discussed in detail in Callender and Eckert (in preparation, 1983). Soils 

 are used in coastal structures for backfill materials, core materials, slopes 

 and beach restoration. The use of the material is generally associated 

 with the type of development and the type of structure. The choice of 

 material depends on the economy and availability of the material, depth of 

 water, expected water or wave forces, and the purpose of the structure. 

 Some of the various uses are presented in the following paragraphs. 



b. Offshore Construction. 



(1) Breakwaters . In rubble-mound breakwaters, submerged reefs, 

 and other coastal rock structures, sand may be used as core material 

 providing other materials are used to protect against wave damage and 

 piping. Clay may be mixed with the sand to reduce permeability, but is 

 generally not adequate core material by itself. The structures may be 

 designed as permeable or impermeable. The soils are usually dredged 

 materials and are placed hydraulically. The core may be covered with 

 filter material and quarrystone riprap or armor units; the number of 

 covering layers depends on the water depth, the design storm waves, and the 

 desired degree of permeability. 



(2) Caissons . Concrete caissons and sheet-pile cells may be 

 filled with sand and clay. If the surface is to be paved and used for load 

 bearing, sand is preferable to clay because of its higher bearing capacity. 

 A filter layer and armor rock must be provided to cover the fine soils 

 where waves or water currents are expected to impinge on earthfill. 



c. Shore-Connected Construction. 



(1) Breakwaters, Jetties and Groins. These structures of rubble- 

 mound construction, caissons, or sheet-pile cells may be filled with soil 

 as described for offshore construction. 



(2) Low-Cost Shore Protection, Fabric Bags . Low- cost groins and 

 breakwaters have also been constructed by means of fabric bags filled with 

 medium sand or sand-cement. The bags are generally made of nylon, and may 

 be coated with polyvinyl chloride or acrylic to delay fiber degradation by 

 ultraviolet rays. The bags may be filled with available beach sand and 

 used as a low-cost shore protection device. The bags may be filled using a 

 19-millimeter diaphragm pump or, for more efficiency, a small front-end 

 loader, a hopper, and a jet pump. Typical filled bags measure approximately 

 3 by 1.5 by 0.5 meter (10 by 5 by 1.5 feet), hold about 1.9 cubic meters 

 (2.5 cubic yards) of sand, and weight about 31 kilonewtons (7 000 pounds). 

 The sand used should be saturated so as to eliminate air pockets which 

 would cause a buoyant force on the bags. Small bags filled with sand (Fig. 

 13) or concrete (Fig. 14) may be used for protection against erosion. 



(3) Bulkheads, Quaywalls, and Seawalls. Usually soil materials 

 are used as backfill or foundation materials for bulkheads and walls. 

 Their primary purpose is to provide a level surface or to fill a void 

 behind the structure. The materials can be placed from land, end-dumped 

 from trucks or conveyor belts, or they can be placed hydraulically from 

 dredges; however, the relative density achieved by each method may be 

 widely different. The backfill may be composed of a mixture of all or part 



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