While angularity is most desirable, the stones should be approximately- 

 rectangular in shape. For large stone, the greatest dimension should be no 

 greater than three times the least dimension. Sharp points should be 

 avoided as they may cause a stone to wobble or the point may break off 

 under stress, disturbing the stability of the section. Even if dislodged 

 or partially dislodged, an angular stone will tend to find a stable 

 position, whereas a rounded stone will tend to roll to the toe of the 

 structure. 



d. Specific Gravity . Required stone size is a function of the specific 

 gravity and, unless unreasonably low, specific gravity should not be a 

 limitation on its use. In fact, excellent results have been reported for 

 lava with a specific gravity of 1.5. Once the stone size has been selected 

 on the basis of a certain specific gravity, specifications should then 

 prohibit the use of stones with specific gravity appreciably lower. Low 

 density stone may be used in the core (and underlayers) , and high density 

 armor stone can be used, providing an adjustment is made in the thickness, 

 for the armor layer. Armor is generally priced by the ton. Core and 

 underlayer materials may be priced by volume to control the use of over- 

 weight stone in these zones. 



e. Absorption. There is a general correlation between absorption and 

 weathering. Use of the absorption test is more significant when the rock 

 is to be used in areas subject to freezing and thawing. A limit of 2- 

 percent absorption is reasonable. 



f. Soundness. Rocks that are laminated, fractured, porous, or other- 

 wise physically weak are subjected to a soundness test (use of sodium 

 sulphate) . Stones showing a loss of less than 5 percent should be satis- 

 factory. 



g. Abrasion. The Los Angeles rattler test and Wetshot rattler test 

 measure resistance to abrasion. Use of these tests is more significant 

 when the rock is to be used in shore protection where it is subjected to a 

 pounding surf carrying sand, gravel, and smaller stones. Stones having 

 relatively high losses in these tests have performed satisfactorily in 

 shore protection and therefore a rather lenient value is permissible. A 40- 

 percent maximum loss for the Wetshot rattler and 45 percent for the Los 

 Angeles rattler are considered reasonable. 



4 . Quarrying Methods . 



a. Quarry Development. Quarries produce most of the rock required for 

 construction in this country. In most quarries, all the material mined is 

 usually consumed as an end product. The size and quality of material 

 obtained from a quarry depend largely on the geology of the site and the 

 method of blasting (duPont de Nemours and Lo, 1977). Depending on the 

 area's topography, a quarry will generally be developed either as a side 

 hill or as a pit-type operation. Where the area is hilly and the rock 

 outcrops, the quarry will be developed by opening a face into the side of 

 the hill. The point of entry is usually at the bottom of the rock seam or 

 in a very thick seam. A convenient point should be chosen to provide an 

 almost level floor with just enough slope for natural drainage. When the 



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