explosive. Its low brisance is compensated for by its high gas volume. 

 Hence, it is capable of producing as much work as some of the more expensive 

 brisant explosives. 



The majority of blast-induced fractures produced in the rock are radial 

 from the charge location, and are associated primarily with the propagating 

 stress waves (duPont de Nemours and Lo, 1977). Spalling at the bench face 

 from reflected stress waves produces very little fragmentation with the 

 burdens normally used under typical field conditions. Thus, it is apparent 

 that the inherent fracture planes in the rock are important and should be 

 considered in determining the fragmentation; hence, they should also be 

 considered in determining the blast design. If the inherent fracture 

 planes are closely spaced, the material can be broken more easily and with 

 larger diameter holes at greater spacing. 



Production of large stones is usually a more difficult problem than 

 production of crusher feed. If the rock is overblasted, and the particles 

 are too small, there is no way, of course, to make them larger. However, 

 if rock sizes are too large, it is at least physically possible to break 

 them to smaller sizes, although at greater cost. For the production of 

 large stone, it is customary to detonate simultaneously a row of holes 

 behind an open face, using relatively light charges. 



c. Loading Equipment . The degree of fragmentation required is also 

 related to the type and size of the loading equipment, and the size and type 

 of crusher available. Obviously, larger equipment can tolerate larger rock 

 fragments. However, the main advantage of larger equipment is its ability to 

 handle a larger volume of material, not simply larger particles. It is poor 

 economy to use larger blast-hole spacings and burdens to produce larger rock 

 sizes because large loading equipment has been acquired. Under these circum- 

 stances, the loading and crushing equipment is not being utilized to its 

 maximum capabilities. It is much less expensive to do more work with explo- 

 sives. Of course, if the needed product is large-size stone, such as riprap, 

 it is essential to have equipment capable of handling it. 



d. Processing of Materials . The properties and quantities of the 

 various types of materials are not only dependent on the onsite geological 

 conditions, but also on the construction procedures; therefore, it is 

 imperative that suitable processing methods be used in the quarry operation. 

 Further, it should be anticipated that variations and changes from the 

 anticipated geologic conditions in the quarry may occur and methods of 

 construction may vary. 



The large number of material types generally obtained from a quarry 

 require separating materials into various sizes and gradations. Very large 

 material, up to 267 kilonewtons (30 short tons), may require special equip- 

 ment. It is anticipated that large stone material, e.g., 1- to 8-ton 

 stone, will be separated by the excavating equipment. The material larger 

 than 0.6 meter (24 inches) and smaller than 38 millimeters (1.5 inches) is 

 generally removed and separated by some type of screening process. Removal 

 of fines (material passing a No. 200 mesh sieve) may require some type of 

 washing process. The various operations could have a significant effect on 

 the material gradation and generation of fines which would ultimately 

 affect the available quantity of some of the material types. It is there- 



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