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GEOTECHNICAL ENGINEERING 303-242-4220 <br /> MINING ENGINEERING <br /> 303-241-1270 <br /> NUCLEAR WASTE ISOLATION <br /> ENVIRONMENTAL ENGINEERING <br /> NUMERICAL MODELING <br /> J. F. T. AGAPTTO & ASSOCIATES, INC. <br /> CONSULTING GEOTECHNICAL AND MINING ENGINEERS <br /> 715 HORIZON DRIVE, SUITE 340 <br /> GRAND JUNCTION, COLORADO 81506 <br /> 112-3 <br /> August 15, 1988 <br /> Mr. Larry Petrino <br /> Chief Mining Engineer <br /> Sunnyside Mine <br /> Alta Gold <br /> Sunnyside Project <br /> P. O. Box 177 <br /> Silverton, CO 81433 <br /> Re: Modification of Blasting Practice to Enhance Pit Wall Stability <br /> This letter discusses potential modifications of the blasting practices that are being <br /> employed at the Sunnyside and Washington pits. Design of the most effective blast pattern is <br /> highly site specific due to geologic and operational variables, and we expect that the final blast <br /> design will be based upon direct experience and experimentation by your staff. However, based <br /> upon the description of current practice relayed to me by Mike Fouts, we have identified some <br /> modifications that will be important for enhancing final wall stability. <br /> Blast damage is a strong function of the peak particle velocity induced into the rock. <br /> There are three aspects of the current blasting practice that could be modified to reduce particle <br /> velocity, and thereby, damage to the final wall: <br /> • Powder Factor <br /> • Delays Between Holes and Rows <br /> • Smooth-Wall Blasting at the Final Wall <br /> Powder Factor <br /> The current practice, as described to me by Mike Fouts, includes: <br /> • Square hole pattern with burden and spacing equal to five feet. <br /> • Hole diameter equal to 3.5 inches. <br /> • Hole depth equal to 11 feet. <br />