GEOLOGICAL EFFECTS Blasting results are influenced more by rock properties than explosive properties . Rock properties: Compressive strength >> Tensile strength Rock Structure: Rock fragmentation is primarily controlled by bedding, jointing, and faulting. Smaller drill pattern minimize the adverse effects of bedding and fractures but increase drill and blast costs. Explosives with high gas production (ANFO) are appropriate for highly jointed or fractured rock. The orientation of the free face to the joints sets is also a key consideration for fragmentation and wall control.
W a t e r Static water Dynamic water Multiple priming is advised in wet blast hole GEOLOGICAL EFFECTS
Dipping seams of factures into pit: unstable walls excessive backbreak Dipping seams into rockmass: unbroken toe overhang potential Joints parallel to free face: good wall control can be best orientation Joints angled to free face: blocky face excessive end break
Simplified blocky rockmass poor fragmentation f ree face zone expanded pattern prevents even energy distribution uniform fragmentation tight pattern promotes even energy distribution
bench Spacing should be reduced Presplit Evaluation open pit open pit bench Spacing can be expanded
EXPLOSIVES Hard massive rock – High density explosive Soft / Fractured rock – Low density explosive Explosive with high gas production (such as ANFO) for D isplacement are appropriate for highly jointed or fractured rock. Water resistance Chemical stability Fume characteristics Bulk ANFO :
Zero Oxygen Balance = 94.3% AN + 5.7% FO Over fuel mix, example: 92% AN + 8% FO Prod. 6% less energy CO Under fuel mix, example: 96% AN + 4% FO Prod. 18% less energy N O2 Increase sensitivity It’s generally better to over fuel ANFO rather than under fuel it. P r i m e r s : Primer diameter should closely match hole dia. Two primers are recommended for blasthole over 15 meters deep [ANFO] & 10 meters deep [Emulsion Blend].
Spacing Burden crest toe Explosives Coloumn Sudut Pemboran Sub Drilling Stemming Kedalaman Pemboran Tinggi Bench SURFACE BLASTING GEOMETRY
BENCH HEIGHT If the height is not predetermined : BH (m) >> Blasthole Dia. (mm) / 15 BLASTHOLE DIAMETER To achieve excellent energy distribution : DIA (mm) = Bench Height (m) x 8 If charge diameter is less than the blast hole diameter, the “decoupling effect” must be taken into account. As blasthole diameters increase the cost of drilling, loading & explosive generally decrease. Smaller blast holes distribute the explosive energy better than large blast holes. BURDEN Burden (m) are normally equal the charge diameter (mm) x (20 – 35). Initial Burden Estimation Guide (see table) BURDEN STIFFNESS RATIO Equal to the Bench height divided by burden << 2 : stiff and poor fragmentation. 2 – 3.5 : good fragmentation. >> 3.5 : excellent fragmentation. BSR can be improved by using smaller hole diameter or greater bench height.
Decoupling Effect on Detonation Pressure % reduction in wet Diameter of Explosive Blastholes equals Diameter of Blasthole % reduction in dry Diameter of Explosive Blastholes equals Diameter of Blasthole Example : the detonation pressure of a 127 mm diameter explosive in a 165 mm diameter blasthole will be reduced by 38% in a wet hole and 49% in a dry hole. Initial Burden Dimension Explosive Density x 2 + 1.8 x Explosive Diameter Rock Density 84 = 1- = 1- 1.8 2.6 Burden (m) =
SPACING Normally ranges from (1 to 1.8) x Burden Optimum energy distribution: S = 1.15 x B Pattern is laid out in “Staggered” SUBDRILLING Normally ranges from ( 0.3 to 0.5 ) x Burden or ranges from (8 – 12) x Hole diameter to much Sub drilling produces “Excessive Ground Vibration” Less Sub drilling produces “Excessive toe” To improve fragmentation the blast hole primer should be placed at grade level. DECKING / AIR DECKING Minimum decking for dry holes: Deck = hole diameter x 6 Minimum decking for wet holes: Deck = hole diameter x 12 Air decking can reduce the amount of explosives to achieve good results by efficiently utilising the available explosive energy.
UNIFORM ENERGY DISTRIBUTION Square Square, Staggered Pattern Pattern S = B S = B Slighty Rectangular Rectangular Staggered Pattern Staggered Pattern S = B x 1.15 S = B x 1.5
Decking Alternatives Dry Hole Wet Hole Air Deck Deck = hole diameter x 6 deck = hole diameter x 12 Stemming Explosives Deck Explosives Stemming Explosives Deck Explosives Stemming Plug Air Deck Explosives
S T E M M I N G Normally ranges from (20 to 30) x Hole dia. or equal to 0.7 x Burden. Crushed rock confine explosive energy Better than drill cuttings. Wet blast holes require more stemming for confinement than dry blast holes. Relative Confinement (RC): >> 1.4 : Confine << 1.4 : Fly rock & stemming ejection Vertical Energy Distribution (VED): Charge length divided by Bench height >> 80% to produce uniform fragmentation To improve VED : Reduce charge dia. or Increase Bench height. Then recalculate Burden and stemming dimensions.
1 Poor Energy Distribution 2 Fair Energy Distribution 3 Good Energy Distribution ENERGY DISTRIBUTION Bench Height 10 m Charge Diameter 311 m Burden 10 m Stiffness Ratio 1 Stemming 7 m Vert. Energy Dist. 30% Bench Height 10 m Charge Diameter 145 m Burden 5 m Stiffness Ratio 2 Stemming 3.5 m Vert. Energy Dist. 65% Bench Height 10 m Charge Diameter 92 m Burden 3.3 m Stiffness Ratio 3 Stemming 2.3 m Vert. Energy Dist. 77% Note : the energy factor is the same for each example
Step #2 Place small explosives deck in hard zone. If downhole delays are used the deck should be fired 25 ms before the main charge. Cap Rock Step #3 Drill satellite holes between production holes and if possible load into hard zone. reduce Step #1 Increase charge length while maintaining explosives confinement and or reduce the pattern size. STEPS TO IMPROVE TOP BREAKAGE Cap Rock Cap Rock
ANGLE DRILLING ADVANTAGES >> Better energy distribution >> Reduced over break >> Better floor control >> Improve high wall stability DISADVANTAGES >> Requires attention to drill set-up >> Generally shorter bit life >> Greater hole deviation >> Higher drilling cost per meter >> Require expert drillers >> Require wider drill benches Normally : 10 – 18 Degree Requires “Profiling Technique” for fresh wall.
ADVANTAGES OF ANGLE DRILLING POOR FRAGMENTATION USEFUL ENERGY WASTED ENERGY POOR FRAGMENTATION
Potential For Flyrock Potential For Boulder IMPROPER DRILLING CORRECT DRILLING
HOLE DEVIATION ON MINING OPERATION MINING OPERATIONS EXAMPLES OF EFFECTS OF HOLE DEVIATIONS Extra drilling, rods, bits, coupling, man-hours and delay. Extra explosives, man-hours and delay. Build-ups, hang-ups, poor fragmentation, ore loss, hoh dilution and pillar weakening. Handling of unwanted rock material, accelerated wear of loaders, conveyors etc., choking of ore passes, grizzley work, chute boxes runaways and haulage spillage. Extra support, extra drilling for support and man-hour. Accelerated wear of crushers, extra crushing and delays. Extra hoisting and delays Extra grinding/milling and loss of metal Total Costs Drilling Charging Blasting Rock Support Mucking/Lashing, Loading and Transportation Crushing Hoisting Mineral Dressing Planned Operational Extra Operational Costs
TIMING DESIGN / DELAY PURPOSE The blast’s performance will be reduced if the explosive has too little or too much delay time. Reduce ground vibration. Delay sequencing will not overcome improper blast design (confinement, energy distribution large toe, etc.). FRAGMENTATION REQUIRED Optimum fragmentation in massive rock occurs when one hole is detonated per delay and the the delay between holes in a row is – 40 ms. The delay between rows should be at least 2 to 3 times the delay between holes in a row.
MUCKPILE DISPLACEMENT Short delay intervals (<25 ms) between holes in a row reduce fragmentation but improve displacement. Longer delay intervals (> 100 ms) are required between rows to maximize displacement. The type of excavator will often determine the degree of displacement required which will dictate the delay interval between rows of blast holes. WALL CONTROL To short of delay intervals between holes in a row and between rows can cause excessive over break. If the delay between blast holes in the back row is less than 42 ms, the charges can act together to damage the back wall. Too short of delay interval between rows (<35 ms) can promote back break due to over confinement.
TIMING DESIGN / DELAY (cont.) BASIC TIMING DESIGN Select the time between holes in a row based on one third to one half the time between rows. Delay intervals between holes in a row less than 3 ms per meter of spacing are not recommended due to air blast and fragmentation considerations. Delay intervals between rows less than 6 ms per of burden can cause stemming ejection, fly rock, and excessive back break. Multiple row blast (> 4 rows) use longer intervals in back rows. Bottom delay has generally the shortest delay and delay between decks in the same hole should range 10 to 50 ms (For Deck Loading).
Blast Timing and Design Configuration Simplicity Cost Site Sensitivity Fragmentation Muckpile Displacement Wall Control Water Conditions Explosives Used Geology Safety