Laserfiche WebLink
Mining Methods and Slope Stability Evaluation for Expanded Development of the Walstrum Aggregate Quarry <br /> walls is reduced when blasts are timed to direct rock movement perpendicularly away from walls. <br /> This design technique should always be applied when blasting is closer than 60 m(192 ft) to final <br /> walls. <br /> Adequate row-to-row timing relief is needed between rows to provide un-choked lateral <br /> movement of the blasted rock. The optimum delay time will vary for different applications. <br /> Different rock types have different movement response times. Softer less stiff rocks(low Young's <br /> Modulus) like shale will not move as quickly as very hard and elastic rocks like basalt. Many <br /> blasters also believe that results improve when more inter-row delay time is used between rows in <br /> the back portion of large blasts. When row-to-row delay time is too great,the benefit of inter-row <br /> collision breakage is lost and the potential pre-mature ground movement cut-offs is increased. <br /> "Free Faces"created <br /> by delay timing <br /> Cov do `pov Lam, <br /> v , <br /> 17 <br /> Q 4 g�QD .y&dv <br /> �0 0"' c�Q e •�v • �� <br /> Figure 4.6—Blast with adequate row-to-row delay timing <br /> Hole-to-hole and inter-row millisecond timing delays for blasts at the Walstrum Quarry should <br /> conform to the guidelines in Table 4.1. <br /> Millisecond Timing Guidelines <br /> Inter-row Delay Range Hole to Hole Delay Range <br /> (Per unit of burden) <br /> 3 to 10 ms/ft 8 to 17 ms <br /> Table 4.1 —Millisecond delay timing guidelines <br /> REVEY Associates, Inc. Page 12 of 14 October,2001 <br />