Explosive is a compound or mixture which is capable of undergoing extremely rapid decomposition.

1. Explosives, Theory
of Breakage and
Blasting Operations
Author: Partha Das Sharma, B.Tech(Hons.) in Mining Engineering,
E.mail: sharmapd1@gmail.com, Website: http://miningandblasting.wordpress.com/

2. Introduction
General types of Explosives
• Commercial explosives
• Military explosives
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3. Explosive Ingredients and their Function
Ingredient Chemical formula Function
Ethylene glycol dinitrate C2H4(NO3)2 Explosive base – lowers freezing point
Nitrocellulose (guncotton) C6H7(NO3)2O2 Explosive base – gelatinizing agent
Nitroglycerin C3H5(NO3)3 Explosive base
Nitrostarch Explosive base
Trinitrotoluene (TNT) C7H5N3O6 Explosive base
Metallic powder Al Fuel sensitizer : used in high density slurries
Black powder NaNO3 + C+ S Explosive base
Pentaerythritol tetranitrate C3H8N4O12 Explosive base
(PETN)
Lead azide Pb(N3)2 Explosive used in blasting caps
Mercury fulminate Hg(ONC)2 Explosive used in blasting caps
Ammonium nitrate NH4NO3 Explosive base : oxygen carrier
Liquid oxygen O2 Oxygen carrier
Sodium nitrate NaNO3 Oxygen carrier – lowers freezing point
Potassium nitrate KNO3 Oxygen carrier
Ground coal - Charcoal C Combustible, or fuel
Paraffin CnH2n+2 Combustible, or fuel
Sulfur S Combustible, or fuel
Fuel oil (CH3)2(CH2) Combustible, or fuel
Wood pulp (C6H16O3)n Combustible, absorbent
Lampblack C Combustible
Kieselguhr SiO2 Absorbent – prevents caking
Chalk -Calcium carbonate CaCO3 Antacid
Zinc oxide ZnO Antacid
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Sodium chloride NaCI Flame depressant (permissible explosives)

4. Chemical explosives
• is a compound or mixture which is capable of
undergoing extremely rapid decomposition.
• An explosion can be broken down into four
phases
• Release of gas
• Intense heat
• Extreme pressure, and
• The explosion
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5. Chemical explosives
When the explosive is detonated,
• gas is released,
• temperature of the gas increases,
• pressure also increases (Charles’ law).
• move and break the rock.
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6. How to compare explosives
• Strength
• Detonating velocity
• Fume class • Detonation pressure
• Water resistance • Energy
• Density • Sensitivity
• Physical
characteristics • Sensitiveness
• Storage • Flammability
• Freezing
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7. How to compare explosives
• Strength : % of active material
• Velocity of Detonating (VOD): is the velocity at
which the detonation wave moves through the
explosive (ft/s or m/s)
• Fume class : the amount of toxic fumes which
determine its safety to be used in particular
situation such as underground operations.
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8. How to compare explosives
• Detonation pressure : is the pressure behind
the detonation front.
• Energy
• Sensitivity : the minimum energy/pressure
needed for detonation.
• Sensitiveness: measure of explosion wave
spreading from one stick to another.
• Flammability : easiness to ignite by flame or
heat
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9. How to compare explosives
• Water resistance : is the ability to resist
contamination or a reduction in strength when
exposed to water. Sometimes determined by the
length of time it can be submerged in water and
still perform as designed.
• Density : is the explosive wt per given volume.
Aid in blast design.
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10. How to compare explosives
• Physical characteristics: commercial
explosives can take three basic forms:
granular, gelatin, slurry and emulsion. The
choice of form depends on the usage
required.
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11. How to compare explosives
• Storage: how explosive can be stored without
affecting its safety, reliability, and performance.
Early nitroglycerin (NG) dynamites were
extremely poor for storing due to separation of NG
from the other components and creates an
extremely hazardous condition.
• Freezing : important for safety and performance
especially in cold climate. Anitfreezing additives
may be used.
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12. Drills and Drilling
• The drilling system consists of the drill: the drill
steel, or rod; and the bit. The bit penetrates the
rock by the force it imposes on the rock. Bits are
designed for percussion, rotary drilling, or both.
• Hand held drills
• External –percussion drills
• Down-the-hole drills
• Rotary drills
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13. Theory of Breakage
Purpose of blasting
• One solid piece → smaller pieces (fragmentation)
→ to be moved or excavated (movement).
• Underground blasting, for example, requires
greater fragmentation than surface blasting
because of the size of the equipment that can be
used and the difficulty of access.
• Get the desired results with a minimum cost
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14. Theory of Breakage
Involves two basic processes:
• Radial cracking
• Flexural rupture
• Rock is stronger in compression than in tension.
Therefore, the easiest way to break rock is to
subject it to a tensile stress greater than its ultimate
strength in tension.
• Rocks are heterogeneous (contain different types
of rocks). They differ in their density.
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15. Theory of Breakage
Free face
Compression
Borehole waves
Radial cracking
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16. Theory of Breakage
• The distance from the borehole to the free face is
the burden.
• The denser the rock the faster the waves
• Proper fragmentation when enough to travel to the
face and back overcoming the tensile strength of
the rock.
• Along the face the outermost edge is stretched in
tension which causes cracks.
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17. Flexural Rupture
• The second process in breaking rock by bending
the rock to the point where the outside edge, the
side in tension, breaks.
• Caused by the rapid expansion of gases in
borehole.
• Analogous to the bending and breaking of a beam.
• Movement or displacement are required in
addition to cracking.
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18. Flexural Rupture
• After detonation the redial cracks expands
and the gas starts to the movement by
putting a CS against the borehole wall
causing its bending.
• The deeper the hole, the greater the burden
and borehole spacing.
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19. Blast Design
• Is the safe and economic way to do blasting
• Factors affecting blasting design
• Geological factors (out of blaster’s control)
• Controllable factors
• Borehole dia.
• Burden
• Spacing
• Stemming
• Design of the delay firing system.
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20. Burden & spacing
Burden is the distance from the blast hole to the nearest perpendicular free face.
Spacing
Burden
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Free face

21. Burden & spacing determination
Andersen Formula B= (dL)0.5
• B : burden, ft d : borehole dia, in
• L : borehole Length, ft
• Langefors’ Formula V= (db/33) [Ps/cf(E/V)]0.5
• V : burden, m db : dia of drill bit, mm
• P : degree of packing = 1-1.6 kg/dm3
• s : wt strength of explosives (1.3 for gelatin)
• c : rock constant, generally 0.45
• f : 1 degree of fraction, for straight hole = 1
• E/V = ratio of spacing to burden
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22. Spacing determination
Spacing is the distance between blast holes fired in
the same row
• It is necessary to complete burden calculations
before determining the spacing.
S= (BL)0.5
• B : burden, ft
• L : borehole Length, ft
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23. Controlled Blasting
To control overbreak and to aid the stability of
the remaining rock formation.
• There are following methods:
• Line drilling (unloaded),
• Cushion blasting
• Smooth-wall blasting
• Presplitting
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24. Controlled Blasting – Line drilling
• Provides a plane of weakness to which the rock can break.
• Helps to reflect shock waves,
• Reduces the shattering effect of the rock outside the
perimeter.
• Do not exceed 3 in in dia and are spaced one to four
diameters apart (due to cost).
• Are not loaded
• Requires more drilling more than the other controlled
blasting methods.
• Is not very effective in non-homogeneous formations.
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25. Controlled Blasting – Line drilling
Free Unloaded
face line drill
holes
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26. Cushion Blasting
• Requires a single row of holes ( 2 to 3.5 in) in dia.
• Permits a reduction in the No. of holes required by line-drilling
• Unlike line-drilling holes, the cushion holes are loaded with
light charges.
• Holes are fully stemmed between charges, allowing no air gap,
and are fired after the production shot has been excavated.
• The stemming acts as a cushion to protect the finished wall from
the shock waves. The larger the borehole, the greater the
cushion.
• Not suitable for underground - tough stemming requirements.
• Drawbacks: (1) requires removal of excavated material before
firing (costly due to production delay – no excavation for entire
area at once). (2) Sometimes the production shot can break back
to the cushion holes, creating redrilling problems and causing
loading changes. 26

27. Smooth-wall Blasting
• Similar to cushion blasting
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28. Pre-splitting
• Creates a plane of shear in solid rows along
the desired excavation before the production
blast.
• All holes are loaded like cushion blasting
• Reduces overbreak
• Reduces the vibration
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