Blasting Rock

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• A. J. Clark School of Engineering •Department of Civil and Environmental Engineering

Sixth Edition

CHAPTER

13

Construction Planning, Equipment,and Methods

BL STING ROCKL STING ROCK

ByBy

Dr. Ibrahim Assakkaf Dr. Ibrahim Assakkaf

ENCEENCE 420420 – – Construction Equipment and MethodsConstruction Equipment and Methods

Spring 2003Spring 2003

Department of Civil and Environmental EngineeringDepartment of Civil and Environmental Engineering

University of Maryland, College ParkUniversity of Maryland, College Park

CHAPTER 13. BLASTING ROCKENCE 420 ©Assakkaf

Slide No. 1



CHAPTER 13. BLASTING ROCK

ENCE 420 ©Assakkaf

Slide No. 2


Slide No. 3

INTRODUCTIONINTRODUCTION

BLAST DESIGN BLAST DESIGN is not an exactis not an exact

science, but by considering thescience, but by considering the

rock formation it is possible torock formation it is possible to

produce the desired result.produce the desired result.This is a stepThis is a step--byby--step procedure forstep procedure for

designing the blast hole layout anddesigning the blast hole layout and

calculating the amount ofcalculating the amount of

explosives for blasting rock.explosives for blasting rock.




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Slide No. 4


””BlastingBlasting" is performed to break rock so" is performed to break rock so

that it may be quarried for processing inthat it may be quarried for processing inan aggregate production operation, or toan aggregate production operation, or toexcavate a rightexcavate a right--of of --way.way.

Blasting is accomplished by dischargingBlasting is accomplished by dischargingan explosive that has either beenan explosive that has either beenplaced in an unconfined manner, suchplaced in an unconfined manner, suchas mud capping boulders, or is confinedas mud capping boulders, or is confined

as in a borehole.as in a borehole.


Slide No. 5


There are two forms of energy releasedThere are two forms of energy released

when high explosives are detonated,when high explosives are detonated,

shock and gas. An unconfined chargeshock and gas. An unconfined charge

works by shock energy, whereas aworks by shock energy, whereas a

confined charge has a high gas energyconfined charge has a high gas energy

output.output.

There are many types of explosives andThere are many types of explosives and

methods for using them.methods for using them.




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Slide No. 6

Blast designBlast designPowder factor Powder factor

VibrationVibration

Trench rockTrench rock

PresplittingPresplitting

ProductionProduction

TOPICSTOPICS


Slide No. 7

GLOSSARY OF TERMSGLOSSARY OF TERMS

Face

Bench height

Burden distance

Spacing

Blasthole depth

Stemming

Subdrilling




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Slide No. 9

OVERVIEWOVERVIEW

Rock breakage results from gasRock breakage results from gas

pressure in the blasthole.pressure in the blasthole.

Radial crackingRadial cracking

Individual wedgesIndividual wedges Flexural ruptureFlexural rupture

Stiffness ratioStiffness ratio

bench height

burden distance




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Slide No. 10

BURDENBURDEN

It is the distance

to the free face

of theexcavation.

Burden distance is the most

criticaldimension in

blast design.


Slide No. 11

COMMERCIALCOMMERCIAL

EXPLOSIVESEXPLOSIVES

There are four main categories ofThere are four main categories of

commercial high explosives:commercial high explosives:

1. Dynamite,2. Slurries,

3. ANFO, and

4. Two-component explosives.




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Slide No. 14

DYNAMITEDYNAMITE

The approximate strength of a dynamiteThe approximate strength of a dynamiteis specified as a percentage (weight ofis specified as a percentage (weight of

nitroglycerin to the total weight of anitroglycerin to the total weight of a

cartridge.cartridge.

Cartridges vary in size fromCartridges vary in size from

approximately 1 to 8 in. in diameter andapproximately 1 to 8 in. in diameter and

8 to 24 in. long.8 to 24 in. long.

Dynamite is used extensively forDynamite is used extensively forchargingcharging boreholesboreholes, especially for the, especially for the

smaller sizes.smaller sizes.


Slide No. 15

Dynamite Cartridge




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Slide No. 16

DynamiteCartridge


Slide No. 17

SLURRIESSLURRIES

Slurries is generic term used for bothSlurries is generic term used for both

water gelswater gels andand emulsionemulsion

They are water They are water --resistant explosiveresistant explosive

mixtures of ammonium nitrate and amixtures of ammonium nitrate and afuel sensitizer fuel sensitizer

The primary sensitizing methods are:The primary sensitizing methods are:

introduction of air throughout the mixture

the addition of aluminum particles

or the addition of nitrocellulose




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Slide No. 18

In comparison to different explosives (suchIn comparison to different explosives (such

as ANFO), slurries have a higher cost peras ANFO), slurries have a higher cost perpound and have less energypound and have less energy

However, their higher cost can be justified ifHowever, their higher cost can be justified if

used in wet conditionused in wet condition

They are not water They are not water --sensitivesensitive

An advantage of slurries over dynamite is An advantage of slurries over dynamite is

that the separate ingredients can be hauledthat the separate ingredients can be hauled

to the project in bulk and mixedto the project in bulk and mixedimmediately before loading theimmediately before loading the blastholesblastholes

SLURRIESSLURRIES


Slide No. 19

ANFOANFO

ANFO is blasting agent that is ANFO is blasting agent that is

produced by mixingproduced by mixing prilledprilled ammoniumammonium

nitrate and fuel oilnitrate and fuel oil

This explosive is used extensively onThis explosive is used extensively onconstruction project and representsconstruction project and represents

about 80% of all explosives used inabout 80% of all explosives used in

the United Statesthe United States

ANFO is the cheapest and safest ANFO is the cheapest and safest

among othersamong others




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Slide No. 20

ANFOANFOANFO is an explosive used

extensively on construction projects.

Texas City, 16 April 1947


Slide No. 21

ANFOANFO

The ANFO is made by blending 3.5The ANFO is made by blending 3.5

quarts of fuel oil with 100 lb ofquarts of fuel oil with 100 lb of

ammonium nitrate blastingammonium nitrate blasting prillsprills

This the optimum ratio.This the optimum ratio.

The detonation efficiency is controlledThe detonation efficiency is controlled

by this ratio.by this ratio.

Because the mixture is freeBecause the mixture is free--flowing, itflowing, it

can be blown orcan be blown or augeredaugered from the bulkfrom the bulk

trucks directly into thetrucks directly into the blasholesblasholes..




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Slide No. 22

INITIATING AND DELAYINITIATING AND DELAY

DEVICESDEVICES

It is common practice to fireIt is common practice to fireseveral holes or rows of holes atseveral holes or rows of holes at

one time.one time.

Fragmentation,Fragmentation, backbreakebackbreake,,

vibration, and violence of a blastvibration, and violence of a blast

are all controlled by the firingare all controlled by the firing

sequence of the individualsequence of the individualblastholes.blastholes.


Slide No. 23

INITIATING AND DELAYINITIATING AND DELAY

DEVICESDEVICES

The order and timing of theThe order and timing of the

detonation of the individual holesdetonation of the individual holes

is regulated by the initiationis regulated by the initiation

system. Electric and nonsystem. Electric and non--electricelectricinitiation systems are available.initiation systems are available.

When selecting the properWhen selecting the proper

system, one should consider bothsystem, one should consider both

blast design and safety.blast design and safety.




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Slide No. 24

ELECTRIC BLASTING CAPSELECTRIC BLASTING CAPS

With an electric cap an explosion isWith an electric cap an explosion is

caused by passing an electric currentcaused by passing an electric current

through a wire bridge, similar to anthrough a wire bridge, similar to an

electric light bulb filament.electric light bulb filament.

A current of approximately 1.5 amps A current of approximately 1.5 amps

heats the bridge to ignite a heatheats the bridge to ignite a heat-- sensitivesensitive

flash compound.flash compound.

The ignition sets off a primer which in turnThe ignition sets off a primer which in turnfires a base charge in the cap.fires a base charge in the cap.


Slide No. 25

DELAY BLASTINGDELAY BLASTING

SYSTEMSSYSTEMSDelay blasting caps are used to obtain aDelay blasting caps are used to obtain a

specified firing sequence.specified firing sequence.

These caps are available forThese caps are available for delay intervalsdelay intervals

varying from a small fraction of second tovarying from a small fraction of second toabout 7 seconds.about 7 seconds.

When explosives charges in two or moreWhen explosives charges in two or more

rows of holes parallel to the face are fired inrows of holes parallel to the face are fired in

one shot, it is desirable to fire the charges inone shot, it is desirable to fire the charges in

the holes nearest the face a short timethe holes nearest the face a short time

ahead of those in the second row.ahead of those in the second row.




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Slide No. 26

DELAY BLASTINGDELAY BLASTING

SYSTEMSSYSTEMS

This procedure will reduce the burdenThis procedure will reduce the burdenin the second row, and hence, willin the second row, and hence, will

permit the explosives in the secondpermit the explosives in the second

row to break more effectively.row to break more effectively.

In the case of more than two rows ofIn the case of more than two rows of

explosives, this same delayed firingexplosives, this same delayed firing

sequence will be followed for eachsequence will be followed for eachsuccessive row.successive row.


Slide No. 27

DETONATING CORDDETONATING CORD

The detonating cord is a nonThe detonating cord is a non--

electric initiation system consistingelectric initiation system consisting

of a flexible cord having a centerof a flexible cord having a center

core of high explosive.core of high explosive.It is used to detonate dynamite andIt is used to detonate dynamite and

other capother cap--sensitive explosives.sensitive explosives.




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Slide No. 28

ROCK BREAKAGEROCK BREAKAGE

The major mechanisms of rockThe major mechanisms of rockbreakage result from the sustained gasbreakage result from the sustained gaspressure buildup in the borehole by thepressure buildup in the borehole by theexplosion.explosion.

First, this pressure will cause radialFirst, this pressure will cause radialcracking. Such cracking is similar tocracking. Such cracking is similar towhat happens in the case of frozenwhat happens in the case of frozenwater pipeswater pipes--a longitudinal split occursa longitudinal split occurs

parallel to the axis of the pipe.parallel to the axis of the pipe.


Slide No. 29

ROCK BREAKAGEROCK BREAKAGE

A A borehole is analogous to the frozenborehole is analogous to the frozen

pipepipe in that it is a cylindrical pressurein that it is a cylindrical pressure

vessel. But there is a difference in thevessel. But there is a difference in the

rate of loading. Arate of loading. A blastholeblasthole isispressurized instantaneously. Failure,pressurized instantaneously. Failure,

therefore, instead of being at the onetherefore, instead of being at the one

weakest seam, is inweakest seam, is in manymany seamsseams

parallel to the borehole.parallel to the borehole.




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Slide No. 30

BLAST DESIGNBLAST DESIGN

Every blast must be designed toEvery blast must be designed to

meet the existing conditions ofmeet the existing conditions of

the rock formation andthe rock formation and

overburden, and to produce theoverburden, and to produce the

desired final result. There is nodesired final result. There is no

single solution to this problem.single solution to this problem.


Slide No. 31


Rock is not a homogeneousRock is not a homogeneous

material. There are fracturematerial. There are fracture

planes, seams, and changes inplanes, seams, and changes inburden to be considered.burden to be considered.

Wave propagation is faster inWave propagation is faster in

hard rock than in soft rock.hard rock than in soft rock.




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Slide No. 32


Initial blast designs use idealizedInitial blast designs use idealizedassumptions. The engineer does thisassumptions. The engineer does this

realizing that discontinuities will berealizing that discontinuities will be

encountered in the field. Because ofencountered in the field. Because of

these facts, it must always bethese facts, it must always be

understood that the theoretical blastunderstood that the theoretical blast

design is only the starting point fordesign is only the starting point for

blasting operations in the field.blasting operations in the field.


Slide No. 33


A A trial blasttrial blast should always beshould always be

performed. It will either validateperformed. It will either validate

the initial assumptions orthe initial assumptions orprovide the information neededprovide the information needed

for final blast design.for final blast design.




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Slide No. 34

BURDENBURDEN

The most critical dimension in blastThe most critical dimension in blast

design is thedesign is the burden distanceburden distance asas

shown in Figure 1 (Fig 13shown in Figure 1 (Fig 13--1, Text)1, Text)

Burden distance is the shortestBurden distance is the shortest

distance to stress relief at the time adistance to stress relief at the time a

blasthole detonates. It is normally theblasthole detonates. It is normally the

distance to the free face in andistance to the free face in an

excavation, whether a quarry situationexcavation, whether a quarry situationor a highway cut.or a highway cut.


Slide No. 35

BURDENBURDEN

Figure 1. Blasthole Dimensional Terminology




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Slide No. 36


Slide No. 37

BURDENBURDEN

Internal faces can be created byInternal faces can be created by

blastholesblastholes fired on an earlier delayfired on an earlier delay

within a shot. When the burdenwithin a shot. When the burden

distance is insufficient, rock will bedistance is insufficient, rock will bethrown for excessive distances fromthrown for excessive distances from

the face, fragmentation may bethe face, fragmentation may be

excessively fine, and air blast levelsexcessively fine, and air blast levels

will be high.will be high.




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Slide No. 40

BURDENBURDEN

Table 1. Density by Nominal Rock Classifications (Table 13-1, Text)

Rock Classification Specific Gravity Density Broken (ton/cu yd)Basalt 1.8 – 3.0 2.36 – 2.53

Dibase 2.6 – 3.0 2.19 – 2.53

Diorite 2.8 – 3.0 2.36 – 2.53

Dolomite 2.8 – 2.9 2.36 – 2.44

Gneiss 2.6 – 2.9 2.19 – 2.44

Granite 2.6 – 2.9 2.19 – 2.28

Gypsum 2.3 – 2.8 1.94 – 2.26

Hematite 4.5 – 5.3 3.79 – 4.47

Limestone 2.4 – 2.9 1.94 – 2.28

Marble 2.1 – 2.9 2.02 – 2.28

Quartzite 2.0 – 2.8 2.19 – 2.36

Sandstone 2.0 – 2.8 1.85 – 2.36

Shale 2.4 – 2.8 2.02 – 2.36

Slate 2.5 – 2.8 2.28 – 2.36

Trap Rock 2.6 – 3.0 2.38 – 2.53


Slide No. 41

BURDENBURDEN

Explosive density is used inExplosive density is used in EqEq. 1 because. 1 because

of the proportional relationship betweenof the proportional relationship between

explosive density and strength.explosive density and strength.

There are, however, some explosiveThere are, however, some explosive

emulsions which exhibit differing strengthsemulsions which exhibit differing strengthsat equal densities.at equal densities.

In such a caseIn such a case EqEq. 1 will not be valid.. 1 will not be valid.

An equation based on relative bulk strength An equation based on relative bulk strength

instead of density can be used in suchinstead of density can be used in such

situations.situations.




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Slide No. 42

Example 1Example 1

A contractor plans to use dynamite that has specific A contractor plans to use dynamite that has specific

gravity of 1.3 to open an excavation in granite rock. Thegravity of 1.3 to open an excavation in granite rock. Thedrilling equipment available will drill a 3drilling equipment available will drill a 3--inin blastholeblasthole..

Dynamite comes packaged in 2 3/4Dynamite comes packaged in 2 3/4--in diameter sticks.in diameter sticks.

What is the recommended burden distance for the firstWhat is the recommended burden distance for the first

trial shot?trial shot?

From Table 1 (Table 14From Table 1 (Table 14--1 Text):1 Text):

ft7.6)75.2(5.18.2

)3.1(25.12

8.22

2.92.6Graniteof GravitySpecific

=

+=

+=

=+

=

e

r

e DSGSG B


Slide No. 43

BULK STRENGTHBULK STRENGTH

Relative bulk strength is the strengthRelative bulk strength is the strength

ratio for a constant volume compared toratio for a constant volume compared to

a standard explosive such as ANFOa standard explosive such as ANFO

ANFO, ammonium nitrate and fuel oil, is ANFO, ammonium nitrate and fuel oil, is

the standard explosive with an energythe standard explosive with an energy--level rating of 100level rating of 100

The relative bulk strength rating shouldThe relative bulk strength rating should

be based on test data under specifiedbe based on test data under specified

conditionsconditions




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Slide No. 44

ANFOANFO

ANFO is an explosive used

extensively on construction projects.

Texas City, 16 April 1947


Slide No. 45

Explosive diameter and

blasthole size are the same.

ANFO




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Slide No. 46

BULK STRENGTHBULK STRENGTH

The burden distance,The burden distance, BB, based on, based onrelative bulk energy is given byrelative bulk energy is given by

367.0r

ve

SG

St D B = (2)

SGr = specific gravity of the rock

De = diameter of the explosive, in.St v = relative bulk strength compared to ANFO


Slide No. 47

BURDEN DISTANCEBURDEN DISTANCE

When one or two rows ofWhen one or two rows of blastholesblastholes

are used, the burden distanceare used, the burden distance

between rows will usually be equal.between rows will usually be equal.

If more than two rows are to be firedIf more than two rows are to be fired

in a single shot, either the burdenin a single shot, either the burden

distance of the rear holesdistance of the rear holes must bemust be

adjustedadjusted or delay devices must beor delay devices must be

used to allow the face rock from theused to allow the face rock from the

front rows to move.front rows to move.




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Slide No. 48


The burden distance should also beThe burden distance should also be

adjusted because of the geologicaladjusted because of the geological

variations.variations.

Rock is not homogeneous materialRock is not homogeneous material

as assumed by all formulasas assumed by all formulas

Therefore, it is always necessary toTherefore, it is always necessary to

useuse correction factorscorrection factors for specificfor specific

geological conditions.geological conditions.


Slide No. 49

K d = ?

BURDENcorrected




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Slide No. 50


The corrected burden distance can beThe corrected burden distance can becomputed from the following equation:computed from the following equation:

WhereWhere

K K d d = correction factor for rock deposition= correction factor for rock deposition

K K ss = correction factor for rock structure= correction factor for rock structure

Table 2 gives burden distance correction factors forTable 2 gives burden distance correction factors forrock deposition and rock structurerock deposition and rock structure

sd K K B B ××=corrected (3)


Slide No. 51


CORRECTION FACTORSCORRECTION FACTORS


Rock Depostion KdBedding steeply dipping into cut 1.18

Bedding steeply dipping into face 0.95

Other cases of depostion 1.00

Rock Structure KsHeavily cracked, frequent weak joints, weakly

cemented layers

1.30

Thin, well-cemented layers with tight joints 1.10

Massive intact rock 0.95




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Slide No. 52

Example 2Example 2

A new quarry is being opened in a limestone A new quarry is being opened in a limestone

formation having horizontal bedding withformation having horizontal bedding with

numerous weak joints. From a borehole testnumerous weak joints. From a borehole test

drilling program it is believed that the limestonedrilling program it is believed that the limestone

is highly laminated with many weakly cementedis highly laminated with many weakly cemented

layers. Because of possible wet conditions, alayers. Because of possible wet conditions, a

cartridgedcartridged slurry (relative bulk density of 140)slurry (relative bulk density of 140)

will be used as explosive. The 6.5will be used as explosive. The 6.5--inin blastholesblastholes

will be loaded with 5will be loaded with 5--in diameter cartridges.in diameter cartridges.

What is the burden distance?What is the burden distance?


Slide No. 53

Example 2 (continued)Example 2 (continued)

From Table 1 (Table 13From Table 1 (Table 13--1, Text):1, Text):

For limestone, the specific gravity is between 2.4 andFor limestone, the specific gravity is between 2.4 and

2.92.9

Kd Kd = 1 (horizontal bedding, see Table 2)= 1 (horizontal bedding, see Table 2)

KsKs = 1.3 (numerous weakly cemented layers, Table 2)= 1.3 (numerous weakly cemented layers, Table 2)

ft65.126.2

140)5(67.067.0

9.22

2.92.4 GravitySpecificAverage

33 ===

=+

=

r

ve

SG

St D B

ft4.16)3.1)(1(65.12corrected ==××= Ks Kd B B




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Slide No. 54

Example 2 (continued)Example 2 (continued)

Table 1. Density by Nominal Rock Classifications (Table 13-1, Text)Rock Classification Specific Gravity Density Broken (ton/cu yd)

Basalt 1.8 – 3.0 2.36 – 2.53

Dibase 2.6 – 3.0 2.19 – 2.53

Diorite 2.8 – 3.0 2.36 – 2.53

Dolomite 2.8 – 2.9 2.36 – 2.44

Gneiss 2.6 – 2.9 2.19 – 2.44

Granite 2.6 – 2.9 2.19 – 2.28

Gypsum 2.3 – 2.8 1.94 – 2.26

Hematite 4.5 – 5.3 3.79 – 4.47

Limestone 2.4 – 2.9 1.94 – 2.28

Marble 2.1 – 2.9 2.02 – 2.28

Quartzite 2.0 – 2.8 2.19 – 2.36

Sandstone 2.0 – 2.8 1.85 – 2.36

Shale 2.4 – 2.8 2.02 – 2.36

Slate 2.5 – 2.8 2.28 – 2.36Trap Rock 2.6 – 3.0 2.38 – 2.53


Slide No. 55

STEMMINGSTEMMING

Definition:Definition:

Stemming is the adding of an inertStemming is the adding of an inert

material, such as drill cuttings, onmaterial, such as drill cuttings, on

top of the explosive in atop of the explosive in a blastholeblastholefor the purpose of confining thefor the purpose of confining the

energy of the explosiveenergy of the explosive

To function property the materialTo function property the material

used for stemming must lock intoused for stemming must lock into

the borehole.the borehole.




ENCE 420 ©Assakkaf

Slide No. 56


Slide No. 57

STEMMINGSTEMMING

It is common practice to useIt is common practice to use drilldrill

cuttingscuttings as the stemming material.as the stemming material.

To function properly, the stemmingTo function properly, the stemming

material should have an averagematerial should have an averagediameterdiameter 0.05 times the diameter of the0.05 times the diameter of the

holehole and should be angular.and should be angular.

If the stemming distance is too great,If the stemming distance is too great,

there will be poor top breakage from thethere will be poor top breakage from the

explosion andexplosion and backbreakbackbreak will increase.will increase.




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Slide No. 58

STEMMINGSTEMMING

When the stemming distance isWhen the stemming distance isinadequate, the explosion will escapeinadequate, the explosion will escape

prematurely from the hole.prematurely from the hole.

Under normal conditions, properlyUnder normal conditions, properly

designed burden and explosive, anddesigned burden and explosive, and

good stemming material, a stemminggood stemming material, a stemming

distance,distance, T T , of 0.7 times the burden, of 0.7 times the burden

distance,distance, BB, will be satisfactory., will be satisfactory.T T = 0.7 x= 0.7 x BB (4)


Slide No. 59

SUBDRILLINGSUBDRILLING

A shot will normally not break to the very A shot will normally not break to the very

bottom of the blasthole. This can bebottom of the blasthole. This can be

understood by remembering thatunderstood by remembering that thethe

second mechanism of breakage issecond mechanism of breakage is

flexural rupture.flexural rupture.To achieve a specified grade, one willTo achieve a specified grade, one will

need to drill below the desired floorneed to drill below the desired floor

elevation. This portion of the blastholeelevation. This portion of the blasthole

below the desired final grade is termedbelow the desired final grade is termed

"subdrilling.""subdrilling."




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Slide No. 60


TheThe subdrillingsubdrilling distance,distance, J J , required, requiredcan be approximated by the followingcan be approximated by the following

formula:formula:

J J = 0.3 x= 0.3 x BB

SubdrillingSubdrilling represents the depthrepresents the depth

required for explosive placementrequired for explosive placement, not, nota field drilling deptha field drilling depth

(5)


Slide No. 61


During the drilling operation thereDuring the drilling operation there

will be random drilling depthwill be random drilling depth

errors, holes will slough, anderrors, holes will slough, and

material will accidentally fall intomaterial will accidentally fall intosome holes. Therefore, forsome holes. Therefore, for

practical reasons drilling shouldpractical reasons drilling should

be to a depth slightly greater thanbe to a depth slightly greater than

that calculated.that calculated.




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Slide No. 62

BLASTHOLEBLASTHOLE SIZESIZE

The size (diameter) of the blasthole willThe size (diameter) of the blasthole will

affect blast considerations concerningaffect blast considerations concerning

fragmentation, air blast, flyrock, andfragmentation, air blast, flyrock, and

ground vibrationground vibration..

The economics of drilling is the secondThe economics of drilling is the second

consideration in determining blastholeconsideration in determining blasthole

size.size.

Larger holes are usually moreLarger holes are usually more

economical to drill but they introduceeconomical to drill but they introduce

possible blast problemspossible blast problems..


Slide No. 63


Once again, the second mechanismOnce again, the second mechanism

of rupture and the stiffness ratio (SR)of rupture and the stiffness ratio (SR)

need to be considered.need to be considered.

TheThe stiffness ratio (SR)stiffness ratio (SR) for blastingfor blastingpurposes is the bench height (purposes is the bench height (LL))

divided by the burden distance (divided by the burden distance (BB))..

B

LSR = (6)




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Slide No. 66

In the case of

deep cuts it may

be possible to

adjust the bench

height with

stepped cuts.

STIFFNESS RATIOSTIFFNESS RATIO


Slide No. 67

The bench

height should

be matched to

the reach ofthe excavation

equipment

(optimum

height of cut).

STIFFNESS RATIOSTIFFNESS RATIO




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Slide No. 70


One of the parameters in bothOne of the parameters in both EqsEqs. 1. 1and 2 was the diameter of the explosive,and 2 was the diameter of the explosive,

DDee. The diameter of the explosive is. The diameter of the explosive is

limited by the diameter of thelimited by the diameter of the blastholeblasthole

If it is desirable to drill largerIf it is desirable to drill larger blastholesblastholes

for economic reasons (usually cheaper),for economic reasons (usually cheaper),the burden distance will be affectedthe burden distance will be affected

e

r

e DSG

SG B

+= 5.1

2367.0

r

ve

SG

St D B =


Slide No. 71

Explosive diameter and bore hole

diameter may not be the same.

LINER or FILLER

EXPLOSIVE

BORE HOLE





ENCE 420 ©Assakkaf

Slide No. 72

Example 3Example 3

A contractor plans to use dynamite that has A contractor plans to use dynamite that has

specific gravity of 1.3 to open an excavation inspecific gravity of 1.3 to open an excavation ingranite rock. The drilling equipment availablegranite rock. The drilling equipment availablewill drill a 5will drill a 5--inin blastonesblastones. Dynamite comes. Dynamite comespackaged in 2.75packaged in 2.75--in and 4.5in and 4.5--diameter sticks. Ifdiameter sticks. Ifthe specifications call for a 13the specifications call for a 13--ft bench heightft bench heightand the extent of the excavation perpendicularand the extent of the excavation perpendicularto the face is 100 ft,how many rows ofto the face is 100 ft,how many rows ofblastholesblastholes will be required for both the 2.75 andwill be required for both the 2.75 and4.54.5--diameter packages? Which package ofdiameter packages? Which package of

dynamite will result in lesser blasting problems?dynamite will result in lesser blasting problems?


Slide No. 73

Example 3 (cont’d)Example 3 (cont’d)

For the 2.75For the 2.75--inin diadia. package:. package:

For the 4.5For the 4.5--in.in. diadia, package:, package:

rows1693.1516.7100requiredrowsof No.

ft7.675.2(5.18.2

)3.1(25.1

2

8.22


1

≈=+=

=

+=

+=

=+

=

e

r

e DSG

SG B

rows1017.10110.9

100 requiredrowsof No.

ft9.105.4(5.18.2

)3.1(25.1

22

≈=+=

=

+=

+= e

r

e DSG

SG B




ENCE 420 ©Assakkaf

Slide No. 74


For the 2.75For the 2.75--in.in. diadia. explosive package:. explosive package:

For the 4.5For the 4.5--in.in. diadia. explosive package:. explosive package:

Comparing the results of the stiffness ratios using Table 3Comparing the results of the stiffness ratios using Table 3

(Table 13(Table 13--3, Text), the 2.53, Text), the 2.5--in. diameter explosive packagein. diameter explosive packagehas lesser blasting problemhas lesser blasting problem

94.17.6

13

1

1 === B

LSR

19.19.10

13

2

2 === B

LSR


Slide No. 75


Stiffness Ratio (RS) 1 2 3 > 4*

Fragmentation Poor Fair Good Excellent

Air Blast Severe Fair Good Excellent

Flyrock Severe Fair Good Excellent

Ground Vibration Severe Fair Good Excellent*Stiffness Ratios above 4 yield no increase in benefit

Table 3. Stiffness Ratio’s Effect on Blasting Factors (Table 13-3, Text)




ENCE 420 ©Assakkaf

Slide No. 76

Example 4Example 4

Suppose that the rock blasting in Example 3 should beSuppose that the rock blasting in Example 3 should be

accomplished with a minimum stiffness ratio of 3, what willaccomplished with a minimum stiffness ratio of 3, what willbe the ideal explosive diameter?be the ideal explosive diameter?

33.43

13 ===⇒=

SR

L B

B

LSR

OK 306.325.4

13 25.4)75.1(5.1

8.2

)3.1(2

:CKECK

diameter -3/41or1.75diameterexplosiveideal

in783.1

ft33.45.18.2

)3.1(25.1

2

>===⇒=

+=

=∴

=∴

=

+=

+=

B

LSR B

D

D DSG

SG B

e

ee

r

e


Slide No. 77

SPACINGSPACING

Proper spacing of blastholes isProper spacing of blastholes is

controlled by the initiation timing and thecontrolled by the initiation timing and the

stiffness ratiostiffness ratio..

When holes are spaced too close andWhen holes are spaced too close and

fired instantaneously, venting of thefired instantaneously, venting of theenergy will occur with resultingenergy will occur with resulting air blastair blast

and flyrockand flyrock..

When the spacing is extended, there is aWhen the spacing is extended, there is a

limit beyond which fragmentation willlimit beyond which fragmentation will

become harsh.become harsh.




ENCE 420 ©Assakkaf

Slide No. 78

SPACINGSPACING

Before beginning a spacingBefore beginning a spacinganalysis, two questions must beanalysis, two questions must be

answered concerning the shot:answered concerning the shot:

1. Will the charges be fired

instantaneously or will delays be

used?

2. Is the stiffness ratio greater than 4?


Slide No. 79

SPACINGSPACING

Instantaneous initiation Instantaneous initiation:: SR SR

greater than 1 but less than 4greater than 1 but less than 4

Instantaneous initiation Instantaneous initiation:: SR SRequal to or greater than 4equal to or greater than 4

Text p. 388, equations (13Text p. 388, equations (13--6 and 136 and 13--7)7)

Spacing is controlled by initiation

timing and stiffness ratio.




ENCE 420 ©Assakkaf

Slide No. 80

SPACINGSPACING

Delayed initiation Delayed initiation:: SR greaterSR greater

than 1 but less than 4than 1 but less than 4

Delayed initiation Delayed initiation:: SR equal toSR equal to

or greater than 4or greater than 4

Text p. 388, equations (13Text p. 388, equations (13--8 and 138 and 13--9)9)

Spacing is controlled by initiationtiming and stiffness ratio.


Slide No. 81

SPACINGSPACING

An SR of less than 4 is considered a

low bench and a high bench is a SR

value of 4 or greater. This means that

there are four cases to be considered:

1. Instantaneous initiation. with the SR

greater than I but less than 4.

where S = spacing

L = bench height

3

2 B LS

+= (7)




ENCE 420 ©Assakkaf

Slide No. 82

SPACINGSPACING

2. Instantaneous initiation , with the SR

equal to or greater than 4.

3. Delayed initiation , with the SR

greater than I but less than 4.

BS 2= (8)

(9)8

7 B LS

+=


Slide No. 83

SPACINGSPACING

4. Delayed initiation, with the SR

equal to or greater than 4.

Note: The actual spacing utilized in the

field should be within 15% plus or

minus the calculated value.

BS 4.1= (9)




ENCE 420 ©Assakkaf

Slide No. 84

SPACINGSPACING

Spacing in the field shouldbe within plus or minus 15%

of the calculated value.

Calculated spacing

-15% +15%


Slide No. 85

Example 5Example 5

It is proposed to load 4It is proposed to load 4--in diameterin diameterblasholesblasholes with bulkwith bulk ANFO ANFO. The. Thecontractor would like to use an 8 Xcontractor would like to use an 8 X

8 drill pattern. Assuming the8 drill pattern. Assuming theburden distance is correct, will theburden distance is correct, will the88--ft spacing be acceptable? Theft spacing be acceptable? Thebench height is 35 ft and each holebench height is 35 ft and each holeis to be fired on separate delay.is to be fired on separate delay.




ENCE 420 ©Assakkaf

Slide No. 86


Check the stiffness ratio,Check the stiffness ratio, LL//BB for high or low bench:for high or low bench:

Delay timing; therefore, useDelay timing; therefore, use EqEq. 9:. 9:

The spacing is not OK. As a minimum, the patternThe spacing is not OK. As a minimum, the pattern

should be:should be:

8 X 9.58 X 9.5

ft35 andft8 == L B

ft4.48

35==

B

L

ft12.9to5.9 :0.15(11.2)11.2Range

ft2.11)8(4.1

=±=

==

S

S


Slide No. 87

Example 6Example 6

A project in granite rock will have an average bench A project in granite rock will have an average bench

height of 20 ft. An explosive having a specific gravity ofheight of 20 ft. An explosive having a specific gravity of

1.2 has been proposed. The contractor’s equipment1.2 has been proposed. The contractor’s equipment

can easily drill 3can easily drill 3--in diameter holes. Assume thein diameter holes. Assume the

packaged diameter of the explosives will be 2.5 in.packaged diameter of the explosives will be 2.5 in.

Delay blasting techniques will be used. Develop a blastDelay blasting techniques will be used. Develop a blastdesign for the project.design for the project.

From Table 1 (Table 13-1 Text):

ft93.5)5.2(5.175.2

)2.1(25.1

2

75.22


=

+=

+=

=+

=

e

r

e DSG

SG B




ENCE 420 ©Assakkaf

Slide No. 88



Rock Classification Specific Gravity Density Broken (ton/cu yd)Basalt 1.8 – 3.0 2.36 – 2.53

Dibase 2.6 – 3.0 2.19 – 2.53

Diorite 2.8 – 3.0 2.36 – 2.53

Dolomite 2.8 – 2.9 2.36 – 2.44

Gneiss 2.6 – 2.9 2.19 – 2.44

Granite 2.6 – 2.9 2.19 – 2.28

Gypsum 2.3 – 2.8 1.94 – 2.26

Hematite 4.5 – 5.3 3.79 – 4.47

Limestone 2.4 – 2.9 1.94 – 2.28

Marble 2.1 – 2.9 2.02 – 2.28

Quartzite 2.0 – 2.8 2.19 – 2.36

Sandstone 2.0 – 2.8 1.85 – 2.36

Shale 2.4 – 2.8 2.02 – 2.36

Slate 2.5 – 2.8 2.28 – 2.36

Trap Rock 2.6 – 3.0 2.38 – 2.53


Slide No. 89


Hence, use 6 in for the burden distance B.

Use 4 ft for the stemming depth, T.

Use 2 ft for subdrilling depth, J

As a first trial, use a 6-ft burden X 8-ft spacing pattern

ft8.1)6(3.03.0)(gsubdrillinThe ==×= B J

ft2.4)6(7.07.0)(depthstemmingThe

3)Tableto(accordinggood3.36

20

==×=

⇒===

BT

B

LSF

ft75.78

)6)(7(20

8

7 initiationdelayedand 41 =

+=

+=⇒<<

B LS SR

ft8.9to6.6 :0.15(7.75)7.75Range =±= S




ENCE 420 ©Assakkaf

Slide No. 90


Stiffness Ratio (RS) 1 2 3 > 4*

Fragmentation Poor Fair Good Excellent

Air Blast Severe Fair Good Excellent

Flyrock Severe Fair Good Excellent

Ground Vibration Severe Fair Good Excellent*Stiffness Ratios above 4 yield no increase in benefit

Table 3. Stiffness Ratio’s Effect on Blasting Factors (Table 13-3, Text)


Slide No. 91

POWDER COLUMN ANDPOWDER COLUMN AND

POWDER FACTOR POWDER FACTOR

The amount of explosive required toThe amount of explosive required to

fracture a cubic yard of rock is afracture a cubic yard of rock is a

measure of economy of blast design.measure of economy of blast design.

Table 5 (Table 13Table 5 (Table 13--4, Text) is a4, Text) is a

loading density chart which allowsloading density chart which allows

the engineer to easily calculate thethe engineer to easily calculate the

weight of explosive required for aweight of explosive required for a

blastholeblasthole..




ENCE 420 ©Assakkaf

Slide No. 94




“The powder column length is the total

hole length less stemming” that is

T J L −+= LengthPowder (10)


Slide No. 95




“The powder factor is the ratio of the total

weight (lb)of explosive in powder column

length to the total volume (cu yd) of rock

fractured by one blasthole under the pattern

area to a depth of bench depth equal L” that

is

yd)(cuAreaPatternunderVolumeTotal

LengthColumnPowderof (lb)WeightTotal FactorPowder = (11)




ENCE 420 ©Assakkaf

Slide No. 98



A stick dynamite ( A stick dynamite (GGss = 1.3) will require a= 1.3) will require aminimum of 8 in (0.667 ft). Therefore, there willminimum of 8 in (0.667 ft). Therefore, there will

be 208 in (17.33 ft) of ANFO and 8 in (0.67 ft) ofbe 208 in (17.33 ft) of ANFO and 8 in (0.67 ft) of

dynamitedynamite

The weight of explosives based on a 2.5The weight of explosives based on a 2.5--inin

explosive diameter will be:explosive diameter will be:

1.70 lb/ft X 17.33 ft = 29.46 lb

2.77 lb/ft X 0.67 ft = 1.85 lb

31.31 lb

The total per hole is 31.31 lb for 18 ft of powder column


Slide No. 99

MATERIAL HANDLINGMATERIAL HANDLING

CONSIDERATIONSCONSIDERATIONSThe economics of handling the fracturedThe economics of handling the fractured

rock is a factor which should berock is a factor which should be

considered in blast design.considered in blast design.

Although it is critical to achieve good Although it is critical to achieve goodbreakage, the blast pattern will affectbreakage, the blast pattern will affect

such considerations as the type ofsuch considerations as the type of

equipment and the bucket fill factor.equipment and the bucket fill factor.

The appropriate piling of the blasted rockThe appropriate piling of the blasted rock

by the shot is dependent on the blastby the shot is dependent on the blast

design.design.




ENCE 420 ©Assakkaf

Slide No. 100


CONSIDERATIONSCONSIDERATIONS

To utilize the blast to accomplish goodTo utilize the blast to accomplish goodbreakage and appropriate piling, one shouldbreakage and appropriate piling, one should

apply the following principles:apply the following principles:

1.Rock movement will be parallel to the burden

dimension.

2.Instantaneous initiation along a row causes more

displacement than delayed initiation.

3.Shots delayed row- by- row scatter the rock more

than shots fired in a V pattern.4.Shots designed in a V- pattern firing sequence

give maximum piling close to the face.

CHAPTER 13. BLASTING ROCKENCE 420 ©Assakkaf Slide No. 101


CONSIDERATIONSCONSIDERATIONS




ENCE 420 ©Assakkaf

Slide No. 102

PRESPLITTINGPRESPLITTING ROCK ROCK

PresplittingPresplitting Rock is a technique ofRock is a technique ofdrilling and blasting which breaks rockdrilling and blasting which breaks rockalong a relatively smooth surface (seealong a relatively smooth surface (seenext figure).next figure).

The holes usually are 2.5 to 3 in. inThe holes usually are 2.5 to 3 in. indiameter and are drilled along thediameter and are drilled along thedesired surface atdesired surface at spacingsspacings varyingvaryingfrom 18 to 36 in depending on thefrom 18 to 36 in depending on the

characteristic of the rock.characteristic of the rock.


PRESPLITTINGPRESPLITTING

Presplitting breaks rock alonga relatively smooth surface.




ENCE 420 ©Assakkaf

Slide No. 104


The holes are loaded with one orThe holes are loaded with one ortwo sticks of dynamite at thetwo sticks of dynamite at the

bottoms, with smaller charges,bottoms, with smaller charges,

such as 1.25 x 4such as 1.25 x 4-- in. sticks spacedin. sticks spaced

at 12at 12--in intervals to the top of thein intervals to the top of the

portion of the holes to be loaded.portion of the holes to be loaded.



It is important that the charges be less thanIt is important that the charges be less than

half thehalf the blastholeblasthole diameter and they should notdiameter and they should not

touch the walls of the holestouch the walls of the holes

The appropriate load of explosive per foot ofThe appropriate load of explosive per foot of

presplitpresplit blastholeblasthole is given byis given by

where d ec = explosive load, lb per ft

Dh = diameter of blasthole, in

28

2

hec

Dd = (12)




ENCE 420 ©Assakkaf

Slide No. 106


When the formula given byWhen the formula given by EqEq. 12 is used to. 12 is used to

arrive at an explosive loading, the spacingarrive at an explosive loading, the spacingbetweenbetween blastholesblastholes can be determined by thecan be determined by the

following equation:following equation:

where S p = presplit blasthole spacing, in

PresplitPresplit blastholesblastholes are not extended beloware not extended below

grade. In the bottom of the hole agrade. In the bottom of the hole a

concentrated charge of 2 to 3 timesconcentrated charge of 2 to 3 times d d ec ec shouldshouldbe placed instead ofbe placed instead of subdrillingsubdrilling

h p DS 10= (13)


Example 8Example 8

By contract specification the walls of a highwayBy contract specification the walls of a highway

excavation through rock must beexcavation through rock must be presplitpresplit. The. The

contractor will be using drilling equipmentcontractor will be using drilling equipment

capable of drilling a 3capable of drilling a 3--in hole. What explosivein hole. What explosive

load and hole spacing should he try for the firstload and hole spacing should he try for the first

presplitpresplit shot on the project?shot on the project?

lb0.960.323 beshouldload bottomThe

in30)3(1010

ft

lb32.0

28

)3(

28

22

=×

===

===

h p

hec

DS

Dd




ENCE 420 ©Assakkaf

Slide No. 108

SAFETY CONSIDERATIONSSAFETY CONSIDERATIONS

An accident involving explosives may An accident involving explosives may

easily kill or cause serious injury.easily kill or cause serious injury.

TheThe prevention of such accidentsprevention of such accidents

depends on careful planning anddepends on careful planning and

faithful observation of proper blastingfaithful observation of proper blasting

practices.practices.

There are federal and state regulationsThere are federal and state regulations

concerning the transportation andconcerning the transportation andhandling of explosives.handling of explosives.



Safety information on specific productsSafety information on specific products

is provided by the manufacturer.is provided by the manufacturer.

In addition to regulations and productIn addition to regulations and product

information, there are recommendedinformation, there are recommended

practices, such as the evacuation of thepractices, such as the evacuation of the

blast area during the approach of anblast area during the approach of an

electrical storm whether electric orelectrical storm whether electric or

nonelectricnonelectric initiation systems are used.initiation systems are used.




ENCE 420 ©Assakkaf

Slide No. 110


A good source for material on recommended A good source for material on recommended

blasting safety practices is the Institute ofblasting safety practices is the Institute ofMakers of Explosives in New York City.Makers of Explosives in New York City.

Misfire:Misfire: In shooting charges of explosives,In shooting charges of explosives,

one or more charges may fail to explode.one or more charges may fail to explode.

This is referred to as a “This is referred to as a “misfiremisfire..””

It is necessary to dispose of this explosiveIt is necessary to dispose of this explosive

before excavating the loosened rockbefore excavating the loosened rock

The most satisfactory method is to shoot it ifThe most satisfactory method is to shoot it if

possible.possible.


FACTORS AFFECTINGFACTORS AFFECTING

VIBRATIONVIBRATION

Some of the critical factors that should be

considered are:1. Burden 10. Rock Type

2. Spacing 11. Rock Physical Properties3. Subdrilling 12. Geological Features

4. Stemming Depth 13. Number of Holes in a Row

5. Type of Stemming 14. Number of Rows

6. Bench Height 15. Row-to-Row Delays

7. Number of Decks 16. Initiator Precision

8. Charge Geometry 17. Face Angle to Structure

9. Powder Column Length 18. Explosive Energy




ENCE 420 ©Assakkaf

Slide No. 112

Throw rock

SPACING donSPACING don’’t forgett forget ----SAFETYSAFETY


FACTORS AFFECTINGFACTORS AFFECTING

VIBRATIONVIBRATIONThe U.S. Bureau of Mines has proposed aThe U.S. Bureau of Mines has proposed a

formula to evaluate vibration and as a way toformula to evaluate vibration and as a way to

control blasting operation as follows:control blasting operation as follows:

wherewhere DDss = scaled distance (= scaled distance (nondimensionalnondimensional factor)factor)

d d = distance from shot to structure, ft= distance from shot to structure, ft

W W = maximum charge weight per delay, lb= maximum charge weight per delay, lb

A scale value of 50 or greater indicates that a A scale value of 50 or greater indicates that a

shot isshot is safesafe with respect to vibrationwith respect to vibration

Some regulatory agencies require a value of 60Some regulatory agencies require a value of 60

or greater or greater

W

d D s = (14)




ENCE 420 ©Assakkaf

Slide No. 114

VIBRATIONVIBRATION

D

d

W s =

Check vibration by formula

13-12 and adjust amount of

explosive per delay if

necessary.

Text p. 397


VIBRATIONVIBRATION

How many

holes atone time.

Blasting Rock

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