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<br /> <br />Rocky Mountain Asphalt <br />January 20, 7989 <br />Page 2 <br />breaks the rock. The amount of explosive used is a function of the number, <br />size, depth, and spacing of the blast holes required to loosen a desired volume <br />of rock. <br />The blasting process imparts energy into the ground. Some of this energy <br />travels beyond the immediate blasting area in the form of vibrations. As the <br />vibrations move away from the blast, they tend to "attenuate" or lose energy. <br />As a result, the further a location of interest is from a given blast, the lower the <br />magnitude of vibrations tnat can be expected to reach the location. <br />The magnitude of blast vibrations Is typically measured In terms of "peak <br />particle velocity." However, the use of peak particle velocity alone to evaluate <br />potential for blasting-related problems is Insufficient. Research has found that <br />not only is the peak particle velocity important, but the frequency~(in terms of <br />Hertz or cycles per second) of the vibration must also be considered. As a <br />result, when evaluating a specific site, the vibration attenuation characteristics <br />of the rock must be considered for both vibrations and preferential adsorption . <br />of various vibration wave frequencies. <br />Damage to surface structures or underground openings cause by blast <br />vibrations normally requires relatively large peak particle velocities. However, <br />when dealing with facilities that are open to the public, physical damage is not <br />normally a limiting criteria The ability for humans to perceive or feel a blast <br />vibration, and, therefore, become "uncomfortable" In their surroundings is of <br />major concern. This "perception range" is probably the criteria of greater <br />importance to the mining operations at the Summit Pit and the Cave of the Winds. <br />Research • has been completed to evaluate the levels of human vibration <br />perception as a function of peak particle velocity for the range of vibration <br />frequencies normally observed during blasting. Blast vibrations in relatively <br />competent rock normally have a frequency of greater than 2 Hertz. Research has <br />shown that for transient (short-term) vibrations with a frequency of greater than <br />2 Hertz, the following perception criteria have been developed: <br />Schnabel Engineering <br />