on standby or deployed in a particularly environmentally sensitive location. 

 The confined retained pollutant can then be cleaned up by a simple surface 

 skimming operation. 



c. Molded Forms. 



(1) Guards and Rubbing Strips . Fenders or guards are frequently 

 fabricated from rubber and high strength synthetic plastics or plastic- 

 fabric combinations. Examples of these structures are illustrated in 

 Figure 88. 



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