Figure 1. Coral riprap in Kosrae, Micronesia (photo 

 courtesy of Woodward-Clyde Consultants) . 



crusher run fines or unclassified waste from production of riprap, are used 

 for fill. Miscellaneous soil, rock and rubble fills may be used as random 

 or temporary shore protection (Fig. 2). 



c. Rockfill . Sound rock is ideal for producing rockfill materials. 

 Some weathered or weak rocks, including sandstones and cemented shales (but 

 not clay shales), may also be suitable (U.S. Army, Corps of Engineers, 

 1971b) . Rocks or stones that break down to fine sizes during blasting, 

 excavation, placement, or compaction are unsuitable as rockfill; such 

 materials should be treated as soils. Processing by passing rockfill 

 materials over a grizzly may be required to remove excess fine sizes or 

 oversize material. Quarry-run and quarry-waste materials are commonly used 

 as core materials for breakwaters and jetties. This material should be 

 reasonably well graded and no skip grading or scalping of certain sizes 

 should be allowed. The material should also generally contain no more than 

 5 to 10 percent fines. 



d. Riprap . Riprap is generally heavy irregular fragments of broken 

 stone or other resistant substances, well-graded within wide size limits, 

 and randomly placed without mortar to provide protection for an embankment 

 or bluff toe from the physical erosive action of water. The stability of 

 the stone layer depends on the density and mass of the stones, and on the 

 evenness of their gradation. The stability increases as the stones become 

 more well graded. This means that, for riprap of small stones, finer 

 material is included in the gradation, making voids smaller, the face 

 smoother, and wave reflectance higher. As long as the physical require- 

 ments for stone are fulfilled, any type of rock may be used for riprap; 

 chemical and mineral composition of the rock is generally of minor 

 importance . 



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