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Mining Methods and Slope Stability Evaluation for Expanded Development of the Walstrum Aggregate Quarry <br /> RAI strongly recommends that air-deck smoothwall blasting methods be employed to improve the <br /> appearance and stability of final rock slopes. This relatively low-cost method of controlled <br /> blasting has been successfully applied in hundreds of mines and quarries. With this method of <br /> smoothwall blasting, the spacing of blastholes drilled along final slope walls are reduced and <br /> decoupled charges are employed to reduce borehole pressures, which in turn significantly reduces <br /> rock damage. The burden of rock in front of the air-deck holes should also be reduced to <br /> compensate for the lighter charges. For the Walstrum Quarry, the spacing between holes should <br /> range between 20 to 25 hole-diameters. For instance if the hole-diameter is 6 inches (0.5 ft), the <br /> spacing would range between 10 and 12.5 feet. Burden distance from the last row of holes and <br /> the closest row of regularly loaded production holes should be around 20 hole-diameters. <br /> SMOOTHWALL BLASTING AIR-DECK METHOD <br /> Detonator <br /> 8 to 10-foot <br /> Stemming <br /> Charge Weig�+ht Calculation Hole <br /> W = HXSX0.1 Plug <br /> Where: <br /> H = Bench Height (ft) <br /> S = Hole Spacing (ft) <br /> W = Charge Weight (lb) <br /> Example: 5112 to 61/2"Hole <br /> H =60ft, S = 12ft <br /> W = 60 x 12 x 0.1 =72 lb. <br /> ANFO Column <br /> Charge or Packaged <br /> Explosive if Hole is Wet 1-lb Cast <br /> Primer <br /> Figure 4.7—Air-deck Smoothwall Blasting Method <br /> REVEY Associates,Inc. Page 13 of 14 October,2001 <br />