Its a presentation about the design aspect of open cast mine. The author believes it will surely help the mining engineering students at the beginning level.

1. BLAST DESIGN IN
OPENCAST MINES
Presented by
Gopal Karmakar
(Id- 511214015 )
and Jagat kumar
(Id- 511214014)
Mining Engineering
IIEST Shibpur

2. Outline
• Introduction
• Drilling
• Explosive used in opencast mine
• Types of variables in blast design
• Blasting patterns used in Indian
opencast mines
• Concept of optimum blasting
• Conclusion

3. Introduction
• Drilling and blasting is the major
unit operation.
• Basic objective should be
optimum fragmentation.
• Blasting should be modified as
per geologic condition.
• Drilling and blasting cost can be
as high as 25-30%.

4. Drilling
• Process of making hole by means of
hammering or rotary effect.
• Mechanism of drilling

5. Drilling
• Major types – percussive(63-150 mm and
120-219 mm) and rotary drill(90-165 mm).
• Under percussive – top hammer
drilling(22-250 mm) and DTH drilling(100-
200 mm).
• Jack hammer(32-38 mm) and wagon
drill(above 50 mm).
• Drill bits- Roller bits, drag bits, Button bits.

6. Explosive
Explosive Composition Velocity of
detonation
Slurry Explosive Prilled ammonium
nitrate -65%
TNT- 20%
Water- 15%
5500m/s
Emulsion Micro drop-lets of
supersaturated,
oxidizer salt solutions,
dispensed in a
continued medium of
carbonaceous fuel(oil)
Very high around
7000m/s
ANFO Ammonium nitrate -
94%
Fuel oil – 6%
3000m/s

7. Blasting
 There are two types of variables in
blasting design
1. Uncontrollable variables- geology,
rock characteristics and local
specifications
2. Controllable variables- Burden and
spacing, Hole diameter, hole depth,
Number of holes in the blast, Sub-
grade drilling, Stemming distance,
Stemming material, Powder factor

8. Blasting parameters
 Burden- the shortest distance between
two holes perpendicular to the face. It
should be adequate. In practice,
burden = ½ to 1/3 of bench height.
 Spacing- distance between two
consecutive holes in a row parallel to
face. It should be adequate. In
practice, spacing = 1.0 to 1.5 of
burden.

9. Blasting parameters
 Stemming distance – 0.7 to 1.0 of
burden is adequate. To much could
lead to excessive vibration and poor
fragmentation.
 Sub-grade drilling – blast holes may
not break to full depth, especially
when blasting takes place in dense
rock. In practice, sub-grade drilling =
0.2 to 0.5 of burden.

10. Blasting parameters
 Bench height – for determining bench
height stiffness ratio should be followed
stiffness ratio(bench height to burden)
must be between 2.5 to 4.
 Decking – the technique of decking is to
divide the explosive column into two or
more charges using inert materials. It
confines explosive gases to assure
better energy distribution for soft seam.
Minimum deck thickness= 6 times of hole
diameter.

11. Blasting parameters
 Powder factor – powder factor is the
amount of explosive in kg required to
achieve 1 ton mineral.
amount of rock per hole, V= B*S*H
Where , B= burden
S= spacing
H= height of bench
and V = volume of rock (Cum)

12. Blasting parameters
 Explosive consumption - The amount of
explosive required to break the rock into
an average size is called blasting
consumption. Explosive consumption
depends on rock strength and geology,
kind of explosive, size of hole, delay
system, initiation system, product size,
available free face etc.
 Energy factor – energy factor describes
the energy distribution within a given
units of rock. Proper energy distribution
is important in obtaining desired
fragmentation also to avoid toe
formation.

13. Blasting patterns followed in
opencast mine
There are two types of blasting patterns
followed in opencast mine –
 Single Row blasting pattern.
 Multi-row blasting pattern.
Generally multi- row blasting patterns
are followed for better fragmentation
and less explosive consumption.

14. Multi-row blasting patterns

15. Optimum blast design
concept
It is a holistic approach by identifying and
measuring costs involved in different process to
maximize the overall profit. The concept
developed by Mackenzie describes the total
blasting cost as:
Ct= Cd + Cb + Cl + Ch+ Cc/P
Where,
Ct = Total blasting cost per tonne of finish product,
Cd = Cost of Drilling,
Cb = Cost of blasting,
Ch = Cost of hauling,
Cc = Cost of Crushing,
Cl= Cost of loading.
P = Total tonnage of production.

16. Conclusion
 Explosive energy must be evenly
distributed to achieved uniform
fragmentation. This requires proper hole
diameter to bench height relationship,
appropriate S/B ratio and careful design.
 Explosive energy must be confined long
enough after detonation for better
fragmentation. This requires accurate
delays, proper stemming and stemming
material, holes must be loaded according
to geology.

17. Thank you