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42 E&MJ; • SEPTEMBER 2017 www.e-mj.com BLASTING Modern Delay Design In conventional design, the pairs of V holes are shot on the same delay, howev- er, cap scatter of conventional-fused caps such as shock tube and electric delay caps dictates that two paired holes with the same delay number caps will not fi re at the same time especially if long delay periods are used. Therefore with a mod- ern separated V, caps with different but close delays may be used. In addition, a central three-row V cut can be extended from fl oor to roof. This is made possible with modern high-reach drilling rigs, especially those with auto- mation. This is the technique that has been used successfully at Springfi eld Un- derground in Missouri for many years, as illustrated in Figure 3. The work described by Lusk was un- dertaken to dramatically reduce blast vi- brations so that mining could be extended 80 ft below a large surface structure and still comply with a 2-in./second vibration limit. In this example, standard Spring- fi eld Underground design the V extends from fl oor to roof and the right hand side of the round is delayed with an additional 17 ms. After incorporating signature hole analysis, a hole-to-hole delay of 11 ms was chosen and buster holes incorporat- ed and used as sacrifi cial holes. The key to vibration suppression was "rhythmic blasting," which meant that every hole in the shot fi red in sequence with an 11 ms delay from start to fi nish. The sequence was as follows: the busters fi ring fi rst in sequence, then the V and then each successive vertical row of holes outward, such that each row of holes was 132 ms apart with no two holes fi ring on the same delay. The achieved result was a sub- stantially reduced ground vibration level with the best fragmentation they had ever achieved, with no boulders thanks to the buster holes. Other Applications An unusual application of the V-Cut is in coal. In the 1980s the rapid spread of continuous miners throughout the Unit- ed States signaled the near eradication of blasting in underground coal mines in the U.S. This resulted in a huge surplus of under cutters and the manufacturers subsequently discontinued their manu- facture. Many of these under cutters were purchased by South American companies. Around 2010, these under cutters were eventually wearing out, with few replace- ment parts available. As such, companies especially in Brazil were having to turn to other blast designs and one of the authors was asked to present in Brazil on blast- ing coal. The course was very successful with one company having just discovered the solution to the problem using a V-Cut. The author was invited to the mine and personally got to charge and shoot a pat- tern, which is shown in Figure 4. The design although odd in appearance works well. This is partly attributable to coal being very weak in tension and the discontinuity spacing being very close. A single pair of V holes was used to start a blasted undercut comprising the bottom row of holes. Two-in.-plus-diameter holes, 8 ft 8 in. deep were loaded with 2- x 16- in. chubs of emulsion (2 per hole). The delay sequence is shown in Figure 4. Conclusion The Modern V-Cut is a cost-effective meth- od of breaking and moving rock, especially when combined with LHDs and other low profi le equipment that can dig a more scattered muckpile. With proper design methods boulders can be signifi cantly re- duced and deadpressing and precompres- sion of modern explosives can be elim- inated, leading to large cost savings and increased fragmentation. When designing a V-Cut, or any other blasting round, a full mine-to-mill optimization approach must be used to ensure that the blasting process is working in tandem with other mining op- erations to produce for the lowest cost. References 1. Bullock, R. L. (1982). Production Methods of Non-Coal Room-and-Pil- lar Mining. In Hustrulid, Underground Mining Methods Handbook (p. 235). Society of Mining Engineers. 2. Konya, C. (2015). Rock Blasting and Overbreak Control. Montville: Preci- sion Blasting Services. 3. Langfors, U., & Kihlstrom, B. (1967). Rock Blastin. Sweden. 4. Lusk, B., Worsey, P., Oakes, K., Chambers, J., Crabtree, S., Brasier, T., & Wheeler, R. (2006). Destructive Wave Interference in Underground Blasting Utilizing Precise Timing. Proceedings of the Thirty-Second Annual Conference on Explosives and Blasting Technique Volume I, 365-375. 5. Worsey, P. N. (2015). Alternative V-Cut Design, Section 3.8. Under- ground Heading Design, Missouri S&T; Course Explosive Engineering 5612 "Blasting Technology and De- sign." Rolla, Missouri. 6. Worsey, P.N. Utilizacao de Explo- sivos em Minas de Carvao e Tenden- cias Mundiais, Britanite, Fundacao Luiz Englert, UFRGS, SATC, Criciu- ma, Brazil, DVD, July 20-23, 2010. Figure 4—Underground coal blast design incorporating V-Cut (Courtesy: Carbonifera Criciuma).