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Review of Blasting Operations at Robinson Brick Company's Siloam Clay Mint <br /> Near field damage can be estimated by applying the findings from several carefully controlled <br /> blast-induced rock damage studies. Researchers have used many different measuring techniques to <br /> predict the rock damage zone—Cracking Radius (CR) is based on the radius (Ro) of longitudinal <br /> explosive charges. These studies have used core logs, borehole periscopes, permeability tests and <br /> various other measures to determine the extent of blast damage. <br /> Results from carefully controlled and documented blast damage studies by the U.S. Bureau of <br /> mines (RI 7901, 1983), and Butkovitch & Hearst (1976) indicate that the extent of localized <br /> blasthole damage in the form of radial cracking is generally a function of radial charge diameter, <br /> explosive type, and rock characteristics. It is important to note that the damage findings in RI <br /> 7901 are consistent with those of other researchers. In light of this correlation, it is reasonable to <br /> conclude that their damage prediction formula (CR = 20 to 26 Ra) can be used to predict the <br /> extent of rock rupture damage. <br /> Assuming the highest rupturing ratio (R = 26r), the blasting at the Siloam Clay Operation, using <br /> up to a 3 1/2-inch diameter charge, maximum rupturing would not extend more than 91 inches <br /> (7.6 ft) beyond the blastholes. To prevent any possibility of damage to the buried telephone lines, <br /> GEOTEK recommends that a minimum distance of 100 feet should be maintained between any <br /> buried lines and the nearest blasthole. At this cautious distance, it is extremely unlikely that <br /> blasting or any other normal mining activities would cause any damage to buried utility lines. <br /> GEOTEK& Associates, Inc. Page I I January 99 <br />