1	Air-deck design and use First patented in 1893 Primary use was in dimensional stone production, with black powder Currently used extensively in wall control Applications in production holes
2	Applications - production Top air deck – improve fragmentation in surface (stemming) zone of blast Mid-column air deck – replace inert decks with improved fragmentation in the central (inert deck) zone of the blast Bottom air decks – reduced for sub-drilling Generally improve energy distribution
3	Applications – wall control Replace expensive and time consuming use of lineal decoupled charges Expand spacings and/or reduce loads used with open hole, bottom charge designs Reduce air-blast complaints Extend time of pressure pulse on wall
4	Air bags
5	Modern design tools Computer modelling High speed photography Precise electronic detonators Recognition of benefits Controlled test environment Cost reduction incentives
6	Computer models Standard load, fully stemmed hole Top air deck of 1.44 meters mid-column air deck bottom hole air deck pre-shear with inert decks pre-shear with lineal decoupled charge pre-shear with air deck
7	Standard load
8	Top air deck
9	Mid-colmn air deck
10	Bottom-hole air deck
11	Pre-shear – inert decks
12	Pre-shear - decoupled
13	Pre-shear – air deck
14	Top air deck - formulae Stemming depth = 50% to 75% original stemming depth Length of air deck = 20% to 40% x (air + explosives) +/- Maximum explosives to remove = 20% of original explosives load Minimum explosives to remove = cost of air deck device
15	Mid-column air deck - formulae Stemming depth = adjust to maintain SDOB constant Length of air deck = 20% to 40% x (air + explosives) +/- Maximum explosives to remove = 20% of original explosives load Minimum explosives to remove = cost of air deck device Precise timing to initiate both charges simultaneously
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18	Bottom-hole air deck - formulae Stemming depth = adjust to maintain SDOB constant Length of air deck = 20% of (air + explosives) +/- Maximum explosives to remove = 20% of original explosives load Minimum explosives to remove = calculate based on savings due to reduced drilling cost plus cost of air deck device Precise drilling control to maintain center of all air decks at the desired floor elevation
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23	Pre-shear air deck - formulae Stemming = 9 to 12 x borehole diameter Spacing = 12 to 15 x borehole diameter Burden = 15 to 18 x borehole diameter Charge = 0.5 to 1.0 kg/square meter of wall per hole Deep holes, support 1/3 of total charge at mid-point Very deep holes, support 1/3 of total charge at 2/3 depth, 1/6 of total charge at 1/3 depth
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25	Test results – Peru and Venezuela Wide variety of materials iron ore, soft to very hard, production limestone quarry, production copper, production, wall control poly-metallic, wall control coal, production gold, production and wall control
26	Iron mine 1 – standard design Using air decks prepared with jute bags manually filled with drill cuttings, lowered and secured with rope Three man crew, 3 minutes per hole to prepare 1.5 meter air deck 7.0 meters stemming on top of bag
27	Iron mine 1 - test Air bags, inflated with brake system of bulk loading truck One man (ground technician with truck) placing air bags – 15 seconds per hole Approximately 50% reduction in loading cycle time Recommended reducing stemming to 6.0 meters, maintain same explosives charge
28	Iron mine 2 – standard design Three decks with inert stemming Three man crew, 5 minutes per hole to complete 3.0 meters top stemming Individual Nonel and primer in each deck
29	Iron mine 2 - test 3.0 meters top stemming Top air deck of 3.3 meters Single bottom charge, sum of three decks normally used Single Nonel and primer One man (ground technician with truck) placing air bags – 15 seconds per hole
30	Iron mine 2 - test Approximately 33% reduction in loading cycle time Same fragmentation results as with standard design Recommend testing with 4.0 meter mid-column air deck, top stemming of 2.75 meters
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33	Copper mine 1 - design Using 1.5 meter bottom hole air decks as standard Mechanical plug, rope supported Between 90 and 120 seconds per hole to measure hole, prepare and place plug Two crew operation, plugs placed in advance of loading operations
34	Copper mine 1 - test Air bags, inflated with brake system of bulk loading truck One man (ground technician with truck) measure holes and place air bags – 15 to 20 seconds per hole Maintained same air deck configuration Same fragmentation results and floor conditions as with standard design
35	Copper mine 2 - design Production Holes 8.0 meters top stemming Wall control 65 kg bottom load 2 to 4 meters stemming immediately on top of bottom load
36	Copper mine 2 - test Production Removed 1.0 meter of explosives Stemming at 6.0 meters, 3.0 meter air deck Stemming at 5.3 meters, 3.7 meter air deck Wall control Maintain same bottom load Air bag at 3.0 meter, fully stemmed above
37	Copper mine 2 - test Production At 6.0 meters stemming, improved swell At 5.3 meters stemming, improved swell, surface fragmentation Wall control Reduced back-break No cratering
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52	Poly-metallic – wall control Standard load 150 kg bottom charge, open hole approximately 1.3 kg/sq meter of wall Tests, maintained same charge 1/3 of charge supported on air bag at mid-depth of hole Air bag at 3.0 meters from top of hole, fully stemmed above air bag
53	Poly-metallic - results Standard load surface craters of from 2.0 to 2.5 meters radius Supported charge surface craters of approximately 1.0 meter radius Air bag at 3.0 meters surface craters of from 2.5 to 3.0 meters radius
54	Poly-metallic - recommendations Reduce charge to 1.0 kg/sq meter of wall Test with combination of supported charge and top stemming : 75 kg bottom load 37.5 kg supported at mid-point air bag at 2.0 meters, fully stemmed above air bag