Blasting Design Blasting 1. Good Blasting and Good Drilling go hand in hand. 2. Drilling is the Foundation of the Blast Design. Explosion – A chemical reaction involving an extremely rapid expansion of gasses usually associated with the liberation of heat. Detonation – An explosive reaction that moves at a velocity greater than the speed of sound. Explosive - a substance that contains a great amount of stored chemical energy that can produce an explosion.

Explosives

1) Dynamite – Contains Nitroglycerin and Sensitizer a. Granular b. Gelatin c. Semi Gelatin

2) Ammonium Nitrate Based a. ANFO – Ammonium Nitrate & Fuel Oil

No water resistance b. Slurry (water gel) – water resistant ANFO

Good water resistance c. Emulsion – Stable Oil/Water Emulsion

Excellent water resistance

Explosive Properties

1) Density 2) Strength 3) Specific Gas Volume 4) Detonation Velocity 5) Detonation Pressure 6) Blasthole Pressure

Explosive Density (d) – The weight per volume of an explosive expressed as (kg/m3 or g/cm3 or lb/ft3).

69%

11%

10%

8% 2%

The U.S. consumed 3.76 million tons of explosives in 2008

Coal Mining

Construction

Quarrying, Non‐Metal

Metal Mining

Other

33anfo cm

g0.8

m

kg800d

Weight Strength/Energy – The energy content of an explosive expressed as an amount of energy per weight (kcal/kg or MJ/kg). Specific gas volume – The volume of gas produced per unit weight of explosive (liters/kg). Detonation Velocity

1) Detonation Velocity – The speed at which the reaction front moves through a cylindrical charge.

2) Typical values ranges from 1500 m/s (5500 f/s) to 7500 m/s (25,000 f/s). 3) Faster velocities provide a shattering effect to strong rocks while slower

velocities provide a heaving effect. Detonation Pressure

1) Detonation Pressure – The pressure of the detonation wave propagating through the explosive column.

2) Typical values ranges from 500 MPa (5 kilobars) to 15,000 MPa (150 kilobars). 3) Higher detonation pressures provide a better shattering effect for stronger

rocks. Blasthole Pressure

1) Blasthole Pressure – The pressure exerted on the walls of the blasthole perpendicular to the detonation pressure.

2) Typical values ranges from 1000 MPa (10 kilobars) to 6000 MPa (60 kilobars). 3) Higher blasthole pressures provide a stronger breaking force for stronger

rocks. Bulk Strength – The energy content of an explosive expressed as an amount of energy per volume. Bulk strength is the weight strength times the density (kcal/cm3). Relative Strength – The blasting energy of an explosive relative to the blasting energy of ANFO. Relative Weight Strength – The weight strength of an explosive relative to the weight strength of ANFO.

kg

kcal912Str anfow

d*StrStr wB

ANFO-W

A-WA-W Str

StrStr-Rel

Relative Bulk Strength – The bulk strength of an explosive relative to the bulk strength of ANFO.

ANFOANFO-W

AA-W

ANFO-B

A-BA-B d*Str

d*Str

Str

StrStr-Rel

Table. Explosive Properties

Explosive Property UnitsDynamite 

Gelatin

Dynamite 

Semi‐

Gelatin

ANFO 

AN(94%) 

+ FO(6%)

Emulsion 

(1000)

Emulsion 

(1070)

Density g/cc 1.51 1.30 0.82 1.24 1.28

Energy/Strength  (Weight) cal/g 1,055 955 880 650 730

                                  (Bulk) cal/cc 1,510 1,240 720 800 935

Relative Weight Strength 1.20 1.09 1.00 0.74 0.83

Relative Bulk Strength 2.10 1.72 1.00 1.11 1.30

Detonation Velocity m/s 5,300 4,300 3,900 5,800 5,500

ft/s 17,400 14,100 12,800 19,000 18,000

Detonation Pressure Kbars 106 60 31 91 97

Gas Volume (moles/kg) 32 37 43 44 44

Water Resistance Excellent Good None Excellent Excellent Bulk Strength (Problem) One particular mix of ANFO has a Weight Strength (StrW) of 912 kcal/kg and a Density (d) of 800 kg/m3. Explosive A has a Weight Strength (StrW)of 850 kcal/kg and a Density (d) of 1200 kg/m3. What is the Bulk Strength (StrB) of the ANFO in kcal/cm3? Relative Weight Strength (Problem) What is the Relative Weight Strength (Rel-StrW-A) of explosive A? Relative Bulk Strength (Problem) What is the Relative Bulk Strength (Rel-StrB-A) of explosive A?

3

36

3

3

ANFOANFO-WANFO-B

cm

kcal0.7296

cm 1x10

m*

m

kg800*

kg

kcal912

d*StrStr

93.0

kcal/kg 912

kcal/kg 850

Str

StrStr-Rel

ANFO-W

A-WA-W

1.4800*912

1200 *850

d*Str

d*Str

Str

StrStr-Rel

ANFOANFO-W

AA-W

ANFO-B

A-BA-B

Relative Blasting Energy – The blasting energy of an explosive relative to the blasting energy of ANFO. Explosive Selection

1) Rock Properties 2) Water Conditions in Hole 3) Hole Diameter 4) Number of Holes / Required Production

Rock Properties

1) Compressive Strength 2) Tensile Strength

a. 8-10 times lower than compressive strength 3) Density 4) Sonic Velocity – Compressive Wave Speed 5) Fracture Conditions

Rock Properties

Rock Type Min. Max. Mean Mean Mean Mean Min. Max.

Granite 2.6 2.7 24,070 1,740 6,525 0.23 13,700 19,700

Gneiss 2.6 2.9 23,055 3,020 8,410 0.22 12,000 19,000

Basalt 2.8 3.0 21,750 1,885 7,685 0.22 17,000 22,000

Dolomite 2.8 2.9 11,400 22,700

Marble 2.4 2.7 22,000 22,000

Limestone 2.3 2.7 14,790 1,740 6,960 0.25

  Soft " " 5,500 13,800

  Hard " " 9,100 20,990

  Crystalline " " 1,600 21,000

Salt 2.5 2.6

Sandstone 2.2 2.8 13,920 725 3,190 0.24 4,600 14,800

Quartzite 2.6 2.8 36,540 3,625 13,050 0.16 16,000 16,000

Shale 2.4 2.8 13,775 435 4,060 0.14 7,500 15,400

Water 1.0 1.0 0.50 1,000 1,000

ft/sec

Specific 

Gravity

Uniaxial 

Comp. 

Strength

Uniaxial 

Tensile 

Strength

Modulus 

of 

Elasticity

Poisson's 

RatioSonic Velocity

psi psi ksi

ANFO. of volumegas SpecificV

A. explosive of volumegas SpecificV

ANFO.strength weight Str

A. explosive ofstrength weight Str

A. explosive ofstrength relativeStr-Rel

V

V

6

1

Str

Str

6

5Str-Rel

ANFO-G

A-G

ANFO-W

A-W

A

ANFO-G

A-G

ANFO-W

A-WA

Explosive Selection In general, the Detonation Velocity (Vd) of the explosive should match, as closely as possible, the Sonic Velocity (Vs) of the rock to be blasted. There is no value in using an explosive which has a Vd greatly in excess of the Vs of the rock (Example) If the rock to be blasted is a hard limestone with a sonic velocity (Vs) of 17,500 ft/sec, then a 1070 Emulsion (Vd = 18,000 ft/sec) might be appropriate. Teller (1985) Approach: 1. Determine the Characteristic Impedance (Z) of the rock:

Where: SG = the Specific Gravity of the rock Vs = the Sonic Velocity of the rock, in ft/sec 2. Determine the Characteristic Powder Factor (CPF) for the rock and particular

explosive: Where: K = the Detonation Pressure of the explosive, in kbars 3. The CPF should be between 0.75 and 1.00. A. If CPF < 0.75 – The explosive has a Vd and/or density which is Higher than required. B. If CPF > 1.00 – The explosive has a Vd and/or density which is too Low for the rock (Problem) Using Teller’s approach, determine if the 1000 Emulsion will be appropriate for a hard limestone which has a Vs of 19,000 ft/sec. 1. The Characteristic Impedance (Z) of the Limestone is:

2. The Characteristic Powder Factor (CPF) for the Limestone and 1000 Emulsion is:

1000

V*SG*1.31Z s

KZ CPF

22.621000

000,19*5.2*31.1

1000

V*SG*1.31Z s

68.09122.62KZ CPF

3. No, the 1000 Emulsion has a Detonation Velocity and/or Density that is slightly higher than required.

Design of Drilling and Blasting Pattern: Parameters:

1) Hole Diameter 2) Burden 3) Spacing 4) Sub-Drilling 5) Hole Length 6) Hole Inclination 7) Stemming 8) Charge Length 9) Charge Concentration 10) Column Concentration 11) Bottom Concentration 12) Total Charge 13) Total Explosives 14) Volume of Rock per Foot Hole 15) Volume of Rock per Hole 16) Weight of Rock per Hole 17) Powder Factor 18) Number of Required Holes 19) Specific Drilling 20) Total Required Drilling 21) Hole Pattern 22) Delay Component 23) Firing Sequence 24) Blasting Cost

75.068.0 CPF

Blasting Notation Blasthole Diameter (D) – The diameter of the blasthole, it depends on:

1) Production Requirements - The higher the production requirements, the larger the hole diameter.

2) Bench Height – The higher the bench, the larger the hole diameter. 3) Environmental Restrictions – The larger the amount of explosives, the greater

the ground vibration. Blasthole Diameter

1) The larger the diameter, the greater the amount of explosives and the lower drilling cost per ton

2) Ranges from 1 in to 17 in (25 mm to 440 mm) Bench Height (H) – The height of the blasting bench.

J

Cross SectionCross Section

JCh

arg

e L

eng

thC

har

ge

Len

gth

B

S

Plan View

BD

T

HL

DD

LH

T

D B

Plan View

S

B

Charge Length = L - TJ = Sub-Drilling DistanceT = StemmingS = SpacingB = BurdenL = Blasthole LengthD = Blasthole DiameterH = Bench Height

J = Sub-Drilling DistanceT = StemmingS = SpacingB = BurdenL = Blasthole LengthD = Blasthole DiameterH = Bench Height

Figure 1. Bench Height vs. Recommended Blasthole Diameter (from Sandvik Tamrock, 1999)

(Example) According to the chart, if the Bench Height is 12 m (40 ft), then the Blasthole Diameter should be between 64 mm (2.5 in) and 127 mm (5 in). Sandvik Tamrock Formula: Where: D = the Blasthole Diameter (in inches) H = the Bench Height (in feet) (Example) If the Bench Height is 40 ft, then using the Sandvik Tamrock Formula, the Blasthole Diameter should be between 2.4 in and 4.8 in Burden (B) – The distance from the blasthole to the bench face or nearest free-surface. Also, the distance between rows of holes perpendicular to the bench face. Spacing (S) – The distance between the blastholes parallel to the bench or free-surface.

H*0.12) to(0.06D

in 4.8 ft 40 * 0.12H*0.12 D

in to 2.4ft 40 * 0.06H* 0.06D

Blasthole Length (L) – The length of the blasthole. Sub-Drilling Distance (J) – The length of the blasthole drilled below the bench level. If the blasthole is inclined at an angle (α), then the Blasthole Length (L) is: Stemming (T) – The length of the blasthole filled with non-explosive material to contain the blast. Burden Factor (KB) – Specifies the burden distance as a function of the blasthole diameter. For using ANFO with rocks that have a specific gravity of 2.5, KB averages about 25 for surface mines and 20 underground. Burden Factor - Ingersoll Rand recommends a Burden Factor of between 20 and 40:

1) 20 for difficult rocks 2) 40 for easy rocks

Burden Factor – Austin Powder Formula: Where: B = the Burden (ft) de = the Density of the Explosive (g/cc) dr = the Density of the Rock (g/cc)

D = the Blasthole Diameter (in) Problem Determine the Burden (B) for shale rocks if the explosive “Emulsion 1070” will be used with a 6 in Blasthole Diameter (D)? From the explosive and rock properties tables: de = 1.28 and dr = 2.6; therefore (Note: the “12” in the above equation is to properly convert the factor in the original equation, which takes inches and gives feet, into a dimensionless burden factor)

H-LJ

D*KB B

JHL

D*1.5d

d*2B

r

e

8.2912*1.52.6

1.28*2K

ft 14.9in 6*1.52.6

1.28*2B

B

α cosJHL

The Burden Factor for explosive A (KB-A) can be related to the Burden Factor for ANFO (KB-ANFO) using the Relative Bulk Strength (Rel-StrB-A) relationship: (Problem) For the previous explosive A, what would be the burden factor? Spacing Factor (KS) – Specifies the blasthole Spacing as a function of the Burden. KS typically equals about 1.0 - 1.3 for sequenced rows and 1.8 - 2.0 simultaneous rows. Spacing Factor – Ingersoll Rand and Sandvik Tamrick recommend a Spacing Factor (KS) of 1.25. Spacing Factor – Austin Powder Formula: Where: H = the Bench Height (ft) B = the Burden (ft) S = the Spacing (ft) (Problem) What will be the Spacing (S) if the Bench Height (H) is 50 ft and the Burden (B) is 15 ft? Based on Ingersoll Rand and Sandvik Tamrock: Based on Austin Powder:

B*KS S

6.29

4.1*25

Str-Rel*KK A-BANFO-BA-B

8

B*7H S 4;

B

H if

1.4K B*1.4 S 4;B

H if S

ft 18.75ft 15 * 1.25 B*1.25 S

ft 19.4

8

ft 15*7ft 50

8

B*7H S

43.3315

50

B

H

A-BANFO-BA-B Str-Rel*KK

Sub-Drilling Factor (KJ) – Specifies the distance of sub-drilling as a function of the burden. KJ typically equals about 0.2 - 0.3 for hard rock, but J typically equals -3 - -5 ft for coal. Ingersoll Rand and Sandvik Tamrock Recommend a Sub-Drilling Factor (KJ) between 0.2 -0.4. Austin Powder Recommends a Sub-Drilling Factor (KJ) between 0.2 - 0.5. Stemming Factor (KT) – Specifies the length of stemming as a function of the burden. Stemming Factor - Austin Powder Recommends a Stemming Factor (KT) between 0.7 – 1.3. The Particle Size (P) in the stemming is recommended to be 1/12 to 1/18 of the Blasthole Diameter (D)

B*KT T

B*KJ J

18) toD/(12P

Rock Volume (V) – The volume of rock broken per unit length of blasthole (m3/m or ft3/ft). Total Rock Volume (VT) – The total volume of rock broken per blasthole (m3 or ft3). Rock Weight (W) – The weight of rock broken per unit length of blasthole (kg/m or lb/ft). Total Rock Weight (WT) – The total weight of rock broken per blasthole (kg or lb). Explosive Charge (C) – The weight of explosive per unit length of blasthole (kg/m). Total Explosive Charge (CT) – The total weight of explosive per blasthole. Weight Powder Factor (PFweight) – The amount of explosive needed to fragment a certain mass of rock (kg/ton or lbs/ton).

d*D*4

πC 2

T)(L*d*D*4

πC exp

2T

H*)D*K*(K*d

T)(L*d*D*4

π

H*D)*K*(K*D)*(K*d

T)(L*d*D*4

π

H*S*B*d

T)(L*d*D*4

π

W

CPF

22BSrock

ANFO2

BSBrock

ANFO2

rock

ANFO2

T

Tweight

S*BV

H*S*BVT

rockrock d*S*Bd*VW

rockrockTT d*H*S*Bd*VW

Volume Powder Factor (PFvolume) – The amount of explosive needed to fragment a certain volume of rock (kg/m3 or lb/yd3).

H*D*K*K

T)(L*d*D*4

π

H*D)*K*(K*D)*(K

T)(L*d*D*4

π

H*S*B

T)(L*d*D*4

π

V

CPF

22BS

ANFO2

BSB

ANFO2

ANFO2

T

Tvolume

(Problem) At a surface mine, we have a 4 in Blasthole Diameter (D)using ANFO with a Density(dANFO) of 0.8 g/cm3. The rock has a Density (drock)of 2.5 g/cm3 and it has been found that a Burden Factor (KB) of 20 and a Spacing Factor (KS)of 1.2 effectively fragment the rock. What is the Weight-Based Powder Factor (PFweight) of this blast design? (We assume, since they do not say anything about bench height, stemming or sub-drilling, that the stemming and subdrilling are functionally zero compared to the drillhole length.) Burden & Spacing In some situations, you may know the Powder Factor (PF) for the rock and for a given blasthole Diameter (D), you are looking for the Burden (B) and Spacing (S).

H*D*K*K*d

T)(L*d*D*4

π

PF22

BSrock

ANFO2

weight

kg/tonnes 0.52

L*)(.1m)*20*(1.2*m

kg2500

0)(L*m

kg800*(.1m)*

4

π

H*D*K*K*d

T)(L*d*D*4

π

PF

223

32

22BSrock

ANFO2

weight

Sweightrock

ANFO2

weightrock

ANFO2

2S

rock

ANFO2

weight

K*PF*H*d

T)(L*d*D*4

π

B

PF*H*d

T)(L*d*D*4

π

B*KS*B

or H*S*B*d

T)(L*d*D*4

π

PF

(Problem) Assuming that the hole diameter is 100 mm, the spacing factor is 1.3, the explosive is ANFO with a density of 800 kg/m3 and the required powder factor is 0.31 kg /tonne, what is the Burden? (Again, we assume that the stemming and subdrilling are functionally zero.)

Sample Test Question #50. (Total Explosive Charge) Given a 35-ft deep, 7-7/8 in, diameter hole, 10 ft of stemming, and a prill specific gravity of 0.85; the charge (lb) of free poured ammonium nitrate and fuel oil (ANFO) prill is most nearly?

Sweightrock

ANFO2

K*PF*H*d

T)(L*d*D*4

π

B

2.5mB

1.3*tonnes

kg0.31*L*

m

tonnes2.5

0)(L*m

kg800*(0.1m)*

4

π

B

K*PF*H*d

T)(L*cm

g0.8

m

kg800d*D*

4

π

B

3

32

SWeightANFO

ANFO33anfo

2

lb 448.5

10)ft(35*ft

lb 62.4*0.85*

ftin12

in 7.875*

4

π

T)(L*d*D*4

πC

3

2

exp2

T

Sample Test Question #51. (Powder Factor) Given a 12-1/4 in. diameter blast hole, massive volcanic tuff overburden, poured ANFO prills, prill specific gravity of 0.85, 30 ft X 36 ft pattern, 8 ft of sub-drill, 21 ft of stemming and a 50 ft shovel bench height; the powder facter (pounds of explosive per bank cubic yard) is most nearly? Other Blasting: Ring Blasting – Holes are drilled from a central point and radiate outwards (also Fan Blasting). Used for: sublevel stoping, draw bell creation, tunneling, etc. Crater Blasting – Uses a spherical, or near spherical, charge in a half space to create a crater. Used for Vertical Crater Retreat (VCR), other.

3

3

3

3

2

ANFO2

T

Tvolume

ydlb0.803

ft 27yd 1

*50*36*30

21)ft8(50*ftlb

62.4*0.85*ftin12

12.25in*

4π

H*S*B

T)(L*d*D*4π

V

CPF

Flyrock

1) Uncontrolled material fragments generated by the effects of blasting 2) Rock fragments are thrown at excessive distances and can result in human

injuries, fatalities, property damage, litigation, etc. Causes of Flyrock

1) Insufficient burden 2) High explosive concentration 3) Improper blast design 4) Discontinuity in the overburden 5) Inadequate stemming 6) Improper delays

Air Blast

1) Transient increase in air pressure 2) Pressure wave travels at the speed of sound 3) Caused by the gas released during the detonation of the explosives

Controlling Air Blast To control air blasts, the delay between holes must be greater than tmin: Where: tmin = minimum delay time (in ms) S = the Blasthole Spacing (in feet)

1.127Stmin

Blast Vibrations 1) Shaking of the ground due to elastic waves emanating from the blast 2) Measured in inches per second (in/sec) of particle velocity 3) Can result in structural damage

The Peak Particle Velocities (PPV) are calculated as: Where: k = the Ground Response Factor where 24.2 < k < 242 with low to high confinement 160 is average SD = the Scaled Distance Factor The Scaled Distance Factor (SD) is calculated as: Where: Dist = the Distance to the nearest structure CT = the Total weight of explosive Charge per delay or per hole The Office of Surface Mining has established the following Peak Particle Velocities based on distance

(Problem) – For the following conditions: Blasthole Diameter (D) = 4 in, Blasthole Length (L) = 33 ft, Sub-Drilling (J) = 7 ft, ANFO with a Density (d) of 0.85 g/cm3, distance to nearest structure (Dist) = 600 ft, determine the Peak Particle Velocity (PPV) First, we calculate the total explosive charge in a hole (see above), being careful to keep the units consistent:

1.6SDkPPV

TCDistSD

lb 120

ft 7ft 33*cmg1

ftlb62.4*cmg0.85*

ftin12

in 4*

4

π

T)(L*d*D*4

πC

3

33

2

exp2

T

Then the Scaled Distance (SD) is: and the Peak Particle Velocity (PPV) is: This is less than the allowable 1.00 in/sec at 600 ft (see table above)

secin54.7120600CDistSD T

secin 0.26554.7160/SDkPPV 1.61.6