Drilling and blasting

1. Drilling And Blasting
Compiled by Jyoti Anischit
MSc , Engineering Geology
TU , Kathmandu

2. Drilling Types
Rotary Type by using:
- Tricone bit (water & oil).
- Drag bit (core drilling).
Rotary & Percussion Type by using:
- Top Hammer (drifter.) < 20m.
- Down The Hole (DTH) > 15m.

3. Rotary Drilling
Rotary drilling can be subdivided into
rotary cutting and rotary crushing.
Rotary cutting creates the hole by
shear forces, breaking the rock’s tensile
strength. The drill bit is furnished with
cutter inserts of hard metal alloys, and
the energy for breaking rock is provided
by rotation torque in the drill rod.
This technique is limited to rock with
low tensile strength, such as salt, silt,
and soft limestone not containing
abrasive quartz minerals.
Rotary crushing breaks the rock by
high point load, accomplished by a
toothed drill bit, which is pushed
downwards with high force. The bit,
being of tricone roller type fitted with
tungsten carbide buttons, is simultaneously
rotated, and drill cuttings are
removed from the hole bottom by
blowing compressed air through the
bit. Drill rigs used for rotary drilling are
large and heavy. The downwards
thrust is achieved by utilising the
weight of the drill rig itself, and
the rotation, via a hydraulic or
electric motor, applied at the end
of the drill pipe.

4. Contd.
Common hole diameters
range from 8 to 17.5 in
(200-440 mm) and, because adding
the heavy drill pipes is cumbersome,
most blasthole drillrigs use long
masts and pipes to accommodate
single-pass drilling of maximum 20 m
(65 ft). Electric power is usually
chosen for the large rigs, whereas
smaller rigs are often powered by
diesel engines.
Rotation rates vary from 50 to
120 rev/min, and the weight applied
to the bit varies from 0.5 t/in of bit
diameter in soft rock, to as much as
4 t/in of bit diameter in hard rock.
Recent technical advances include:
improved operator cab comfort; automatic
control and adjustment of optimum
feed force and rotation speed to
prevailing geology and bit type and
diameter; and incorporation of the
latest technology in electric and
hydraulic drive systems.
Rotary drilling, which is still the
dominant method in large open pits,
has limitations in that the rigs are not
suited to drill holes off the vertical line.
As blasting theories and practice have
proved, it is generally beneficial to
design, drill and blast the bench
slopes at an angle of approximately 18
degrees off vertical.
Many rotary rig masts have pinning
capabilities permitting drilling at
angles as much as 30 degrees out of
the vertical. However, the inclined hole
drilling capabilities in rotary drilling are
limited by the heavy feed force
required, since part of this force is
directed backwards. This causes rig
stability problems, reduced penetration,
and shorter life of drilling consumables.
Consequently, most blast
hole drilling using rotary drillrigs is for
vertical holes.

5. Percussive Drilling
Percussive drilling breaks the rock by
hammering impacts transferred from
the rock drill to the drill bit at the hole
bottom. The energy required to break
the rock is generated by a pneumatic
or hydraulic rock drill. A pressure is
built up, which, when released, drives
the piston forwards. The piston strikes on
the shankadapter, and the kinetic energy of the
piston is converted into a stress wave
travelling through the drill string to
the hole bottom. In order to obtain
the best drilling economy, the entire
system, rock drill to drill steel to rock,
must harmonise.
Percussion Pressure
The higher the pressure, the higher
will be the speed of the piston, and
consequently, the energy. Where the
bit is in good contact with hard and
competent rock, the shock wave
energy can be utilised to its maximum.
Conversely, when the bit has poor
contact, the energy cannot leave the
drill string, and reverses up the drill
string as a tensile wave.
It is only when drilling in sufficiently
hard rock that the maximum energy
per blow can be utilised. In soft
rock, to reduce the reflected energy,
the percussion pressure, and thus
the energy, will have to be lowered

6. For any given percussion pressure,
the amplitude, and hence the
stress in
the drill steel, will be higher with
reduced cross-section of the drill
rods.
To get the longest possible service
life
from shank adapters and rods, it is
important to ensure that the
working
pressure is matched to the drill
string
at all times.

8. Chemical explosives
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

9. 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.

10. How to compare explosives
• Strength
• Detonating velocity
• Fume class
• Water resistance
• Detonation pressure
• Energy
• Density
• Physical
characteristics
• Storage
• Freezing
• Sensitivity
• Sensitiveness
• Flammability

27. 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

28. Theory of Breakage
Involves two basic processes:
• Radial cracking
• Flexural rupture
14
• 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.

30. 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.

31. 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.

32. 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

33. 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

34. Controlled Blasting – 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,
26
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.

35. 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

36. Rock Excavation
Excavation Methods (e.g.)
Underground:
• Drill and split
• Mechanical (e.g. hydraulic breaker/hammer)
• Tunnel Boring Machine
• Drill and Blast
Surface:
• Drill and break / Diamond-saw cuts
• Mechanical (e.g. hydraulic breaker/hammer; WBE)
• Drill and Blast

37. Blasting Mechanism

38. Body Waves
P-wave (Longitudinal)
S-wave (Transverse or shear)
R-wave (Rayleigh)
Love wave

39. Body Waves
P-wave (Longitudinal)
Resultant vibration
S-wave (Transverse)
Rayleigh wave

40. Wave Motion (Undamped Free
Vibration)
ẋ
ẍ
Considered as a Simple Harmonic Motion (SHM)
A = Initial displacement from equilibrium 0 at time t = 0
x = Displacement from equilibrium 0 at time t
= A·Cos (ω·t) (ω = angular velocity or frequency)
ẋ = Velocity of body (or particle)
= -A·ω Sin (ω·t) = -A·ω Cos (ω·t + π/2)
ẍ = Acceleration of body (or particle)
= -A·ω² Cos (ω·t) = -A·ω² Cos (ω·t + π)
T = Period of Oscillation
= 2 π / ω
f = Frequency of Oscillation
= ω / 2 π (i.e. ω = 2 π f)

41. Risks of Ground Vibration
• Property loss
► Damage to buildings/structures
► Damage to underground services or
utilities
• Failure occurred of geotechnical features
• Nuisance
• Complaints

42. Introduction to EXPLOSIVES
• An explosive material, also called explosive, is a
reactive substance that contains a great amount of
potential energy that can produce an explosion if
released suddenly, usually accompanied by the
production of light, heat, sound, and pressure.
• This potential energy stored in an explosive material
may be chemical energy , pressurized gas or nuclear
energy.

43. Classification of Explosives :
Primary Explosives
Low Explosives
High Explosives

44. Primary Explosives :
• Initiating Explosives or detonators.
• They are highly sensitive explosives , which
explode on receiving a slight shock or by fire.
1. Lead azide :
2. Mercury Fulminate :
3. Tetracene :
4. Diazodinitro phenol :

45. Low Explosives
• They simply burn and do not explode
suddenly.
• The chemical reactions taking place in such
explosives are comparatively slow and their
burning proceeds from the surface inward in
layers at an approximate rate of 20 cm per
second.

46. Examples :
1. Black powder or gun-powder :
• It is a mixture of 75 % potassium nitrate, 15%
charcol and 10% sulphur.
• Uses : for blasting, in shells, igniters for
propellants, practice bombs.

47. 2. Smokeless powder (nitrocellulose) :
• It is prepared by treating cellulose with nitric
and sulphuric acids.
• It is called smokeless powder because it
produces carbon dioxide, carbon monoxide,
nitrogen, water vapour and almost no smoke.

48. High Explosives
• They have higher energy content than primary
explosives.
• They are stable and quite insensitive to fire
and mechanical shocks.

49. Single compound explosives
Ammonium nitrate :
2:4:6 – trinitrotoluene (TNT):
Pentaerythritol tetranitrate :
Cylonite (RDX) :

50. Binary Explosives
• They consist of mixture of TNT with other
explosives.
• TNT is an important ingredient of these binary
explosives, because it has low melting point.
• Ex : 1. Amatol: TNT + Ammonium nitrate.
2. pentolite : TNT + PETN, 50% each
3. Tropex : 40% RDX + 40% TNT + 20% Al
powder.

51. Plastic Explosives
• Combination of explosives which are in plastic
state and can be hand moulded and made into
various shapes, without any serious risk.

52. Dynamites
• They are containing of nitroglycerine(NG) as a
principal ingedient.
• NG is an oily-liquid, which detonates by
pressure, shock, or spontaneosly above 50%.
1. Straight-dynamites :
2. Blasting gelatin-dynamites :
3. Gelignite : 65% blasting gelatine + 35% of
absorbing powder. It can be used under water.

53. LEAD AZIDE
Pb(N3)2

54. • It is prepared by reacting aqueous solutions of
sodium azide and lead nitrate with each other.
2NaN3 + Pb(NO3)2 = Pb(N3)2 + NaNO3
• During the preparation, the formation of large crystals must be
avoided, since the breakup of the crystalline needles may
produce an explosion.
• Accordingly, technical grade product is mostly manufactured
which contains 92–96% Pb(N3)2, and is precipitated in the
presence of dextrin, polyvinyl alcohol, or other substances
which interfere with crystal growth.

55. MERCURY FULMINATE
Hg(CNO)2

56. • Mercury fulminate is prepared by dissolving mercury in
nitric acid, after which the solution is poured into 95%
ethanol.
• After a short time, vigorous gas evolution takes place and
crystals are formed.
• When the reaction is complete, the crystals are filtered by
suction and washed until neutral.
• The mercury fulminate product is obtained as small,
brown to grey pyramid-shaped crystals; the color is
caused by the presence of colloidal mercury.

57. TRINITROTOLUENE
(TNT)

58. • In industry, TNT is produced in a three-step process. First,
toluene is nitrated with a mixture of sulfuric and nitric acid
to produce mononitrotoluene (MNT).
• The MNT is separated and then renitrated to dinitrotoluene
or DNT.
• In the final step, the DNT is nitrated to trinitrotoluene or
TNT using an anhydrous mixture of nitric acid and oleum.
• Nitric acid is consumed by the manufacturing process, but
the diluted sulfuric acid can be reconcentrated and reused

59. GUN POWDER

60. • Gunpowder, also known as black powder, is a
chemical explosive—the earliest known. It is a mixture
of sulfur, charcoal, and potassium nitrate (saltpeter).
• The sulfur and charcoal act as fuels, and the saltpeter is
an oxidizer.
• Because of its burning properties and the amount of
heat and gas volume that it generates, gunpowder has
been widely used as a propellant in firearms and as
a pyrotechnic composition in fireworks.
• Gunpowder is classified as a low explosive because of
its relatively slow decomposition rate and consequently
low brisance.

61. • Gunpowder's burning rate increases with pressure,
so it bursts containers if contained but otherwise
just burns in the open.
• A simple, commonly cited, chemical equation for
the combustion of black powder is
10 KNO3 + 3 S + 8 C → 2 K2CO3 + 3K2SO4 + 6 CO2 + 5 N2.
• Because of its low brisance, black powder causes
fewer fractures and results in more usable stone
compared to other explosives, making black powder
useful for blasting monumental stone such
as granite and marble.

62. NITROGLYCERIN
(NG)

63. • Nitroglycerine is prepared by running highly concentrated,
almost anhydrous, and nearly chemically pure glycerin
(dynamite glycerin) into a highly concentrated mixture of nitric
and sulfuric acids, with constantly efficient cooling and
stirring.
• At the end of the reaction the nitroglycerine acid mixture is
given to a separator, where the nitroglycerine separates by
gravity. Following washing processes with water and an
alkaline soda solution remove the diluted residual acid.

64. BLASTING FUSES

65. A fuse is, a thin water
proof canvas length
of tube containing
gun powder(or TNT)
arranged to burn at a
given speed for
setting off charges of
explosives.

66. SAFETY FUSE
• A major contributor to progress in the use of explosives was
William Bickford in 1831 he conceived the safety fuse: a core of
black powder tightly wrapped in textiles, one of the most
important of which was jute yarn.
• The present-day version is not very different from the original
model. The cord is coated with a waterproofing agent, such as
asphalt, and is covered with either textile or plastic.
• Once ignited, safety fuses will burn underwater, and have no
external flame that might ignite methane or other fuels such as
might be found in mines or other industrial environments.
• Safety fuses are manufactured with specified burn times per
30 cm, e.g. 60 seconds, which means that a length of fuse 30 cm
long will take 60 seconds to burn.

67. DETONATING FUSE
• It is a thin, flexible plastic tube usually filled with
pentaerythritol tetra nitrate (PETN).
• With the PETN exploding at a rate of approximately 4 miles
per second, any common length of detonation cord appears
to explode instantaneously.
• It is a high-speed fuse which explodes, rather than burns, and
is suitable for detonating high explosives. The velocity of
detonation is sufficient to use it for synchronizing multiple
charges to detonate almost simultaneously even if the
charges are placed at different distances from the point of
initiation.
• It is used to reliably and inexpensively chain together multiple
explosive charges. Typical uses include mining, drilling,
demolitions, and warfare.

68. ROCKET PROPELLENTS

69. • Rocket propellant is a material used by a rocket as, or to produce
in a chemical reaction, the reaction mass (propulsive mass) that
is ejected, typically with very high speed, from a rocket engine to
produce thrust, and thus provide spacecraft propulsion.
• A chemical rocket propellant undergoes exothermic chemical
reactions to produce hot gas.
• There may be a single propellant, or multiple propellants; in the
latter case one can distinguish fuel and oxidizer.
• The gases produced expand and push on a nozzle, which
accelerates them until they rush out of the back of the rocket at
extremely high speed.
• For smaller attitude control thrusters, a compressed gas escapes
the spacecraft through a propelling nozzle.

70. CHARACTERISTICS
OF
GOOD PROPELLENTS

71. • should have high specific impulse that is the propellant
should produce greater thrust (downward force or
push) per second for 1 kg of the fuel burnt.
• should produce high temperatures on combustion.
• should produce low molecular weight products during
combustion and should not leave any solid residue
after ignition.
• should burn at a slow and steady rate (that is
predictable rate of combustion).
• should possess low ignition delay (that is it should burn
as soon as it is lighted up).
• should possess high density to minimize container
space.

72. • should be stable at a wide range of temperatures.
• should be safe for handling and storage.
• should be readily ignitable at predictable burning rate.
• should leave no solid residue after ignition.
• should not be corrosive and hygroscopic(ability to attract
and hold water molecules).
• should not produce toxic gases or corrosive gases during
combustion.

73. Blasting
Most basic unit operation of any
mining activity

74. OBJECTIVE
• Rock is blasted either to break in to smaller pieces such
as in most mining and quarrying operations or large
blocks for dimensional stone mining and some civil
engineering application, or to create space.
• In mining and quarrying operation, the main objective
is to extract the largest possible quantity at minimum
cost. The material may include ore, coal, aggregate for
construction and also the waste rock required to
remove the above useful material.
• The blasting operation must be carried out to provide
quality and quantity requirements of production in such
a way that overall profit of mining are maximized.

75. TYPE OF EXPLOSION
• The explosion is, according to Berthelot, 'The
sudden expansion of gases in a volume much
larger than the initial, accompanied by noise and
violent mechanical effects'.
• The types of explosion are the following:
 Mechanical
 Electric
 Nuclear
 Chemical, From the Mining point of view, only the
last are of interest

76. EXPLOSIVE
“Explosive is a solid or liquid substance or a mixture of substances
which on application of a suitable stimulus is converted in a very
short time interval into other more stable substances, largely or
entirely gaseous, with the development of heat and high
pressure”.
Or
“Commercial explosives are those that are a mixture of
compounds, some combustible and some oxidizing which, when
properly initiated, have an almost instantaneous exothermic
reaction that generates a series of high temperature gaseous
products that are chemically more stable and take up a larger
volume”

77. DETONATION AND DEFLAGRATION
• Chemical explosives, depending upon the conditions to which they
are exposed, can offer different behavior than would be expected
from their explosive nature. The decomposition processes of an
explosive compound are:
 combustion: This can be defined as any chemical reaction capable of
giving off heat, whether it is actually felt by our senses or not.
 the deflagration: This is an exothermic process in which the
transmission of the decomposition reaction is mainly based upon
thermal conductivity. It is a superficial phenomenon in which the
deflagration front advances through the explosive in parallel layers at
a low speed which, usually, is not over 1.000 m/s.
 the detonation: In the detonating explosives, the speed of the first
gasified molecules is so great that they do not lose their heat through
conductivity to the unreacted zone of the charge but transmit it by
shock, deforming it and provoking its heating and adiabatic explosion,
generating new gases

78. PROPERTIES OF EXPLOSIVE
• The properties of each group of explosives give prediction of
the probable results of fragmentation, dis-placement and
vibrations. The most important characteristics are:
• strength and energy developed
• detonation velocity
• Density
• detonation pressure
• water resistance
• sensitivity
• Other properties which affect their use and must be taken into
account are: fumes, resistance to high and low temperatures,
de-sensitization by external causes, etc.

79. EXPLOSIVE
TYPE
LOW EXPLOSIVE
• Slow and deflagrating
explosive (under 2000 m/s)
• Includes Gunpowder,
propulsive compounds for
fireworks.
• Practically no application in
mining and civil engg.
• With exception of
ornamental rocks.
HIGH EXPLOSIVE
• Rapid and Detonating explosive ( between
2000-7000 m/s)
Primary explosive
• Sensitive to Stimuli like weak
mechanical shock, spark or
flame.
• Mercury fulminate, Lead
Azide, Lead Styphnate
• Generally used in Detonators
Secondary explosive
• Capable of detonation
only under the influence
of shock wave generated
by PE.

80. INDUSTRIAL
EXPLOSIVE
BLASTING
AGENT
• Mixtures, with few
exceptions, do not
contain ingredients
classified as
explosive.
• Explosive needing
another high
explosive
• ANFO
• ALANFO
• Slurries and Water
gels
• Emulsions
• Heavy ANFO
CONVENTIONAL
EXPLOSIVE
• Essentially made up of
explosive substances.
• Best known that act as a
sensitizers of the mixtures.
• Gelatin dynamite
• Granular dynamite
PERMISSIBLE
EXPLOSIVE
• Designed for use in U/G coal
mines. where the presence
of explosive gases and dust is
dangerous for normal
blasting.
• Low explosion temperature.
• Medium or low strength
• Detonation velocity between
2000-4500 m/s.
• Density between 1.0-1.5 g/cc
• Generally poor water
resistance

81. Primers and Boosters
• A PRIMER CHARGE IS AN EXPLOSIVE IGNITED BY AN INITIATOR, WHICH, IN TURN,
INITIATES A NON CAP-SENSITIVE EXPLOSIVE OR BLASTING AGENT.
• A PRIMER CONTAINS CAP-SENSITIVE HIGH EXPLOSIVE INGREDIENTS. OFTEN HIGHLY
SENSITIZED SLURRIES, OR EMULSIONS ARE USED WITH BLASTING CAPS OR
DETONATING CORD.
• BOOSTERS ARE HIGHLY SENSITIZED EXPLOSIVES OR BLASTING AGENTS, USED
EITHER IN BULK FORM OR IN PACKAGES OF WEIGHTS GREATER THAN THOSE USED
FOR PRIMERS.
• BOOSTERS ARE PLACED WITHIN THE EXPLOSIVE COLUMN WHERE ADDITIONAL
BREAKING ENERGY IS REQUIRED.
• OFTEN-TIMES, CARTRIDGE OR PLASTIC-BAGGED DYNAMITES OR SENSITIZED WET
BLASTING AGENTS ARE USED AS PRIMERS AS WELL AS BOOSTERS.
• BOOSTERS ARE OFTEN USED NEAR THE BOTTOM OF THE BLASTHOLE AT THE TOE
LEVEL AS AN ADDITIONAL CHARGE FOR EXCESSIVE TOE BURDEN DISTANCES. THEY
ARE ALSO PLACED WITHIN THE EXPLOSIVE COLUMN ADJACENT TO GEOLOGICAL
ZONES THAT ARE DIFFICULT TO BREAK OR INTERMITTENTLY WITHIN THE MAIN
EXPLOSIVE CHARGE TO ENSURE CONTINUOUS DETONATION.

82. Initiating system
• ELECTRICAL SYSTEM- TILL DETONATOR OF PRIMING, ONLY ELECTRICAL
WIRES ARE ATTACHED.
• NON-ELECTRIC SYSTEM- THERE IS NO ELECTRIC WIRE IS REQUIRED IN
THE HOLE.
• D-CORD OR DETONATING FUSE

83. Electrical system
• There are mainly three types of electrical
initiation system which are widely used in
mines.
• INSTANTANEOUS ELECTRIC DETONATORS
• LONG/SHORT ELECTRIC DELAY DETONATOR
• ELECTRONIC DETONATOR

84. Electric detonators
• In electric detonators electric energy/current (ac/dc) is
sent through copper leg wire to heat an internal
connecting bridge wire.
• The heat initiates the high primary explosive present in
the detonator which, in turn, detonates the secondary
explosive present in the detonator.
• Electric detonators are used to initiate other explosive,
detonating cord and shock tube.
• For delay purpose pyrotechnical delay charge is used.
• three types of electric detonators
 Instantaneous electric detonators
 Short delay detonators (millisecond delay)
 Long delay detonators (half second delay)
• Time delays with intervals of 25, 50, 100, 500, and 1000
ms are available for short- (ms) or long-period (LP) delays

85. Electric detonators
• Safe blasting
practices dictate that
precautions are used
to avoid blasting in
the vicinity of
extraneous
electricity such as
stray current, static
electricity, electrical
storms, and radio
frequency energy
when using electric
caps.

86. Delay timing

87. Electronic detonators
• Electronic detonator have an electronic counter on a
microchip in place of pyrotechnic delay charge.
• Advantages:
 Higher timing precision (10 Microsecond than 1-10 ms
scatter)
 Increase control time delay
 Greater safety against accidental ignition (coded firing
signals)
• Disadvantages
 Higher price because of chip and capacitor
 Back to electric wiring-risk of ground faults or poor
contacts

88. Electronic detonators

89. Non electric system
• Non-electric initiation systems include a cap similar to that of an
electric cap, but they are connected to plastic tubing or a
transmission line that carries an initiation (shock and heat) to
initiate the cap.
• The energy source in the tubing is either a gas mixture or an internal
coating of special explosive.
• not used in underground coal or gassy mines
• provide nearly infinite numbers of delays in blasting patterns.
• Delays are available in short and long periods as well as in-hole and
surface delays.
• advantage
 ability to design blasts with a greater number of holes than
traditional electric blasting.
 Danger of stray currents are eliminated with the use of non-electric
systems.

90. Non electric system

91. Detonating cord
• Detonating cord consists of a core of PETN enclosed in a
tape wrapping that is further bound by counter-laced
textile yarns. The cord is either reinforced or completely
enclosed by strong waterproof plastic.
• Their energy release depends on the amount of PETN in
the core, which generally varies from 1.5 g/m to 70 g/m.
• 10 g/m is the PETN weight of standard detonating cord
whose VOD is about 7000 m/s.
• A detonator is required to initiate a length of detonating
cord which cannot be normally initiated by fire.

92. Detonating cord
• Detonating cord has two functions:
• to provide simultaneous detonation of several
interconnected blasthole charges, thus avoiding
the need for multiple electric or plain detonators
• to provide continuous initiation of the full length of
an explosive column in a blasthole, as distinct from
point initiation with individual detonators.

93. Blast design

94. Preliminary guidelines

95. • drilled burden (B) - is defined as the distance between the individual
rows of holes. It is also used to describe the distance from the front
row of holes to the free face. When the bench face is not vertical the
burden on this front row of holes varies from crest to toe.
• spacing (S) - is the distance between holes in any given row.
• Subgrade (J) - Generally the holes are drilled below the desired final
grade. This distance is referred to as the subgrade drilling or simply the
sub-drill
• Stemming (T) - A certain length of hole near the collar is left
uncharged. This will be referred to as the stemming length (T) whether
or not it is left unfilled or filled with drill cuttings/crushed rock.
• Bench height (H) – is the vertical height from the toe to the crest.
• drilled length (L) - is equal to the bench height plus the sub-drill.
• length of the explosive column (Le) - is equal to the hole length minus
the stemming. This column may be divided into sections (decks)
containing explosives of various strengths separated by lengths of
stemming materials.

96. BENCH HEIGHT
BENCH HEIGHT IS DECIDED BY
• PRODUCTION REQUIRED
• TYPE OF DEPOSITE
THICKNESS
GEOLOGY
QUALITY
• EQUIPMENT

97. Drilling parameters
• Hole diameter
• Burden
• Spacing
• Subgrade drilling
• Drilling pattern

98. burden
Some important empirical formulas for burden
• B = 24*d+0.85 (vutukuri)
• B = (25-30)*d (hagan)
• B = k*d*(p*t)^0.5 (pearse), where k = constant
(0.7-1), more for weak rock
P = peak explosive pressure, kg/cm^2
T = tensile strength of rock, kg/cm^2
• Burden is generally 25-40% of bench height
depending upon rock properties, fragmentation,
and explosive used.

99. spacing
• Generally we take spacing as 1.1-1.5 times of burden.
SUBGRADE DRILLING
• HOLES ARE DRILLED LONGER THAN BENCH HEIGHT TO AVOID TOE
PROBLEMS. THIS EXTRA DRILLING IS CALLED AS SUBGRADE DRILL.
• Sd = 0.1*H
• Sd = 0.3*B

100. Relationships used in blast design

101. Drilling pattern
• There are mainly three types of drilling
patterns:
• Square pattern
• Staggered pattern
• Rectangle pattern

102. Initiating pattern
• Parallel
• Diagonal
• Through or v-pattern
• Extended through or extended-V

103. Other parameters
• Powder factor
• Stemming and decking
• Delay timing
• Decoupling ratio
• Base charge
• Column charge

104. Thank you