BLAST DESIGN BLAST DESIGN IN SURFACE IN SURFACE MINESMINES

Objectives of Blast Objectives of Blast DesignDesign

Obtaining optimum fragment sizeObtaining optimum fragment size Proper degree of fragmentation to Proper degree of fragmentation to

achieve the lowest combined cost of achieve the lowest combined cost of miningmining

Utilising explosive’s energy properly Utilising explosive’s energy properly through suitable blast design in the through suitable blast design in the minesmines

Controlling the unwanted effects of Controlling the unwanted effects of blasting blasting

Minimising the environmental impactsMinimising the environmental impacts

Steps in Designing Of a Steps in Designing Of a BlastBlast

Generate the geometry of the rock Generate the geometry of the rock mass mass

Determine the burden and spacing Determine the burden and spacing Establish the pattern of blast holes Establish the pattern of blast holes Determine the type of drilling Determine the type of drilling Determine the blast geometry Determine the blast geometry

parametersparameters Charge the holes with type of Charge the holes with type of

explosives selected, including decking explosives selected, including decking & stemming& stemming

Development of Initiation sequence Development of Initiation sequence systemsystem

Analyze the blast results obtainedAnalyze the blast results obtained

Design of Blast – An Design of Blast – An ApproachApproach

Keep knowledge on uncontrollable Keep knowledge on uncontrollable factors which affects the blastingfactors which affects the blasting

Concentrate on controllable factors Concentrate on controllable factors during the designing processduring the designing process

Controllable factors of Controllable factors of Blast DesignBlast Design

Bench Height and Blast hole DiameterBench Height and Blast hole Diameter Blast hole InclinationBlast hole Inclination BurdenBurden Burden Stiffness Ratio (BSR)Burden Stiffness Ratio (BSR) SpacingSpacing StemmingStemming Energy DistributionEnergy Distribution Sub grade drillingSub grade drilling

Controllable factors of Controllable factors of Blast DesignBlast Design

Blast hole length and Charge lengthBlast hole length and Charge length Volume CalculationsVolume Calculations Charging CalculationsCharging Calculations Powder FactorPowder Factor / Energy Factor / Energy Factor Block SizeBlock Size DeckingDecking Initiation sequence/Timing effectsInitiation sequence/Timing effects Initiation PatternInitiation Pattern

Un-Controllable factors of Un-Controllable factors of Blast DesignBlast Design

GeologyGeology Material StrengthMaterial Strength Material PropertiesMaterial Properties Structural discontinuitiesStructural discontinuities Weather conditionsWeather conditions WaterWater Environmental conditionsEnvironmental conditions

Bench Height and Blast Bench Height and Blast hole Diameterhole Diameter

Nature of deposit and Type of loading Nature of deposit and Type of loading equipment dictates the Bench heightequipment dictates the Bench height

Effect of diameter on fragmentation Effect of diameter on fragmentation and drilling economicsand drilling economics

Bench height,Environmental Bench height,Environmental constraints, Rock structure and Cost of constraints, Rock structure and Cost of Production decides the hole diameterProduction decides the hole diameter

ddminmin == 10 H10 H

ddmaxmax == 16.66 H + 5016.66 H + 50  

ddminmin = minimum hole diameter (mm) = minimum hole diameter (mm)

ddmaxmax = maximum hole diameter (mm) = maximum hole diameter (mm)H = bench height (m)H = bench height (m)

Blast hole InclinationBlast hole Inclination Less back breakLess back break Elimination of Toe problemsElimination of Toe problems Better displacementBetter displacement Increased fragmentation Increased fragmentation Stable faceStable face Blast hole inclination of 15Blast hole inclination of 1500- 25- 2500 is recommended for is recommended for

blasting in surface minesblasting in surface mines Bench height can be increased which reduces the Bench height can be increased which reduces the

number of haulage levelsnumber of haulage levelsDisadvantages:Disadvantages: Harder to collar holesHarder to collar holes Difficult to maintain accurate angleDifficult to maintain accurate angle More problems with geologic discontinuitiesMore problems with geologic discontinuities Easier to hang steel in holesEasier to hang steel in holes Difficult to charge (cartridge) explosivesDifficult to charge (cartridge) explosives Availability of drill machines with angle attachments Availability of drill machines with angle attachments

is poor (Often impossible with drilling machine being is poor (Often impossible with drilling machine being used)used)

BurdenBurden

Distance from a charge axis to the nearest Distance from a charge axis to the nearest free face free face

1.1. Konya (1983)Konya (1983)  

Burden, B (in ft) = [(2 SGBurden, B (in ft) = [(2 SGee / SG / SGrr + 1.5)] D + 1.5)] De e

Burden, B (in ft) = 0.67 [De] [RBe / SGBurden, B (in ft) = 0.67 [De] [RBe / SGrr ] ]0.330.33

Where, Where,

DDe e = Diameter of explosive to be used (inches) = Diameter of explosive to be used (inches)

SGSGe e = Specific gravity of explosive (g/cc)= Specific gravity of explosive (g/cc)

SGSGr r = Specific gravity of rock (g/cc)= Specific gravity of rock (g/cc)

RBRBe e = Relative Bulk strength of explosive= Relative Bulk strength of explosive  

BurdenBurden

2.Vutukuri and Bhandari (1973)2.Vutukuri and Bhandari (1973)  B = 0.024D + 0.85B = 0.024D + 0.85Where B is in meters and D is the hole diameter in mm.Where B is in meters and D is the hole diameter in mm.

  3.3.T.N.HaganT.N.Hagan  B,(m) = 20d – 35dB,(m) = 20d – 35d4.Rule of Thumb:4.Rule of Thumb: B = [{(explosive density/ rock density) 2 + B = [{(explosive density/ rock density) 2 +

1.8} d1.8} dee] / 84] / 84

Where B is in meters and ‘dWhere B is in meters and ‘dee’ is the Explosive ’ is the Explosive diameter in mm.diameter in mm.

Explosive density, rock density is in g/cc.Explosive density, rock density is in g/cc.  

Burden Stiffness Ratio Burden Stiffness Ratio (BSR)(BSR)

BSR = Bench height / Burden BSR = Bench height / Burden If BSR < 2, Poor FragmentationIf BSR < 2, Poor Fragmentation If BSR 2 – 3.5, Good Fragmentation If BSR 2 – 3.5, Good Fragmentation If BSR > 3.5, Excellent BreakageIf BSR > 3.5, Excellent Breakage BSR decides the need of Sub-grade BSR decides the need of Sub-grade

drilling, Spacing –distance, Type of drilling, Spacing –distance, Type of Explosive,etc.Explosive,etc.

SpacingSpacing Distance between adjacent blast holes Distance between adjacent blast holes

measured perpendicular to the burden measured perpendicular to the burden 1.1.Konya (1983)Konya (1983) Spacing, S = 1.15 – 1.4 BSpacing, S = 1.15 – 1.4 B2.T.N.Hagan2.T.N.Hagan  Spacing, S = B, for adequate results.Spacing, S = B, for adequate results. Spacing, S = 1.15 B, for hard, massive rocksSpacing, S = 1.15 B, for hard, massive rocks 3.Vutukuri and Bhandari (1973)3.Vutukuri and Bhandari (1973)  S = 0.9B + 0.91S = 0.9B + 0.91Where, Spacing(S) and Burden (B) are in meters.Where, Spacing(S) and Burden (B) are in meters.  

Mode of Mode of InitiationInitiation

L/B < 4L/B < 4 L/B L/B >> 4 4 L = Hole L = Hole depthdepth

B = BurdenB = Burden

S = SpacingS = SpacingInstantaneouInstantaneouss

S = (L+2B)/3S = (L+2B)/3 S = 2BS = 2B

DelayDelay S = (L+2B)/8S = (L+2B)/8 S = 1.4 BS = 1.4 B

StemmingStemming

To confine the gases produced by the explosive To confine the gases produced by the explosive until they have adequate time to fracture and until they have adequate time to fracture and move the groundmove the ground

1.Rule of Thumb:1.Rule of Thumb: Stemming, S = 0.7 B, for dry holesStemming, S = 0.7 B, for dry holes S ≥ B, for wet and heavily fractured S ≥ B, for wet and heavily fractured

holesholes2.T.N.Hagan2.T.N.HaganStemming, S = 20D – 60DStemming, S = 20D – 60DWhere, Burden, Stemming is in meters and D is the Where, Burden, Stemming is in meters and D is the

Diameter of blast hole in mm.Diameter of blast hole in mm. Crushed angular stone of about 1/20 times the Crushed angular stone of about 1/20 times the

diameter can be used for effective stemmingdiameter can be used for effective stemming

Energy DistributionEnergy Distribution

Energy Distribution, (%) = [(Bench height – Energy Distribution, (%) = [(Bench height – Stemming length) / Bench height] X 100Stemming length) / Bench height] X 100

Where,Stemming length,Bench height-Where,Stemming length,Bench height-values are in meters.values are in meters.

It should not be less than 80% in hard It should not be less than 80% in hard formationsformations

Sub-grade drillingSub-grade drilling Drilling below the floor levelDrilling below the floor level 1.Konya1.KonyaSub drilling, U = 0.3 BSub drilling, U = 0.3 BWhere, Sub drilling and Burden (B) - values are Where, Sub drilling and Burden (B) - values are

given in meters.given in meters.2.T.N.Hagan2.T.N.HaganSub drilling, U = 8 D, for satisfactory resultsSub drilling, U = 8 D, for satisfactory results U=10– 12 D, in the front rows/ toe U=10– 12 D, in the front rows/ toe

formationsformations-Diameter of the blast hole (D) is in mm.-Diameter of the blast hole (D) is in mm. 3. Rule of Thumb 3. Rule of Thumb Sub drilling, U = 10% of the Bench HeightSub drilling, U = 10% of the Bench Height

Blast hole lengthBlast hole length Blast hole length (m) = BH + Sub Blast hole length (m) = BH + Sub

drilling, for vertical holesdrilling, for vertical holes Blast hole length (m) = BH + Sub Blast hole length (m) = BH + Sub

drilling / cos (angle), for angle holesdrilling / cos (angle), for angle holes

Charge lengthCharge length Charge length, L (m)= Blast hole Charge length, L (m)= Blast hole

length – Stemming Lengthlength – Stemming Length

Volume CalculationsVolume Calculations

1.1.Bank cubic meters/ Hole,(mBank cubic meters/ Hole,(m33/hole) = /hole) = Burden (m) X Spacing (m) X Bench Burden (m) X Spacing (m) X Bench height (m)height (m)

2. 2. Bank cubic meters/ Hole, Bank cubic meters/ Hole, (tonnes/hole) = Burden (m) X Spacing (tonnes/hole) = Burden (m) X Spacing (m) X Bench height(m) X Rock (m) X Bench height(m) X Rock Density (g/cc)Density (g/cc)

  

Charging CalculationsCharging Calculations

1. 1. Loading Density(Kg of explosive / m of Loading Density(Kg of explosive / m of bore hole)bore hole)

= = 0.000785 X explosive density X 0.000785 X explosive density X (explosive diameter)(explosive diameter) 2 2

2. Explosive Energy (kcal. /kg of 2. Explosive Energy (kcal. /kg of explosive) explosive)

= = Same as Actual Weight Strength Same as Actual Weight Strength (kcal/gm)(kcal/gm)

3. Loading Energy (Cal of energy / meter 3. Loading Energy (Cal of energy / meter of bore hole)of bore hole)

= explosive energy X loading density= explosive energy X loading density

Powder FactorPowder Factor Relationship between how much rock Relationship between how much rock

is broken and how much explosives is broken and how much explosives are used to break itare used to break it

Specific charge, charge factor, specific Specific charge, charge factor, specific explosive consumption are used in explosive consumption are used in place of powder factor, in the fieldplace of powder factor, in the field

ISRM commission on blasting has ISRM commission on blasting has suggested to use either powder factor suggested to use either powder factor or specific charge or specific charge

Expressed in kg/mExpressed in kg/m33 or kg/t or kg/t

Powder Factor-Powder Factor-ApproachesApproaches

1.1. Based on Seismic wave velocity Based on Seismic wave velocity (Broadbent,1974)(Broadbent,1974)

2.2. Based on Drilling data (Leighton, Based on Drilling data (Leighton, 1982; Muftuoglu,1991)1982; Muftuoglu,1991)

3.3. Based on energy balance concept Based on energy balance concept (Berta,1990)(Berta,1990)

4.4. Based on rock properties Based on rock properties (Muftuoglu,1991)(Muftuoglu,1991)

5.5. Based on rock mass properties Based on rock mass properties (Kutuzov and Varenichev,1977)(Kutuzov and Varenichev,1977)

6. Based on Empirical procedure 6. Based on Empirical procedure (Adhikari, 1990)(Adhikari, 1990)

Powder Factor-Rule of Powder Factor-Rule of ThumbThumb

Powder factor(kg/cu.m) = Powder factor(kg/cu.m) = (Loading density X Explosive (Loading density X Explosive column length) / (BCM/hole)column length) / (BCM/hole)

Where, BCM - Bank cubic meters/ Where, BCM - Bank cubic meters/ Hole Hole

Loading Density-Kg of explosive / Loading Density-Kg of explosive / m of holem of hole

Explosive column length - Explosive column length - metersmeters..

Energy FactorEnergy Factor

Amount of explosive energy required Amount of explosive energy required to fragment and displace rockto fragment and displace rock

Better indicator than the powder Better indicator than the powder factor.factor.

Energy factor (KJ/cu.m) = (loading Energy factor (KJ/cu.m) = (loading energy X Explosive column length) / energy X Explosive column length) / (BCM/hole)(BCM/hole)

  

SELECTION OF SELECTION OF EXPLOSIVES AND EXPLOSIVES AND

ACCESSORIESACCESSORIES

Type of ExplosivesType of Explosives Rock mass properties, hardness, density, Rock mass properties, hardness, density,

moisture and geological featuresmoisture and geological features Quantity of ExplosivesQuantity of Explosives Dynamic tensile strength of the rock Dynamic tensile strength of the rock

mass and the fragmentation to be mass and the fragmentation to be achievedachieved

Type of Initiation systemType of Initiation system Timing accuracy and fragmentation, Timing accuracy and fragmentation,

Ground vibration controlGround vibration control

DeckingDecking

To give confinement of gases near soft To give confinement of gases near soft seam/void is encounteredseam/void is encountered

To assure a better energy distributionTo assure a better energy distribution To control ground vibrationTo control ground vibrationMin.decking length to separate charges (m) Min.decking length to separate charges (m)

= 10 X Charge diameter (mm), for dry holes= 10 X Charge diameter (mm), for dry holesMin.decking length to separate charges (m) Min.decking length to separate charges (m)

= 20 X Charge diameter (mm), for wet = 20 X Charge diameter (mm), for wet holesholes

primer/booster should be placed for each primer/booster should be placed for each individual chargeindividual charge

Block SizeBlock Size Depends on the number of joints present and Depends on the number of joints present and

joint spacing, RQD joint spacing, RQD

1. J1. JVV =Σ (1/ S =Σ (1/ Sii))

2. J2. JVV = 33 – (RQD/3.3) = 33 – (RQD/3.3)

Where, JWhere, JV V is the number of joints/cu.m of rock is the number of joints/cu.m of rock massmass;; S Sii is the i is the ithth joint spacing joint spacing

If JIf JVV-value < 3, the block can be large size-value < 3, the block can be large size

If JIf JVV-value is 3 -10, the block can be medium -value is 3 -10, the block can be medium sizesize

If JIf JVV-value > 10, only small size blocks can exit.-value > 10, only small size blocks can exit.

Initiation sequenceInitiation sequence Delay timings are governed by the desired Delay timings are governed by the desired

end results based on their priorityend results based on their priority Delay timing of 10 ms/m of the burden for Delay timing of 10 ms/m of the burden for

hard rock to 30 ms/m of burden for soft hard rock to 30 ms/m of burden for soft rockrock

Delay timing of 5 ms/m of effective burden Delay timing of 5 ms/m of effective burden for strong massive rocks to about 10 ms/m for strong massive rocks to about 10 ms/m for weak / highly fractured stratafor weak / highly fractured strata

Optimum delay is 3-6 ms/m of effective Optimum delay is 3-6 ms/m of effective burdenburden..

Initiation PatternInitiation Pattern Need to tailor muck pile shape to a Need to tailor muck pile shape to a

particular loading machine or particular loading machine or operating environmentoperating environment such as ramp- such as ramp-construction,etcconstruction,etc

V pattern, VI pattern, Diagonal V pattern, VI pattern, Diagonal pattern, Row-by-row initiation, Sink pattern, Row-by-row initiation, Sink cut, Slice cut, etc.cut, Slice cut, etc.

Critical design elements - burden Critical design elements - burden relief and timing vary according to relief and timing vary according to rock mass properties and the required rock mass properties and the required muck pile shape.muck pile shape.

SECONDARYSECONDARY BLASTINGBLASTING

To break oversize boulders, produced during To break oversize boulders, produced during the primary blasting in u/g or surface.the primary blasting in u/g or surface.

To produce a size suitable for crushing plant To produce a size suitable for crushing plant or hauling systemor hauling system

If crusher width is‘ b’ m, shovel dipper size is If crusher width is‘ b’ m, shovel dipper size is ‘ cd’ m3 then, the boulder size ‘ a’ should be ‘ cd’ m3 then, the boulder size ‘ a’ should be a=0.8b m and a=0.8 3a=0.8b m and a=0.8 3 cd m cd m

Secondary blasting techniquesSecondary blasting techniques Pop shooting or blockholing Pop shooting or blockholing Plaster shooting or mud cappingPlaster shooting or mud capping Shaped charge shooting Shaped charge shooting Snake holing Snake holing

Secondary Blasting TechniquesSecondary Blasting Techniques

POP SHOOTINGPOP SHOOTING PLASTER SHOOTINGPLASTER SHOOTING

SHAPED CHARGE SHAPED CHARGE SHOOTINGSHOOTING SNAKE HOLINGSNAKE HOLING

EVALUATION OF DRILLING EVALUATION OF DRILLING AND BLASTING - AND BLASTING -

CONSIDERATIONSCONSIDERATIONS Clear separation along planned bench slope.Clear separation along planned bench slope. Breakage along designated smooth bench floor.Breakage along designated smooth bench floor. Floor clean-up cost-dozer time.Floor clean-up cost-dozer time. Fragmentation- digging rates/hour averaged over a Fragmentation- digging rates/hour averaged over a

month.month. Haulage rates/hour averaged over a month.Haulage rates/hour averaged over a month. Secondary blasting cost (boulder, toe).Secondary blasting cost (boulder, toe). Average crusher output rate.Average crusher output rate. Disruption to mine operation.Disruption to mine operation. Ground vibration and air over pressure within limit.Ground vibration and air over pressure within limit. Number and duration of crusher hold-up time due Number and duration of crusher hold-up time due

to boulder jammingto boulder jamming Maintenance costs especially ground engaging Maintenance costs especially ground engaging

tools, dipper life, crusher concave life, etc.tools, dipper life, crusher concave life, etc. Dilution.Dilution.