drilling & blasting · 2018. 7. 14. · drilling definition- the process of making a hole in...

DRILLING & BLASTING

DRILLING EQUIPMENTS

DRILLS

PERCUSSION DRILLS

ABRASION DRILLS

FUSION PIERCING

DRILL BITS

DETACHABLE BITS

FORGED BITS

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.

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

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

It is having mainly two types

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.

This type of machine having also two types

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.

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.

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.

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.

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.

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.

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.

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.

DRILLING PATTERN

There are mainly three types of drilling patterns:

Square pattern

Staggered pattern

Rectangle pattern

INITIATING PATTERN

Parallel

Diagonal

Through or v-pattern

Extended through or extended-V

OTHER PARAMETERS

Powder factor

Stemming and decking

Delay timing

Decoupling ratio

Base charge

Column charge

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

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.

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.

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.

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.

FIRING CHARGE

common practice to fire several holes using parallel

circuit,series circuit or combined parallel and series circuit

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.

BLASTING CAPS

DEFINITION- Small explosive

device used to detonate a

larger, more powerful explosive

such as dynamite.

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.

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.

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.

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

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”

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

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.

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.

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

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

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

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

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

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.

DELAY TIMING

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

ELECTRONIC DETONATORS

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.

NON ELECTRIC SYSTEM

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.

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.

BLAST DESIGN

PRELIMINARY GUIDELINES

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.

BENCH HEIGHT

BENCH HEIGHT IS DECIDED BY

PRODUCTION REQUIRED

TYPE OF DEPOSITE

THICKNESS

GEOLOGY

QUALITY

EQUIPMENT

DRILLING PARAMETERS

Hole diameter

Burden

Spacing

Subgrade drilling

Drilling pattern

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.

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

RELATIONSHIPS USED IN BLAST DESIGN