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Managing Muckpile Fragmentation
Scott G. Giltner
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Topics to be Covered
� The purpose of drilling & blasting in producing crushed stone
� Relative cost of drilling & blasting vs other quarrying activities
� Cost/production opportunities offered with optimized
fragmentation
� Factors affecting fragmentation� Factors affecting fragmentation
� Self-evaluation of fragmentation
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Why Drill and Blast ?
Blasting intensity
� Drill and Blast is the first step in the breakage and separation
process. Therefore, it impacts all the the subsequent downstream
process efficiencies.
� Drill and Blast is still the most cost effective method to break and
move the large volumes of rock – when done correctly!
Blasting intensity
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Rock Breakage Phases
60%
80%
100%
Cum %
passing
In-situ
ROM
Crusher Product
10000
0%
20%
40%
0.1 1 10 100 1000Size mm
Cum %
passing Product
Energy $
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Relative Energy and Costs
Specific energy kwh/t
Energy factor
Cost factor
Drill and Blast 0.1 – 0.25 1 1
Load and haul 0.2 – 0.5 1 - 5 2 - 10
Crushing 1 – 2 4 - 20 2 - 10
Generally the harder the rock, the higher the factor.
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Drilling & Blasting - Leverage
$0.24
$0.26
$0.02
$0.78Drilling
Blasting
Secondary Breakage
Loading
$0.35
$0.71
Loading
Hauling
Crushing
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Drilling & Blasting - Leverage
� Drilling and blasting is the first step in the comminution processes
� A 10% increase in drilling and blasting cost can be compensated by
� 4.6% reduction in excavation and hauling costs
or� 6.4% reduction in crushing� 6.4% reduction in crushing
1¢ decrease in excavation/hauling = 2.2¢ increase in D&B
or
1¢ decrease in crushing/benefaction = 1.6¢ increase in D&B
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Fragmentation Optimization
Optimum
Total mining cost
$/t
D&B cost
Digging cost
Hauling cost
Blasting effort $/t
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Common Fragmentation Issues
� Oversize breakage costs
� Excavator costs (diggability)
� Crusher costs (throughput)
� Recovery (fines)
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Fragmentation Optimization Opportunities
� Better digging and bucket fill factors
� Potential to produce better priced end product
� Reduction in material losses (more saleable product)
� Reduction in blast induced damage
� Consistent crusher throughput and power draw
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Factors Affecting Fragmentation
Joint SpacingJoint Condition
Geology
BurdenSpacing
Design
EnergyEnergy Partitioning
Explosives
Fragmentation
Joint ConditionJoint Strike & DipBedding Planes Strike & DipBedding Plane ConditionBedding Plane SpacingRock StrengthRock ElasticityHard/Soft SeamsGrain SizeSonic Velocity
SpacingHole DiameterStemmingSubdrillingDelay Timing &AccuracyBench HtStaggered/SquarePattern
Energy PartitioningDensityVelocity of DetonationCoupling
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Structure describes the features which primarily determine the fragmentation performance of the rock mass.
� Jointing/Bedding
� Defines maximum fragment size
� Influences transmission of stress wave
� Influences gas penetration
Geology Factors
� Influences gas penetration
� Rock Strength & Elasticity
� Determines how the rock mass responds to the explosive energy applied
� Influences confinement on explosive
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Block size < 0.7 ft (0.2 m)
Rock Structure
Friable and Powdery
Massive
Block size > 6.5 ft (2 m)
Friable and Powdery
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Block size 0.6 – 3 ft(0.2 – 1 m)
Rock Structure
Blocky
Block size0.3 – 0.8 ft (0.1 – 0.25 m)
Fractured
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Rock Type Density
(g/cm3)
Compressive
Strength
(psi)
Tensile
Strength
(psi)
Young's
Modulus
(psi)
Poisson's
Ratio
P Wave
Velocity
(ft/s)
Basalt 2.9 21,610 8,992,340 0.27 17,155
Dolomite 2.5 7,977 4,061,057 0.32 13,202
Gneiss 2.8 32,488 11,748,600 0.22 18,805
Granite 2.7 26,977 6,236,623 0.33 15,892
Limestone 2.7 23,061 7,977,076 0.25 16,404
1,595
435
2,030
1,305
725
Rock Properties
Limestone 2.7 23,061 7,977,076 0.25 16,404
Marble 3.1 36,404 16,374,000 0.28 21,998
Sandstone 2.5 19,435 1,015,264 - 12,903
Sandstone 1.8 1,595 870,226 0.31 6,873
Schist 2.9 24,076 11,167,910 0.2 17,985
Slate 2.6 12,328 9,572,491 0.17 16,955
Taconite 2.9 36,404
725
2,175
145
0
1,305
870
2,465 13,488,510 0.25 20,144
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Rock Properties - Rock Stiffness
Pressure
A
B
High rock stiffnessA
Low rock stiffness
Pressure
Volume
2
C
O
3
4 5
1
a)
D E Volume
1
2
B
C
O
3
4 5
b)
D E
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Blast Design Factors
� Hole Diameter
� Influences energy distribution and burden stiffness
� Burden/Spacing
� Influences energy distribution and burden stiffness
� Relationship with joint spacing affects oversize
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Hole Diameter & Burden/Spacing
Free FaceLarge dia holes
Free Face Small dia holes Poor fragmentation zones
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Blast Design Factors
� Hole Diameter
� Influences energy distribution and burden stiffness
� Burden/Spacing
� Influences energy distribution and burden stiffness
� Relationship with joint spacing affects oversize
� Bench Height
� Influences burden stiffness
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Burden Stiffness
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Blast Design Factors
� Hole Diameter
� Influences energy distribution and burden stiffness
� Burden/Spacing
� Influences energy distribution and burden stiffness
� Relationship with joint spacing affects oversize
� Bench Height
� Influences burden stiffness
� Delay Time & Accuracy
� Influences interaction between detonating holes
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Interhole Delay Time & Fragmentation
1.5
2
2.5
X50 (in)
0
0.5
1
0 1 2 3
ms/ft Burden
X50 (in)
(after Cunningham, 2005)
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Blast Design Factors
� Hole Diameter
� Influences energy distribution and burden stiffness
� Burden/Spacing
� Influences energy distribution and burden stiffness
� Relationship with joint spacing affects oversize
� Bench Height� Bench Height
� Influences burden stiffness
� Delay Time & Accuracy
� Influences interaction between detonating holes
� Staggered/Square pattern
� Determines distribution of energy in rock mass
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Explosive Energy Distribution
Square Pattern
Staggered Pattern
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Explosives Factors
� Velocity of Detonation
� Indication of energy available
� Indicator of energy partitioning (shock vs gas)
� Determines how explosive energy is applied to rock mass
� Density
� Influences total explosive energy available in a hole
� Coupling
� Influences transfer of explosive energy to rock mass
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Explosive Selection
Pressure
Volume
2
A
B
C
O
Rock stiffness
3
4 5
1
D E Volume
1
2
A
B
C
O
Rock stiffness
34 5
D E
Hard and Brittle Rock Soft and Plastic Rock
High
VOD
c)
VolumeO
a)
D E VolumeO
b)
D E
2
C
O
34 5
1
Volume
2
A
C
O
34 5
1
Volume
Pressure B
Rock stiffness
D E
C
O
1
Volume
23
4 5
A
B
d)
D E
Rock stiffnessLow
VOD
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Explosive Selection to Meet Rock Structure and Strength Properties
Strength
High VODHigh VOD
High densityHigh density
Medium VODMedium VOD
High densityHigh density
Structures
Strength
Low VODLow VOD
Low densityLow density
High VODHigh VOD
Low densityLow density
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Explosive Selection to Meet Blast Objectives
Throw requirement
Low VODLow VOD
MedMed--High densityHigh densityHigh VODHigh VOD
High densityHigh density
Throw requirement
High VODHigh VOD
Med densityMed density
Low VODLow VOD
Low densityLow density
Fragmentation requirement
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In Summary Fragmentation Results..
� Have significant impact on quarry economics
Therefore Fragmentation Optimisation F..
� Should consider all the downstream processes rather than just drill and blast costsdrill and blast costs
� Should consider quality as well as quantity
� Should be site specific
� Should be flexible to cope with site specific changes and market conditions
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‘Take Home’ Questions on Fragmentation
� Does the shovel/loader bucket fill with a single smooth pass?
� Does the shovel/loader remain stable during digging (no rocking
or violent movements)?
� Does the muckpile flow during digging?� Does the muckpile flow during digging?
� Do the haul trucks dump at the crusher without delay?
� Is the throughput and power draw of the crusher consistent?
� Is secondary breakage required on a regular basis?
� Are the desired product sizes produced without waste (fines or
other unsaleable/low profit products)?
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