BLASTING MOST BASIC UNIT OPERATION OF ANY MINING ACTIVITY

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.

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

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”

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

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.

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

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