individual armor stone is roughly inversely proportional to its density. 

 This flexibility of size versus density of stone permits some latitude in 

 choice between two quarry sites. Stones larger than about 223 to 267 

 kilonewtons (26.1 to 30.0 short tons) are generally not easily handled. 

 The greatest dimension of each individual large stone should be no greater 

 than three times the least dimension. 



The reverse of this size-density factor can be used for a more efficient 

 consideration of choice of rock source for core and underlayers where 

 density is not a critical design consideration. Frequently a savings in 

 cost can be affected by bidding the armor stone in tons and the underlying 

 stone in solid cubic yards. Underlayers placed beneath the armor units 

 should be an adequate size to prevent withdrawal of the units through the 

 interstices of the cover layer and to prevent excess movement and subsequent 

 breakage. The weight of underlayer stone may range from 3 to more than 30 

 kilonewtons. 



The most frequently used core is of a quarry- run material, the gradation 

 of which is governed by economics or by the desired degree of imperme- 

 ability. A rubble structure may also need protection from settlement 

 (resulting from leaching, piping, undermining, or scour) by use of a bedding 

 layer or blanket. The gradation requirements of a bedding layer depend 

 primarily on the littoral chracteristics in the area and on the foundation 

 conditions. However, quarry spoil, ranging in size from about 4 newtons (1 

 pound) to about 220 newtons (50 pounds), will generally suffice. 



Typical classifications from the State of California Standard Specifica- 

 tions for rock slope protection are shown in Table 1 (California Department 

 of Public Works, 1960). The weights by which the classes are designated do 

 not necessarily correspond to the weights called for by the various design 

 formulas. For example, if a shore protection formula, such as Hudson's 

 equation in the Shore Protection Manual (SPM) (U.S. Army, Corps of Engineers, 

 CERC, 1977), should call for 5-ton (44 kilonewton) armor stone, it may be 

 proper to use the 8-ton (71 kilonewton) class, as approximately 80 percent 

 of this class would be larger than 5 ton. For the same example, the SPM 

 suggests that for a cover layer with a two stone thickness, approximately 

 75 percent of the stones may be greater than 5 tons and the range should be 

 between approximately 3.75 and 6.25 tons (33.3 and 55.6 kilonewtons). 



c. Stone Shape . Stone block structures may be closely fitted seawalls, 

 groins, jetties, or breakwaters such as are built along the coasts of 

 Hawaii (Fig. 3), the Gulf of Mexico, and the Great Lakes. For these 

 structures the stone blocks should be rectangular and of sufficient uni- 

 formity in size and shape to be closely fitted together. These structures 

 depend on the close fitting of the armor stone and chinking or grouting to 

 prevent loss of the underlying rubble stone through the interstices of the 

 fitted armor stones. However, there must be sufficient space or openings 

 between the armor stones to relieve the hydrostatic uplift pressures that 

 occur during storm waves. 



Rounded stones, particulary for the armor layers, are to be avoided 

 whenever possible. They are difficult to place and are not stable, either 

 due to wave forces or their inherent instability on steep slopes. For 

 these reasons, field or streambed stone are generally not acceptable. 



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