terrain is almost flat, it is necessary to ramp down into the rock creating 

 a pit that is entirely below the surface of the surrounding terrain. 



The height of the quarry face may be determined by the thickness of the 

 formation. However, since most formations being mined exceed the practical 

 limits of bench heights, the determining factor in the choice of bench 

 heights is usually that of safety. Bench heights must be selected to be 

 compatible with the loading equipment so that the broken rock can be safely 

 removed from the muck pile. If a single piece of loading equipment, such 

 as a shovel or front-end loader, is incapable of reaching high enough to 

 remove all unstable rock from the broken bench face, then it is customary 

 to use a dozer to work the rock down to a safe height for the loader. The 

 use of the proper blast design will result in the utilization of the 

 maximum safe bench heights and the optimum use of loading equipment. 



A somewhat special method used in quarry development is called "Coyote 

 Tunneling." This is a method in which tunnels are excavated into a bluff 

 or hillside and partially filled with explosives. In a crude sense, they 

 might be considered large-diameter horizontal boreholes, with the additional 

 option of turning corners or excavating "tee" sections. With this method, 

 it is extremely important that the natural jointing characteristics of the 

 rock have the capability of producing the desired material, since there is 

 relatively limited additional fragmentation by this blasting method itself. 

 The method is economically attractive if there is a vertical or steep rock 

 face and the rock has the desired jointing characteristics. For example, 

 it has proved to be very successful for producing riprap in columnar 

 basalts, and for producing crusher feed in diced basalts. 



Dimension stone quarries may be developed in some formations such as 

 sandstone, marble, or granite. Drill holes are generally spaced close 

 together along the desired break line and small charges of blasting powder 

 are used in these quarries. The purpose is to move a block of stone a 

 short distance in one piece without any damaging cracks. 



b. Blast Design. In general, the blasting method is determined by the 

 geology of the material to be broken, the fragmentation required, the hole 

 diameter, and the type of explosive. The type of equipment available for 

 handling and loading should also be taken into consideration (e.g., in 

 determining bench height) . 



(1) Geology. The geological and physical characteristics of the 

 material to be broken are the most important factors in determining the end- 

 product stone size and the overall blast design. There are at least a half 

 dozen or more factors reported by researchers as being related to the manner 

 in which rock is fragmented under the action of explosives. These include 

 such factors as the maximum sonic velocity, the minimum sonic velocity, the 

 ratio of these two (the sonic anisotropy), the lowest tensile strength, the 

 specific gravity, and the number of joints intersecting a blasting round. 

 Factors such as hardness and brittleness may also be included, but these are 

 related to those previously mentioned. At least a part of these properties 

 are measured or estimated in a typical site investigation for a quarry. 

 Even the most cursory of quarry investigations will provide an estimate of 

 rock quality and jointing. In turn, rock quality and jointing are probably 

 the two most important factors used in preliminary design of blasting 



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