drilling & blasting · 2018. 7. 14. · drilling definition- the process of making a hole in...
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DRILLING & BLASTING
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DRILLING EQUIPMENTS
DRILLS
PERCUSSION DRILLS
ABRASION DRILLS
FUSION PIERCING
DRILL BITS
DETACHABLE BITS
FORGED BITS
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DRILLING
DEFINITION- The process of
making a hole in hard materials
such as rocks and earth.
COMPONENTS –
Drill- Type of tool which holds
the drill bit and rotates it to
provide axial force to create a
hole.
Drill bits- Cutting tools used to
create cylindrical holes.
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TYPES OF DRILLS
PERCUSSION DRILLS
1.JACKHAMMER OR SINKERS 2.TRIPOD DRILLS
3.STOP HAMMER 4.DRIFTERS
5.CHURNS OR WELL DRILLS 6.PISTON DRILLS
7.WAGON DRILLS
ABRASION DRILLS
1.BLAST-HOLE DRILLS 2.SHOT DRILLS
3.DIAMOND DRILLS
FUSION PIERCING
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It can be work at any position and any
where
Machine is operated by hand power.
This machine contain small motor.
It having high speed and small drilling size.
The diameter of hole do not contain more
than 12 to 18 mm size
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It is having mainly two types
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This machine is designed for drilling a
small hole and at high speed in light job.
It can not contain arrangement of
automatic feed mechanisms.
The drill is purely feed into the work by
hand control .
This machine are capable rotating drill of
diameter from 1.5 to 15.5 mm
The speed of rotating drill is 2000 r.p.m.
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This type of machine having also two types
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PERCUSSION DRILLS Jackhammer or Sinkers- Air operated drill,
mainly used for drilling vertical holes.
Tripod drills- Mounted on tripod to provide
sufficient stability,used for very hard rocks.
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Stop hammers- Thrust end to hold the drill against the work and
usually used for “up” holes.
Drifters- Similar to jackhammer, but so large that it requires
mechanical mounting.
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Churns or Well drills- Reciprocating
Drill consisting of a long steel bit
mechanically lifted and dropped
to disintegrate the rock.
Piston drills- Drill rod is securely
fastened to the piston and travels
the full length of the piston stroke.
Wagon drills- Drifter mounted on a
mast supported by two or more
wheels used to drill holes at any
angle from down to slightly
above horizontal.
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ABRASION DRILLS
DEFINITION- Grind rock into small
particles through abrasive effect of bit
that rotates in hole.
TYPES-
1.Blast-hole drills
2.Shot drills
3.Diamond drills
Blast hole drills- Rotary drill consisting
of steel pipe drill stem on bottom of
which is roller bit that disintegrates the
rock as it rotates over it.
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Shot drills- Rotary drill whose bit consists of a steel pipe with a
roughened surface at bottom.
Diamond drills- Rotary drill whose bit consists
of metal matrix consisting a large number of
diamonds disintegrating the rock while rotating.
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FUSION PIERCING
Recent development in drilling holes for blasting purpose.
Produced by burning a mixture of oxygen and flux bearing fuel, such as kerosene at the end of a blow pipe.
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DRILL BITS
TYPES OF DRILL BITS-
Detachable bits- Removable from the drill when required.
Forged bits- Made up of single length of drill steel and are
available at several shapes.
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DRILLING PATTERNS
Selection of drilling pattern varies with the type and size of
the drill’s used, depth of hole, kind of rock, quantity,
rapidity of the explosive & amount of steaming.
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DRILLING PATTERN
There are mainly three types of drilling patterns:
Square pattern
Staggered pattern
Rectangle pattern
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INITIATING PATTERN
Parallel
Diagonal
Through or v-pattern
Extended through or extended-V
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OTHER PARAMETERS
Powder factor
Stemming and decking
Delay timing
Decoupling ratio
Base charge
Column charge
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BLASTING
DEFINITION- The process of
breaking rocks into smaller
pieces by use of explosives.
TYPES OF EXPLOSIVES-
Explosives based on chemical
nature
Explosives based on
availability
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OBJECTIVE
Rock is blasted either to break in to smaller pieces such as inmost mining and quarrying operations or large blocks fordimensional stone mining and some civil engineering application,or to create space.
In mining and quarrying operation, the main objective is toextract the largest possible quantity at minimum cost. Thematerial may include ore, coal, aggregate for construction andalso the waste rock required to remove the above useful material.
The blasting operation must be carried out to provide quality andquantity requirements of production in such a way that overallprofit of mining are maximized.
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EXPLOSIVES BASED ON
CHEMICAL NATURE
High or detonating explosives-
Process is extremely rapid, almost
instantaneous.
Low or deflagrating Explosives-
Low velocity of burning and
produce pressure by progressive
burning.
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EXPLOSIVES BASED ON
AVAILABILITY
Powder explosives- Slow burning , slow acting and low strength
explosives made either from potash nitrate or sodium nitrate.
Disruptive explosives or Dynamites-
Available in various sizes and
strength. Approximate strength
is specified as a percentage of
ratio of weight of nitroglycerine
to the total weight of a cartridge.
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DETONATORS DEFINITION- Cylindrical metal
shells close at one end having 6.8 mm
dia & 50 mm height.
The ignition of detonator is done by
blasting fuse or electric ignitors.
Following is required for electric
ignition:
1. Detonator.
2.Power source-dynamo.
3.Circuit line-iron or copper wires.
4.Electric ignitor-comprising 2 supply
wires detonator shell and priming
charge.
5.Line testing apparatus-galvanoscope or
measuring bridge.
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FIRING CHARGE
common practice to fire several holes using parallel
circuit,series circuit or combined parallel and series circuit
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FUSES
Fuses are required to ignite
explosives.
They are in the form of a small rope
of cotton with core of continuous
thread of gun powder.
The rate of burning is about 1
cm/sec.
They enable the person firing the
charge to move to a safe distance
before the explosion takes place.
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BLASTING CAPS
DEFINITION- Small explosive
device used to detonate a
larger, more powerful explosive
such as dynamite.
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TOOLS FOR BLASTING
1.Dipper 2.Jumper
3.Priming needle 4.Scraping spoon
5.Tamping bar
Dipper- Used to drill hole to the required depth.
Jumper- Used to make blast hole & more effective in boring a
nearly vertical hole.
Priming needle- Used to maintain the hole while tamping is done &
is in the form of a thin copper rod with a loop at one end.
Scraping spoon- Used to remove dust of crushed stone from blast
hole.
Tamping bar- Used to tamp the material while refilling a blast hole.
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PROCESS OF BLASTING
1.The blast holes are made and
cleaned by using the tools.
2.The charge of explosive placed
at the bottom.
3.Remaining portion is filled
with clay and tamped.
4.Fuse is inserted, kept
projecting 15-20 cm above the
rock surface.
5. Thereafter free end of fuse is
fired by detonator.
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TRANSPORTING AND HANDLING OF
EXPLOSIVES
1. Dynamite and detonators should be
kept separately when storing and
transporting.
2. Vehicle carrying explosives should
carry a warning sign and operated
with care.
3. The smoking or the carrying of
matches and lighteners etc., should
not be permitted on or around a
vehicle transporting explosives.
4. Wiring on motor-truck used for
moving explosives should be heavily
insulated.
5. Explosives should be stored in dry
ventilated bullet proof and fire
resistant magazines, away from
buildings and roads.
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TYPE OF EXPLOSION
The explosion is, according to Berthelot, 'The suddenexpansion of gases in a volume much larger thanthe initial, accompanied by noise and violentmechanical effects'.
The types of explosion are the following:
Mechanical
Electric
Nuclear
Chemical, From the Mining point of view, only the lastare of interest
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EXPLOSIVE“Explosive is a solid or liquid substance or a mixtureof substances which on application of a suitablestimulus is converted in a very short time intervalinto other more stable substances, largely or entirelygaseous, with the development of heat and highpressure”.
Or “Commercial explosives are those that are amixture of compounds, some combustible and someoxidizing which, when properly initiated, have analmost instantaneous exothermic reaction thatgenerates a series of high temperature gaseousproducts that are chemically more stable and take upa larger volume”
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DETONATION AND DEFLAGRATION Chemical explosives, depending upon the conditions to which
they are exposed, can offer different behavior than would beexpected from their explosive nature. The decompositionprocesses of an explosive compound are:
combustion: This can be defined as any chemical reactioncapable of giving off heat, whether it is actually felt by oursenses or not.
the deflagration: This is an exothermic process in which thetransmission of the decomposition reaction is mainly based uponthermal conductivity. It is a superficial phenomenon in whichthe deflagration front advances through the explosive in parallellayers at a low speed which, usually, is not over 1.000 m/s.
the detonation: In the detonating explosives, the speed of thefirst gasified molecules is so great that they do not lose theirheat through conductivity to the unreacted zone of the chargebut transmit it by shock, deforming it and provoking its heatingand adiabatic explosion, generating new gases
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PROPERTIES OF EXPLOSIVE
The properties of each group of explosives give prediction ofthe probable results of fragmentation, dis-placement andvibrations. 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 takeninto account are: fumes, resistance to high and lowtemperatures, de-sensitization by external causes, etc.
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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.
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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
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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.
• .
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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
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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
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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
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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
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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.
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DELAY TIMING
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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
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ELECTRONIC DETONATORS
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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.
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NON ELECTRIC SYSTEM
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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.
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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.
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BLAST DESIGN
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PRELIMINARY GUIDELINES
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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
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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.
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BENCH HEIGHT
BENCH HEIGHT IS DECIDED BY
PRODUCTION REQUIRED
TYPE OF DEPOSITE
THICKNESS
GEOLOGY
QUALITY
EQUIPMENT
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DRILLING PARAMETERS
Hole diameter
Burden
Spacing
Subgrade drilling
Drilling pattern
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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.
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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
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RELATIONSHIPS USED IN BLAST DESIGN