EXPLOSIVES

1. Hard massive rock – High density explosive

2. Soft / Fractured rock – Low density explosive

3. Explosive with high gas production (such as ANFO) for displacement are appropriate for highly jointed or fractured rock.

4. Water resistance

5. Chemical stability

6. Fume characteristics

7. Bulk ANFO :
a. Zero Oxygen Balance = 94.3% AN + 5.7% FO
b. Over fuel mix, example: 92% AN + 8% FO, Prod.
6% less energy
CO
c. Under fuel mix, example: 96% AN + 4% FO
Prod. 18% less energy
NO2
Increase sensitivity
d. It’s generally better to over fuel ANFO rather than under fuel it.

8. P r i m e r s :
a. Primer diameter should closely match hole dia.
b. Two primers are recommended for blasthole over 15 meters deep [ANFO] & 10 meters deep [Emulsion Blend].
 
BASIC DRILL / BLAST DESIGN
 
1. BENCH HEIGHT
2. BLASTHOLE DIAMETER
3. BURDEN
4. BURDEN STIFFNESS RATIO
5. SPACING
6. SUBDRILLING
7. STEMMING
8. DECKING / AIR DECKING
9. ANGLE DRILLING
10. TIMING DESIGN / DELAY


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.

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



Decking Alternatives



S T E M M I N G
1. Normally ranges from (20 to 30) x Hole dia. or equal to 0.7 x Burden.
2. Crushed rock confine explosive energy
3. Better than drill cuttings.
4. 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

5. To improve VED : Reduce charge dia. or
6. Increase Bench height. Then recalculate
7. Burden and stemming dimensions.

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SAFE AND EFFICIENT BLASTING TECHNIQUE

Blast Design Principles

The Free Face
1. A free face is where the rock and air meet – the surface of the bench is not a free face.
2. Free faces enable the explosives’ energy to perform the greatest amount of work on the rock mass.
3. A blast will be more efficient if it has two free faces rather than one.
Open joints are also free faces.



Two free faces




Blast Patterns
Two basic blast patterns are used:
1. Box pattern, also known as a Square pattern, and
2. Staggered pattern.

Box (Square) Pattern



Staggered Pattern



Chevron Patterns
1. When only one free face exists, you can use the blast design to create more free faces.
2. A chevron design initiates the first hole in the middle of the face.
3. Subsequent holes then have two free faces to blast into.

Chevron – Staggered V



Effects of Blast Patterns

1. Fragmentation is enhanced
2. Muckpile profile is enhanced
3. Overbreak is minimised
4. Vibrations are minimised

Controlling Movement

1. The Blast Pattern is used to control where the muckpile will land.
2. This makes clearing of the muckpile more efficient.

Controlling Movement



Controlling Movement



Controlling Movement



Individual Hole Initiation

1. Blasts are not initiated one row at a time.
2. Much better results are achieved using patterned blasts with each hole firing individually.
3. This gives each hole at least two free faces to blast in to.
4. Smartdets and Shocktubes make this easy to achieve.

Individual Hole Initiation



MAJOR FACTORS INFLUENCING BLAST EFFICIENCY

1. ATTITUDE
a. PAYING ATTENTION TO DETAILS
b. EACH OPERATION MUST BE COMPLETED
c. AS PRECISELY AS POSSIBLE
d. TOTAL QUALITY MANAGEMENT (T.Q.M)
e. GROUP EFFORT

2. COMMUNICATION
a. SAFE BLASTING PRACTICES REQUIRE
b. GOOD COMMUNICATION.
c. COMMUNICATION BETWEEN MEMBERS OF
d. SAME GROUP AND BETWEEN GROUPS.
e. OPTIMUM BLAST DESIGNS DEPEND ON
f. INPUT FROM EACH GROUP.

3. BLAST DESIGN
KEYS TO EFFICIENT BLAST DESIGN
a. UNIFORM ENERGY DISTRIBUTION
b. APPROPRIATE ENERGY CONFINEMENT
c. PROPER ENERGY LEVEL
d. ADJUSMENT OF DESIGN TO MEET
e. EXISTING CONDITIONS





4. GEOLOGICAL EFFECTS
Blasting results are influenced more by rock properties than explosive properties.
a. Rock properties:
b. Compressive strength >> Tensile strength
c. 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.
d. W a t e r
*) Static water
*) Dynamic water
*) Multiple priming is advised in wet blast hole







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MINE GASES

Normal Air is made up of :

Nitrogen 78%
Oxygen 21%
Trace Gases 1%

Specific Gravity :

The weight of a gas compared to an equal volume of normal air at the same temperature and pressure.

Normal air has a specific gravity of 1

This determines where in mine atmospheres, or within a confined space, we will find concentrations of particular gases

Examples:

Carbon Dioxide 1.529 floor to mid drift
Hydrogen 0.0695 against back or roof
Oxygen 1.105 evenly distributed
Hydrogen Sulfide 1.2 floor to mid drift
Carbon Monoxide 0.967 evenly distributed
Sulfur Dioxide 2.264 floor

Gases can and do pool
Gases tend to flow as fluids in quantity
These effects can displace Oxygen.


Ventilation:
Heavier gases are harder to ventilate than lighter gases.
WHY ?
What are we ventilating with ?
Normal Air specific gravity of 1.0
THE EXPOLSIVES!
Methane 5-15 %
Carbon Monoxide 12.5-75 %
Hydrogen 4-74 %
Hydrogen Sulfide 4.3-45 %

Hazards of ventilating concentrations of any of these are:
IGNITION SOURCES!
MOVING IRRESPIRABLE GAS!

In a mine or within a confined space, what is the minimum percentage of Oxygen necessary?
19.5%
Anything less means VENTILATE!
Most digital Oxygen detectors are set to alarm at 19.5%

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Good Mining Practice

Aims of Coal Mining

1. Quality
2. Recovery
3. Cost

Success to Date

1. Quality has been adequate, although there are frequent problems with dilution and moisture
2. Recovery, 90.5% in 2006, is unacceptable for a mine that enjoys thick seams and little structural disturbance

Causes of High Coal Loss

1. Complacency
2. Laziness
3. Poor training
4. Poor supervision
5. Lax contract provisions

Lax Contract Provisions

1. “for coal that is exposed and subsequently becomes irrecoverable, the contractor will be made liable for the cost of uncovering the coal
2. Although inadequate, this has not often been enforced.
3. At present, the contractor is paid the same money for hauling 1 bcm of coal at 1,26 t/m3 to the dump as for hauling 1 bcm of OB at 2.2 t.m3. This is an incentive !


Seam Geometry

1. Thick Seam (+20 m)
2. Medium Seam (5-20 m)
3. Thin Seam (1-5 m)
4. Steep/Gentle Seam Dip Angle

Cleaning of Coal Roof

1. Excavation of overburden to withing 0.5 m of the coal roof
2. ‘Touching’ of coal every 30-40 m2 to ensure that minimal OB is left
3. Final clean up by small excavator
4. Must be done promptly to avoid having to clean high faces later
5. Considering the implementation of a ‘sign-off’ by Adaro supervision

Thickness of Cut

1. Current SOP states 3m mining thickness
2. This is quite variable in practice
3. Recent estimate of coal lost in fines is 0.10 tonnes per m2
4. Equipment currently in use is more than capable of digging 4 m lifts

Size of Equipment

1. For coal roof and floor cleaning, 30 tonne excavator is adequate, 20 tonne excavator is somewhat lacking in reach
2. For coal mining, coal geometry will determine preferred equipment size, from maybe 40 tonne for the thinnest seams to For coal roof and floor cleaning, 30 tonne excavator is adequate, 20 tonne excavator is somewhat lacking in reach
3. For coal mining, coal geometry will determine preferred equipment size, from maybe 40 tonne for the thinnest seams to 300 tonne for the thick seams

Faults and Intrusions

1. For coal that is affected by faulting, washouts or intrusions, smaller equipment must be used and mining restricted to daylight hours only
2. Thickness of cut may also be reduced to increase selectivity

Partings Removal

Where partings thickness is 100 mm or more, it needs to be removed

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