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2.1.1 Review of Blasting Vibration Phenomena: <br />When explosive charges detonate in rock, nearly all of the available energy is used in breaking and <br />displacing the rockmass. However, a small portion of the energy is released in the form ol~vibration <br />waves, which radiate away from blast charges. When these elastic strain-waves pass through rock <br />or earth, they cause an oscillating motion in the ground particles. <br />Abbreviations: <br />SH =Shear wave, horizontal <br />SV =Shear wave, vertical <br />R =Rayleigh wave <br />P =Compressional wave <br />~P <br />Wave EMeuY~~---_~ <br />SH <br />Figure 2. 1 -Vibration Waves <br />Seismic waves decay with distance as they travel through the surrounding area. These waves have <br />dillerent lorms, such ati body and surface waves. "Their characteristics will vary somewhat with <br />changes in local geology but the rate at which thry die out is reasonably consistent, and allows <br />regulatory agencies to control blasting operations by rncaus of relationships between distance and <br />the explosive charge quantities. Each time the distance is doubled, the vibration intensity drops to <br />about l/3 of its former value. "1'he consistency of ground motion attenuation is supported by <br />research done by U.S. Bureau of Mines (Nichols et al., 1979). The researchers found that under <br />widely varying conditions, if a scaled distance of 50-ft/Ih" 2 is used to limit charge weights, it is <br />highly unlikely that ground motion would cause an damage. For the purposes of ground vibration <br />assessments, scaled distance (SD) is distance from the blast divided <br />