Blasting Technology - Blast Design
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Transcript of Blasting Technology - Blast Design
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Blasting Course
Designing BlastsDesigning Blasts
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Two important aims in blasting.
To fragment the rock to a desirable size and
To displace the fragments a desirable distance
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At the best overall cost
0
1
2
3
4
5
6
0.5 0.7 0.9 1.1
Powder Factor (kg/m3)
Cos
t/m3
Explosive
Drilling
Load & Haul
Crushing & Milling
Overall Cost
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Three things that affect outcome
ExplosiveRock
Blast Geometry
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Rock
Rock StrengthRock Strength
Rock DensityRock Density
Rock StructureRock Structure
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Rock Strength and elasticity
UCS and Tensile Strength
Has an influence on creation of cracks during blasting
Measured in MPa
Tensile strength about 1/10th UCS
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Rock Density
Influences the displacement distance during a blast
Influences fragmentation
Higher density = higher energy for same end result
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Rock Structure
Rock Structure has largest influence on fragmentation results.
Sometimes fragmentation completely controlled by structure
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Rock Structure
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Rock Structure
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Rock Blastability Index
Rock UCS
Rock density
Joint Spacing
Joint Orientation
RMDJPSJPODensityRockUCSRBI ++++
+=
6.477.235.0
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Blast Geometry
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Burden and Spacing
Hoof vrye front
Breeklas
Effektiewe breeklas Spasiring
BreeklasInterimvryefront
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Equilateral Pattern
A B
C
A = B =Cor
Base = 1.15 x height
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Spacing = 1.15 x Burden(in plan, energy distributed evenly.)
Spacing > 1.15 x Burden
(in plan, energy not distributed evenly
and more overlap can be seen in the
energy contours in one direction.)
Red circles represent
contours of equal energy
around each borehole.
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Staggered Pattern
Wherever possible use a
staggered pattern. A
square pattern is only
suitable for narrow box-
cut blasts
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Deciding on Burden - Scaled Burden
cM
BurdenBurdenScaled =
cMBurdenScaledBurden =
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Scaled Burden
RBI = 20 to 40 RBI = 40 to 60 RBI = 60 to 80
Shale/Mudstone 1.3 1.2 1.1
Sandstone 1.2 1.1 1
Limestone/Dolomite 1.2 1 1
Granite 1.2 1 0.9
Dolerite 1.1 1 0.9
RBI = 20 to 40 RBI = 40 to 60 RBI = 60 to 80
Shale/Mudstone 1 0.8 0.7Sandstone 1 0.8 0.7
Limestone/Dolomite 0.9 0.75 0.65
Granite 0.9 0.7 0.6
Dolerite 0.8 0.7 0.6
For Reduced Heave or coarser fragmentation
For increased heave or finer fragmentation
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Burden Stiffness
5.2= burden
heightbench
Sb
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Burden Stiffness - Matching bench height to hole diameter
Poor explosive distribution. Only the bottom half of the benchcontains explosive.
Tendency to crater because the surface is closer than thevertical free face. This results in
A tendency for uncontrolled fly rock
Poor fragmentation in top half of bench
Uneven floors
Very little muckpile movement
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Explosives Energy
HeightBenchSpacingBurden
holeperkgFactorPowderDesign =
RWSFactorPowderFactorEnergy =
volumeblockkgtotalFactorPowderActual =
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Stemming
Stemming affects the following results in a blast:
Fly rock
Air blast
Fragmentation
HeaveAll blasts require stemming
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Ineffective Stemming
Excessive Fly
Excessive Noise
Poor Fragmentation
Poor Heave
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Effective Stemming
Fly rock controlAir blast control
Optimal fragmentation
Optimal heave
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Air
Water
Drill cuttings in water
ClayDrill cuttings in dry hole
Crushed aggregate - ungraded
Crushed aggregate - graded
Worst
Best
Stemming Effectiveness:
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Factors affecting stemming performance
Stemming material
Stemming length
Rock strength
Explosive energy
Stemming length = 15 to 30 x diameter
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Scaled Depth of Burial
= 1000
4
1000
833.0
cs
MDS
Scaled
Depth of
Burial
0.7 1 1.2 1.5 1.7
Hard rock much fly normal fly little fly no flyno surface
ex ression
Soft rock much fly much fly normal fly little fly no fly
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Crater tests to determine site specific
values
Scale depth of burial
Maximum Burdens
Explosives performance and comparisons
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Crater tests:
Surface ExpressionFragmentation
Crater Volume
Vertical Displacement Velocity
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Sub-drill
Uneven floors with high bottoms
Difficult digging conditions at the bottom of the muckpile
Insufficient Sub-drill =
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Sub-drill
Usually set at 20 to 50% of burden
BMQc
39.0=
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Uniformity
1 10 100 1000 10000
Fragment Size (mm)
0
20
40
60
80
100
%
Passing
uniformity = 1.4
uniformity = 0.8
uniformity = 0.4
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The final fragmentation influences:
Diggability: Impacts loading rates and wear and tear onequipment
Coal exposure rates: Impacts mine profitability
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Kuzram model
Explosive Energy
Explosive distribution (burden, spacing, hole diameter, sub-drill,stemming length)
Bench Geometry
Rock Blastability
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Kuzram
633.0
6/1
8.0
50115
100
=
RWSMEFRx cf
1.0
5.0
1.01001
2
1
142.2
+
=
c
c
b
c
h
c L
SubL
H
SubL
b
bb
s
bn