ANALYZING EFFECTS OF AIRDECKS ON FRAGMENTATION ...

ANALYZING EFFECTS OF AIRDECKS ON FRAGMENTATION AND

ECONOMICS OF BENCH BLASTING

Submitted by

Shahab Saqib

2007-PhD-MIN-02

Supervisor

Prof. Dr. Syed Muhammad Tariq

Co-Supervisor

Dr. Zulfiqar Ali

Department of Mining Engineering

University of Engineering and Technology

Lahore, Pakistan

(2016)

ii

DECLARATION

I ―Shahab Saqib‖ declare that the thesis entitled: ―ANALYZING EFFECTS

OF AIRDECKS ON FRAGMENTATION AND ECONOMICS OF BENCH

BLASTING” is my own research wok and is being submitted for the partial

fulfilment for the degree of PhD in Mining Engineering. The thesis contains no

material that has been accepted and published for the award of any degree.

___________________

Signature

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External Examiners:

From Aboard:

i) Dr. Paul N. Worsey,

Professor,

Department of Mining & Nuclear Engineering, Missouri University of Science &

Technology, Rolla Missouri, USA.

ii) Dr. Zacharias G. Agioutantis,

Professor,

Department of Mining Engineering, University of Kentucky, Lexington, USA.

iii) Dr. Steven J.Schafrik,

Associate Professor,

Department of Mining and Minerals Engineering, Virginia Polytechnic Institute and

State University, Blacksburg, V A, USA.

From Pakistan:

Dr. F. A. K. Kirmani,

Professor ®

Mining Engineering Department, University of Engineering & Technology,

Lahore.

Internal Examiner:

Prof.(R) Dr. Syed Muhammad Tariq (Supervisor)

Dr. Zulfiqar Ali (Co-Supervisor)

Mining Engineering Department,

University of Engineering and Technology, Lahore

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ABSTRACT

The airdeck blasting technique has been used in the past to reduce the

explosive charge and to improve the rock fragmentation. However, the mining and

construction industry of Pakistan has always been reluctant to use airdecks in their

blasting operations. This is due to the fact that researchers and practitioners have a

divided opinion about the efficiency of this technique. In fact, several attempts in the

past have been made to find out the best position and optimum length of airdeck for

better fragmentation. Since, in the previous studies most of experiments were carried

out under varying geological conditions, it was very difficult to suggest the best

possible location and optimum length for airdeck in an explosive column for better

fragmentation.

In order to find out the best position of airdeck in explosive column that yields

better fragmentation, it was necessary to carry out all experiments on homogeneous

material and in controlled geological conditions. So that research findings indicate a

correlation between the concerned variables only and a benchmark research could be

established. Therefore, special homogeneous concrete blocks were designed for this

research. These concrete blocks eliminated the heterogeneity and anisotropy of rock

material, such as the fractures, folds, faults and joints of rock. Such factors have been

found to play a very crucial role in the size of debris produced from the blasted rock

material. This research will address two fundamental questions; the technical and the

economic efficiency of the airdeck blasting technique.

All the blasting experiments in this study were carried out in two phases. In

the first phase, a series of small scale experiments was conducted using homogeneous

concrete blocks. In order to find out the proper position and optimized length of the

airdeck, it was ensured that the concrete blocks had almost the same uniaxial

compressive strength. More than 40 tests with concrete blocks were performed for

this purpose. The evaluation of fragmentation by sieve analysis revealed that an

improved rock fragmentation was achieved when the airdeck was placed in the center

of the explosive column. Moreover, it was also observed that the mean blasted rock

fragment size increased with the increase in airdeck size and the best results were

achieved at 20% airdeck length.

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In the second phase of this research, the results of experimentation on concrete

blocks were validated on relatively homogeneous limestone at two cement quarries:

DG. Cement Chakwal and Askari Cement Nizampur. Several test blasts were carried

out with full column charge without airdeck and with 20% airdeck length placed at

middle of explosive column. The analysis of fragmentation for the benches after blast

was done using Split Desktop software. Subsequently it was deciphered that at both

the cement quarries, better fragmentation was achieved by placing airdeck at middle

of explosive column as compared to when there was no airdeck in the full column

charge. This research work also includes the use of multiple airdeck lengths placed at

middle position of explosive column for the limestone quarry and the results indicate

improved fragmentation.

The results of this research work clearly indicate that airdeck, when placed at

middle position of an explosive column produce more uniform blasted rock size

distribution compared to that at other positions. Moreover, the optimum length of

airdeck is 20% of the total length of explosive column and it improves environmental

factors like fly rocks, air blast, ground vibrations etc. The underlying reason behind

this is that the airdeck at middle position results in multiple impacts of shock wave

that leads to an efficient transfer of explosive energy in the surrounding rocks.

Economic analysis of explosive cost at both quarries was also conducted in

this study. From economic analysis at DG Cement Chakwal, it was observed that up

to 2.5 rupees per tonne of explosive cost could be saved by adopting 20% mid-airdeck

length in the explosive column as compared to the cost incurred for conventional

blasting techniques. By using above mentioned technique, saving per tonne can be

increased by 16% and rupees 750,000 can be saved at the DG. Cement quarry

monthly assuring an annual saving of rupees 9 million.

Similarly, the economic analysis conducted from the results of blasting at

Askari Cement Nizampur, it was observed that 2.6 rupees per tonne of explosive cost

can be saved by adopting 20% mid-airdeck length in the explosive column to enhance

the fragments as compared to the cost incurred for conventional blasting techniques.

Therefore, using 20% mid-airdeck length in explosive column, saving per tonne can

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be increased by 10.4% and rupees 468,000 can be saved at the Askari Cement quarry

monthly assuring an annual saving of 5.6 million rupees.

By using 20% airdeck lengths in explosive column, Rs. 44.33 million can be

saved annually for explosive used by Punjab, province of Pakistan. This amount can

be calculated for other provinces of the Pakistan as well. There are many other

minerals is Pakistan which require blasting for their production. If we could use the

improved airdeck blasting technique for the production of those minerals, billions of

rupees can be saved annually. Moreover, by incorporating the effect of even

fragmentation from blasting on downstream processes like crushing, milling etc.

millions of rupees can be saved.

It is anticipated that this study will provide answers and guide lines to

researchers and practitioners who were confused about best location and optimum

length of airdeck to be used in explosive column for achieving the optimum

fragmentation.

Keywords: Mining; Quarry; Concrete Block; Explosive; Airdeck; Blasting

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ACKNOWLEDGEMENTS

All praises and thanks to Almighty Allah (SWT),who blessed me and made

me capable to complete my PhD work. Peace and all blessings be upon his beloved

Holy prophet, Hazrat Muhammad (PBUH), whose guidance paved the way of humans

to civilization and saved humanity from the life of ignorance. He (PBUH) taught us

the way to live and be successful not only in this materialistic world but also in the

immortal life hereafter.

I feel privileged to offer my sincerest gratitude to my supervisor, Prof. Dr.

Syed Muhammad Tariq, and co-supervisor Dr. Zulfiqar Ali who have supported me

throughout my thesis with their guidance and knowledge whilst allowing me to

research in my own way under their guidance to achieve the destination. I attribute the

level of my PhD. degree to their encouragement and efforts and without their

supervision this thesis, too, would not have been completed.

I am thankful to the each member of Mining Engineering department who

helped me complete my research work. I am thankful to Dr. Zaka Emad and Mirza

Muhammad Zaid for their sincere help and encouragement during the whole time that

I have spent to do my humble work and to do something better for the mining, in an

effort to give some benefits to humanity. I am also paying my gratitude to the lab staff

of Mining & and Civil Engineering department who sincerely worked to pave my way

towards practical applications of my work.

My special thanks to University of Engineering and Technology because the

institution has always been proud for me and I always feel happy to do my research

work and put my efforts to pay tribute to my alma mater, which provided me this

prestigious opportunity. I am also thankful to M/S DG. Cement Chakwal and M/S

Askari Cement Nizampur who have helped me without any conditions for the

practical applications of my research work.

Last but not the least, I am thankful to my parents who brought me up and

made me capable to get the most esteemed degree of education. My special thanks to

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my wife and children because their help and smiling face always encouraged me to do

something best for them.

Shahab Saqib

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TABLE OF CONTENTS

Chapter Description Page No.

ACKNOWLEDGEMENTS ....................................................................................... VII

TABLE OF CONTENTS ............................................................................................ IX

LIST OF FIGURES ................................................................................................ XXII

CHAPTER 1. INTRODUCTION .............................................................................1

1.1 GENERAL ....................................................................................................1

1.2 PROBLEM STATEMENT ...........................................................................2

1.3 OBJECTIVES ...............................................................................................3

1.4 SCOPE ...........................................................................................................3

1.5 THESIS ORGANIZATION ..........................................................................3

CHAPTER 2. REVIEW OF LITERATURE ............................................................5

2.1 EXPLOSIVES AND BLASTING .................................................................5

2.1.1 Blasting Theories and Rock Breakage .........................................................5

2.1.1.1 Reflection theory (reflected stress waves) .......................................... 6

2.1.1.2 Gas expansion theory ......................................................................... 6

2.1.1.3 Flexural rupture ................................................................................. 6

2.1.1.4 Stress waves and gas expansion theory ............................................. 7

2.1.1.5 Stress waves, gas expansion and stress wave/flaw theory ................. 7

2.1.1.6 Nuclei or stress wave/flaw theory ...................................................... 8

2.1.1.7 Torque theory ..................................................................................... 9

2.1.1.8 Cratering theory ................................................................................. 9

2.1.1.8.1 Cratering mechanism ......................................................................... 9

2.2 DIFFERENT METHODS TO IMPROVE FRAGMENTATION ..............10

ABSTRACT ............................................................................. ................................ IV

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2.2.1 Effect of Timing on Blast Fragmentation...................................................11

2.2.2 New Work with Reference to Blast Fragmentation ....................................12

2.3 AIRDECK BLASTING TECHNIQUE .......................................................14

2.3.1 Understanding the Mechanism of Airdeck Blasting ..................................19

2.3.2 Airdeck Location ........................................................................................19

2.3.3 Airdeck Length ...........................................................................................20

2.3.4 Plugging Devices for Airdecking ...............................................................23

2.3.5 Effect of Airdecking on Fragmentation......................................................25

2.3.6 Economics of Airdeck Blasting ..................................................................26

2.4 METHODS FOR DETERMINING FRAGMENT SIZE DISTRIBUTION ...

.....................................................................................................................29

2.4.1 Sieving ........................................................................................................29

2.4.2 Digital Image Analysis ...............................................................................29

2.5 IMPORTANCE OF BLAST FRAGMENTATION ....................................30

2.5.1 Effects of Blast Fragmentation on Downstream Processes .......................31

2.5.1.1 Loading and hauling ........................................................................ 32

2.5.1.2 Crushing and grinding ..................................................................... 33

2.5.2 Effects of Blast Fragments on Energy Consumption in Crushing and

Grinding .....................................................................................................33

2.5.3 Effects of Blast Fragments from Mine to Mill ...........................................34

CHAPTER 3.LABORATORY SCALE EXPERIMENTATION AND RESULTS ....37

3.1 BACKGROUND .........................................................................................37

3.2 MODEL MATERIAL .................................................................................37

3.2.1 Dimensions of Blocks .................................................................................38

xi

3.3 EXPERIMENTAL SETUP .........................................................................39

3.3.1 Casting of Concrete Block .........................................................................39

3.3.2 Blast Design of Concrete Block .................................................................44

3.4 EXPERIMENTAL PROGRAM ..................................................................45

3.4.1 Different Steps Involved in Charging of Block ..........................................46

3.4.2 Blasting Testing .........................................................................................47

3.5 CONVENTIONAL BLASTING WITH FULL COLUMN CHARGE .....48

3.5.1 Charge Loading .........................................................................................48

3.6 MODIFIED BLASTING WITH AIRDECK AT DIFFERENT POSITIONS

OF EXPLOSIVE COLUMN ...........................................................................50

3.6.1 Airdeck Location ........................................................................................50

3.6.1.1 Concrete blocks with 20% airdeck length at top of explosive column

......................................................................................................... 50

3.6.1.1.1 Charge loading in case of 20% top airdeck blast ............................ 51

3.6.1.2 Concrete blocks with 20% airdeck length at mid of explosive column

......................................................................................................... 52

3.6.1.2.1 Charge loading in case of 20%mid-airdeck blast ............................ 53

3.6.1.3 Concrete blocks with 20% airdeck at bottom of explosive column . 55

3.6.1.3.1 Charge loading in case of 20% bottom airdeck blast ...................... 55

3.6.1.4 Results and discussion ..................................................................... 56

3.6.2 Optimum Airdeck Length ...........................................................................61

3.6.2.1 Concrete blocks with 10% airdeck length at the middle of the

explosive column ............................................................................. 61

3.6.2.1.1 Charge loading in case of 10% mid-airdeck blast........................... 61


......................................................................................................... 63

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......................................................................................................... 65


3.6.2.4 Concrete blocks with 40% airdeck length at the middle of the

explosive column ............................................................................. 67



......................................................................................................... 69


3.6.2.6 Results and discussion ..................................................................... 71

CHAPTER 4. VALIDATION AT DG.CEMENT CHAKWAL .............................74

4.1 DG.CEMENT CHAKWAL ........................................................................74

4.1.1 Geology of Study Area ...............................................................................74

4.1.1.1 Limestone deposits at the site .......................................................... 75

4.1.1.2 Sakesar formation ............................................................................ 75

4.1.2 Current Blasting Practices at DG. Cement Chakwal ................................76

4.1.2.1 Drilling ............................................................................................. 76

4.1.2.2 Drilling pattern ................................................................................ 76

4.1.2.3 Blasting ............................................................................................ 77

4.1.2.4 Explosives ........................................................................................ 77

4.1.2.5 Initiation system ............................................................................... 77

4.1.2.6 Blast design ...................................................................................... 77

4.1.2.7 Charging scheme ............................................................................. 78

4.1.2.8 Particle size distribution of conventional blast rock fragmentation 78

4.2 FULL SCALE FIELD EXPERIMENTATION AND RESULTS ..............80

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4.2.1 Conventional Blasting with Full Column Charge at Bench Number-1 .....80

4.2.1.1 Charge loading ................................................................................ 81

4.2.1.2 Conventional blast design parameters at bench number-1 ............. 81

4.2.1.3 Drilling pattern of full column charge holes at bench number-1 .... 82

4.2.1.4 Firing pattern of full column charge holes at bench number-1 ....... 82

4.2.2 Assessment of Blast Performance by Split Desktop ...................................84

4.1.2.1 Introduction of software ................................................................... 84

4.1.2.2 How it works .................................................................................... 85

4.1.2.3 Digital fragmentation analysis ........................................................ 86

4.2.3 Cost Per Tonne of Limestone Extracted by Conventional Blasting with Full

Column Charge at Bench Number-1..........................................................86

4.2.4 Modified Blast using 20% Airdeck Length at the Middle of Explosive

Column at Bench Number-1 .......................................................................87

4.2.4.1 Charge loading ................................................................................ 88

4.2.4.2 Design parameters of each hole for 20% airdeck blast at bench

number-1 ......................................................................................... 89

4.2.4.3 Drilling pattern of blastholes with 20% airdeck length at mid of

explosive column, at bench number-1 ............................................. 90

4.2.4.4 Firing pattern of blastholes with 20% airdeck length at mid of

explosive column, at bench number-1 ............................................. 90

4.2.4.5 Digital fragmentation analysis ........................................................ 92

4.2.4.6 Cost per tonne of limestone extracted by modified blasting method,

using 20% mid-airdeck length of explosive column at bench

number-1 ......................................................................................... 93

4.2.5 Modified Blast using 20% Airdeck Length at the Top of Explosive Column

at Bench Number-1 ....................................................................................94

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4.2.5.1 Charge Loading ............................................................................... 94

4.2.5.2 Drilling pattern of 20% top airdeck blast at bench number-1......... 95

4.2.5.3 Firing pattern of 20% top airdeck blast at bench number-1 ........... 96

4.2.5.4 Fragmentation analysis ................................................................... 96

4.2.6 Modified Blast using 20% Airdeck Length at the Bottom of Explosive

Column at Bench Number-1 .......................................................................97

4.2.6.1 Charge loading ................................................................................ 97

4.2.6.2 Drilling pattern of 20% bottom airdeck blast at bench number-1... 98

4.2.6.3 Firing pattern of 20% bottom airdeck blast at bench number-1. .... 98

4.2.6.4 Fragmentation analysis ................................................................... 99

4.2.7 Comparison of Blast Performance of all the Shots Fired at Bench

Number-1 .................................................................................................100

4.2.7.1 % age reduction in fragment size with respect to FXO series by

using 20% airdeck length in explosive column at bench number-1

....................................................................................................... 100

4.3 FULL SCALE BLASTS ...........................................................................103

4.3.1 Full Scale Conventional Blast with Full Column Charge at Bench

Number-2 .................................................................................................104

4.3.1.1 Conventional blast design parameters at bench number-2 ........... 105

4.3.1.2 Loading scheme of each hole in case of full scale conventional blast

with full column charge at bench number-2 .................................. 105

4.3.1.3 Drilling pattern of conventional blast with full column charge at

bench number- 2 ............................................................................ 106

4.3.1.4 Firing pattern of full scale conventional blast at bench .............

number-2 ............................................................................... 107

4.3.1.5 Fragmentation analysis ................................................................. 108

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4.3.1.6 Cost per tonne of limestone extracted by conventional blasting with

full column charge at bench number-2 .......................................... 109

4.3.2 Modified Full Scale Blast using 20% Airdeck Length at the Middle of

Explosive Column at Bench Number-2 ....................................................110

4.3.2.1 Design parameters of full scale 20% mid-airdeck blast at bench

number-2 ....................................................................................... 110

4.3.2.2 Loading scheme of each blasthole in case of full scale 20% mid-

airdeck blast at bench number-2 ................................................... 111

4.3.2.3 Drilling pattern of full scale 20%mid-airdeck blast at bench

number-2 ....................................................................................... 112

4.3.2.4 Firing pattern of full scale 20% mid-airdeck blast at bench

number-2 ....................................................................................... 112

4.3.2.5 Fragmentation analysis of 20% mid-airdeck blast at bench

number-2 ....................................................................................... 114

4.3.2.6 Cost per tonne of limestone extracted by modified blasting method

with 20% airdeck length at mid of explosive column at bench

number-2 ....................................................................................... 115

4.3.3 Comparison of Blast Performance of all Blasts Fired at Bench Number-2

..................................................................................................................116

4.3.3.1 %age reduction in fragment size with respect to FXO Series by

using 20% mid airdeck length in explosive column at bench

number-2 ....................................................................................... 116

4.3.3.2 Muckpile displacement at bench number -2 .................................. 118

4.3.3.3 Over break at bench number -2 ..................................................... 118

4.3.3.4 Level of floor at bench number-2 ................................................... 119

4.4 USE OF MULTIPLE AIRDECKS IN THE BLAST HOLE ....................119

4.4.1 Conventional Blasting with Full Column Charge at Bench Number-3 ..119

4.4.1.1 Conventional blast design parameters at bench number -3 .......... 119

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4.4.1.2 Charge loading .............................................................................. 120

4.4.1.3 Drilling pattern of conventional blast at bench number-3 ............ 121

4.4.1.4 Firing pattern of conventional blast at bench number-3 ............... 121


4.4.1.6 Cost per tonne of limestone extracted by conventional method at

DG. Cement Chakwal on bench number-3 .................................... 124

4.4.2 Multiple Airdeck Blasting using 20% Airdeck Lengths of Explosive

Column at DG. Cement Chakwal on Bench Number-3 ...........................125

4.4.2.1 Design parameters of multiple airdeck blast at bench number-3 .. 126

4.4.2.2 Charge loading .............................................................................. 126

4.4.2.3 Drilling pattern of holes having multiple airdeck at bench number-3

....................................................................................................... 127

4.4.2.4 Firing pattern of holes having multiple airdeck at bench number-3 ...

....................................................................................................... 127


4.4.2.6 Cost per tonne of limestone extracted by multiple-airdeck blast at

DG. Cement Chakwal on bench number-3 .................................... 129

4.4.3 Comparison of Blast Performance of all the Shots Fired at Bench

Number-3 ...........................................................................................130

4.4.3.1 % reduction in fragment size with respect to FXO series by using

multi- airdeck in explosive column at bench number-3 ............... 130

4.4.3.2 Influence of multi-airdeck blasting on overall blast performance. 133

CHAPTER 5. VALIDATION AT ASKARI CEMENT NIZAMPUR .................134

5.1 ASKARI CEMENT NIZAMPUR .............................................................134

5.1.1 Location and Accessibility .......................................................................134

5.1.2 General Geology ......................................................................................134

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5.1.2.1 Stratigraphy of DG. Cement Chakwal ........................................... 135

5.1.2.2 Lumshiwal limestone ...................................................................... 136

5.2 BLASTING EXPERIMENTS ...................................................................136

5.2.1 Conventional Blasting at Askari Cement Nizampur ................................136

5.2.1.1 Charge loading .............................................................................. 136

5.2.1.2 Conventional blast design parameters........................................... 137

5.2.1.3 Drilling pattern of conventional blast with full column charge holes

at Askari Cement Nizampur .......................................................... 138

5.2.1.4 Firing pattern of conventional blast with full column charge holes at

Askari Cement Nizampur ............................................................... 138

5.2.1.5 Fragmentations results .................................................................. 139

5.2.1.6 Cost per tonne of limestone extracted by conventional blasting at

Askari Cement Nizampur ............................................................... 140

5.2.2 Modified Blast using 20% Airdeck Length at Middle of the Explosive

Column at Askari Cement Nizampur ......................................................141

5.2.2.1 Charge loading .............................................................................. 142

5.2.2.2 Design parameters of modified blast with 20% airdeck length at

middle of explosive column at Askari Cement Nizampur .............. 143

5.2.2.3 Drilling pattern of modified blast with 20% airdeck length at the

middle of the explosive column at Askari Cement Nizampur ........ 144

5.2.2.4 Firing pattern of modified blast with 20% airdeck length at the

middle of the explosive column at Askari cement Nizampur ......... 144

5.2.2.5 Fragmentations results .................................................................. 147

5.2.2.6 Cost per tonne of limestone extracted by modified blast design with

20% airdeck length at middle of explosive column at Askari Cement

Nizampur ....................................................................................... 148

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5.2.3 Comparison of Performance of all Blasts Fired at Askari Cement

Nizampur ..................................................................................................149

5.2.3.1 %age reduction in fragment size with respect to FXO series by

using 20% airdeck length at mid of explosive column at Askari

Cement Nizampur .......................................................................... 149

5.2.3.2 Muckpile displacement................................................................... 151

5.2.3.3 Over break ..................................................................................... 152

5.2.3.4 Level of floor .................................................................................. 152

CHAPTER 6. ECONOMIC ANALYSIS .............................................................153

6.1 GENERAL .....................................................................................................153

6.2 COMPARISON OF COST OF EXPLOSIVE USED FOR CONVENTIONAL

AND MODIFIED BLAST WITH 20% AIRDECK LENGTH OF

EXPLOSIVE COLUMN AT DG. CEMENT CHAKWAL ..........................153


AND MODIFIED BLAST WITH 20% MID-AIRDECK LENGTH OF

EXPLOSIVE COLUMN AT ASKARI CEMENT NIZAMPUR ..................155

6.4 DISTRICT/MINERAL WISE LIMESTONE PRODUCTION IN MINING

INDUSTRY OF PUNJAB .............................................................................157

CHAPTER 7. CONCLUSIONS AND RECOMMENDATIONS ........................159

7.1 CONCLUSIONS .......................................................................................159

7.2 RECOMMENDATIONS ..........................................................................162

REFERENCES ........................................................................................................165

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LIST OF TABLES

Table Description Page No.

Table 2-1 Design parameters used for airdeck blasting [34] ......................................26

Table 2-2 Blast performance of airdeck blasts [34] ....................................................27

Table 2-3 Advantages of airdeck blasting [34] ...........................................................27

Table 2-4 Economics of airdeck blast [34] .................................................................28

Table 3-1 Concrete blocks composition for one block ................................................38

Table 3-2 Calculation of UCS of all blocks using universal testing machine .............43

Table 3-3 Different parameters used in the experimentation .......................................48

Table 3-4 Experimental results with respect to location of airdeck .............................57

Table 3-5 Experimental results in terms of mean fragment size .................................58

Table 3-6 Comparison of cumulative percent-passing of fragmentation of solid

charge vs. 20% airdeck at different positions ........................................59

Table 3-7 Experimental results with the varying lengths of the airdecks at the

middle position of the explosive column ...............................................71

Table 3-8 Mean fragmentation size for varying length of airdeck at middle

position of explosive column .................................................................71

Table 4-1 General geology of the DG. Cement Chakwal ............................................74

Table 4-2 Specifications of drill machine used at DG. Cement Chakwal ...................76

Table 4-3 Explosive used at DG. Cement Chakwal ....................................................77

Table 4-4 Blast design parameters used at DG. Cement Chakwal ..............................78

Table 4-5 Conventional blast design parameters at bench number-1 ..........................81

Table 4-6 Cost of the explosives used in a conventional blast at bench number-1 .....87

Table 4-7 The design parameters of each hole for 20% airdeck blast at bench

number-1 ................................................................................................89

Table 4-8 Cost of the explosives used in 20% mid-airdeck blast at bench

number-1 ................................................................................................93

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Table 4-9 Fragmentation results of conventional, 20% mid,20% top and 20%

bottom airdeck blasts at bench number-1 ............................................101

Table 4-10 Full scale conventional blast design parameters at bench number-2 ......105

Table 4-11 Cost of the explosive used in full scale conventional blast with full

column charge at bench number-2 .......................................................109

Table 4-12 Blast design parameters of full scale 20% mid-airdeck blast at bench

number-2 ..............................................................................................111

Table 4-13 Cost of the explosive used for full scale 20% mid-airdeck blast at

bench number-2....................................................................................115

Table 4-14 Fragmentation results of full scale conventional and 20% mid-

airdeck blast at bench number-2 ..........................................................116

Table 4-15 Muckpile distances ..................................................................................118

Table 4-16 Design parameters for conventional blast with full column charge at

DG. Cement Chakwal on bench number-3 ..........................................120

Table 4-17 Cumulative percentage passing of fragments of conventional blast at

DG. Cement Chakwal on bench number-3 ..........................................123

Table 4-18 Total quantity and cost of the explosive used per hole in

conventional blast with full column charge at DG. Cement

Chakwal on bench number-3 ...............................................................124

Table 4-19 Design parameters of multiple airdeck blast at bench number-3 ............126

Table 4-20 Cumulative percentage passing verses sieve sizes for fragments of

multi- airdeck blast...............................................................................128

Table 4-21 Total quantity and cost of the explosive used per hole in multi-

airdeck blast at bench number-3 ..........................................................129

Table 4-22 Comparison of percentage passing of conventional and multi-airdeck

blast for different sieve sizes at bench number-3 .................................131

Table 4-23 Cost comparison of conventional and multi-airdeck blast at bench

number-3 ..............................................................................................132

Table 4-24 Blast performance of multi-airdecked blast at bench number-3 .............133

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Table 5-1 Stratigraphical sequence of the site at Askari Cement Nizampur .............135

Table 5-2 Conventional blast design parameters with full column charge at

Askari Cement Nizampur.....................................................................137

Table 5-3 Total quantity and cost of the explosive used in conventional blast

with full column charge at Askari Cement Nizampur .........................140

Table 5-4 Modified blast design parameters with 20% airdeck length at middle

of explosive column at Askari Cement Nizampur ...............................143

Table 5-5 Total quantity and cost of the explosive used in the blast with 20%

airdeck length at middle of explosive column at Askari Cement

Nizampur ..............................................................................................148

Table 5-6 Fragmentation results of conventional and 20% mid-airdeck blast at


Table 5-7 Muckpile distances ....................................................................................152

Table 6-1 Comparison of cost of explosive used for conventional and modified

blast with 20% airdeck length of explosive column at DG. Cement

Chakwal ...............................................................................................153

Table 6-2 Cost per tonne of full scale conventional and modified blast with

20% airdeck length at mid of explosive column at DG. Cement

Chakwal ...............................................................................................155

Table 6-3 Comparison of cost of explosive used for conventional and modified

blast with 20% airdeck length of explosive column at Askari

Cement Nizampur ................................................................................156

Table 6-4 Cost/tonne of conventional and modified blast with 20% mid-airdeck

length of explosive column at Askari Cement Nizampur ....................157

Table 6-5 District/Mineral wise limestone production in mining industry of the

Punjab ..................................................................................................158

xxii

LIST OF FIGURES

Figure Description Page No.

Figure 2.1 Oscillogram, showing displacement speeds of medium in case of

conventional blasting [27] ......................................................................15

Figure 2.2 Oscillogram, showing displacement speeds of medium in case of air

gap [27] ..................................................................................................15

Figure 2.3 The developing crack networks in Plexiglas under the influence of an

air-decked explosive charge [28] ...........................................................16

Figure 2.4 Fracture and stress profiles resulting from different charge

geometries and distribution [30] ............................................................18

Figure 2.5 Relationship between angle (β) at 00-45

0, average fragment size and

discontinuity spacing [40] ......................................................................22

Figure 2.6 Wooden spacer for airdecking [33] ............................................................23

Figure 2.7 Adjustable plastic plug for airdecking [31] ................................................24

Figure 2.8 Stem lock gas bag [39] ...............................................................................24

Figure 2.9 Wooden plug for airdecking in boulders [42] ............................................25

Figure 2.10 Wooden plug for airdecking .....................................................................25

Figure 3.1 Three dimensional sketch of a concrete block with dimensions and

hole to be blasted....................................................................................38

Figure 3.2 Wooden mould with built in hole assembly ...............................................39

Figure 3.3 Mechanical mixer for uniform mixing of concrete ....................................40

Figure 3.4 Mechanical vibrator ....................................................................................40

Figure 3.5 Concrete block inside the wooden mould with a built-in hole

assembly .................................................................................................41

Figure 3.6 Smaller concrete blocks along with model blocks for UCS testing ...........41

Figure 3.7 Curing of concrete blocks in curing tanks ..................................................42

Figure 3.8 Universal testing machine ..........................................................................42

Figure 3.9 Dimensions of concrete block and location of hole ...................................44

xxiii

Figure 3.10 Metallic blasting chamber with reinforced rubber walls ..........................46

Figure 3.11 Explosive cartridges of different sizes .....................................................46

Figure 3.12 Watergel cartridge .......................................................................................... 47

Figure 3.13 Weighing the cartridge on digital balance ................................................47

Figure 3.14 Concrete blocks in field ready for loading ...............................................47

Figure 3.15 Charge loading of concrete block .............................................................47

Figure 3.16 Loading scheme of blasthole with full column charge .............................48

Figure 3.17 Block number-1, full column charge before blasting ...............................49

Figure 3.18 Block number-1, full column charge, fragmentation after blasting .........49

Figure 3.19 Wooden spacers used to give airdeck in the explosive column ...............51

Figure 3.20 Loading scheme of blasthole with 20% airdeck length at the top of

explosive column ...................................................................................51

Figure 3.21 Block number-14 with 20% airdeck length at top of explosive

column, before blasting ..........................................................................52


column, after blasting .............................................................................52

Figure 3.23 Loading scheme of blasthole with 20% airdeck length at mid of


Figure 3.24 Block number-21 with 20% airdeck length at mid of explosive




Figure 3.26 Loading scheme of blasthole with 20% airdeck length at bottom of


Figure 3.27 Block number-16 with 20% airdeck length at bottom of explosive



column, after blast ..................................................................................56

xxiv

Figure 3.29 Sieves of different sizes used for analysis ................................................57

Figure 3.30 Fragmentation of concrete blocks after blast (a) full-column charge

(b) 20% middle airdeck (c) 20% bottom airdeck (d) 20% top

airdeck for comparison ...........................................................................58

Figure 3.31 Comparison between full charges versus 20 % airdeck at different

positions .................................................................................................60

Figure 3.32 Comparison of cumulative percent-passing of fragmentation

between solid charge and 20% airdeck length at different positions

of explosive column against each sieve size ..........................................61



Figure 3.34 Block number-8 with 10% airdeck length at the middle of explosive


Figure 3.35 Block number-8 with 10% airdeck length at the middle of explosive








Figure 3.39 Loading scheme of blasthole with 30% airdeck length at the middle

of the explosive column .........................................................................66





Figure 3.42 Loading scheme of blasthole with 40% airdeck length at the mid of


xxv





Figure 3.45 Loading scheme of blasthole with 50% airdeck length at the middle

of the explosive column .........................................................................70



Figure 3.47 Block number-10 with 50% airdeck length at the middle of

explosive column, after blasting ............................................................70

Figure 3.48 Percentage passing plot, comparing different airdeck lengths at

middle position of explosive column .....................................................72

Figure 3.49 Effect of increasing airdeck size on mean fragment size .........................72

Figure 4.1 Conventional charging scheme ...................................................................78

Figure 4.2 Fragmentation of conventional blast at DG. Cement Chakwal ..................79

Figure 4.3 Size distribution of fragments of conventional blast at DG. Cement

plant ........................................................................................................79

Figure 4.4 Bench number-1 at DG. Cement showing thirty two holes in a single

row .........................................................................................................80

Figure 4.5 Loading scheme of full column charge blastholes at bench number-1 ......82

Figure 4.6 Drilling pattern of full column charge holes at bench number-1 ...............82

Figure 4.7 Firing pattern of full column charge holes at bench number-1 ..................82

Figure 4.8 Front view of bench -1 before blast ............................................................83

Figure 4.9 Plan view of bench-1 before blast showing 32 drill holes in a single

row .........................................................................................................83

Figure 4.10 Measuring the burden distance at bench-1 ...............................................83

Figure 4.11 Measuring the length of Watergel cartridge at bench -1 ..........................83

xxvi

Figure 4.12 Loading of dynamite cartridge at bench-1 Figure 4.13 Loading of

ANFO at bench -1 ..................................................................................83

Figure 4.14 Fragmentation of full column charge holes after blast at bench

number-1 ................................................................................................84

Figure 4.15 Split desktop process stages .....................................................................85

Figure 4.16 Size distribution of fragments of conventional blast at bench

number-1 ................................................................................................86

Figure 4.17 Wooden plug used to give airdeck ...........................................................88

Figure 4.18 Loading scheme of each 20% mid-airdeck blasthole at bench

number-1 ................................................................................................90

Figure 4.19 Drilling pattern of 20% middle airdeck blast at bench number-1 ............90

Figure 4.20 Firing pattern of 20% middle airdeck blast at bench number-1 ...............91

Figure 4.21 Loading of Watergel cartridge as a primer in case of mid-airdeck

blast ........................................................................................................91

Figure 4.22 Loading of wooden plug as an airdeck in the blasthole ...........................91

Figure 4.23 Nonel detonators having same time-delay used in one of the mid-

airdeck blasthole ....................................................................................92

Figure 4.24 Fragmentation of 20% mid-airdeck blast at bench number-1 ..................92

Figure 4.25 Size distribution of fragments of 20% mid-airdeck blast at bench

number-1 ................................................................................................93

Figure 4.26 Loading scheme of 20% top airdeck blasthole at bench number-1 ..........95

Figure 4.27 Drilling pattern of 20% top airdeck blast at bench number-1 ..................95

Figure 4.28 Firing pattern of 20% top airdeck blast at bench number-1 .....................96

Figure 4.29 Fragmentation of 20% top airdeck blast at bench number-1 ....................96

Figure 4.30 Size distribution of fragments of top airdeck blast at bench

number-1 ................................................................................................97

Figure 4.31Loading scheme of 20% bottom airdeck blasthole at bench number-1 .....98

Figure 4.32 Drilling pattern of 20% bottom airdeck blast at bench number-1. ...........98

xxvii

Figure 4.33 Firing pattern of 20% bottom airdeck blast at bench number-1 ...............99

Figure 4.34 Fragmentation of 20% bottom airdeck blast at bench number-1 .............99

Figure 4.35 Size distribution of fragments of bottom airdeck blast at bench

number-1 ..............................................................................................100

Figure 4.36 Comparison of %age passing size of conventional versus 20 %

airdeck length at different positions of explosive column ...................102

Figure 4.37 Inside wall of one of the blasthole showing homogeneity .....................104

Figure 4.38 Loading scheme of full column charge blasthole at bench number-2 ....106

Figure 4.39 Drilling pattern of full scale conventional blast bench number-2 ..........106

Figure 4.40 Firing pattern of conventional blast with full column charge at

bench number-2....................................................................................107

Figure 4.41 Plane view of full scale 20 blastholes at bench number-2 ......................107

Figure 4.42 Front view of bench number-2 before full scale conventional blast ......108

Figure 4.43 Fragmentation after blast of full scale conventional shot at bench

number-2 ..............................................................................................108

Figure 4.44 Size distribution of fragments of full scale conventional blast with

full column charge at bench number-2 ................................................109

Figure 4.45 Loading scheme of each blasthole with 20% airdeck length at mid

of explosive at bench number-2 ...........................................................111

Figure 4.46 Drilling pattern of full scale mid-airdeck blast bench number-2 ...........112

Figure 4.47 Firing pattern of 20% mid-airdeck blast at bench number-2 ..................112

Figure 4.48 Bench number-2 before 20% mid-airdeck blast .....................................112

Figure 4.49 DTH, working at bench number-2..........................................................113

Figure 4.50 Wooden plugs used at bench-number-2 .................................................... 113

Figure 4.51 Loading of mid airdeck at bench number-2 ...........................................113

Figure 4.52 Nonel detonators of same delay ................................................................. 113

Figure 4.53 Network of nonel initiation system ........................................................113

xxviii

Figure 4.54 Fragmentationof full scale 20% mid-airdeck blast at bench

number-2 ..............................................................................................114

Figure 4.55 Size distribution of fragments of full scale 20% mid-airdeck blast at

bench number-2....................................................................................114

Figure 4.56 Comparison of %age passing between full scale conventional and

20 % mid-airdeck blast at bench number-2 .........................................117

Figure 4.57 Back crack produced due to full scale conventional blast at bench

number-2 ..............................................................................................118

Figure 4.58 16 holes in a single row at DG. Cement Chakwal at bench number-3 ...119

Figure 4.59 Loading scheme of the holes fired with conventional blast at bench

number-3 ..............................................................................................121

Figure 4.60: Drilling pattern of Conventional blast at bench no 3 ...........................121

Figure 4.61 Firing pattern of conventional blast at bench number-3 .........................121

Figure 4.62 Bench number-3 at DG. Cement Chakwal before blast .........................122

Figure 4.63 Bench number-3 at DG. Cement Chakwal after blast ............................122

Figure 4.64 Bench number-3 at DG. Cement Chakwal after conventional blast ......123

Figure 4.65 Cumulative percentage passing graph for conventional blast at

bench number-3....................................................................................124

Figure 4.66 Wooden airdeck used at bench number-3 ..............................................125

Figure 4.67 Loading scheme of multi-airdeck blasthole at bench number-3 ............127

Figure 4.68 Drilling pattern of holes with multi-airdeck at bench number-3 ............127

Figure 4.69 Firing pattern of holes with multi-airdeck at bench number-3 ...............127

Figure 4.70 Fragmentation after blast for multi-airdeck blast at bench number-3 ....128

Figure 4.71 Cumulative percentage passing graph for holes having multiple

airdeck at bench number-3 ...................................................................129

Figure 4.72 Comparison of percentage passing of fragmentation of conventional

and multi-airdeck blast for different sieve sizes at bench number-3 ...131

xxix

Figure 4.73 Cost comparison of explosive used for conventional and multi-

airdeck blast for a single hole at bench number-3 ...............................132

Figure 5.1 Limestone bench at Askari Cement Nizampur having 32 blastholes in

a single row ..........................................................................................136

Figure 5.2 Loading scheme of each blasthole with full Column Charge at Askari

Cement Nizampur ................................................................................138

Figure 5.3 Drilling pattern of conventional blast with full column charge holes

at Askari Cement Nizampur .................................................................138

Figure 5.4 Firing pattern of conventional blast with full column charge holes at


Figure 5.5 Bench before conventional blast at Askari Cement Nizampur ................139

Figure 5.6 Fragmentation of bench after conventional blast at Askari Cement

Nizampur ..............................................................................................139

Figure 5.7 Size distribution of fragmentation of a conventional blast with full

column charge at Askari Cement Nizampur ........................................140

Figure 5.8 Wooden plug used for airdecking at Askari Cement Nizampur ...............142

Figure 5.9 Loading scheme of each blasthole with 20% airdeck length at mid of

explosive column at Askari Cement Nizampur ...................................144

Figure 5.10 Drilling pattern of modified blast with 20% airdeck length at mid of

explosive column at Askari cement Nizampur ....................................144

Figure 5.11 Firing pattern of modified blast with 20% airdeck length at mid of

explosive column at Askari cement Nizampur ....................................145

Figure 5.12 Bench before mid-airdeck blast at Askari Cement Nizampur ................145

Figure 5.13 Measuring hole depth ................................................................................... 145

Figure 5.14 Measuring burden distance .....................................................................145

Figure 5.15 Measuring spacing between the holes ....................................................... 146

Figure 5.16 Loading of Dynamite cartridge as primer ..............................................146

Figure 5.17 Loading of Watergel at Askari Cement ................................................... 146

xxx

Figure 5.18 Loading of ANFO at Askari Cement ......................................................146

Figure 5.19 Loading of wooden plug at Askari Cement ...........................................146

Figure 5.20 Firing circuit at Askari Cement ..............................................................146

Figure 5.21 Surface delay detonator at Askari Cement .............................................147

Figure 5.22 Fragmentation after blast with mid-airdeck at Askari Cement

Nizampur ..............................................................................................147

Figure 5.23 Size distribution of fragmentations of 20% mid-airdeck blast at

Askari Cement......................................................................................148

Figure 5.24 Comparison of %age passing of fragmentation between

conventional and 20% mid-airdeck blast at Askari Cement

Nizampur ..............................................................................................150

Figure 5.25 Muckpile profile of 20% mid-airdeck blast at Askari Cement

Nizampur ..............................................................................................151

Figure 5.26 Back crack due to conventional blast .....................................................152

Figure 6.1 Comparison of cost of full scale conventional and modified blast with

20% airdeck length of explosive column at DG. Cement Chakwal ....154

Figure 6.2 Comparison of cost of conventional and modified blast with 20%

airdeck length at Askari Cement Nizampur .........................................156

1

CHAPTER 1.

INTRODUCTION

1.1 GENERAL

Blasting is one of the vital operations in mining and construction industry. Despite the

advancements in mechanical rock excavators, explosives remain highly concentrated and

cheap source for surface and underground mine development and mineral production. In the

past, a number of blasting theories and methods have been developed and exercised to

optimize the blasting operations. Despite continuing efforts of researchers, advancements in

explosive engineering, numerous laboratory scale experiments and field investigations, a

considerable gap still exists in application of these blasting theories. Important factors that

influence the blasting operations include properties of the rock mass, geology, properties of

the explosive and the blast geometry.

In mining projects, one of the key objectives is to get maximum production at

minimum cost without sacrificing the quality and safety requirements. Minimization of

production blasting cost is one of the factors that ensure economic feasibility of the mining

projects. A precise blast design should produce optimal fragmentation with controlled throw

that can be easily handled with available loading and hauling equipments. The other outcome

of good blast is to produce micro fractures within the fragments [1].These fractures make the

fragments weak and easy to break thus increasing productivity and decreasing energy

consumption and wear of machinery. It has been observed that blasting results do affect the

economic efficiency of crushing and grinding circuits [2-5].

In general, poor blast design, lack of necessary theoretical background, and poor or

little information about the geology of the area to be blasted, often produce undesired

fragmentation with large number of boulders and excessive fines. Undesired coarser

fragments need secondary blasting before they can be easily handled by loading and hauling

equipments. The secondary blasting of the boulders not only increases the cost of blasting but

also increases the environmental hazards. The environmental hazards associated with

secondary blasting include fly rocks, excessive blast vibrations and air blast, and the

production of additional dust. On the other hand finer fragments of the blasted rock indicate

excessive use of explosive energy.

2

Poor fragmentation increases the wear and tear of loading and hauling equipments. It

also decreases the efficiency of crushing, grinding and milling circuits.

Thus there is a need to investigate such blasting methodology that not only controls

the improper rock fragmentation, but also economizes the whole blasting operation.

In earlier techniques blast design parameters like spacing, burden, stemming, diameter

of blasthole, sub-drilling etc. were optimized by different researchers and practitioners to get

the desired results of fragmentation. They have shown that the rock structure, rock strength,

frequency, spacing and orientation of joints within the rock mass, type of explosive, specific

charge, degree of confinement, explosive distribution within the rock mass, MS delays and

initiation sequence for multi-row blasting are the major factors effecting fragmentation.

Special techniques like slab holes, satellite holes, stemplug and deck charges have also been

used to get better fragmentation. Airdeck blasting technique is one the unique method to

solve all blast related problems.

In airdeck blasting technique an air space is introduced in the explosive column of

blasthole which is called airdeck. If airdeck is properly located and has optimum length it can

improve fragmentation and reduce air blast, vibrations and fly rocks.

1.2 PROBLEM STATEMENT

The effectiveness of airdeck blasting technique depends upon the position of the

airdeck and its appropriate length in the explosive column. A number of studies have been

carried out in the past to investigate the best position and optimum length of airdeck in the

explosive column for better fragmentation. Although individual researchers have contributed

valuable information under given geological conditions but a simple plug-in-type formula for

predicting best position and optimum length of airdeck in explosive column for improved

fragmentation is yet to emerge. Researchers have different opinions regarding the best

location of airdeck in explosive column. Similarly the length of airdeck which is being used

in the world generally varies from 10 to 35% of explosive column. There is no standardized

practice regarding best position and optimum length of airdeck to be used in explosive

column for better fragmentation. So in order to establish some bench mark for improved

3

fragmentation regarding airdeck blasting technique, detailed experimentation are conducted

in this research work.

1.3 OBJECTIVES

The main objective of this research work is to optimize blasting in terms of fragment

size by using airdeck blasting technique. Another objective of this study is to establish the

optimum length and best position of airdeck in the blasthole for achieving a good

fragmentation. Other objectives of this study are as follows:

1. Introduction of airdeck blasting technique in Pakistan for production blasting.

2. To compare fragmentation performance of airdecks placed at different positions

in explosive column.

3. Design an economical, convenient and commercial plug which could be

manufactured locally to give airdecks in the blastholes for production blasting.

4. Cost analysis to predict the annual savings which a quarry can make by adopting

airdeck blasting technique.

1.4 SCOPE

The scope of this thesis is focused on bench blasting operations for relatively

homogeneous limestone in cement quarries of Punjab, Pakistan.

1.5 THESIS ORGANIZATION

The thesis starts with an abstract and Table of contents, followed by list of Figures

and list of Tables in the thesis. The first Chapter Introduction presents a introduction to the

problem under study, research objectives, scope and thesis organization. Chapter 2 literature

Review is the detailed review of blasting theories, mechanism of airdeck blasting, model

scale and full scale airdeck blasting practices, importance of blast fragmentation and their

effect on downstream processes. Chapter 3 Laboratory Scale Experimentations and Results

deals with the detailed laboratory scale experiments on concrete blocks to find out the best

location and optimum length of airdeck. Chapter 4 Validation at DG. Cement Chakwal and

chapter 5 Validation at Askari Cement Nizampur describes the results of full scale field

4

experimentations using airdeck at DG. Cement Chakwal and at Askari Cement Nizampur

respectively. These chapters compare the conventional blasting practice practiced at DG

Cement factory and Askari Cement factory with the blasting practice by using airdeck

technique. In chapter 6 Economic Analysis of the conventional and airdeck blasting practice

is presented. Chapter 7 Conclusions and Recommendations summarizes the conclusions,

limitations and recommendations for future work. References cited in this study are added at

the end of the thesis.

5

CHAPTER 2.

REVIEW OF LITERATURE

2.1 EXPLOSIVES AND BLASTING

Mining and agriculture are two of the oldest industries known to mankind; both of

them pertain to the mother earth. Agriculture is mainly practiced in soil and soft clays and

does not require hard and abrasive tools. It is unlike mining, where there is constant

interaction of man with hard rocks. Perhaps a reason why man had to form and invent

‗mining machinery‘. But the repeated interaction with much harder rocks prompted man to

use explosives.

The use of explosives in mining goes back to the year 1627 [6], when gunpowder

was first used in place of mechanical tools in the Hungarian (now Slovakian) town of Banská

Štiavnica. The innovation spread quickly throughout Europe and America. With the passage

of time evolution in the explosive's industry became prominent which led to the discovery of

dynamite, ANFO, slurries, emulsions and the much newer, advanced and modern- RDX and

the like.

2.1.1 Blasting Theories and Rock Breakage

The topic of blasting theories has always been a controversial one in rock

excavation. Not a single theory is there which can completely explain the mechanism of rock

breakage in every situation. The list of blasting theories presented here is not exhaustive. The

theories are:

Reflection theory (Reflected stress waves)

Gas expansion theory

Flexural rupture

Stress waves and gas expansion theory

Stress waves, gas expansion and stress wave/flaw theory

Nuclei or stress wave/flaw theory

Torque theory

6

Cratering theory

2.1.1.1 Reflection theory (reflected stress waves)

The first ever theory presented on this topic was the reflection theory and was

founded on the simple fact that rock is always resistant to breakage in compression rather

than in tension. When an explosive charge is detonated within the blasthole near to the free

face a compression strain wave is generated due to detonation of the explosive column which

travels through the rock mass with supersonic velocity in all directions with decaying

amplitude. After reflection from the free face this compressional wave transforms into a

tensile and shear wave. Since the rocks are weakest under tension, they break at the free face

in the form of spalling [7-8].

2.1.1.2 Gas expansion theory

The pressure on the walls of a blasthole immediately after detonation is about one

half of the explosion pressure and traverse outward in the rock in the form of shock wave.

The material of the rock between shock front and borehole is compressed. This will produce

radial cracks next to the hole at about 2 hole radii and propagate radially inward as well as

outward. The frequent presence of these cracks is mainly next to the borehole, but a few

originate distantly. In the absence of free face some of the small cracks turn into larger ones.

When the shock wave reaches the free face, radial crack lengths formed are less

than one quarter of this distance. At this time, the longest of the cracks have extended inward

and arrive at the borehole wall. If the gas pressure is high enough it can enter the cracks and

widen them. The returning tensile wave will also assist the cracks to reach at free face. The

surplus energy of gas inside the cracks will be able to displace the rock [9-11].

2.1.1.3 Flexural rupture

After the detonation of explosive inside the borehole two noticeable pressures are

found: one from detonation itself and other from explosive products or highly heated gases

acting on borehole walls. Gaseous pressure sustained for a longer time period as compared

to the detonation pressure which stays only momentarily. Almost all of the energy required to

7

fragment the rock comes from gaseous pressure. So the gaseous pressure is responsible for

90% of the energy needed for rock fragmentation or flexural rupture.

Radial cracks form only in planes parallel to borehole axis. The reflected strain

waves are only responsible for elongation or widening of the cracks and not for breakage.

Gas pressure compels the radially produced cracks through the burden to the free face and

displaces rock through bending and in the direction of least resistance, generally following

naturally occurring planes of weakness. Rock fragmentation occurs at this point. Breaking of

rock is similar to the bending and breaking of a beam [12].

2.1.1.4 Stress waves and gas expansion theory

In 1971 Kutter and Fairhurst after doing experimentation on homogeneous

Plexiglas and rock models came to the following conclusions:

After detonation of a blasthole the high pressure wave is transmitted into the rock

mass by the rapidly expanding high pressure gases. The gas pressure was assumed to be one

half to one quarter of the detonation pressure. Due to expansion of cavity around the blasthole

the gas pressure decays exponentially but sufficient enough to put pressure against rock mass

for a longer period. This pressure wave first forms radial cracks around the expanding

blasthole cavity then followed by rings of widely spaced radial cracks. The compressional

wave is strong enough to cause breakage. Strain wave- induced fracturing and gas pressure

are the two main components responsible for rock fracturing. Neither the gas pressure nor the

strain wave alone is responsible for rock breakage. Gas pressure contributes more in rock

breakage than the strain wave [13].

2.1.1.5 Stress waves, gas expansion and stress wave/flaw theory

Stage 1

When an explosive is detonated, the region around the blasthole is shattered due to

high pressure. The shock waves traverse outward at 9000-17000 ft/second create tangential

stresses that form radial fractures in the region of the blasthole. First radial cracks occur in

1-2 msec [14].

8

Stage 2

The pressure of the shock wave travelling outward from the blasthole is positive but

as soon as it reaches the free face it reflects and its pressure is reduced suddenly and becomes

negative to form a tensile wave. As the rock mass is more prone to breakage in tension than

in compression, initial cracks will appear. If the tensile stresses are significant enough they

may cause scabbing or spalling at free face [14].

Stage 3

The real breakage of rock is a slow process. Due to the sufficiently intense pressure

of explosive gases the initial cracks will widen by the combined effect of tensile stress

induced by radial compression and by pneumatic wedging [14].The mass of rock in front of

blasthole yields and move outwards, the high compressive stresses within the rock mass

unload itself and this unloading effect induces high tension stresses in the rock mass that

breaks the rock and complete the breaking process [14].

2.1.1.6 Nuclei or stress wave/flaw theory

According to this theory stress waves are responsible for fragmentation process and

induced large amount of cracks initiation at areas which are distant from the blasthole. The

gas pressure does not contribute significantly in the fragmentation process. The theory was

formulated after conducting experimentation at University of Maryland in the fracture

mechanism laboratory on Homolite models both flawed and unflawed. The flawed models

contained joints, fractures, bedding planes and other discontinuities.

In case of unflawed material only 8-12 dominant radial cracks were formed around

the blasthole. Although these cracks grow and covered a significant distance from the

blasthole but they alone are not capable of giving good fragmentation.

The test results in case of flawed model material showed that these discontinuities

act as nuclei for crack formation, development or extension. After forming the cracks around

discontinuities, when these stress waves strike the free face they are reflected back as tensile

wave to meet the out coming stress waves. At this stage there is constructive interference

which produced further cracks or extension of previously formed cracks. This new stress

9

wave dominated mechanism of fragmentation is referred as nuclei theory [15].

2.1.1.7 Torque theory

This theory has a limitation of accurate timing of initiators. As two contiguous

explosive columns are initiated simultaneously from opposite ends, a compressional shock

wave from each explosive column is generated. These compressional waves travel parallel

but opposite in direction. The greatest stress and primary shock front are always normal to

each other. This stress is also supposed to be greatest at the detonation head and decays as it

moves away from the detonation head. When the blastholes are initiated simultaneously but

in different directions a non-uniform division of stress occurs. Following this, the broken

rock will likely be tossed between the explosive columns in an anti-clockwise direction. This

action will produce uniform fragmentation without any tight muckpile.

2.1.1.8 Cratering theory

The concept of the cratering theory was originally proposed by C.W. Livingston and

later modified by others such as Lang and Bauer. It involves a spherical charge of length to

diameter ratio of less than equal to 6:1, detonated at an empirically determined distance

beneath the surface to optimize the greatest volume of permanently fragmented material

between the charge and free surface. According to this theory for a given specific explosive

and rock material, there exist a burden distance between the charge and free surface which

yields the largest crater. This burden is referred to as optimum burden. Similarly, there exists

another burden distance referred to as the critical distance, which is too far below the surface

to result in any crater or expulsion of material at the surface, other than minor radial cracks.

This is the point at which material at the surface just begins to show evidence of failure [16].

2.1.1.8.1 Cratering mechanism

As the high pressure explosive gases expand against the medium immediately

surrounding the explosion, a spherical shock wave is generated causing crushing. As the

shock front moves outward in a spherically diverging shell, the medium behind the shock

front is put into radial compression and tangential tension. These results in the formation of

radial cracks directed outward from the cavity. The peak pressure in the shock front reduces

10

due to spherical divergence and the expenditure of energy in the medium. For shock

pressures above the dynamic crushing strength of the medium the material is crushed, heated

and physically displaced, forming a cavity. In regions outside this limit, the shock wave will

produce permanent deformation by plastic flow, until the peak pressure in the shock front has

decreased to a value equal to the plastic limit of the medium. This is the boundary between

the elastic and plastic zones [17].

When the compressive shock front strikes the free face, it results in generation of

negative or rarefaction wave which moves back into the medium as tensile wave and causes

the medium to break. As the distance from the free face increases the pressure of negative or

rarefaction wave decreases until it no longer exceeds the tensile strength of the medium. The

process explained so far is a short term and takes only few milliseconds. The gas expansion

mechanism after that is a long lasting that imparts acceleration to the medium around

detonation by expansion of gas trapped in the explosion formed cavity.

2.2 DIFFERENT METHODS TO IMPROVE FRAGMENTATION

In earlier techniques blast design parameters like spacing, burden, stemming,

diameter of blasthole, sub drilling etc. were optimized by different researchers and

practitioners to get the desired results of fragmentation. They have shown that the rock

structure, rock strength, orientation of joints within the rock mass, type of explosive, specific

charge, degree of confinement, explosive distribution within the rock mass, MS delays and

initiation sequence for multi-row blasting are the major factors effecting fragmentation.

Special techniques like slab holes, satellite holes, stemplug and deck charges have also been

used to get better fragmentation. The airdeck blasting technique is a unique method to solve

all blast related problems.

Chiappetta in 1998 [18] after performing a number of experiments to improve blast

fragments came to the conclusions that specific charge, explosive distribution within the rock

mass, type of explosive, delay timing and joint system and its orientation with respect to blast

direction are the major factors in order of influence to affect the fragmentation in competent

rock. For soft, weak or highly fractured rock the order of influence changes to joint sets and

its orientation with respect to blast direction, type of explosive, specific charge, explosive

distribution within the rock mass and delay timing.

11

Chiappetta in 1998 [18] also discussed the importance of different initiation design

patterns for multi-row blasting. He observed that a deep V-blast pattern generally gives good

fragmentation with tight and high muckpile which is difficult to dig. The row by row blasting

pattern on the other hand needs higher specific charge for good fragmentation and it gives

low and loose muck which is easy to dig. Further he added that if scatter in firing time is

smaller, the shorter delays between the holes in a row give improved fragmentation.

Moreover the stemming and sub-drill areas of drill hole are one of the main sources of

oversized blasted rock material and stab and pilot holes are the best options to deal with such

type of problems.

Hagen in 1979 [19-20], after doing detailed experimentation to improve blasted

rock fragmentation and to reduce the amount of fines presented the following conclusions:

There should be impedance matching between explosive and rock type.

Explosives in blastholes should be avoided especially in weak strata in order to

control fines.

More fines are generated when there is increase in blasthole diameter, burden and

sub-drilling and decrease in spacing between the holes and stemming length.

Deep V-blast pattern gives more fines than row by row.

Inadequately small delays between the rows and increase in number of rows often

generate more fines.

Use lightly charged stab holes instead of increased column charge length in main

blastholes to minimize fines.

2.2.1 Effect of Timing on Blast Fragmentation

Winzer et al. (1983) [21] and Stagg and Rholl (1987) [22] conducted two

instrumented blast tests in 2-3 m high limestone and 15 m high granite benches. They used

seismic detonators which have high initiation accuracy as ± 0.02 and 80% passing size x80 for

the blasted material as the main source of the resulting fragmentation.

Dynamite cartridges of diameter 12.5 mm in holes having diameter 19 mm with

0.46 m spacing were used in limestone tests. The inert-hole delay interval varied between 1

and 27 ms per meter of spacing. The limestone test showed a sharp decrease in x80 from

12

1-3 ms/m with a little change thereafter when the delay was increased to 20 ms/m. They

observed a reduction in both oversize and fine material with the increase of inter hole delay.

In granite tests blasts they used Atlas powder, Apex 260, in holes of diameter 89

mm on 3 m spacing. Delays of 10,20,30,40 and 60 ms were used in the experimentation. The

results of the test blasts have shown that the best overall fragmentation was generally

obtained for a 20 ms delay i.e. at 2 ms/ft or 7 ms/m. Moreover when the bench face is divided

into massive and a fractured part, the delay for the fractured parts was shifted to the 40 ms

delay [20].

Stagg and Rholl [22] also conducted the instrumented fragmentation tests at the US

Bureau of Mines with 6 single row blasts in 7 m benches in limestone. The holes of diameter

of 64 mm were charged with sticks of dynamite of 50 mm diameter. The 1.8 m burden and

2.1 m spacing gave the specific charge of about 0.59 kg/m3. Delays of 2, 6, 12, 24(twice) or

48 ms between the holes were tried with the accuracy of seismic caps ± 0.11. Each 4-hole

blasted about 270 tons of rock.

Stagg and Rholl concluded that "Most of the finer material was apparently

produced by a process in the region around the blast-holes, while the coarse material came

from the region between the blast-holes and near the free face".

They screened four blasts completely and parts of remaining ones and used x30, x50

and x80 as the main measures of the resulting fragmentation. The main conclusion of their

experiments was that blast-hole delay had no effect on the finer fragment sizes. Their plot of

x30 and x50 were pretty flat.

They used their strain and pressure recordings as indications that the improvement

of fragmentation was due to an interaction of blast-hole stress wave mechanism with the

previously detonated blast-holes‘ late failure processes [22].

2.2.2 New Work with Reference to Blast Fragmentation

Elliot et al. (1999) [23] and Ethier at al. (1999) [24] performed a number of

experiments to improve fragmentation. The rock consists of limestone and dolomite with a

13

density of 2600 kg/m3.

The tests blasts were consisted of 4 two round with 85 mm explosive diameter

charged in holes of 102 mm diameter with burden and spacing of 3 and 3.5 m respectively.

They used alternating pattern with 1m sub-drilling and 2 m stemming. Fragpak SD ANFO

was used in the collar and after two rounds, Tovan Super 4 having length 2 m and 90 mm

diameter was used as bottom charge and specific charge increased to 0.7 kg/m3.

Toe movement was improved due to the presence of bottom charge. In these rounds

2 m decks of Tovite Plus were also used to reduce the back break. There was no positive

effect; hence the conclusion drawn was that back break was effectively governed by the

length of the fractured collar part of the sub-drill layer.

The delays used were 25 ms in row and 66, 75 or 92 ms between the rows, the in

row delay corresponds to 7 ms/m of spacing, which agrees with optimum value from Winzer

et al. (1983) [21]. The between row delay had no significant effect on the fragmentation. The

source of the coarser materials was mainly from the collar layer and the back break zones of

the round. There was also a measuring swelling of the bench behind the crest.

Most of the rock passed straight through the primary crusher‘s output opening of

150 mm. As a result secondary crusher‘s product flow increased 16% i.e. from 995 to 1150

tons/h and the power consumption dropped to 30%.

For the fragmentation analysis Winfrag system was used. Each curve was a result of

merging more than 30 photos per blast. Elliot et al. [23] reported the following results;

A much steeper fragmentation curve was obtained. The undersize x90 decreased from

0.63 m to less than 0.2 m.

The 50% passing fragmentation x50, decreased from 0.15 m to 0.90 m

The -20 mm fines decreased from 4% to 1.5%.

The capacity gain of the system (secondary crusher) was 15-16%. 2 above.

An Engineering approach is the Tmin concept used by Chiappetta [18]. Tmin is the

minimum response time of the burden mass or the delay between charge initiation and

14

appreciable movement of the bench face.

He recommends that "if the application calls for maximizing fragmentation with

minimal movement, inter i.e. between-row delay times less than Tmin should be chosen. If it

calls for maximizing material movement and easy digging between –row delays of 1.5-3.0

Tmin should be chosen". The objective of the latter case to displace the rock material by about

1m apart before the next row is initiated to allow swell and to minimize the inter-row

collisions without jeopardizing the confining pressure [18].

Onoderra and Esen (2003) extract the following philosophy. "In row delay times

should be ≤ Tmin to promote and fragmentation interaction and between–row delay times

should be 1.5-3.0 to promote material movement and easy digging" [25].

Another technique which is already being used in the world to reduce the amount of

oversize and fines is called airdeck blasting technique. In airdeck blasting technique an air

space is introduced in the explosive column of blasthole which is called airdeck. If the

airdeck is properly located and has an optimum length it can improve fragmentation and

reduce all blast related problems like air blast, vibrations and fly rocks, etc.

2.3 AIRDECK BLASTING TECHNIQUE

When a continuous cylindrical explosive charge in a blasthole is detonated, the

blasthole enlarges by crushing the walls of the blasthole due to high pressure. A shock wave

with a high peak pressure propagates outwards in all directions as a compressive stress wave

[26]. The compressive stress wave also produces radial cracks in the strata. At the free face,

this compressive stress wave reflects back as a tensile stress wave. The tensile strength of the

rock is much smaller than its compressive strength, thus the rock mass breaks at the point

where effective tension exceeds the tensile strength of the rock [26]. The gas produced by

explosive detonation penetrates into cracks and expands, resulting in enlargement of cracks

and crushing around the bore hole. In this case the medium comes to static equilibrium soon

after the compression wave has passed and there is no further transfer of energy to the

medium. The following oscillogram in Figure 2.1 shows displacement speeds of the medium

in case of conventional blasting.

15

Figure 2.1 Oscillogram, showing displacement speeds of medium in case of conventional

blasting [27]

On the other hand according to Mel‘nikov and Marchenko, [27] the explosive

column with airdecks develops additional compressional shock waves after the main

compression wave produced in the rock mass due to blasting as shown in displacement speed

oscillogram in Figure 2.2.

Figure 2.2 Oscillogram, showing displacement speeds of medium in case of air gap [27]

This additional compressional wave is produced as a result of collision between the

two gas streams in the center of the air gape. The collision of the gases not only generates

great pressure at the meeting point, but also the gases are reflected back and penetrate in the

fissures thus aiding fragmentation.

Mel‘nikov and Marchenko [27] also found that when an airdeck is placed in the

explosive column, the peak bore hole pressure reduces due to wave collision in the air gap.

16

However, at the same time, multiple impacts of shock wave within the medium are produced

due to collision and reflection of gases in the airdeck area. This may result in 1.5 to 1.7 times

more energy transferred to the medium as compared to blasting a continuous charge. Hence,

an improved rock fragmentation can be achieved by providing air gap in the explosive

column of a blasthole.

Experiments to study the fracture network conducted by Fourney et al. [28] on

Plexiglas models also supported Mel'nikov‘s theory and demonstrated that a shock wave

reaching the stemming is reflected back to strengthen the stress field.

Fourney et al. in 1981 conducted a number of experiments on Plexiglas models to

investigate dynamic crack propagation resulting from a borehole having an air gap. High-

speed photography along with dynamic photo elasticity was used in the experimentation. An

airdeck was placed between the stem plug and the top of the charge. He observed that after

detonation the shock wave travelled up the borehole, reflected back after impacted the

stemming area with the same sign as the incoming wave. This interaction not only increases

pressure at the stem plug by a factor of 2–5 but also acted over a longer period which

appeared to be very helpful in initiating and propagating fractures in this region. Due to this

reason, the fractures in stemming area were more pronounced than in the charge area as

shown in Figure 2.3.

Figure 2.3 The developing crack networks in Plexiglas under the influence of

an air-decked explosive charge [28]

17

High pressures were observed at the interface between stemming and air-deck along

with the near explosive area and extended up into the stemming region. The impact involved

a larger region even though the fractures in this area were not as intense as that in the

explosive area.

A significant reduction in crushing of rock near charge was observed by Marchenko

(1982) [29], and he concluded that it was due to reduced stresses in the region near air-

decked charges, as compared what was produced in the case of solid charges. He reported

that due to airdeck in explosive column about 25% increase in stresses in the farther regions

are observed, which accounted for 50% increase in the utilization of explosive energy for

breakage and improvement of the degree of fragmentation.

Chiappetta and Memmele (1987) [30] reported that an explosive with full column

charge generates a high pressure impulse into the medium that creates many micro-fractures,

but it acts for a very short period and decays quickly. He also suggested that additional stress

waves are required to pass through the medium and enlarge the micro fractures. Moreover, as

the air-deck tends to generate smaller, but repeated production of shock waves, which acts for

a longer time period, there is a tendency for the fragmentation to improve. An air-deck placed

between two explosive charges does the job of an energy accumulator, which first stored the

energy and later released it in the form of additional stress waves to enhance fragmentation.

Chiappetta [31] stated that the bottom airdeck could be used more effectively as compared to

the cylindrical charges because when it is practiced in the right manner, it produces 2 to 7

times more pressure at the bottom of the hole. The fracture and stress profiles produced as a

result from different charge geometries and distributions are shown in Figure 2.4 (Chiappetta

and Memmele 1987).

18

Figure 2.4 Fracture and stress profiles resulting from different charge

geometries and distribution [30]

Chiappetta [31], observed that there was no significant difference in rock

fragmentation produced when a single drill hole is blasted with and without airdecking.

However, it was also observed that the drill hole with airdeck used up 17% to 25% less

explosive than that consumed with a solid charge. He also evaluated two full scale blasts with

and without airdecking and found no significant difference in fragmentation, muckpile throw

and breakage at toe and collar.

When blasting with air-decking is conducted, the presence of air in the airdeck plays

a very important role in obtaining better size distribution of fragments. During the blast, the

air is initially static and at room temperature and pressure. Later, the air material under such

physical conditions offers very little resistance to the expansion of the detonation products

which have temperature and pressure nearly 3–4 orders of magnitude higher. The detonation

products do transfer some energy to the air by compressing and heating it. However, even if

the air is to be as energetic as the detonation products, still very little amount of fraction is

transferred, at the most in the order of one thousandth of the energy retained in the later (Liu

and Katsabanis 1996) [32].

Jhanwar and Jethwa [33] in their work on airdeck blasting concluded that airdeck

blasting results in better fragmentation and improved utilization of explosive energy.

Jhanwar, et al. [34] found that the degree of fragmentation resulting from airdeck blastholes

19

is better than that of produced by conventional blastholes in which solid decks are used.

Moreover, airdeck blasting was also found to be more effective in very low to low strength

moderately jointed rocks as compared to medium strength highly jointed rocks.

Another series of experiments conducted by Thote and Singh (2000) showed that

the powder factor increased from 7.46 t/kg to 8.96 t/kg by using airdeck blasting technique

[35].

In 2003 Lu and Hustrulid [36] did numerical simulation and theoretical analysis to

study the effect of airdeck in an explosive column. They used the theory of shock tube to

investigate the physical process of blasting with a top airdeck and found that the pressure

unloading process caused by the propagation of rarefaction waves and reflected rarefaction

waves in the detonation products plays a vital role to improve fragmentation. They also

proposed the airdeck ratio which was in general agreement to those proposed by Melnikov et

al. in 1979, and Moxon et al. in 1993.

According to Moxon et al. [37] no significant effect on the degree of fragmentation

was observed with the airdecks which occupy 40% or less of the maximum volume of

explosive. He concluded that the maximum length of the airdeck depended upon the structure

and strength of the material to be blasted.

2.3.1 Understanding the Mechanism of Airdeck Blasting

A number of studies have been carried out by different researchers but the

mechanism of airdeck blasting they proposed still does not explain what is actually

happening under field conditions [36].

2.3.2 Airdeck Location

Three types of airdeck positions are commonly used by researchers and

practitioners i.e., top, middle and bottom of the explosive column. Generally, an airdeck

when placed at the top of the explosive column of the blasthole produced a good rock

breakage in the stemming area [38]. Jhanwar et al. [34] suggested that the airdecks were most

effective if placed at the middle position of an explosive column. Jhanwar [38] also observed

20

that bottom airdeck can only be used for blasting of holes with softer bottoms. Moxon et al.

[37] also had the similar point of view and concluded that the middle position of the airdeck

resulted in an improved rock fragmentation due to the interaction of two simultaneous shock

wave fronts from the top and bottom of an explosive charge. Whereas, Chiappetta [31] stated

that the bottom airdeck could be used more effectively than continuous cylindrical charges

because it produces 2 to 7 times more pressure at the bottom of the hole when properly

practiced. Contrary to that, Liu and Katsabanis [32] suggested that only the top position of

airdeck improved the rock fragmentation than that of other two positions.

A bottom airdeck was successfully used by Blast Dynamics Inc. at a gold mine in

Northern Nevada without affecting fragmentation and excavator productivity. Moreover, no

toe problem was encountered [39].

2.3.3 Airdeck Length

In 1979 Mel'nikov et al. developed empirical correlations of airdeck lengths as

shown in the following equations.

La,d = k1Lt(K1= 0.15-0.35)

La,d = k2d (K2= 8-12)

Where, La,d is the air-deck length (m), Lt is the total charge length including air-deck

(m), d is the charge diameter (m) and K1 and K2 are the rock factors.

The results of studies conducted by Moxon et al. (1993) suggest that, relative to the

full column charge there was no significant effect on the degree of fragmentation was

observed with the airdecks which occupy 40% or less of the maximum volume of explosive.

He concluded that maximum length of the airdeck was depending upon the structure and

strength of the material to be blasted.

In 2003 Lu and Hustrulid performed a number of site experiments to find out the

airdeck length for different rock masses and suggested the best airdeck ratio for ANFO.

According to them the airdeck ratio from 0.13 to 0.4 develops the maximum pressure in the

airdecked part of the blasthole. This pressure is due to reflection shock waves. They defined

21

the airdecking ratio, as the ratio between the length of the airdeck and the total length of the

explosive column including the airdeck as follows.

Ra = Le/La+Le

Where Ra is the airdecking ratio, La is the length of the airdeck and Le is the length

of the explosive column [36].

According to Jhanwar et al. (1999), the critical length for an airdeck varies from 15

to 30% of original charge length . However, the general airdeck length varies from 0.1 to 0.35

times the original charge length [34].

The airdecking factor (ADF) is given as

ADF=ADL/OCL

Where ADL is Airdeck length and OCL is Original charge length. It was observed

that when the Airdecking factor (ADF) was kept below 0.35, good to excellent fragment size

distribution was produced. Also, ADF ranges from 0.1 to 0.35. The lower value was found

suitable for blocky rocks and higher value for softer rocks [33].

According to Lu and Hustrulid (2003) the most important parameter during airdeck

blasting is the "Air-Deck Ratio". He theoretically derived the airdeck ratio as between 0.13-

0.39 which was in close agreement with those suggested by Mel'niKov in 1979 and Moxon in

1993.The value of airdeck ratio proposed by Mel'niKov is 0.15-0.35 based on field

experimentations and those proposed by Moxon is 0.30-0.35 based on experimentation on

concrete model.

Rommayawes and Leelasukseree in 2011 [40] performed a number of experiments

to provide guide lines for use of airdeck length in explosive column. Experiments were

performed at two different quarries EGAT and INSEE. The RMR rating for rocks at EGAT

and INSEE quarries was calculated and was found to be 61 and 57 respectively. At EGAT

quarry discontinuity spacing between 3 to 0.1 m was observed, while at INSEE quarry

spacing from 2.2 to 0.05 m was measured. From data collected by field experimentation, a

relationship was established between average fragment size, angle (β) at 00—45

0 and

22

discontinuity spacing, where (β) is the angle between the strike of a particular discontinuity

and strike of free face. This relationship is presented in Figure 2.5.

Figure 2.5 Relationship between angle (β) at 00-45

0, average fragment size

and discontinuity spacing [40]

By using Figure 2.5, one can find the airdeck length for a desired rock fragment size

distribution, provided the discontinuity spacing is known. It was also observed that on

increasing airdeck length the average rock fragmented size was increased. The length of

airdeck for a desired size of rock fragmentation was found to depend upon rock type and

blasting application.

Suttithep Rommayawes et al. in 2013 [41] performed a series of experiments to

determine the optimum airdeck length for suitable fragmentation. In their research work 30

different airdeck blasts were executed with airdeck length between 15 to 65% of explosive

column. They also incorporated the maximum joint spacing and blasting orientation in their

work. The results of test blasts signified that the average fragmentation size increases with

increase of airdeck length, joint spacing and unfavourable blast direction. The relationship

between average fragmentation size and air-deck length was portrayed on a graph for

simplicity of uses.

They also concluded that small to medium opening feed size of a normal primary

23

crusher may vary between 93cm (37inches) to 112cm (44inches) so an air-deck length

between 20-30% of the charge length can be used with a high possibility that the average

fragmentation size will be less than 100cm. With favourable parameters, an air-deck length of

up to 40% can be used in the quarry without scarifying the fragmentation.

2.3.4 Plugging Devices for Airdecking

Different types of airdecking devices have been used by researchers and blasting

experts. The airdeck devices used by Jhanwar and Jethwa, in 2000 [33] were made of wood

and each had the following specifications as shown in Figure 2.6.

Figure 2.6 Wooden spacer for airdecking [33]

Chiappetta in 2004 [31] used the adjustable plastic plug with a wooden stake to

produce airdeck at the bottom of the explosive column. The plug used is shown in the Figure

2.7.

24

Figure 2.7 Adjustable plastic plug for airdecking [31]

Stemlock patent # 4846278 has been used for airdecking in presplit blasting as


Figure 2.8 Stem lock gas bag [39]

Tariq and Zeshan in 2008 [42] used the airdeck in secondary boulder blasting to

mitigate air blast and fly rocks. The plug used by them for airdecking in the boulders is given

in Figure 2.9.

25

Figure 2.9 Wooden plug for airdecking in boulders [42]

In the current study wooden plug as shown in Figure 2.10 was used to give air gap

in an explosive column as it was convenient to use in pilot scale testing.

Figure 2.10 Wooden plug for airdecking

2.3.5 Effect of Airdecking on Fragmentation

Improved utilization of explosive energy in airdeck blasting results in better

fragmentation [34].

According to single hole tests with and without airdeck in an explosive column

resulted in similar fragmentation, while hole with airdeck used 17% less explosive [31].

26

Airdeck blasting has been seen to increase powder factor (t/kg) from 7.46 to 8.96

and still fragmentation was seen to improve [35].

In 1993 Moxon et al. [37] found that as airdeck length was increased the degree of

fragmentation decreased in comparison to a full column charge. He also noted that this

reduction was very small up to a critical length of the airdeck, after that critical length the

fragmentation results were adversely affected. He found that critical length was dependent

upon the structure and strength of the material to be blasted.

2.3.6 Economics of Airdeck Blasting

At an Indian mine, near Nagpur, mining manganese ore, blasts conducted their

present very relevant learnings; blasts were carried out first by placing decks made of drill

cuttings at the middle of the explosive column. Decks of length 2m were used for benches of

height 6-7m, while decks of length 3-3.5m were used for benches with height 10-11m. The

charge used for these blasts ranged from 0.3 to 0.45 kg/m3.

Once the conventional blasts were completed, blasting was carried out on the same

site using airdecks at the middle of the explosive column. The design parameters used for

airdeck blasting are given in the following Table 2-1.

Table 2-1 Design parameters used for airdeck blasting [34]

Blast

No.

Date Location

Bench

height

(m)

Hole

depth

(m)

No. of

holes

Spacing

X burden

(m x m)

Type and

sequence of

detonation

Charge

per

hole

(kg)

Maximum

charge

per delay

(kg)

Airdeck

numbers

and length

1 28Sept.

1995

146'L, Ch.

1097 m 6.0 6 9 1.8 X 2.0

Electric

short delay 11.12 55.60 One, 0.9 m

2 15Feb.

1996

145'L, Ch.

1036 m 7.0 7 6 2.5 X 2.0

Electric


3 16 Feb.

1996

145'L, Ch.

1006 m 8.7 7 11 2.3 X 2.0

Electric

short delay 34.56 207.36 One, 1.35m

4 18 Feb.

1996

130'L, Ch.

1006 m 10.2 10.7 11 2.5 X 2.0

Electric

short delay 39.56 197.80

Two each

of 0.9m

5 10 Apr.

1996

160'L, Ch.

1036 m 6.0 5.5 7 2.75 X 2.0

Electric


6 11 Apr.

1996

130'L, Ch.

1189 m 11.0 10.75 6 3.0 X 2.0

Electric

short delay 34.6 104.00

Two each

of 1.2 m

27

The blast performance of these airdeck blasts is given in the Table 2-2.

Table 2-2 Blast performance of airdeck blasts [34]

Blast

No.

Specific

charge

(kg m-3

)

Fragmentation Over

break Throw Toe

Vibration

(mmS-1

)

Explosive

type

1 0.45 Gooda Almost nil 6-7 m in

front Nil Negligible Slurry

2 0.73 Very gooda 0.15-0.2

Maximum

up to 8-9

m on one

side

Nil 25 mms-1 at 40

m distance ANFO

3 0.89 Gooda Nil, clean,

intact face 15 m Nil

24.51 mms-1 at

25 m distance ANFO

4 0.70 Poora

Clean face,

back break

of 0.5 m

on one side

18.5 m Nil

27.9 mms-1 at

25-30 m

distance

ANFO

5 0.62 Excellent, ideal

muckpilea 0.2-0.3 m

4-5 m,

well

contained

tight muck

pile

Nil

7.87 mms-1 at

100 m

distance28.35

mm s-1 at 25 m

distance

ANFO

6 0.56 Very gooda

2.5 m,

extension

of back

break from

previous

blast

5-7 m,

contained

within the

bench

width

Nil

18.98 mms-1 at

75 m distance

14.00 mm s-1 at

80 m distance

ANFO

The airdecks were placed at the mid of the explosive column. The advantages of the

airdeck blasting in comparison to conventional blasting are listed below in Table 2-3.

Table 2-3 Advantages of airdeck blasting [34]

Advantages of airdeck blasting over blasting without airdecks

Sr. No. Parameter Improvement

1

Fragmentation

MFS Close to the optimum size

Secondary blasting Almost eliminated

Shovel loading efficiency Improved by 50–60%

2 Ground vibration Reduced by 44%

3 Over break Reduced by 60–70%

4 Toe Almost eliminated

5 Throw Reduced by 65–85%

The use of airdecks proved to be very beneficial with respect to economics as

28

shown by the results given in Table 2-4.

Table 2-4 Economics of airdeck blast [34]

Cost reductions by airdeck blasting

Sr.

No. Item

Cost-benefit

Saving per m3 of

overburden

(INRb)

Savings

per year

(INRb)

Per cent

saving

1 Explosive cost 0.95 285 00 31.60

2 Loading cost

(operating)

1.47 441 00 36.30

3 Transportation

cost (operating)

0.08 24 00 24.60

4 Total 2.50 750 00 32.88

a On the basis of yearly overburden handling of 300 000 m

3.

b Indian rupees [34].

It was thereafter established that the use of airdecks in sandstone rocks at an open

pit coal mine instead of solid airdecks resulted in explosive savings of 15kg to 40kg in each

hole, varying a little with the depth of hole and rock formation. Annual savings at this mine

can be projected to 4.46 million Indian rupees. It was also expected to lower powder factor

from 0.35kg/m3 to 0.25kg/m

3 with better fragmentation achieved in comparison to that

achieved with conventional blasting [34].

Moreover, two 30-holes full scale shots were carried out on a quarry. For one of the

shots, the bore holes were loaded with full continuous column of explosive and for the other,

the bore holes were loaded with three feet airdeck at the bottom of the holes. In addition to

that, the holes containing airdeck were drilled with low sub grade that is 3 to 4 feet less

drilling, while all others design factors were maintained. From the analysis of shot results it

was established that airdeck holes in spite of using 16% less explosive than normal shots

achieved relatively better fragmentation, thus reducing explosive cost effectively [31].

Furthermore, in Indian mines the use of airdecking has been reported to effectively

reduce explosive consumption by 15-20% whilst improving the fragmentation [35].

In a study conducted at a gold mine in northern Nevada [39], it was concluded by

29

the blast dynamics company that by using airdeck at the bottom of the 48 feet long hole

following benefits could be achieved.

A reduction of 144,000 feet could be achieved by simply reducing the sub drilling

requirement from 8 feet to 4 feet. This reduction in drilling requirement can bring about a

saving up to $183,240. Furthermore, with the airdeck replacing the explosive at the bottom 4

feet of the balsthole and also reducing the drilling requirement up to 4 feet, an explosive

consumption could be reduced by 8,128,000 lb. This reduction in explosive requirement

allowed the mine management to save up to $1,080,000 annually. Overall, the mine was able

to save $966,240 annually by using airdecks at the bottom of the holes, after adjusting for the

cost of airdecks. Although, less amount of explosive was used as compared to that used for

the conventional blast, the floor was found to be even by GPS survey, also the excavator

productivity was not affected [39].

2.4 METHODS FOR DETERMINING FRAGMENT SIZE DISTRIBUTION

Sieving is an accurate method for size analysis but for larger material digital image

analysis is being used worldwide [31].

2.4.1 Sieving

Sieving of fragmentations of full scale production blast in thousands of tons is

extremely time consuming and expensive method. The sieving procedure usually consists of

loading, hauling, sieving and weighing and then again loading and hauling of the fragmented

rock material. Gynnemo in 1996 [43] sieved 5000 tons of material while Olsson and

Bergqvist in 2002 [44] sieved up to 400 tons of blasted material and came to the conclusion

that sieving should be used for samples only.

2.4.2 Digital Image Analysis

Digital image analysis technique to determine the fragment size distribution of

blasted rock material emerged as an alternative and is being widely used. Carlsson and

Nyberg (1983) [45] were one of the first user of automatic digital image analysis technique to

estimate the fragment size distribution of the blasted rock material. They made the following

rules.

30

I. The size of the largest fragment should be 20 times larger than the smallest fragment.

II. The size of the smallest fragment should be 3 times larger than the resolution.

Cunningham in 1996 gave a review of Digital image analysis technique of assessing

fragment size distribution and found that ―Evaluation of digital images of blast muckpile is

particularly difficult due to its size, depth and internal variation‖. He further added that if we

are looking at the surface only and a major portion of fragments is hidden below the surface,

the assessment will be biased unless the uniformity index is extremely high. This indicates

the major problem in this technique which is mainly due to fine material concealed below

surface.

Liu and Tran (1996) [46] and Katsabanis (1999) [47] indicated the need of

incorporating fines corrections in the image analysis technique. Wipfrag and Split desktop

have incorporated the fine correction in their systems and raised the accuracy of analyzing

data within the narrow range of resolution and also made it possible to extrapolate it outside

this range. Kemeny et al. in 1999 [48] also worked on fines correction for Split desktop

system and defined the procedure of their correctness. Several validation studies have been

conducted using calibration procedure given by Kemeny et al. on muckpiles. The difference

found by sieved distribution and fines corrected split distribution was much smaller. It is

therefore the digital image analysis technique for determining rock fragment size distribution

is being widely used in the world because it provides fast estimates without interfering with

the other production processes. This technique though very fast and easy but have certain

inherent flows and the only alternate is the sieving which is used only in exceptional

conditions.

2.5 IMPORTANCE OF BLAST FRAGMENTATION

Generally, blasting is used in the mining industry to break and fragment the rock

mass. The blast is considered good when it produces fragmentation which is fine and loose

enough to permit the efficient digging and loading operation. This approach does not give

much importance to the downstream operations. In fact blasting is the first step in the

comminution process and plays more vital role than just fragment the rock mass. The effect

of this process can be calculated in some measureable quantity that is connected with cost or

revenue. It varies with the geological conditions and may also vary with the seasonal climate.

31

A positive effect of the blasting process may consist of :

A larger throughput in crusher and mills.

A lower total energy expenditure in the processes.

Smaller volumes of worthless or cost prone fractions like fines and oversize and a

higher quality of the end product.

A higher ore concentration grade or mineral recovery.

An improved or least maintained fragmentation with a lower explosives consumption.

The Swedish Cement Factory production of crushed aggregate rock is about 40

Mton annually. About 2/3 of this consist of product 0-32 mm base gravel. About 4-6 Mton of

the 0-4 mm material produced is unsalable and become an economic and environmental

burden in the quarry‘s operation [49].

Another example is lumps limestone producers. Nordkalk Storugns has the largest

production of 2.5-3 million tons annually. The -25mm fines are in most cases a worthless or

low price product and about 25% of the plant‘s production is fines [49].

The improvement of the fragmentation can cause many benefits if the blasting is

done more carefully and with a controlled technique with less scatter in the outcome.

Whereas the scatter is largely due to deflections in geological conditions and also due to the

poor process control in staking out, drilling and charging.

Societal needs for a sustainable supply of natural resources requires improved yield

from blasting, crushing and grinding, less transport cost and a minimal amount of easily

handled non-toxic waste [50].

2.5.1 Effects of Blast Fragmentation on Downstream Processes

There are two very important effects of blasting on fragmentation; the first is the

size distribution of fragments of the blasted muckpile. A qualitative estimate can be obtained

by visual observation of the blasted muckpile directly as good or poor. Nowadays the image

analysis techniques can also be used to calculate it quantitatively.

The second important effect of the blasting is the crack generation within the

32

fragments of muckpile. These fractures can be of different size as may be macro-fractures or

micro-fractures. Micro cracks can only be seen by microscope. Because of these micro-cracks

mineral grains tend to soften and break easier. Hence this leads to potential benefits towards

productivity, energy expenditures and wear and tear of consumable item.

It is not adequate to only know about the size distribution of the blasted muckpile

but also the effect of blasting on individual fragments like internal fracturing which greatly

affects the downstream processes. While the first factor is now measureable directly, the

second must be assessed through a study of production, energy consumption and supply cost.

The size distribution of the blast fragments and the internal softening of individual

fragments by blasting can greatly affect the efficiency of all downstream processes [3]. The

fragmentation resulting from blasting operation effects two main downstream operations:

Loading and Hauling

Crushing and Grinding

2.5.1.1 Loading and hauling

Poor fragmentation is not only a nuisance in handling processes but hampers the

natural flow of other processes. A good blast produces an even sized yield and also reduced

number of boulders. This expedites the loading and hauling operations of the blasted

material. Less percentage of boulders means no crowding time and an overall even

fragmentation means a smaller cycle time. The reduced cycle time has a great impact on the

cost effectiveness of hauling operations. Moreover, it also decreases the consumption of

power required to haul the same amount of material when it is even-sized. This lower intake

of power is mirrored in the improved efficiency of haulage equipment as damage to machine

parts due to aggravated load curtails. The power requirement dwindles conserving millions

of rupees in the context of lower fuel intake. Wear and tear to the machines by the excessive

number of boulders is also diminished. In short the better fragmentation leads to an increased

life cycle of machines and recurrent maintenance sessions of equipment can correspondingly

be declined.

33

2.5.1.2 Crushing and grinding

The blasted size distribution introduced to the primary crusher will affect the feed

size distribution throughout the crushing stages. Poor fragmentation leads to energy losses at

the secondary and tertiary crushing stages and increases the load at these stages.

Boulders can cause serious damage and disfigure the body of the hopper when

dumped. In the crushing phase, these boulders impede the smooth flow of the crushing

operation and can sometimes cause choking. Damage to hammers of the crusher are

aggravated substantially and require frequent replacements resulting in substantial

expenditure. Enhanced fragmentation not only smoothes out the process but also depresses

the cost of auxiliary hammers as their life cycle is increased due lesser wear and tear.

Boulders in the crusher adversely increase the vibration and temperature of crusher parts thus

decreasing the life expectancy of parts and can cause a great pestering. Improved

fragmentation is the answer to all the problems. An important factor is mineral liberation in

considering the effectiveness of downstream processes. Greater liberation means improved

downstream recovery. A currently unanswered question is whether blasting that creates more

micro-fractures around or through mineral grain will improve liberation and recovery [50].

However, the studies undertaken in the last decade have shown that the micro-

crakes produced in blast fragments have a measurable impact on crushing and grinding not

only in terms of operational efficiency but also in terms of associated cost [51, 52, 53].

2.5.2 Effects of Blast Fragments on Energy Consumption in Crushing and Grinding

Most of the energy is utilised for the grinding purposes of the material. Therefore, it

can be safely said that changes in the properties of the blasted rock fragments that carry

through to the grinding stage, if conducive could result in large savings.

Workman and Eloranta (2003) [54] talk about an increase in specific charge q from

0.33 to 0.45 kg/ton. This is believed to lower the x80 of the blasted muckpile from 0.4 to 0.3m

and energy consumption of the primary crusher goes down to 0.194 kwh/ton and the cost to

0.136 SEK/ton. Therefore, the explosive cost goes up from 0.87 SEK/ton to 1.19 SEK/ton

and consequently the drilling costs also rise etc. Unless there are other incentives such a

34

change would not be advantageous [54].

Kojovic et al. (1995) [55] presented a case for a quarry and restricted its scope to

only crushing stages, where a raise in the powder factor from q = 0.5 to 0.6 kg/m3 had a

positive and desirable overall impact. Factors such as the improved digging of the muckpile

and less boulders to handle saved 4.0 SEK/ton in extraction costs and an increase in the

crushers‘ bypass flows from 10 to 14% saved another 3.0 SEK/ton.

There are other benefits as well apart from the lower energy costs and increased

productivity in crushing and grinding to be had from improving the blasting.

Lower wear in downstream processes i.e. crushing, grinding, loading and hauling.

Increase in shovel efficiency and low energy utilization during loading.

A chance to use lighter equipment, smaller shovels, trucks and primary crushers e.g

with smaller capital costs and energy consumption [55].

Paley and Kojovic (2001) [3] presented ways to increase the throughput of SAG

(Semi-Autogenous Grinding) mill at the Red Dog lead and zinc mine. The SAG mill is

connected directly from a primary crusher. From the experiment conducted by them it can be

concluded that the mining industry could achieve a net benefit of 30 M$/year from an

increased concentrate production by just increasing the powder factor form 0.29 kg/ton to

0.72 kg/ton. Their greatest achievement included the identification of an important factor,

best mine fragmentation, which optimizes the mill‘s performance [3].

2.5.3 Effects of Blast Fragments from Mine to Mill

The potential areas that could bear the impact of blast fragments from Mine to Mill

include:

1. It has been observed that the productivity of loader/excavators through muckpile

digability is increased and also the bucket and truck fill factors are increased.

2. Crusher throughput is increased due to changes in ROM (run of the mine) pad

material size distribution.

35

3. The energy consumption for downstream processing and per ton of processed ore is

reduced.

4. Damage caused by blast is reduced and ore dilution resulting in increased final

product (or metal).

5. Increased liberation of valuables is obtained, increasing the mill recovery.

According to Grundstrom et al. (2001) [56] the following procedure could be

adopted to achieve optimization:

Scoping, to be precise by defining the goal of the optimization.

Auditing; finding out the blasting of rock, its comminution characteristics, how the

drilling and blasting is done in practice, the fragmentation and how the mills work.

Modeling and simulation of fragmentation by blasting, crushing and grinding and the

equipment capacities.

Mine to mill simulations that are simulations of the whole system when for example

the blast design is changed.

Validation phase that is checking that the simulation results accuracy. A 5%

agreement is given as an example.

Implementation phase in which the new designs and plant settings are introduced.

Grunstrom et al. (2001)[56] worked on a gold mine with hornblende diorite and an

in-situ block size of 0.5-0.6m. They achieved a 25% increase throughput in SAG mills by

going from a blasting pattern with burden: Spacing = 5.3:6.3m with holes of diameter = 200

mm to a pattern with burden: Spacing = 4.5:5.5m with holes of diameter = 229mm. The

specific charge was increased from 0.66 to 0.85 kg/m3 [56].

Craig Imrie (2003) [57] has reviewed a couple of case studies in which he cites

common figures of improvement as 2-5% for recovery, 2% for concentrate grade and 5-10%

for mill throughput. Two crucial factors involved are a flow-sheet model of the process

system from geology to customer and a compatible systematic information management.

He also observed regarding the states that benefit and these come in two steps. The

first comes from the improved understanding of the process system that the model and data

give. The second comes from the data and the model which are put into advance use [57].

36

Eloranta published a number of papers regarding the effect of blasting on crushing

and grinding (1995, 1997, 2001, 2002) [58, 59, 60]. Much of this material and findings are

contained in Workman and Eloranta (2003). They draw the following conclusions:

1. The greatest energy savings come from grinding due to the large change in and the

subsequent particle size achieved.

2. Improvements pertaining to blasting in grinding depend primarily on the degree of

micro-fracturing achieved, as it is these cracks that will survive earlier stages of

crushing.

3. Large savings in cost can be achieved.

4. The use of greater energy input in the blasting unit operation will often be less costly

than expending the energy downstream.

5. However, there were still some unanswered questions about drill-to-mill (mine-to-

mill) optimization.

The large cost savings projected, and in some cases seen in actual practice make

research in this field an urgent priority for mining cost minimization.

37

CHAPTER 3.

LABORATORY SCALE EXPERIMENTATION AND RESULTS

3.1 BACKGROUND

Since the theory of airdecking has been proposed by Mel‘nikov and Marchenko

(1971) [9], a number of studies and practical applications have been carried out to find its

effectiveness by different researchers. Researchers are divided on the idea of the location of

the airdeck in explosive column and the optimum length of airdeck. Three types of airdeck

positions are commonly used by researchers and practitioners that is, top, middle and bottom

of the explosive column.

Jhanwar et al. [10] suggested that the airdecks were most effective if placed at the

middle position of an explosive column. Jhanwar [11] also observed that bottom airdeck can

only be used for blasting of holes with softer bottoms. Moxon et.al [12] also had a similar

point of view and concluded that the middle position of the airdeck resulted in an improved

rock fragmentation due to the interaction of two simultaneous shock wave fronts from the top

and bottom of an explosive charge. However Chiappetta [7] stated that the bottom airdeck

can be used more effectively than continuous cylindrical charges because it produces 2 to 7

times more pressure at the bottom of the hole when properly practiced. In contrary to that Liu

and Katsabanis [13] suggested that only the top position of airdeck improved the rock

fragmentation than that of other two positions.

Since most of the experiments in the past were carried out under varying geological

conditions, it was very difficult to suggest the best possible location for airdeck in an

explosive column for better fragmentation. In order to find out the proper position of airdeck

it was decided to carry out all experiments on homogeneous material so that a bench mark

could be established. The details of laboratory scale experimentation are shown below.

3.2 MODEL MATERIAL

Research work performed at the University of Maryland [15] and at SveDeFo [16]

demonstrated that concrete is the most suitable material for this type of research study. Thus,

in the current research work, all the blasting experiments were conducted on concrete blocks.

38

On one hand concrete blocks eliminate the heterogeneity and anisotropy of rock material, and

on the other hand it also removes the effects of geological uncertainties and irregularities

such as fractures, folds, faults and joints on blasting.

3.2.1 Dimensions of Blocks

First of all wooden block model of size 2 meter cube was made to assess the

handling and workability of concrete block. The above purposed concrete block of size 2

meter cube was rejected for two reasons. Firstly, it was very difficult to handle such a huge

and heavy concrete block and secondly large numbers of blocks were required for

experimentation. So keeping in view the convenience, it was decided to use smaller blocks

with dimensions 350 mm × 350 mm × 300 mm as shown in Figure 3.1.

Figure 3.1 Three dimensional sketch of a concrete block with

dimensions and hole to be blasted

The ratio of ingredients per block as shown in Table 3-1 was maintained throughout

the research.

Table 3-1 Concrete blocks composition for one block

Ingredients Weight (kgs)

Ordinary Portland cement 25

Sand 24

Coarse aggregate (12.7 mm) 48

Water 3.6

Chemrite NN 0.6

39

Chemrite NN was used in the concrete mixture to achieve an ultimate compressive

strength of 40 MPa.

3.3 EXPERIMENTAL SETUP

3.3.1 Casting of Concrete Block

Wooden moulds with a small diameter pipe were used to prepare concrete blocks

with a vertical hole. The diameter of the pipe was 12.7mm and a depth of 275mm was

maintained in all concrete blocks. The pipe was installed 125mm away from one of the faces

of the concrete block as shown in Figure 3.2.

Figure 3.2 Wooden mould with built in hole assembly

The concrete blocks were cast using facilities of the Concrete lab at the Civil

Engineering Department, University of Engineering and Technology Lahore. In order to

achieve a uniform mixing all the ingredients were mixed in a mechanical mixer for 5 minutes

as shown in Figure 3.3.

40

Figure 3.3 Mechanical mixer for uniform mixing of concrete

After mixing, the concrete mixture was poured into the wooden moulds. The

wooden mould was placed on mechanical vibrating platform to reduce any entrapped air as

given in Figure 3.4

Figure 3.4 Mechanical vibrator

41

Figure 3.5 Concrete block inside the wooden mould with a built-in hole assembly

For every concrete block, a small concrete block (152× 152 × 152 mm) was also

cast to check its designed strength as shown in Figure 3.6. The blocks were left in the moulds

for 48 hours as shown in Figure 3.5 before being removed and placed in a curing water tank

for 28 days. Figure 3.7 shows the curing of concrete blocks.

Figure 3.6 Smaller concrete blocks along with model blocks for UCS testing

42

Figure 3.7 Curing of concrete blocks in curing tanks

The uniaxial compressive strength (UCS) of the smaller concrete blocks constructed

from the same mixture was determined by using universal testing machine as shown in Figure

3.8. The calculation of UCS of all concrete blocks used in the experimentation is presented in

Table 3-2.

Figure 3.8 Universal testing machine

43

Table 3-2 Calculation of UCS of all blocks using universal testing machine

Sample Width of block

Length

of block Height

of block Area Load

Max

Bearing

Load (N)

UCS

(cm) (cm) (cm) (m2) (kgf) (MPa)

1 15.6 15.5 15.4 0.02418 97400 954520 39.5

2 15.7 15.5 15.3 0.02433 97800 958440 39.4

3 15.8 15.5 15.4 0.02449 98000 960400 39.2

4 15.5 15.4 15.5 0.02387 97000 950600 39.8

5 15.4 15.4 15.5 0.02372 96800 948640 40.0

6 15.6 15.4 15.3 0.02402 96600 946680 39.4

7 15.5 15.5 15.6 0.02403 96800 948640 39.4

8 15.4 15.6 15.4 0.02402 98200 962360 40.1

9 15.6 15.4 15.5 0.02402 99400 974120 40.1

10 15.5 15.5 15.6 0.02403 99800 978040 40.7

11 15.5 15.5 15.4 0.02403 96800 948640 39.4

12 15.5 15.5 15.4 0.02403 99800 978040 40.1

13 15.6 15.4 15.6 0.02402 99600 976080 40.6

14 15.5 15.5 15.4 0.02403 99600 976080 40.6

15 15.5 15.4 15.5 0.02402 97400 954520 39.7

16 15.6 15.5 15.4 0.02418 97400 954520 39.5

17 15.5 15.5 15.6 0.02403 96800 948640 39.4

18 15.4 15.6 15.4 0.02402 98200 962360 40.1

95 15.6 15.4 15.3 0.02402 96600 946680 39.4

02 15.5 15.5 15.6 0.02403 96800 948640 39.4

09 15.4 15.6 15.4 0.02402 98200 962360 40.1

00 15.6 15.4 15.5 0.02402 99400 974120 40.1

02 15.5 15.5 15.6 0.02403 99800 978040 40.7

02 15.5 15.5 15.4 0.02403 96800 948640 39.4

02 15.5 15.5 15.4 0.02403 99800 978040 40.1

02 15.6 15.5 15.4 0.02418 97400 954520 39.5

27 15.7 15.5 15.3 0.02433 97800 958440 39.4

04 15.8 15.5 15.4 0.02449 98000 960400 39.2

05 15.5 15.4 15.5 0.02387 97000 950600 39.8

22 15.4 15.4 15.5 0.02372 96800 948640 40.0

29 15.6 15.4 15.6 0.02402 99600 976080 40.6

20 15.5 15.5 15.4 0.02403 99600 976080 40.6

22 15.5 15.4 15.5 0.02402 97400 954520 39.7

22 15.6 15.5 15.4 0.02418 97400 954520 39.5

22 15.5 15.5 15.6 0.02403 96800 948640 39.4

22 15.4 15.6 15.4 0.02402 98200 962360 40.1

23 15.5 15.5 15.4 0.02403 96800 948640 39.4

24 15.5 15.5 15.4 0.02403 99800 978040 40.1

25 15.6 15.4 15.6 0.02402 99600 976080 40.6

22 15.5 15.5 15.4 0.02403 99600 976080 40.6

Average 39.9

44

The average UCS of all concrete blocks was found to be almost 40 Mpa. The

stemming, explosive and airdeck length in the blocks were painted with different colours as

shown in Figure 3.9. Watergel explosive (Blaster) manufactured by Biafo Industries was used

in all the experiments. The density of the Blaster was 1.15 g/cc with velocity of detonation as

4500 m/s. Nonel initiation system was used for all experiments.

Figure 3.9 Dimensions of concrete block and location of hole

3.3.2 Blast Design of Concrete Block

Blast design parameters used in the experimentation are given by the following

formulas:

Burden factor, kb = 30[SGe/1.3]1/3

[160/dr] 1/3

Where,

dr = density of rock ,lbs/ft3

Burden distance, B = kb (De/12) ft

Stemming length, T = (2/3 B) ft

Sub-drilling, J = 1/3xB ft

Depth of hole H = (L+J) ft

45

Explosive charge length = PC = (H-T) ft

According to calculations the burden was about 300 mm and the size of the block

would have been very large and difficult to handle, as we needed larger number of blocks for

experimentation so for convenience burden was taken as 125 mm instead of 300 mm. Also

similar burden was used by different researchers e.g. Moxon [12] in their model scale

blasting with almost same size of the block.

Depth of hole J = 275 mm

Density of Watergel = 1.15 g/cc

Loading density of Watergel = 0.3405 × Density × (Dia of fully coupled explosive) 2

Loading density of Watergel = 0.3405×1.15× (0.5)2 = 0.098 lb/ft

Now,

Weight of Explosive charge = loading density × Explosive charge length

Weight of Explosive charge = 0.098 lb/ft × 0.629 ft = 0.06164 lb or 27.94 g

So 27.94 g of Watergel explosive was used for full explosive length.

3.4 EXPERIMENTAL PROGRAM

Several field visits were made to select the suitable site for blasting. With the co-

operation of Inspectorate of Mines, the permission was obtained to perform experiments at

DG. Cement Pvt. Ltd. near Kallar Kahar area of Chakwal District in Punjab province of

Pakistan. The concrete blocks were blasted in a reinforced rubber walled blasting chamber.

The blasting chamber was used for protection and collection of blasted fragments as

illustrated in Figure 3.10. The rubber walls of the chamber provided cushioning effect and

reduced the further fragmentation by impact.

46

Figure 3.10 Metallic blasting chamber with reinforced rubber walls

3.4.1 Different Steps Involved in Charging of Block

Special small cartridges as shown in Figure 3.11 were prepared with water proof

paper material in which Watergel was loaded to the designed weight and length. Figure 3.11

to Figure 3.15 presents the different steps involved in charging of concrete blocks.

Figure 3.11 Explosive cartridges of different sizes

47

Figure 3.12 Watergel cartridge Figure 3.13 Weighing the cartridge on digital balance

Figure 3.14 Concrete blocks in field ready for loading Figure 3.15 Charge loading of concrete block

3.4.2 Blasting Testing

Two series of blasting experiments were performed in this phase. The first test

series consisted of baseline blasting experiments with full column charge, six blocks were

blasted in this case. The second test series was performed to find out the most appropriate

position of airdeck in the explosive column.

During baseline testing, six concrete blocks were blasted individually with full

column charge without any airdecking. Table 3-3 shows the different experimental

parameters used in this research work.

48

Table 3-3 Different parameters used in the experimentation

Explosive weight

(g)

Airdeck length

(mm)

Airdeck

proportion (%)

Explosive

length (mm)

Stemming length

(mm)

27.94 0.00 0.00 191.80 83.20

25.29 19.18 10.00 172.62 83.20

22.36 38.36 20.00 153.44 83.20

19.60 57.60 30.00 134.20 83.20

16.85 76.40 40.00 115.40 83.20

13.97 95.90 50.00 95.90 83.20

3.5 CONVENTIONAL BLASTING WITH FULL COLUMN CHARGE

3.5.1 Charge Loading

In this case full column was charged with 27.94 g of explosive in cartridge form as

given in Table 3-3. Nonel detonator was introduced in the explosive cartridge to give proper

priming, which in turn was connected to the plain detonator. The plain detonator was crimped

to the safety fuse. The stemming length of 83 mm with drill cuttings was kept constant in all

concrete block blasting experiments. The blocks were blasted inside a blast chamber and the

fragments of the concrete blocks after the blast were collected for sieve analysis. Figure 3.17

and Figure 3.18 present the images of the block with full column charge before and after blast

respectively. Loading scheme of each concrete block in case of conventional blasting with

full column charge is shown in Figure 3.16.

Figure 3.16 Loading scheme of blasthole with full column charge

49

Figure 3.17 Block number-1, full column charge before blasting

Figure 3.18 Block number-1, full column charge, fragmentation after blasting

50

3.6 MODIFIED BLASTING WITH AIRDECK AT DIFFERENT POSITIONS OF

EXPLOSIVE COLUMN

3.6.1 Airdeck Location

A second test series was performed to find out the most appropriate position of

airdeck. In this series of experiments, airdecks were introduced at three different positions:

top, middle, and bottom of the blasthole. The airdeck proportion of 20% used in the current

research was proposed by Moxon et.al [12] using equation 1.

( )

( ) ( )

Where AP (%) is the airdeck proportion (%)

Eighteen concrete blocks were blasted during this series of experiments. Out of

eighteen blocks, six were blasted with 20% airdeck length located at the top of the blasthole.

The next six were blasted with 20% airdeck length located at the middle portion and the last

six blocks were blasted with 20% airdeck length located at the bottom position of explosive

column. Since many of the researchers have used the airdeck length ranging from 10% to

35% of the total explosive column length in their laboratory and full scale experiments. So

20% airdeck was taken as safe value.

3.6.1.1 Concrete blocks with 20% airdeck length at top of explosive column

In each concrete block a wooden plug of length 38 mm as shown in Figure3.19 was

introduced in the blasthole at the top of the explosive column to create an air space equivalent

to 20% of the explosive charge length as shown in Figure 3.20. This airdeck at the top

reduced the quantity of explosive by 20%.

51

Figure 3.19 Wooden spacers used to give airdeck in the explosive column

3.6.1.1.1 Charge loading in case of 20% top airdeck blast

Loading scheme of each blasthole with 20% airdeck length at top of explosive

column is shown in Figure 3.20. The blocks were blasted in a blast chamber and the

fragmentations of the concrete blocks after blast were collected for sieve analysis. The Figure

3.21 and Figure 3.22 represent the images of block with 20% airdeck length at top of

explosive column before and after blast respectively.

Figure 3.20 Loading scheme of blasthole with 20% airdeck length at the top of

explosive column

52


column, before blasting


column, after blasting


In this case, in each blasthole a wooden plug of length 38 mm was introduced at the

mid of the explosive column to create an air space equivalent to 20% of explosive charge

53

length as shown in Figure 3.23.

. The consumption of explosive was reduced 20% by using airdeck at middle

location of the explosive column.

3.6.1.2.1 Charge loading in case of 20%mid-airdeck blast

The loading configuration of the each blasthole with 20% airdeck at the middle of

the explosive column is shown in Figure 3.23. Top and bottom priming was used in each

blasthole, with airdeck at the middle position of explosive column. It is very important to

note here that the nonel detonators used for top and bottom priming in each single blasthole

in case of mid-airdeck were of same delay. Moreover the amount, type and sequence of

explosive above and below the airdeck was kept same for each mid-airdeck blasthole as

shown inFigure 3.23.The blocks as shown in Figure 3.24 were blasted in a blast chamber and

the fragments of the concrete blocks after blast were collected for sieve analysis as shown in

Figure 3.25.

Figure 3.23 Loading scheme of blasthole with 20% airdeck length

at mid of explosive column

54





55

3.6.1.3 Concrete blocks with 20% airdeck at bottom of explosive column

A wooden plug of 38 mm length was kept at the bottom of the explosive column to

create an air space equal to 20% of explosive charge length as given in Figure 3.26.This

airdeck at the bottom of the explosive column reduced the consumption of explosive by 20%.

3.6.1.3.1 Charge loading in case of 20% bottom airdeck blast

The charging sequence of each blasthole with 20% airdeck length at bottom of

explosive column is shown in Figure 3.26.The blocks were blasted in a blast chamber and the

fragments of the concrete blocks after blast were collected for sieve analysis. Figure 3.27 and

Figure 3.28 show the images of the blocks before and after blast respectively.

Figure 3.26 Loading scheme of blasthole with 20% airdeck length at bottom

of explosive column

56




column, after blast

3.6.1.4 Results and discussion

After blasting, the fragments of each concrete block were collected for sieve

analysis. The sieves used for size analysis (in mm) are 128, 64, 32, 16, 8, 4, 2, and 1 as shown

in Figure 3.29.

57

Figure 3.29 Sieves of different sizes used for analysis

The results of sieve analysis are shown in Table 3-4.

Table 3-4 Experimental results with respect to location of airdeck

Fraction

Size

(mm)

Solid Charge

mean values

20% Airdeck – mean values

(kg)

Top (kg)

Middle

(kg)

Bottom

(kg)

+128 29.77 39.81 19.29 54.45

-128+64 25.23 29.90 22.74 18.93

-64+32 16.80 8.51 21.51 7.54

-32+16 7.44 3.82 12.23 2.39

-16+8 3.45 1.32 5.92 0.84

-8+4 1.18 0.49 1.60 0.25

-4+2 0.40 0.38 0.70 0.12

-2+1 0.30 0.23 0.53 0.09

Total 84.56 84.45 84.52 84.60

It may be inferred from the results shown in the Table 3-4 that the size distribution

of blasted block fragments when airdeck was located at the middle position of explosive

column were more uniform as compared to when solid charge was used or when airdeck was

placed at top and bottom positions of explosive column as shown in Figure 3.30.

58

(a) ( b)

(c) (d)

Figure 3.30 Fragmentation of concrete blocks after blast (a) full-column charge (b)

20% middle airdeck (c) 20% bottom airdeck (d) 20% top airdeck for comparison

The mean size of the blasted block fragments of solid charge and 20% airdeck at

different positions is tabulated in Table 3-5.

Table 3-5 Experimental results in terms of mean fragment size

Fraction Solid

Charge

20% Airdeck

Top Middle Bottom

Mean Fragment

Size (mm) 98.6 117.5 79.9 132.1

59

It is evident from the results that mid column airdeck produced smaller mean

fragment size as compared to that produced in the case of full column explosive charge and

airdeck at top and bottom positions of explosive column. The mean size of the blasted block

fragments was calculated by using the following formula [12].

( ) ∑

( )

Where MFS (mm) is the mean fragment size in mm.

Table 3-6 shows the comparison of cumulative percent-passing of the blasted block

fragments against each sieve size for all the experiments in this phase.

Table 3-6 Comparison of cumulative percent-passing of fragmentation of

solid charge vs. 20% airdeck at different positions

Sieve

Size

(mm)

Cumulative Percentage Passing

Solid

Charge

20% Top

Airdeck

20% Mid-

Airdeck

20%

Bottom

Airdeck

128 64.79% 52.86% 77.18% 35.64%

64 34.96% 17.46% 50.28% 13.27%

32 15.10% 7.38% 24.82% 4.36%

16 6.30% 2.86% 10.35% 1.53%

8 2.22% 1.30% 3.34% 0.54%

4 0.82% 0.72% 1.45% 0.25%

2 0.35% 0.27% 0.63% 0.10%

1 0.00% 0.00% 0.00% 0.00%

0 0.00% 0.00% 0.00% 0.00%

Figure 3.31 shows the cumulative percent-passing plot for the blasted block

fragments for all the experiments in this phase.

60

Figure 3.31 Comparison between full charges versus 20 % airdeck at different

positions

It can be observed from Figure 3.31 that airdeck, when placed at the middle position

of explosive charge, produces a smaller size distribution compared to full column explosive

charge and airdeck at the top and bottom positions. Figure 3.32 represents the comparison of

fragment size distribution of concrete blocks after blast among solid charge, 20% mid, 20%

top and 20% bottom airdeck lengths at different sieve sizes. Almost 77% passing of

fragments with 20% mid-airdeck, 65% passing with solid charge, 53% passing with 20% top

airdeck and 37% passing with 20% bottom airdeck was achieved at 128 mm sieve size.

Moreover 50% passing of fragments at 63 mm with 20% mid-airdeck, 90 mm with solid

charge,120 mm with 20% top airdeck and more than 128 mm sieve size with 20% bottom

airdeck was achieved. It can also be observed that the size distribution of fragments produced

by airdeck placed at middle position is closest to the distribution of fragments produced by

solid explosive charge. Thus overall a better fragmentation was produced when airdeck was

placed at middle position as compared to when full column charge was used and when

airdeck was placed at the top and bottom of an explosive column. These results are in

accordance with the findings of Mel‘nikov and Marchenko [9].

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

1 10 100 1000

Pe

rce

nt F

ine

r B

y W

eig

ht

Grain Size (mm)

Percentage Passing PlotComparision between full charge vs 20 % air deck at different positions

Solid Charge 20 % Air Deck (Top) 20 % Air Deck (Middle) 20 % Air Deck (Bottom)

61

Figure 3.32 Comparison of cumulative percent-passing of fragmentation

between solid charge and 20% airdeck length at different positions of

explosive column against each sieve size

3.6.2 Optimum Airdeck Length

This phase of research, aims at finding the optimum length of the airdeck. For this

purpose, another series of experiments was conducted at the already determined best position

i.e. mid of explosive column but with varying lengths of airdeck. Experiments were

conducted with five different airdeck lengths of 10 %, 20 %, 30%, 40% and 50% of the total

column charge length.

3.6.2.1 Concrete blocks with 10% airdeck length at the middle of the explosive column

In this case, a wooden plug of length 19 mm was introduced in each block, at the

mid of the explosive column to create an air space equivalent to 10% of explosive charge

length as shown in Figure 3.33.When the airdeck was placed at the middle of explosive

column, the quantity of explosive was reduced by 10%.

3.6.2.1.1 Charge loading in case of 10% mid-airdeck blast

Charge loading of each blasthole with 10% airdeck length at the middle of the

explosive column is presented in Figure 3.33.The blasts were conducted in a blast chamber

62

and the fragmentations of the concrete blocks after blast were collected for sieve analysis.

Figure 3.34 and Figure 3.35 present the images of the blocks before and after blast

respectively.


explosive column


explosive column, before blasting

63


explosive column, after blasting


A wooden plug of length 38 mm as given in Table 3-3 was introduced at the middle

of the explosive column to produce an air space equivalent to 20% of explosive charge length

as shown in Figure 3.36.


The loading configuration of each blasthole with 20% airdeck length at the middle

of the explosive column is explained in Figure 3.36.The blocks were blasted and the

fragments of the concrete blocks after blast were collected for sieve analysis. Figure 3.37 and

Figure 3.38 represent the images of the block before and after blast respectively.

64

Figure 3.36 Loading scheme of blasthole with 20% airdeck length at

mid of explosive column



65




A wooden plug of length 58 mm as given in Table 3-3 was loaded at the mid of the

explosive column to generate an air space equivalent to 30% of explosive charge length as



Figure 3.39 explains the loading configuration of blasthole with 30% airdeck length

at mid of the explosive column. Blocks were blasted and fragments after blast were collected

for size analysis. Figure 3.40 and Figure 3.41 give the view of the block before and after blast

respectively.

66

Figure 3.39 Loading scheme of blasthole with 30% airdeck length at the

middle of the explosive column



67



3.6.2.4 Concrete blocks with 40% airdeck length at the middle of the explosive column

In this case, in each blasthole a wooden plug of length 72 mm was introduced in the

blasthole at the mid of the explosive column to create an air space equivalent to 40% of

explosive charge length as shown in Figure 3.42.This airdeck at the mid reduced the

consumption of explosive by 40%.


Loading scheme of each blasthole with 40% airdeck length at mid of the explosive


fragmentations of the concrete blocks after blast were collected for sieve analysis Figure 3.43

and Figure 3.44 present the view of the block before and after blast respectively.

68

Figure 3.42 Loading scheme of blasthole with 40% airdeck length at the mid

of explosive column



69




In this case, a wooden plug of length 96 mm was introduced in each blasthole, at the

middle of the explosive column to create an air space equivalent to 50% of explosive charge

length as shown in Figure 3.45.This airdeck at the middle of the explosive column reduced

the consumption of explosive by 50%.


Loading scheme of each blasthole with 50% airdeck length at mid of the explosive


fragmentations of the concrete blocks after blast were collected for sieve analysis Figure

3.46andFigure 3.47 represent the view of the block before and after blast respectively.

70

Figure 3.45 Loading scheme of blasthole with 50% airdeck length at the

middle of the explosive column




explosive column, after blasting

71

3.6.2.6 Results and discussion

The sieve analysis was performed on each collected fraction. The results of sieve

analysis are shown in Table 3-7. These results suggested that airdeck length equivalent to 20

% of total column charge produced the best fragmentation. Figure 3.48 shows the cumulative

percentage passing plot for the blasted block fragments for all the experiments in this phase.

The mean fragment size for the blasted block was calculated and can be seen in Table 3-8. It

was established that the mean fragment size decreases gradually with the increase in airdeck

size from 0 to 20% and then increases with increasing airdeck size as shown in Figure

3.49.The Figure 3.48 shows that 20% airdeck produces the smallest mean fragment size, and

can play a significant role in the cost saving of subsequent size reduction processes.

Moreover the mean fragment size increases with increasing airdeck size.

Table 3-7 Experimental results with the varying lengths of the airdecks at the

middle position of the explosive column

Fraction

Size

(mm)

Middle Position – Mean Values (Wt, kg)

10%

Airdeck

20 %

Airdeck

30 %

Airdeck

40 %

Airdeck

50 %

Airdeck

+128 23.27 19.29 39.15 45.99 51.80

-128+64 23.37 22.74 25.58 25.81 24.64

-64+32 17.49 21.51 12.16 7.71 5.05

-32+16 10.56 12.23 4.15 2.54 1.78

-16+8 6.37 5.92 2.31 1.44 0.88

-8+4 2.27 1.60 0.70 0.64 0.27

-4+2 0.75 0.70 0.25 0.16 0.12

-2+1 0.46 0.53 0.12 0.07 0.11

Total 84.53 84.52 84.42 84.37 84.63

Table 3-8 Mean fragmentation size for varying length of airdeck at middle position of

explosive column

Fraction

Middle Position

10%

Airdeck

20 %

Airdeck

30 %

Airdeck

40 %

Airdeck

50 %

Airdeck

Mean fragment

Size(mm) 85.7 79.9 117.5 124.1 131.8

72

Figure 3.48 Percentage passing plot, comparing different airdeck lengths at

middle position of explosive column

Figure 3.49 Effect of increasing airdeck size on mean fragment size

After detailed experimentation and analysis of the results from fragmentation, the

following conclusions can be drawn:

Airdeck technique is proved significantly effective in homogeneous concrete block

blasting because it produces more uniform fragmentation with minimum fines and over size

60

70

80

90

100

110

120

130

140

0% 10% 20% 30% 40% 50% 60%

Me

an

Fra

gm

en

t S

ize

, mm

Volume %, Air Deck

73

blasted material as compared to that produced from conventional blast. Sieve analysis of

blasted fragments indicate that blasted rock fragmentation produced by airdeck are as good as

that produced by full column charge.

The airdeck, when placed at the middle position of an explosive column produces

more uniform blasted rock size distribution compared to that produced at other positions. One

explanation is that the airdeck at middle position results in multiple impacts of shock wave

that leads to an efficient transfer of explosive energy in the surrounding rocks. The results of

this work also indicate that the optimum length of airdeck is 20% of the total length of

explosive column.

74

CHAPTER 4.

VALIDATION AT DG.CEMENT CHAKWAL

4.1 DG.CEMENT CHAKWAL

The DG. Khan Cement is located at latitude 32043

‘ 53

‘‘ N and longitude 72

048

‘ 46

‘‘

according to the survey of Pakistan, topographic sheet number 43 D/14. It lies near Khairpur

village along Kallar Kahar-Choa Saidan Shah road at a distance of 12 km to the southeast of

Kallar Kahar, District Chakwal, Punjab, Pakistan. The Rawalpindi-Lahore motorway passes

at about 8 km from the plant site. The plant site is in the mountains of eastern salt range,

district Chakwal, Punjab, Pakistan.

4.1.1 Geology of Study Area

The DG. Cement, site is situated in the mountains of eastern salt range, which rises

out of the Punjab alluvial plains and forms remarkable gorges, scarps and hill slopes. The

plant site has the sequence of sedimentary rocks and contains incompetent salt at its base that

has greatly influenced the salt range‘s structure. The salt range contains, extensive reserves of

cement raw material, salt, coal, laterite, bauxite, clay and some other economic minerals.

These sedimentary rocks belong to lower Permian all the way to Quaternary age in

sequence. Rock sequence in relation to geological age is given in Table 4-1.

Table 4-1 General geology of the DG. Cement Chakwal

Early Permian Age Sardhai formation

Clay

Sand stone

Silt Stone

Late Paleocene age Patala Formation

Limestone

Shale

Marl

Sand stone

Early Eocene age

Nammal Formation Limestone

Marl

Sakesar Formation Limestone

Minor Marl

Chorgali Formation

Limestone

Marl

Shale

75

Lower Miocene age Murree Formation

Sandstone

Shale

Clay

Conglomerate

Middle to Late

Miocene age Kamalial Formation

Sand Stone

Clay

Conglomerate

Late Quaternary

Period Overlain Alluvium

Clay

Slit

Gravel Material

4.1.1.1 Limestone deposits at the site

The raw material used to form cement at DG. Cement Chakwal is obtained from

following three formations:

1. Nammal formation

2. Sakesar formation

3. Chorgali formation

DG. Cement Chakwal has almost 500 million tons of limestone deposit. The

Sakesar formation is composed of relatively homogeneous limestone as compared to other

formations. Therefore, the current research work has been carried out on the Sakesar

formation and for this purpose, three different benches were selected for experimentation.

4.1.1.2 Sakesar formation

Due to the abundance of calcareous material in this formation, it has the potential to

be the chief source of raw materials for cement production. This material can be seen visibly

in the project area and is mainly composed of limestone with subordinate interstratification of

marl and shale. The limestone is cream to light grey coloured, medium to thick bedded,

massive and finely crystalline. It is also nodular, sheared, jointed, fractured and contains

ferruginous affixation of yellow and reddish brown colour. The marl is white to light grey in

colour, soft, and friable and usually present in lower part. The marly portion is very rich in

foraminifera and other fauna. This type of section is clearly visible near Sakesar peak (Lat.

32‖ 31‘ N; Long. 71⁰ 65‘ E) in the Salt Range. The lower and upper contacts of the formation

are gradational with Nammal and Chorgali (limestone formation) Formation respectively.

The fossilized remains of foraminifera, molluscs and echinoids exhibit an Early Eocene age.

76

4.1.2 Current Blasting Practices at DG. Cement Chakwal

At DG. Cement Chakwal, limestone is produced by the quarrying method. The

quarry is divided in 3 to 4 working faces called the benches. The benches are drilled and then

blasted to produce limestone. This blasted limestone is then loaded into the dumpers with the

help of front end loaders or shovels, which takes it to the crusher. Then the crusher, crushes

the limestone to the required size, which is later taken to the cement plant for the cement

manufacturing.

The details of the drilling and blasting process are as follows:

4.1.2.1 Drilling

Atlas Copco‘s drill machines were used at the DG. Cement Chakwal for quarrying.

These machines have the following specifications as shown in Table 4-2.

Table 4-2 Specifications of drill machine used at DG. Cement Chakwal

Hole dia 95-140 mm

Weight 18480 kg

Mount Crawler mounted

Grad ability 20 degrees

Rate of penetration 0.33 m/minute

Engine Diesel

Drilling fluid Compressed air (25 bar)

Drilling time 30 minute

Type Down the hole

The bit diameter used nowadays at the quarry is 110 mm.

4.1.2.2 Drilling pattern

Staggered rectangular drilling pattern is being used at DG. Cement quarry which

gives better fragmentation results than other patterns. In order to avoid toe problems and to

reduce back break, 150 angle of drilling is being used at DG. Cement Chakwal.

77

4.1.2.3 Blasting

Currently three benches are being used at DG. Cement Chakwal to fulfil the

limestone requirement of the plant.

4.1.2.4 Explosives

The explosives used in the DG. Cement quarry Chakwal are shown in Table 4-3.

Table 4-3 Explosive used at DG. Cement Chakwal

Trade name of explosive Type of explosive Company

Wabox 80% Dynamite Wah Nobel (pvt) ltd

Blaster Watergel BIAFO (pvt) ltd

Emulite Emulsion Wah Nobel (pvt) ltd

Two types of ANFO are prepared on the site:

1. Fertilizer grade

2. Prilled

Fertilizer grade ANFO is prepared by mixing diesel oil and fertilizer grade

ammonium nitrate, while in case of prilled ANFO, diesel oil is mixed with blasting grade

ammonium nitrate prills. Both fertilizer grade and prilled ANFO are mixed before loading

into the blastholes.

4.1.2.5 Initiation system

Bottom priming is used to blast all the holes at DG. Cement Chakwal. For this

purpose both Nonel and detonating cord are being used for down the hole initiation. Only

Nonel is used as trunk line in order to control air blast.

4.1.2.6 Blast design

The blast design parameters used at DG. Cement Chakwal are presented in the

following Table4-4.

78

Table 4-4 Blast design parameters used at DG. Cement Chakwal

Sr. No Blast Design Parameters Values

1 Hole diameter 100-110 mm

2 Spacing 3.5-4.75 m

3 Burden 3-3.5 m

4 Sub-drilling 1 m

5 Stemming 2.5-3 m

6 Bench height 10-15 m

4.1.2.7 Charging scheme

At the selected project site, Dynamite is being used as primer, ANFO as column

charge, while Emulsion and Watergel are used as bottom charge and booster. The

conventional charging scheme of a blasthole at the site is shown in Figure 4.1.

Figure 4.1 Conventional charging scheme

4.1.2.8 Particle size distribution of conventional blast rock fragmentation

The conventional method with full column charge holes is presently being used at

DG. Cement Chakwal. This blast design produces wide range of particle size distribution

79

with large number of boulders and excessive fine materials. A digital image of one of the

conventional blast at DG. Cement is shown in Figure 4.2.

Figure 4.2 Fragmentation of conventional blast at DG. Cement Chakwal

Figure 4.3 presents the digital image analysis of the fragments from the

conventional blast, using Split Desktop Software.

Figure 4.3 Size distribution of fragments of conventional blast at DG. Cement plant

The result of fragmentation analysis shows that there are a large number of oversize

materials which need secondary blasting before use.

0

20

40

60

80

100

0.0 0.1 1.0 10.0 100.0

Pe

rce

nt P

as

sin

g

Size [in]

Size Distribution

80

4.2 FULL SCALE FIELD EXPERIMENTATION AND RESULTS

After performing experimentation on homogeneous concrete blocks to find out the

best location and optimum length of airdeck to be used in explosive column for the

achievement of optimal fragmentation, the results of experimentation on concrete blocks

were validated on actual rock material on full scale bench in the field.

For this purpose two relatively homogeneous limestone benches, in Sakesar

formation, were selected at DG. Cement Chakwal for further experimentation.

At bench number-1 thirty two holes were drilled in a single row as shown in Figure 4.4.

Figure 4.4 Bench number-1 at DG. Cement showing thirty two holes in a single row

The first eight holes of the bench number-1 from the left side of the row were

blasted conventionally without airdecking. The remaining holes were blasted with 20%

airdeck length of explosive column and the position of the airdeck was also varied: top,

middle and bottom. Eight holes, starting from the right end, were blasted with 20% airdeck

length at the middle of explosive column. Then the next eight holes 17 to 24 were blasted

with 20% airdeck length at top of explosive column. The remaining 8 blastholes 9 to 16 were

blasted with 20% airdeck length at the bottom of the explosive column as shown in Figure

4.4.

The purpose of conducting tests on the sets of eight different holes, at bench

number-1, was not only to verify the work of concrete blocks but also to ascertain the control

parameters in transition from laboratory scale to full scale testing and the proper functioning

of wooden plug during loading process.

4.2.1 Conventional Blasting with Full Column Charge at Bench Number-1

The blasts were conducted using conventional blasting techniques at bench number-

1 and first set of eight-holes were blasted in a single row as shown in Figure 4.4.

81

4.2.1.1 Charge loading

Loading scheme of each blasthole in case of conventional blast with full column

charge was maintained as shown in Figure 4.5. High Explosives, Dynamite and Watergel

(Blaster) were used as bottom charge and blasting grade ANFO was used as column charge in

each blasthole. Charge loading was done by first putting 3.57 kg of Dynamite cartridge

attached to the nonel detonator as primer charge followed by 4 cartridges of watergel

weighing 14.28 kg to make a bottom charge. The diameter, length and weight of each

explosive cartridge was 100 mm, 0.5 m and 3.57 kg respectively. The bottom charge was

then followed by the column charge of 75 kg ANFO. One cartridge of Watergel, cut in 3

equal parts, was used as a booster in the column charge, as shown in Figure 4.5. For

stemming drill cuttings were used and a length of 3 m was maintained in all blastholes.

Progressive firing pattern was used and a time delay of 25 ms was maintained after each hole

was blasted. Nonel detonators were used for this purpose. All holes were connected by

instantaneous nonel detonators which in turn were connected to the plain detonator. The plain

detonator was crimped to a safety fuse as shown in Figure 4.7.

4.2.1.2 Conventional blast design parameters at bench number-1

The details of conventional blast design parameters are presented in Table 4-5.

Table 4-5 Conventional blast design parameters at bench number-1

S.No Blast Design Parameters Values

1 Hole diameter 110 mm

2 Spacing 4.75 m

3 Burden 3.5 m

4 Sub-drilling 1 m

5 Stemming 3 m

6 High Explosive (1 Dynamite + 4 Watergel

cartridges)

(3.57 + 14.28) = 17.85 kg

7 Booster (1 Watergel cartridge cut into 3 pieces) 3.57 kg

8 ANFO 75 kg

9 No. of holes 08

10 No. of rows 01

11 Depth of hole 15 m

12 Bench height 14 m

82

Figure 4.5 Loading scheme of full column charge blastholes at bench number-1

4.2.1.3 Drilling pattern of full column charge holes at bench number-1

The drilling pattern used for conventional blast at bench number-1 is shown in

Figure 4.6.

Figure 4.6 Drilling pattern of full column charge holes at bench number-1

4.2.1.4 Firing pattern of full column charge holes at bench number-1

The firing pattern used for conventional blast at bench number-1 is shown in Figure

4.7.

Figure 4.7 Firing pattern of full column charge holes at bench number-1

83

A front and plan view of bench number-1 before blast is given in Figure 4.8 and

Figure 4.9 respectively.

Figure 4.8 Front view of bench -1 before blast Figure 4.9 Plan view of bench-1 before blast showing 32

drill holes in a single row

Figure 4.10 to Figure 4.13 are showing different steps involved in preparing the

bench number-1 for blast.

Figure 4.10 Measuring the burden distance at bench-1 Figure 4.11 Measuring the length of Watergel cartridge

at bench -1

Figure 4.12 Loading of dynamite cartridge at bench-1 Figure 4.13 Loading of ANFO at bench -1

84

Digital image of fragmentation after conventional blast (first eight holes) at bench

number-1 as shown in Figure 4.14 was taken for analysis by the digital fragmentation

analysis software.

Figure 4.14 Fragmentation of full column charge holes after blast at bench

number-1

4.2.2 Assessment of Blast Performance by Split Desktop

Several images were taken from appropriate distance of blasted muckpile in a

proper light environment with a canon digital camera having a resolution of 3456 pixels. The

images were cropped before being used in the software in order to remove all unwanted

background information such as ground, sky etc. The images were then scaled and delineated

by the image analysis software.

4.1.2.1 Introduction of software

Split-Desktop is a software that uses the digital image analysis technique to

determine the size distribution of fragments. Split-Desktop refers to the "user-assisted"

version of the Split rock fragmentation measurement software. Digital images acquired in the

field can be analyzed on a laptop in the field or in the office to determine the size distribution

of fragmented rock after blast at any stage in the comminution process.

85

The images of blasted fragments can be captured from the muckpile, haul truck,

leach pile, draw point, waste dump, stockpile, conveyor belt, or any other situation where

clear images of rock fragments can be obtained. Split-Desktop then manually scales and edits

these images for optimum accuracy.

4.1.2.2 How it works

Split-Desktop can be easily run by engineers or technicians on-site locations. We

just have to acquire the suitable images to put into the software to determine the size

distribution of your fragmented rock at any stage in the comminution process.

Figure 4.15 Split desktop process stages

The first step is for the user to acquire images in the field and download these

images onto the computer. Split-Desktop then assists the user in properly scaling the images.

Next, the fragments in each of the images are delineated automatically and the size

distribution of the rock fragments is determined as shown in Figure 4.15.

Split-Desktop plots the resulting size distributions in various forms (linear-linear,

log-linear, log-log, and Rosin-Rammler). The size distribution results can be stored in a tab-

86

delineated file for use in spread sheet and plotting programs. In addition, Split-Desktop

automatically generates results reports in HTML.

4.1.2.3 Digital fragmentation analysis

Split Desktop software was used to analyze the fragmentation after each blast.

Digital fragmentation analysis of the conventional blast at bench number-1 is presented in

Figure 4.16.

Figure 4.16 Size distribution of fragments of conventional blast at bench number-1

The graph in Figure 4.16 shows that almost 100% of fragmentation from a

conventional blast of bench number-1 (first eight holes) is under the sieve size of 75 inches.

The size of sieve at 50% passing is about 20.37 inch.

4.2.3 Cost Per Tonne of Limestone Extracted by Conventional Blasting with Full

Column Charge at Bench Number-1

Table 4-6 shows the total quantity and cost of the explosive used in a conventional

blast at bench number-1.

87

Table 4-6 Cost of the explosives used in a conventional blast at bench number-1

Sr No. Entity Quantity Cost per Unit Total cost (Rs)

1 Dynamite 28.56 kg 415.9 Rs/kg 11878.10

2 Watergel 142.80 kg 242.19 Rs/kg 34584.73

3 ANFO 600 kg 48.68 Rs/kg 29208.00

4 Nonel (20 m) 8 367.65 Rs/nonel 2941.20

5 Nonel instantaneous (10 m) 2 174.33 Rs/nonel 348.66

6 Safety fuse 1 m 8.14 Rs/m 8.14

7 Plain Detonator # 8 1 13.60 Rs/det 13.60

Total Cost 78982.43 Rs

Total volume blasted = 3.5 x 4.75 x 14 x 08

= 1862 m3

Total tonnage blasted = 1862 x 2.7

= 5027.4 tonnes

(where density of limestone = 2.7 tonnes/m3)

Explosives Consumed=Dynamite +Watergel +ANFO

=28.56+142.80+600

=771.36 kg

Powder Factor = Explosive consumed (kg) /Rock blasted (m3)

= 771.36/1862=0.414 kg/m3

Cost of explosives per tonne of rock blasted = Total cost of explosives/tonnes of rock

blasted

=78982.43/5027.4

=15.71 Rs/tonne

4.2.4 Modified Blast using 20% Airdeck Length at the Middle of Explosive Column at

Bench Number-1

In this case another set of eight-holes were blasted with 20% airdeck length at

middle of explosive column in a single row at the same bench number-1 as shown in Figure

88

4.4. Same blast parameters were maintained as that used in conventional blast at bench

number-1, other than introducing a wooden plug or a spacer in the middle of the explosive

column to create an air space equivalent to 20% of explosive charge length. This airdeck at

the middle of the explosive column reduced the quantity of explosive by 20% as compared to

conventional blast with continuous charge and was supposed to enhance the effect of the

explosive on the rock. The wooden plug used in the experimentation is shown in the Figure

4.17. Top and bottom priming was used due to mid-airdeck.

Initially self-inflating gas bags were considered for the experiments, as these bags

provide proper airdecking in the explosive column. However, these bags are not

manufactured in Pakistan and had to be procured from another country. Thus it was decided

to make use of a wooden plug keeping in view the equally good alternate, the convenience

and the rationalization of budget.

Figure 4.17 Wooden plug used to give airdeck


The loading scheme of each blasthole in case of 20% mid-airdeck blast at bench

number-1 was maintained as shown in Figure 4.18.

Charge loading was done by first putting 3.57 kg of Watergel cartridge in the

blasthole, attached to the nonel detonator as primer charge, it is shown in Figure 4.18.

Followed by one cartridge of Watergel weighing 3.57 kg and half cartridge of Dynamite

100 mm

2400 mm

19mm

89

weighing 1.78 kg as bottom charge. The bottom charge was followed by 25 kg of ANFO. A

wooden spacer of 2.4 m equivalent to 20% of explosive charge length was then introduced in

the middle of explosive column. The wooden spacer overlain by 25 kg ANFO followed by

half cartridge of Dynamite weighing 1.78 kg and two cartridges of Watergel weighing 7.14

kg. The last cartridge was attached with the nonel detonator for top priming. It is very

important to note here that the same delay was maintained using nonel detonators for top and

bottom priming in each single blasthole as shown in Figure 4.23. Moreover, the amount, type

and sequence of explosive above and below the airdeck was kept exactly the same for each

blasthole as shown in Figure 4.18, so that the gases produced by the explosive columns above

and below should meet at the centre of airdeck and produce further shock waves to enhance

fragmentation [9,61]. The stemming length of 3m was maintained in each blasthole. Figure

4.21 and Figure 4.22 show the loading of Watergel cartridge and airdeck respectively.

4.2.4.2 Design parameters of each hole for 20% airdeck blast at bench number-1

The details of modified blast design with 20% airdeck at middle of explosive

column at bench number- 1 are shown in Table 4-7.

Table 4-7 The design parameters of each hole for 20% airdeck blast at bench number-1

Sr.No. Parameters Values


2 Spacing 4.75 m

3 Burden 3.5 m

4 Sub-drilling 1 m

5 Stemming 3 m

6 High Explosive (1Dynamite+4Watergel

cartridges)

(3.57 + 14.28) = 17.85 kg

7 ANFO 50 kg

8 No. of holes 08

9 No. of rows 01



12 Airdeck length 2.4 m

90

Figure 4.18 Loading scheme of each 20% mid-airdeck blasthole at bench

number-1

4.2.4.3 Drilling pattern of blastholes with 20% airdeck length at mid of explosive

column, at bench number-1

The drilling pattern of blastholes with 20% airdeck length at middle of explosive

column at bench number-1 is given in Figure 4.19.

Figure 4.19 Drilling pattern of 20% middle airdeck blast at bench number-1

4.2.4.4 Firing pattern of blastholes with 20% airdeck length at mid of explosive column,

at bench number-1

The firing pattern used for 20% mid-airdeck blast at bench number-1 is shown in

Figure 4.20.

91

Figure 4.20 Firing pattern of 20% middle airdeck blast at bench number-1

Figure 4.21 Loading of Watergel cartridge as a primer in case of mid-airdeck

blast

Figure 4.22 Loading of wooden plug as an airdeck in the blasthole

92

Figure 4.23 Nonel detonators having same time-delay used in one of the mid-

airdeck blasthole

Digital image of fragmentation after 20% mid-airdeck blast at bench number-1 as

shown in Figure 4.24 was taken for size analysis using the Split Desktop software.

Figure 4.24 Fragmentation of 20% mid-airdeck blast at bench number-1

4.2.4.5 Digital fragmentation analysis

Fragmentation analysis of the digital image was performed with split desktop as


93

Figure 4.25 Size distribution of fragments of 20% mid-airdeck blast at bench number-1

The graph in Figure 4.25 shows that 100% of fragmentation from 20% mid-airdeck

blast at bench number-1 is under the sieve size of 25 inches. The size of sieve at 50% passing

is about 4.44 inch.

4.2.4.6 Cost per tonne of limestone extracted by modified blasting method, using 20%

mid-airdeck length of explosive column at bench number-1

Table 4-8 shows the total quantity and cost of the explosive used in this blast.

Table 4-8 Cost of the explosives used in 20% mid-airdeck blast at bench number-1

Sr.

No. Entity Quantity Cost Per Unit Total Cost (Rs)

1 Dynamite 28.56 kg 415.90 Rs/kg 11878.10

2 Watergel 114.24 242.19 Rs/kg 27667.78

3 ANFO 400 kg 48.68 Rs/kg 19472

4 Nonel (20 m) 8 367.65 Rs/nonel 2941.20

5 Nonel inst. (10 m) 2 174.33 Rs/nonel 348.66



8 Air plugs 8 250 Rs/plug 2000

9 Nonel (10 m) 8 260.50 Rs/nonel 2084

Total Cost of explosives 64413.48 Rs

Total Cost of explosives + Air plugs = 66413.48 Rs

94

Total volume blasted = 3.5 x 4.75 x 14 x 08 = 1862 m3

Total tonnage blasted= 1862x 2.7 = 5027.4 tonnes

(Where density of limestone = 2.7 tonnes/m3)

Explosives Consumed=Dynamite +Watergel+ ANFO

=28.56 + 114.24 + 400 = 542.8 kg

Powder Factor = Explosive Consumed (kg)/Rock Blasted (m3)

= 542.8 / 1862 = 0.2915 kg/m3

Cost of explosives per tonne of rock blasted = Total Cost of explosives/tonnes of rock

blasted

= 64413.48 / 5027.4

= 12.81 Rs/tonne

Total cost per tonne = Cost of explosives + Air plug cost / tonnes of rock blasted

= 66413.48 /5027.4

= 13.21 Rs/tonne

4.2.5 Modified Blast using 20% Airdeck Length at the Top of Explosive Column at

Bench Number-1

Another set of eight holes was blasted using the same bench number-1 with 20%

airdeck length at top of explosive column as shown in Figure 4.4. In each blasthole a wooden

plug of length 2.4 m was introduced at the top of the explosive column to create an air space

equivalent to 20% of explosive charge length as shown in Figure 4.26. This airdeck at the top

reduced the quantity of explosive by 20% as compared to that used by full column charge

blast without any airdeck.

4.2.5.1 Charge Loading

The loading scheme of each blasthole with 20% airdeck length at top of explosive

column is shown in Figure 4.26. High explosives, Dynamite and Watergel (blaster) were

used as bottom charge and blasting grade ANFO was used as column charge. Charge loading

95

was done by putting 3.57 kg of Dynamite cartridge in the blasthole, and cartridge was

attached to the Nonel detonator as primer charge in the bottom of the hole followed by 3

cartridges of Watergel weighing 10.71 kg. The diameter, weight and length of cartridges were

same in all experiments at bench number-1. The bottom charge was then followed by the

column charge of 50 kg ANFO. One Watergel cartridge cut in 3 equal parts was loaded as a

booster charge and is shown in Figure 4.26. Wooden spacer of 2.4 m, equivalent to 20% of

explosive charge length, was then introduced at top of explosive column. The stemming

length of 3m was also kept same as in all other experiments at bench number-1.

Figure 4.26 Loading scheme of 20% top airdeck blasthole at bench number-1

4.2.5.2 Drilling pattern of 20% top airdeck blast at bench number-1

The drilling pattern of blastholes with 20% airdeck length at top of explosive

column at bench number-1 is presented in Figure 4.27.

Figure 4.27 Drilling pattern of 20% top airdeck blast at bench number-1

96

4.2.5.3 Firing pattern of 20% top airdeck blast at bench number-1

The firing pattern used for 20% top airdeck blast at bench number-1 is shown in

Figure 4.28.

Figure 4.28 Firing pattern of 20% top airdeck blast at bench number-1

A digital image of the fragments after blast for 20% airdeck length at top of

explosive column at bench number-1 was taken for analysis by Split Desktop software. It is


Figure 4.29 Fragmentation of 20% top airdeck blast at bench number-1

4.2.5.4 Fragmentation analysis

The results of the fragmentation analysis of 20% top airdeck blast at bench number-

1 are given in Figure 4.30.

97

Figure 4.30 Size distribution of fragments of top airdeck blast at bench number-1

The graph in Figure 4.30shows that 100% of fragmentation from 20% top airdeck

blast at bench number-1 is under the sieve size of 50 inches. The size of sieve at 50% passing

is about 7.22 inches.

4.2.6 Modified Blast using 20% Airdeck Length at the Bottom of Explosive Column at

Bench Number-1

The final set of eight holes was blasted with 20% airdeck length placed at bottom of

explosive column at the same bench number-1 at DG. Cement Chakwal. In each blasthole a

wooden plug of 2.4 m length was kept at the bottom of the explosive column to produce an

air space equivalent to 20% of explosive charge length.


The loading scheme of each blasthole with 20% airdeck length at bottom of

explosive column at bench number- 1 is shown in Figure 4.31. A wooden plug of length 2.4

m was first of all loaded at the bottom of the blasthole, a primer charge of Dynamite cartridge

was placed at the top of bottom airdeck followed by 3 cartridges of Watergel, these were then

overlain by 50 kg ANFO. One cartridge of Watergel cut in 3 pieces was used as a booster

charge as shown in Figure 4.31. The diameter, weight and length of cartridges were same as

in all the experiments performed at the bench number-1. The drilling and firing pattern was

kept same in all test blasts at bench number-1.

98

Figure 4.31Loading scheme of 20% bottom airdeck blasthole at bench number-1

4.2.6.2 Drilling pattern of 20% bottom airdeck blast at bench number-1

The drilling pattern of blastholes with 20% airdeck length at bottom of explosive

column at bench number-1 is shown in Figure 4.32.

Figure 4.32 Drilling pattern of 20% bottom airdeck blast at bench number-1.

4.2.6.3 Firing pattern of 20% bottom airdeck blast at bench number-1.

The firing pattern of blastholes with 20% airdeck length at bottom of explosive

column at bench number-1 is shown in Figure 4.33.

99

Figure 4.33 Firing pattern of 20% bottom airdeck blast at bench number-1

The shot was fired at bench number-1 and image of the fragmentation of 20%

bottom airdeck blast was taken with digital camera to be used in Split Desktop for size

analysis, as shown in Figure 4.34.

Figure 4.34 Fragmentation of 20% bottom airdeck blast at bench number-1


The analysis of fragmentation was done for 20% bottom airdeck blast at bench

number-1, as shown in Figure 4.35.

100

Figure 4.35 Size distribution of fragments of bottom airdeck blast at bench number-1

The graph in Figure 4.35shows that almost 100% of fragmentation from 20%

bottom airdeck blast at bench number-1 is under the sieve size of 75 inches. The size of sieve

at 50% passing is about 17.56 inches.

4.2.7 Comparison of Blast Performance of all the Shots Fired at Bench Number-1

Comparison of performance of all the shots fired at DG. Cement Chakwal on bench

number-1 was done for following parameters: fragmentation, muckpile, throw and back break

at the toes or at the collars.

4.2.7.1 % age reduction in fragment size with respect to FXO series by using 20%

airdeck length in explosive column at bench number-1

The FXO series is a virtual set of percent-passing values that you create. The

purpose is to mimic the size distribution results provided by a lab that does actual sieve

analysis.

FXO series represents the first 10%, 20%, 30% ….≈ 100% (Top Size) passing with

their respected sizes in inch. Table 4-9 represents the comparison of fragmentation results of

conventional and blasts with 20% airdeck length at different positions of explosive column in

terms of percentage passing at bench number-1.Average value of three images were used for

101

each percentage passing size, to avoid any biases and to ensure that more accurate results

were obtained.

Table 4-9 Fragmentation results of conventional, 20% mid,20% top and 20% bottom airdeck

blasts at bench number-1

Des

crip

tion

(

per

cen

tage

pass

ing)

Con

ven

tion

al

Bla

st

Aver

age

Valu

es (

inch

es)

20%

Mid

-air

dec

k B

last

Aver

age

Valu

es (

inch

es)

20%

Top

Air

dec

k B

last

Aver

age

Valu

es (

inch

es)

20%

Bott

om

Air

dec

k B

last

Aver

age

Valu

es (

inch

es)

%age

Red

uct

ion

wit

h 2

0%

Mid

-air

dec

k B

last

as

Com

pare

d t

o C

on

ven

tion

al

Bla

st

%age

Red

uct

ion

wit

h 2

0%

Mid

-air

dec

k B

last

as

Com

pare

d t

o 2

0%

Top

Air

dec

k B

last

%age

Red

uct

ion

wit

h 2

0%

Mid

-air

dec

k B

last

as

Com

pare

d t

o 2

0%

Bott

om

Air

dec

k B

last

F10 2.39 0.63 0.76 2.08 74% 17% 70%

F20 5.24 1.38 1.65 4.28 74% 16% 68%

F30 8.3 2.17 2.59 6.53 74% 16% 67%

F40 11.58 3.01 3.6 8.85 74% 16% 66%

F50 14.93 3.93 4.61 11.16 74% 15% 65%

F60 18.2 4.91 5.69 13.44 73% 14% 63%

F70 21.81 6.17 7.22 16.04 72% 15% 62%

F80 26.38 8.01 10.14 19.39 70% 21% 59%

F90 33.32 10.77 16.52 25.13 68% 35% 57%

Top size

measured 63.5 22.25 38.77 48.48 65% 43% 54%

Comparison of each % age passing size of fragmentation for conventional and 20%

airdeck at different positions of explosive column is further shown by bar and cumulative

percentage passing graph in Figure 4.36.

102

Figure 4.36 Comparison of %age passing size of conventional versus 20 %

airdeck length at different positions of explosive column

It may be observed from the Figure 4.36 that airdeck, when placed at the middle

position of explosive charge, produces a small size distribution compared to that produced by

full column explosive charge and airdeck at top and bottom positions. Moreover, the average

50% passing of fragments was achieved at 3.93 inches with 20% mid-airdeck, 14.93 inches

with solid charge, 4.61 inches with 20% top airdeck and 11.16 inches with 20% bottom

airdeck blast.

The fragment size reduction with 20% mid-airdeck blast as compared to

conventional blast of approximately 74% for F10 to F50 passing size, 73% for F60 passing

size, 72% for F70 passing size, 70% for F80 passing size, 68% for F90 passing size and 65%

for top size was observed as shown in Table 4-9.

The fragment size reduction with 20% mid-airdeck blast as compared to 20% top

airdeck blast of approximately, 17% for F10 passing size, 16% for F20 to F40 passing size,

15% for F50 passing size, 14% for F60 passing size, 15% for F70 passing size, 21% for F80

passing size,35% for F90 passing size and 43% for top size was observed.

Similarly, the fragment size reduction with 20% mid-airdeck blast as compared to

20% bottom airdeck blast of approximately 70% for F10 passing size, 68% for F20 passing

103

size, 67% for F30 passing size, 66% for F40 passing size, 65% for F50 passing size, 63% for

F60 passing size, 62% for F70 passing size, 59% for F80 passing size, 57% for F90 passing

size and 54% for top size was observed.

The above analysis established that 20% airdeck length at top, middle and bottom of

the explosive column produced better fragmentation as compared to that produced when a

conventional blasting method was employed with full column charge without any airdeck.

The results of the test blasts at bench number-1 of DG. Cement quarry were in accordance

with the test blasts performed on concrete blocks. It was also very clear that 20% airdecks,

when placed at middle position of the explosive column produced more uniform blasted rock

size distribution compared to that produced at other positions and full column charge without

any airdeck.

Moreover, there was no back break and toe problem found with 20% mid-airdeck

blast at bench no 1. The degree of muckpile formed by fragmentation of the blast with 20%

airdeck at middle of explosive column was better than that produced by conventional blast

with controlled throw and the scattering of material was also non-existent to make it easy for

the loading equipment. The more significant aspect was that in the airdeck blast 20% less

explosive was used.

4.3 FULL SCALE BLASTS

Full scale blasts were conducted on two different sets of 20 holes. These blasts were

executed in the same limestone formation (Sakesar formation) at DG. Cement Chakwal in

Pakistan on a relatively homogeneous bench number-2 to differentiate the blast performance

between the conventional hole loads with full column charge without any airdecking as

shown in Figure 4.38 and the hole loads with airdecking at middle of explosive column as

shown in Figure 4.45. The holes with airdecks were loaded with 20% less explosive as

compared to conventional blast but all other design parameters were kept constant for both

blasts.

In order to check the homogeneity and consistency of limestone bench, each

blasthole was inspected for any discontinuity such as faults, voids and cavities etc which

could alter the results. The blastholes which differed drastically from other blastholes were

104

discarded and new holes were drilled in their place. The Figure 4.37 shows the homogeneity

of one of the test blasthole.

Figure 4.37 Inside wall of one of the blasthole showing homogeneity

First of all the shot was fired at that specific bench number-2 by the conventional

method, then on the same bench another shot was fired by introducing an airdeck in the

middle of explosive column. The airdeck length was kept at 20% of the explosive column

length. The blast design parameters and geometry of blast at bench number-2 were optimized

before both shots. The results of both shots were compared on the following parameters:

fragmentation, back break, floor break, throw, muckpile profile, and blast economics.

4.3.1 Full Scale Conventional Blast with Full Column Charge at Bench Number-2

In this shot 20 blastholes were fired in two rows by conventional method with full

column charge without any airdeck on bench number-2.

105

4.3.1.1 Conventional blast design parameters at bench number-2

The details of blast design for full scale conventional blast with full column charge

without any airdeck at bench number-2 are shown in Table 4-10.

Table 4-10 Full scale conventional blast design parameters at bench number-2

S.No. Parameters Values


2 Spacing 4.75 m

3 Burden 3.5 m

4 Sub-drilling 1 m

5 Stemming 3 m

6 High-Explosive(1Dynamite+4Watergel cartridges) (3.57 + 14.28) = 17.85 kg

7 Booster (1 Watergel cartridge cut into 3 pieces) 3.57 kg

8 ANFO 75 kg

9 No. of holes 20

10 No. of rows 2



4.3.1.2 Loading scheme of each hole in case of full scale conventional blast with full

column charge at bench number-2

The charge loading of all 20 blastholes in case of full scale conventional blast at

bench number-2, as shown in Figure 4.38 was kept exactly the same as that in the

conventional blast at bench number-1.

106

Figure 4.38 Loading scheme of full column charge blasthole at bench number-2

4.3.1.3 Drilling pattern of conventional blast with full column charge at bench

number- 2

A rectangular staggered pattern as shown in Figure 4.39 was achieved using down

the hole drill (DTH) in full scale blasting at bench number-2. Operation of a DTH is shown in

Figure 4.49. This pattern gives better distribution of explosive energy and optimum muckpile

for easy digging of loading equipment.

Figure 4.39 Drilling pattern of full scale conventional blast bench number-2

107

4.3.1.4 Firing pattern of full scale conventional blast at bench number-2

Twenty in hole delay nonel detonators (delay-multiple of 25ms), 5 instantaneous

nonel detonators and 1 plain detonator along with safety fuse were used to give the firing

pattern as shown in Figure 4.40.

Figure 4.40 Firing pattern of conventional blast with full column charge at bench number-2

Figure 4.41 and Figure 4.42 represent the plane and front view respectively of

bench number-2 before conventional blast and Figure 4.43 gives the view of fragmentation

after blast.

Figure 4.41 Plane view of full scale 20 blastholes at bench number-2

108

Figure 4.42 Front view of bench number-2 before full scale conventional blast

Figure 4.43 Fragmentation after blast of full scale conventional shot at bench

number-2


Digital image analysis of the fragmentation after blast of full scale conventional

blast was evaluated by using Split Desktop software as shown in Figure 4.44.

109

Figure 4.44 Size distribution of fragments of full scale conventional blast with full

column charge at bench number-2

The graph in Figure 4.44 shows that 100% of fragmentation from conventional blast

at bench number-2 is under the sieve size of 75 inches.

4.3.1.6 Cost per tonne of limestone extracted by conventional blasting with full column

charge at bench number-2

Table 4-11 shows the total quantity and cost of the explosives used in case of a full

scale conventional blast without any airdeck at bench number-2.

Table 4-11 Cost of the explosive used in full scale conventional blast with full column charge

at bench number-2

Sr.No. Entity Quantity Cost Per Unit Total cost (Rs)

1 Dynamite 71.4 kg 415.9 Rs/kg 29695.26

2 Watergel 357 kg 242.19 Rs/kg 86461.29

3 ANFO 1500 kg 48.68 Rs/kg 73024.55

4 Nonel (20 m) 20 367.65 Rs/Nonel 7353

5 Nonel inst. (10 m) 5 174.33 Rs/Nonel 871.65


7 Plain Detonator # 8 1 13.60 Rs/Det 13.60

Total Cost 197,427.485 Rs

110


= 4655 m3

Total tonnage blasted = 4655 × 2.7

= 12,568.5 tonnes

(where density of limestone = 2.7 tonnes/m3)

Explosives Consumed = Dynamite +Watergel+ANFO

=71.4+357+1500=1928.4 kg


=1928.4/4655=0.414 kg/m3

Cost of explosives per tonne of rock blasted = Total Cost of explosives/Tonnes of rock

blasted

=197,427.485/12,568.5

=15.708 Rs/tonne

4.3.2 Modified Full Scale Blast using 20% Airdeck Length at the Middle of Explosive

Column at Bench Number-2

In this case, in each blasthole a wooden plug of 2.4 m length as shown in Figure

4.51 was loaded at the middle of the explosive column to create an air space equivalent to

20% of explosive charge length. This airdeck at the middle of the explosive column was

supposed to enhance the effect of the explosive on the rock and reduce its consumption up to

20%.

4.3.2.1 Design parameters of full scale 20% mid-airdeck blast at bench number-2

Table 4-12 shows the design specifications of full scale 20% mid-airdeck blast at

bench number-2.

111

Table 4-12 Blast design parameters of full scale 20% mid-airdeck blast at bench number-2

Sr. No. Parameters Values


2 Spacing 4.75 m

3 Burden 3.5 m

4 Sub-drilling 1 m

5 Stemming 3 m

6 High Explosive (1 Dynamite + 4

Watergel cartridges)

(3.57 + 14.28) =

17.85 kg

7 ANFO 50 kg

8 No. of holes 20

9 No. of rows 2



12 Airdeck length 2.4 m

4.3.2.2 Loading scheme of each blasthole in case of full scale 20% mid-airdeck blast at

bench number-2

The loading scheme of each borehole in case of full scale 20% mid-airdeck blast at

bench number-2 as shown in Figure 4.45 was kept exactly the same as was in 20% mid-

airdeck blast at bench number-1.

Figure 4.45Loading scheme of each blasthole with 20% airdeck length at mid

of explosive at bench number-2

112

4.3.2.3 Drilling pattern of full scale 20%mid-airdeck blast at bench number-2

The drilling pattern for full scale 20% mid-airdeck blast, as shown in Figure 4.46

was kept exactly the same as was in the conventional blast at bench number-1.

Figure 4.46 Drilling pattern of full scale mid-airdeck blast bench number-2

4.3.2.4 Firing pattern of full scale 20% mid-airdeck blast at bench number-2

The firing pattern as shown in Figure 4.47 was kept exactly the same as was in the

full scale conventional blast. As amid-airdeck divides the explosive column in two equal

parts, so top and bottom priming, with same delay nonel detonators, was achieved in each

blasthole. The loading of 20% mid-airdeck can be seen in Figure 4.51. The network of nonel

initiation system is also shown in Figure 4.53.

Figure 4.47 Firing pattern of 20% mid-airdeck blast at bench number-2

Figure 4.48 and Figure 4.54 present the image of bench number-2 before and after

full scale 20% mid-airdeck blast respectively.

113

Figure 4.48 Bench number-2 before 20% mid-airdeck blast Figure 4.49 DTH, working at bench number-2

Figure 4.50 represents the wooden plugs of length 2.4 m used to give airdecks in the

explosive columns at bench number-2.

Figure 4.50 Wooden plugs used at bench-number-2 Figure 4.51 Loading of mid airdeck at bench number-

2

Figure 4.52 Nonel detonators of same delay Figure 4.53 Network of nonel initiation system

114

Figure 4.54 Fragmentationof full scale 20% mid-airdeck blast at bench number-2

4.3.2.5 Fragmentation analysis of 20% mid-airdeck blast at bench number-2

Digital image analysis of the fragmentation of 20% mid-airdeck blast was

performed by using Split Desktop software as shown in Figure 4.55.

Figure 4.55 Size distribution of fragments of full scale 20% mid-airdeck blast at

bench number-2


blast at bench number-2 is under the sieve size of 50 inches.

115

4.3.2.6 Cost per tonne of limestone extracted by modified blasting method with 20%

airdeck length at mid of explosive column at bench number-2

Table 4-13 shows the total quantity and cost of the explosive used in full scale 20%

mid-airdeck blast at bench number-2.

Table 4-13 Cost of the explosive used for full scale 20% mid-airdeck blast at bench number-2

Sr.No. Entity Quantity Cost Per Unit Total Cost (Rs)

1 Dynamite 71.4 kg 415.90 Rs/kg 29695.26

2 Watergel 285.6 242.19 Rs/kg 69169.03

3 ANFO 1000 kg 48.68 Rs/kg 48,683.03

4 Nonel (20 m) 20 367.65 Rs/nonel 7353.00

5 Nonel inst. (10 m) 5 174.33 Rs/nonel 871.65



8 Air plugs 20 250.00 Rs/plug 5000.00

9 Nonel (10 m) 20 260.50 Rs/nonel 5204.00

Total cost of explosive 160,997.72 Rs

Total cost of explosives + Air plugs = 165,997.715 Rs


= 4655 m3

Total tonnage blasted = 4655x 2.7

= 12568.5 tonnes


Explosives consumed=Dynamite +Watergel+ ANFO

=71.4 + 285.6 + 1000

= 1357 kg

Powder factor = Explosive consumed (kg)/Rock blasted (m3)

= 1357 / 4655 = 0.2915 kg/m3

Cost of explosives per tonne of rock blasted = Total cost of explosives/Tonnes of rock

blasted

=160997.715 / 12568.5

116

= 12.8 Rs/tonne

Total cost per tonne = Cost of explosives + Air plug cost / Tonnes of rock blasted

= 165997.715 / 12568.5

= 13.20 Rs/tonne

4.3.3 Comparison of Blast Performance of all Blasts Fired at Bench Number-2

Blast performance of conventional and 20% mid-airdeck blast at bench number-2

was evaluated on following parameters: fragmentation, muckpile displacement, over break,

toe and level of floor.

4.3.3.1 %age reduction in fragment size with respect to FXO Series by using 20% mid

airdeck length in explosive column at bench number-2

Comparison of fragmentation results of full scale conventional and 20% mid-

airdeck blast in terms of cumulative percent passing at bench number-2 are presented in

Table 4-14.Average value of three images were used for each percentage passing size, to

ensure that more accurate results were obtained.

Table 4-14 Fragmentation results of full scale conventional and 20% mid-airdeck blast at

bench number-2

Description of

% age passing

Conventional

Blast.

Average

values Size(in)

20% Mid-

airdeck Blast.

Average values

Size(in)

% age Reduction with

20% Mid-Airdeck Blast

as Compared to

Conventional Blast

F10 1.16 0.63 45%

F20 2.70 1.37 49%

F30 4.50 2.17 52%

F40 6.55 2.99 54%

F50 8.86 3.86 56%

F60 11.36 4.73 58%

F70 14.32 5.88 59%

F80 18.15 8.21 55%

F90 37.05 14.85 60%

Top size measured 87.31 32.22 63%

117

Comparison of each %age passing of fragmentation for conventional and 20%

airdeck length at middle position of explosive column at bench number-2 is further explained

by the bar and cumulative percentage passing graph in Figure 4.56.

Figure 4.56 Comparison of %age passing between full scale conventional and

20 % mid-airdeck blast at bench number-2

It may be observed from the Figure 4.56 that 20% airdeck, when placed at the

middle position of explosive charge, produces a small fragment size distribution as compared

that produced by full column explosive charge. Moreover, the average50% passing of

fragments at 3.86 inch with 20% mid-airdeck and 8.86 inch with conventional blast was

achieved.

As shown by Table 4-14, the fragment size reduction with 20% mid-airdeck blast as

compared to conventional blast of approximately 45% for F10 passing size, 49% for F20

passing size, 52% for F30 passing size, 54% for F40 passing size, 56% for F50 passing size,

58% for F60 passing size, 59% for F70 passing size, 55% for F80 passing size, 60% for F90

passing size and 63% for top size was observed.

The mid-airdeck produced even fragmentation with no oversize boulders and

conventional blast with full column charge produced uneven fragmentation with large

number of boulders which require secondary blasting. It was also worth noting that mid-

airdeck used 20% less explosive.

118

4.3.3.2 Muckpile displacement at bench number -2

Muckpile distances were measured for both full scale conventional and 20% mid-

airdeck blasts as presented in Table 4-15. The throw was significantly reduced in case of mid-

airdeck blasting compared to that for conventional blasting with no airdecking in which

muckpile was scattered showing inefficient use of energy.

Table 4-15 Muckpile distances

Entity Conventional Blast 20% Mid-airdeck Blast

Throw (m) 22 10

The mid-airdeck showed efficient use of explosive energy even though the blast

used 20% less explosive.

4.3.3.3 Over break at bench number -2

There was no back break or end break found in the case of 20% mid-airdeck blast

and a clean face without any cracks was available for the next round. The conventional blast

on the other hand produced some back cracks as shown in Figure 4.57 which showed not

only waste of energy but uneven face for the next round.

Figure 4.57 Back crack produced due to full scale conventional blast at bench

number-2

Back Crack

119

4.3.3.4 Level of floor at bench number-2

In both modified 20% mid-airdeck and conventional blast without airdeck at bench

number-2, the floor level was analyzed very carefully to check for any toe or disruption of

floor after the blasted material was removed. The floor was smooth and no toe was found in

both cases. It was very significant because airdeck blast used 20% less explosive.

4.4 USE OF MULTIPLE AIRDECKS IN THE BLAST HOLE

Another homogeneous limestone bench number-3 in Sakesar formation was

selected for experimentation at DG. Cement Chakwal. At this bench number-3, sixteen holes

were blasted in a single row as shown in Figure 4.58.

Out of the 16 holes first 8 holes were blasted by placing two airdeck lengths

equivalent to 20% of explosive column in each blasthole as shown in Figure 4.67. The next

eight holes were blasted with full column charge without any airdeck. Fragmentation for each

case was analyzed and results were compared.

Figure 4.58 16 holes in a single row at DG. Cement Chakwal at bench number-3

4.4.1 Conventional Blasting with Full Column Charge at Bench Number-3

In conventional blast eight holes were blasted in a single row. The drilling and the

firing pattern adopted at bench number-3 is shown in Figure 4.60 and Figure 4.61

respectively.

4.4.1.1 Conventional blast design parameters at bench number -3

The details of conventional blast design parameters used at bench number-3 are

presented in Table 4-16.

120

Table 4-16 Design parameters for conventional blast with full column charge at DG.

Cement Chakwal on bench number-3

Hole diameter 110mm

Spacing 4.5m

Burden 4m

Stemming 2.5m

High explosive

(1 unit Dynamite + 3 units of Watergel)

(3.57kg + 3* 3.57) = 14.28

kg

Column Charge ANFO 86 kg

No of holes 8

No of rows 1

Hole depth 14m

Bench height 13m


The loading scheme of each blasthole in case of the conventional blast with full

column charge at bench-3 was maintained as shown in Figure 4.59. Dynamite and Watergel

(Blaster) were the high explosives used as bottom charge and blasting grade ANFO was used

as column charge in each blasthole. The charge loading was done by putting 3.57 kg of

Dynamite cartridge attached to the nonel detonator as primer charge followed by 2 cartridges

of Watergel weighing 7.14 kg to make a bottom charge. The diameter, length and weight of

each explosive cartridge were 100 mm, 0.5 m and 3.57 kg respectively. The bottom charge

was then followed by the column charge of 85 kg ANFO. One cartridge of Watergel cut in 3

equal parts was used as a booster in the column charge as shown in Figure 4.59. The

stemming of length 3m with drill cuttings was maintained in all blastholes. Progressive firing

pattern was achieved by using multiple of 25ms in hole delay nonel detonators. All holes

were connected, in a row, by instantaneous nonel detonators which in turn were connected to

the plain detonator. The plain detonator was crimped to safety fuse as shown in Figure 4.61.

121

Figure 4.59 Loading scheme of the holes fired with conventional blast at bench number-3

4.4.1.3 Drilling pattern of conventional blast at bench number-3

Drilling pattern used for conventional blast at bench number-3 is shown in Figure 4.60.

Figure 4.60: Drilling pattern of Conventional blast at bench no 3

4.4.1.4 Firing pattern of conventional blast at bench number-3

Firing pattern used for conventional blast at bench number-3 is shown in Figure 4.61.

Figure 4.61 Firing pattern of conventional blast at bench number-3

122

Figure 4.62 and Figure 4.63 represents the bench number-3 at DG. Cement Chakwal

before and after blast.

Figure 4.62 Bench number-3 at DG. Cement Chakwal before blast

Figure 4.63 Bench number-3 at DG. Cement Chakwal after blast


Several digital images of fragmentation after conventional blast at bench number-3

were taken for analysis with the digital analysis software as shown in Figure 4.64. The

average % passing of three images were used for analysis as shown in Table 4-17.

.

123

Figure 4.64: Bench number-3 at DG. Cement Chakwal after conventional blast

Table 4-17 Cumulative percentage passing of fragments of conventional blast at DG. Cement

Chakwal on bench number-3

Conventional blasting

Sizes[in] % passing

for Image 1

% passing

for Image 2

% passing

for Image 3

Average %

Passing

75 100 100 98.69 99.56

50 93.56 87.93 82.82 88.1

25 61.09 57.62 62.78 60.49

15 41.97 41.14 38.93 40.68

10 31.07 30.87 27.44 29.79

8 26.81 27.16 24.31 26.09

6 21.93 22.55 19.6 21.36

4 16.51 17.34 14.29 16.04

2 10.16 11.06 8.33 9.85

1 6.24 7.04 4.85 6.04

0.75 5.1 5.84 3.87 4.93

0.5 3.83 4.48 2.82 3.71

0.38 3.13 3.71 2.25 3.03

0.25 2.35 2.84 1.64 2.27

0.19 1.91 2.35 1.33 1.86

0.08 1.03 1.33 0.66 1

Graphical representation of cumulative % age passing of fragmentation from

conventional blast against different sieve sizes at bench number-3 is given in Figure 4.65.

124

Figure 4.65 Cumulative percentage passing graph for conventional blast at bench number-3

It can be seen from the fragmentation results that 100% passing of fragmentation

from conventional blast is under the sieve size of 75 inch. Also 50% passing size of the

fragments is about 19 inch as shown in Figure 4.65.

4.4.1.6 Cost per tonne of limestone extracted by conventional method at DG. Cement


Table 4-18 shows the total quantity and cost of the explosive used per hole in a

conventional blast with full column charge at DG. Cement Chakwal on bench number-3.

Table 4-18 Total quantity and cost of the explosive used per hole in conventional blast

with full column charge at DG. Cement Chakwal on bench number-3

Explosive &

Accessories Conventional blasting

No of Units Unit Cost in Rs Overall Cost Rs./hole Dynamite 1 unit of 3.57kg 415.90 415.90

Blaster 3 units of each

3.57 kg 242.19 726.57

ANFO ≈ 86 kg 48.68 4186.74

Nonel 1 length of 15 m 290.21 290.21 - - -

Detonator 1 13.60 13.60 Safety Fuse 1m 8.14 8.14 Airdeck - - -

Total 5641.16

Volume of rock blasted for 8 holes = 8×13×4×4.5 = 1872 m3

0

20

40

60

80

100

0.0 0.1 1.0 10.0 100.0

Pe

rce

nt P

as

sin

g

Size [in]

Size Distribution

125

Density of Limestone = 2.45 tonnes/m3

Tonnage of rock blasted = 2016 x 2.45 = 4586.4 tonnes

Cost of explosive per hole = 5641.15 Rs

Cost of explosive for 8 holes = 45129.27 Rs

Cost of explosive per tonne of blasted rock =45129.27/4586.4 = 9.84 Rs/tonne

Powder factor = Explosive consumed in kg /m3 of the Rock = 802.24 kg/1872m

3 = 0.43kg/m

3

4.4.2 Multiple Airdeck Blasting using 20% Airdeck Lengths of Explosive Column at

DG. Cement Chakwal on Bench Number-3

Two dumble-shaped wooden sticks each of 1.15 m length as shown in Figure 4.66

were introduced in the center of explosive columns of each blasthole as shown in Figure 4.67.

All other blast parameters e.g. burden, spacing, stemming, bench height etc. were kept

constant as were in conventional blast at bench number-3.

In this case the next eight blasts holes were blasted using airdecked charges. The

blast was monitored for fragmentation, throw, back break, ground vibration, powder factor

and explosive consumption.

Figure 4.66 Wooden airdeck used at bench number-3

126

4.4.2.1 Design parameters of multiple airdeck blast at bench number-3

The details of blast design parameters used for multiple airdeck blast at bench

number-3 are presented in Table 4-19.

Table 4-19 Design parameters of multiple airdeck blast at bench number-3

Hole diameter 110mm

Spacing 4.5m

Burden 4m

Stemming 2.5m

High explosive (1 unit of Dynamite + 2 units

of Watergel)

(3.57kg + 2* 3.57) = 10.71 kg

Column charge ANFO = 69 kg

No of holes 8

No of rows 1

Hole depth 14m

Bench height 13m

Airdeck 16,each of length 1.15 m and dia 95 mm


Charging was done by sinking 1.18 kg of Dynamite tied to the nonel detonator as

primer charge followed by 2.5 kg of Blaster in the bottom of the hole in cartridge form. The

bottom charge was then followed by 18.7 kg of ANFO as column charge which was overlain

by an airdeck of 1.15m.The airdeck was followed by 18.7 kg of ANFO which was overlain

by second primer charge of 1.18 and 2.5 kg cartridges of Dynamite and Blaster respectively.

This second primer charge was then followed by 18.7 kg of ANFO which was overlain by

second airdeck of 1.15 m length. Second airdeck was followed by 18.7 kg of ANFO which

was overlain by third primer charge of 1.18 and 2.5 kg cartridges of Dynamite and Blaster

respectively. This sequence of charging is described in the hole configuration in Figure 4.67.

A stemming column of 2.5 m length was maintained at the top of each blasthole using the

drill cuttings. Nonels tied with primer explosives in the blast hole ran through the hole length

and were kept protruding the surface. Initiation was done by using safety fuse and detonator

combination at the surface as shown in Figure 4.69.

127

Figure 4.67: Loading scheme of multi-airdeck blasthole at bench number-3

4.4.2.3 Drilling pattern of holes having multiple airdeck at bench number-3

The drilling pattern used for multi-airdeck blast at bench number-3 is shown in

Figure 4.68.

Figure 4.68 Drilling pattern of holes with multi-airdeck at bench number-3

4.4.2.4 Firing pattern of holes having multiple airdeck at bench number-3

The firing pattern used for multi-airdeck blast at bench number-3 is shown in Figure

4.69.

Figure 4.69 Firing pattern of holes with multi-airdeck at bench number-3

128


Several digital images of fragmentation after multi-airdeck blast at bench number-3

were taken for analysis by the digital analysis software as shown in Figure 4.70. The average

% passing of three images was used for analysis as shown in Table 4-20.

Figure 4.70 Fragmentation after blast for multi-airdeck blast at bench number-3

Table 4-20 Cumulative percentage passing verses sieve sizes for fragments of multi-

airdeck blast

Airdeck Blast

Sizes

[in]

% passing

for Image-1

% passing

for Image-2

% passing for

Image-3

Average %

passing

50 100 100 95.63 98.54

25 97.57 85.15 62.23 81.65

15 76.81 62.10 39.19 59.36

10 54.52 43.12 28.78 42.14

8 44.36 35.61 23.98 34.65

6 34.67 27.57 18.95 27.06

4 24.18 19.22 13.59 18.99

2 13.06 10.37 7.70 10.37

1 7.05 5.59 4.36 5.66

0.75 5.46 4.33 3.44 4.41

0.5 3.81 3.01 2.47 3.09

0.38 2.95 2.33 1.95 2.41

0.25 2.05 1.62 1.39 1.68

0.19 1.58 1.25 1.1 1.31

0.08 0.73 0.58 0.54 0.61

A graphical representation of cumulative %age passing of fragmentation of multi-

airdeck blast against sieve size at bench number-3 is given in Figure 4.71.

129

Figure 4.71 Cumulative percentage passing graph for holes having multiple airdeck at

bench number-3

The graph in Figure 4.71 shows that almost all the blast fragments were passed from

the 50 inch size sieve. Moreover, the 50% passing size of fragments is 13.55 inch.

4.4.2.6 Cost per tonne of limestone extracted by multiple-airdeck blast at DG. Cement


Table 4–21 shows the total quantity and cost of the explosive used per hole in a

multi-airdeck blast at DG. Cement Chakwal on bench number-3.

Table 4-21 Total quantity and cost of the explosive used per hole in multi-airdeck

blast at bench number-3

Explosive &

Accessories

Airdeck Blasting

No of Units Unit Cost in Rs. Overall Cost

Rs./hole

Dynamite 1 unit of 3.57kg 415.90 415.90

Blaster 2 units of each 3.57

kg 242.19 484.38

ANFO 69 kg 48.68 3359.13

Nonel 1 length of 15 m 290.21 290.21

2 lengths of 10 m 174.33 348.66

Detonator 1 8.14 13.60

Safety Fuse 1m 50.00 8.14

Airdeck 2 units 50.00 100.00

Total 5020.02

0

20

40

60

80

100

0.0 0.1 1.0 10.0 100.0

Pe

rce

nt P

as

sin

g

Size [in]

Size Distribution

130

Volume of rock blasted for 8 holes = 8×13×4×4.5 = 1872 m3

Density of limestone = 2.45 tonnes/m3

Tonnage of rock blasted = 1872×2.45=4586.4 tonnes

Cost of explosive per hole =5020.0 Rs

Cost of explosive for 8 holes =40160.12 Rs

Cost of explosive per tonne of blasted rock = 40160.12/4586.4 = 8.7 Rs/tonne

Powder Factor = Explosive consumed in kg /m3 of the Rock

= 589.68kg/1872 m3 =0.31 kg/m

3

Saving per tonne = Cost of explosive per tonne of rock - Cost of explosive per tonne of rock

(Conventional blast) (Airdeck blast)

Saving per tonne = 9.84 – 8.7 = 1.14 Rs per tonne

It means 4586.4 tonnes of rock has been blasted for both the blasts at bench

number- 3, but the explosive consumed per hole is less for airdecked blast as compared to

conventional blast.

4.4.3 Comparison of Blast Performance of all the Shots Fired at Bench Number-3

4.4.3.1 % reduction in fragment size with respect to FXO series by using multi- airdeck

in explosive column at bench number-3

The average sieve sizes of three images from both the blasts at bench number-3

were taken for comparison as shown in the Table 4-22.

131

Table 4-22 comparison of percentage passing of conventional and multi-airdeck blast for

different sieve sizes at bench number-3

% Passing

Conventional

Blast. Average

Size [in]

Multi-Airdeck

Blast. Average

Size [in]

% Reduction in

Size with 20%

Airdeck Length

F10 2.06 2.04 0.97

F20 5.47 4.6 15.9

F30 10.11 7.4 26.8

F40 14.64 10.55 27.9

F50 19.25 13.55 29.61

F60 24.85 16.5 33.6

F70 29.94 19.83 33.7

F80 41.38 24.02 41.9

F90 52.92 30.15 43.02

Top size (99.95%) 71.64 47.99 33.01

Table 4-22 shows that top size is reduced almost 33% by the use of two airdecks in

the explosive column at bench number-3. Comparison of each % passing size for

conventional and multiple airdeck blast is further shown by bar and cumulative percentage

passing graph in Figure 4.72.

Figure 4.72 Comparison of percentage passing of fragmentation of conventional and multi-

airdeck blast for different sieve sizes at bench number-3

132

This graph shows a clear reduction in fragment size distribution in case of multi-

airdeck blast as compared to conventional blast at bench number-3.

A cost comparison of explosive used for conventional and multi-airdeck blast for a

single hole is shown in Figure 4.73.

Figure 4.73 Cost comparison of explosive used for conventional and multi-airdeck blast for a

single hole at bench number-3

The Figure 4.73 represents the overall cost of each explosive and their accessories

used in the form of bars for a single hole. It is clearly visible that the total cost of explosive

used for conventional blast is greater than multi-airdeck blast.

Table 4-23 represents a cost comparison of explosives used per tonne of rock

blasted between multi-airdeck blast and conventional blast at bench number-3.

Table 4-23 Cost comparison of conventional and multi-airdeck blast at bench number-3

Type of Blast Tons of

Rock

Blasted

(tonnes)

Powder

Factor

Explosive

Cost for 1

Hole (Rs)

Explosive

Cost for 8

Holes(Rs)

Explosive Cost

Per Tonne of

Rock Blasted

(Rs/tonne)

Savings

(Rs/tonne)

Conventional

Blast 4586.4 0.43 5641.15 45129.27 9.84

1.14 Blast with

Airdeck 4586.4 0.31 5020.00 40160.12 8.70

133

4.4.3.2 Influence of multi-airdeck blasting on overall blast performance

Table 4-24 describes the advantages gained with the use of multi-airdeck in

blastholes.

Table 4-24 Blast performance of multi-airdecked blast at bench number-3

Parameters Improvements

Explosive Charge Reduced

Fragmentation Less number of boulders

Secondary blasting Almost eliminated

Shovel loading efficiency Improved

Over break Reduced

Toe Almost eliminated

Throw Remained same

134

CHAPTER 5.

VALIDATION AT ASKARI CEMENT NIZAMPUR

5.1 ASKARI CEMENT NIZAMPUR

After conducting successful experimentation on actual heterogeneous and

anisotropic rock material at DG. Cement Chakwal, the next step was to validate and verify

the applicability of these tests at some other limestone quarries in Pakistan. In order to further

validate the results, permission was obtained from the management of Askari Cement to

perform experiments at Askari Cement quarry Nizampur. To proceed further, all the required

information regarding present blasting practice, stratigraphy and geology at Askari Cement

quarry Nizampur was acquired and assessed thoroughly. The details of the site are given in

the following text.

5.1.1 Location and Accessibility

Askari cement factory was established in Nizampur, in the Khyber Phakhtoon

Khawa province (earlier known as North Western Frontier Province) of Pakistan and can

produce approximately 6000 tons of limestone daily. Its location according to Geological

Survey of Pakistan topographic sheet No. 43 C/1 is: longitude 72 2‘ 00‖ to 72o 6‘ 00‖ and

latitude 33 47‘ 30‖ to 33 49‘ 00‖. It is bounded between the village of Assukhel and Kahi

and is located about 20 km south west of old and about 24 km from the new Attock Bridge

and 8 km to the north east of Nizampur village. It lies within the administrative boundary of

District Nowshera. The area is approachable by a metalled road which bifurcates from the

G.T. road near the old Attock Bridge and runs parallel to the Indus River through the project

area and leads to Nizampur. The area has no rail link. The nearest railway station is

Khairabad.

5.1.2 General Geology

The investigated area is the north western (Trans Indus) extension of the Kala Chita

range. It is mostly underlain by sedimentary rocks which range in age from Jurassic to

Quaternary. The general strike trend of the rock is nearly east –west with a gentle to moderate

dip toward south. The rock in this area is highly folded with a few thrust and strike slip faults.

135

The highest elevation in this area is 387 m above mean sea level and lowest elevation is 300

m above mean sea level. The area is drained by dendritic drainage pattern in which the flow

is like tree branches. The direction of flow of all seasonal water channel are south-wards,

which ultimately fall in River Indus.

5.1.2.1 Stratigraphy of DG. Cement Chakwal

Table 5-1describes the stratigraphical sequence of the site at Askari Cement Nizampur.

Table 5-1 Stratigraphical sequence of the site at Askari Cement Nizampur

For the manufacture of Portland cement the possible calcareous materials including

limestone of Samamasuk, Lumshiwal, Lockhart and Patala formation can be considered,

Age Rock Unit Thickness Lithology

Quaternary Surficial

deposit 0.30 m

Undifferentiated surficial deposits

consisting of alluvium clay boulders

and other clay boulders and other

clayey material.

Eocene Middle

Murree

Formation

and Eocene

200m Dark red and purple alternation of clay

and sand stone beds.

Late Paleocene

to Early Eocene

Patala

Formation 10m-150m

Greenish grey to yellowish brown

shale with inter bedded limestone.

Later Paleocene Lockhart 10-200m Light grey to dark grey thin to

medium bedded, nodular limestone.

Late Cretaceous Kawagarh

Formation 15-100m

Yellowish grey to brownish grey thin

marl with cleaved calcareous shale.

Early

Cretaceous

Lumshiwal

Formation 5-30m

Light to dark grey glauconitic

limestone and sandstone, with reddish

brown quartzite.

Early

Cretaceous

Chichali

Formation 5-15m

Dark green to greenish grey

glauconitic sandstone with black

shale.

Jurassic Samanasuk

Formation 20-150m

Light grey to yellowish brown, hard

limestone.

136

while for argillaceous material the marl of Kawagarh formation and shale of Patala formation

can be considered.

5.1.2.2 Lumshiwal limestone

This limestone mostly underlies the Lockhart limestone and has a very small

thickness of 3 m. The limestone is yellowish grey to brownish grey, thin to medium bedded,

well jointed and fractured. Due to the limited reserves, the limestone of this formation is not

considered in exploitation.

5.2 BLASTING EXPERIMENTS

A relatively homogeneous limestone bench in Lumshiwal formation was selected at

Askari cement Nizampur for experimentation. This was done to compare the results of

experiments conducted in DG. Cement quarry. In this phase on a single limestone bench,

having almost same characteristics, thirty two holes were drilled in a single row as shown in

Figure 5.1. Out of thirty two holes first sixteen holes were blasted with 20% airdeck length

located at the middle position of explosive column, the next sixteen holes were blasted with

full column charge without airdecking.

Figure 5.1Limestone bench at Askari Cement Nizampur having 32 blastholes in a single row

5.2.1 Conventional Blasting at Askari Cement Nizampur

In a conventional blast at Askari cement Nizampur 16 holes were blasted in a single

row. The drilling and firing pattern used for conventional blasting is shown in Figure 5.3 and

Figure 5.4 respectively.


High explosives, Dynamite and Watergel (Blaster), were used as bottom charge and

blasting grade ANFO was used as column charge. Loading was done by putting 8.34 kg of

137

Dynamite in cartridge form with first cartridge of Dynamite tied to the detonating cord for

priming as shown in Figure 5.2, followed by 4 cartridges of Watergel weighing 10.32kg to

make a bottom charge. The diameter and length of each explosive cartridge was 75 mm and

0.5 m respectively. The weight of Dynamite and Watergel cartridge was 2.78 and 2.5kg

respectively. The bottom charge was then followed by the column charge of 49 kg of ANFO.

One cartridge of Watergel cut in 2 equal parts was used as a booster in the column charge as

shown in Figure 5.2. The stemming of length 3 m was maintained in all blastholes in this

phase of experimentation. The stemming was done by drill cuttings. Progressive firing pattern

was used with surface delay detonators of 25 ms each as shown in Figure 5.4. The detonating

cord of first hole was connected to the plain detonator. The plain detonator was crimped to

safety fuse as shown in Figure 5.4. Figure 5.5 and Figure 5.6 presents the view of the bench

before and after blast.

5.2.1.2 Conventional blast design parameters

The design parameters used for conventional blast with full column charge at Askari

Cement Nizampur are shown in Table 5-2.

Table 5-2 Conventional blast design parameters with full column charge at Askari Cement

Nizampur


2 Spacing 4.5 m

3 Burden 3.5 m

4 Sub-drilling 1 m

5 Stemming 3 m

6 High explosive (3 units of Dynamite + 4 units of

Watergel )

(8.34 + 10.32) = 18.66 kg

7 Booster (1 unit of Watergel cut into 2 pieces) 2.58 kg

8 ANFO 49 kg

9 No. of holes 16

10 No. of rows 1



138

Figure 5.2 Loading scheme of each blasthole with full Column Charge at Askari

Cement Nizampur

5.2.1.3 Drilling pattern of conventional blast with full column charge holes at Askari

Cement Nizampur

The drilling pattern of conventional blast with full column charge holes at Askari

Cement Nizampur is shown in Figure 5.3.

Figure 5.3 Drilling pattern of conventional blast with full column charge holes at Askari

Cement Nizampur

5.2.1.4 Firing pattern of conventional blast with full column charge holes at Askari

Cement Nizampur

The firing pattern of conventional blast with full column charge holes at Askari

Cement Nizampur is shown in Figure 5.4.

139

Figure 5.4 Firing pattern of conventional blast with full column charge holes at Askari

Cement Nizampur

Figure 5.5 Bench before conventional blast at Askari Cement Nizampur

Figure 5.6 Fragmentation of bench after conventional blast at Askari Cement Nizampur

5.2.1.5 Fragmentations results

Digital images of the fragmentation after conventional blast at Askari cement

Nizampur with full column charge were taken for analysis by Split desktop software. The

140

results of Split Desktop in terms of cumulative percentage passing are shown in Figure 5.7

Figure 5.7 Size distribution of fragmentation of a conventional blast with full column charge

at Askari Cement Nizampur

The graph in Figure 5.7shows that 100% of fragmentation from the conventional

blast at Askari Cement Nizampur is under the sieve size of 75 inches.

5.2.1.6 Cost per tonne of limestone extracted by conventional blasting at Askari

Cement Nizampur

Table 5-3 shows the total quantity and cost of the explosive used in a conventional

blast with full column charge at Askari cement Nizampur.

Table 5-3Total quantity and cost of the explosive used in conventional blast with full column

charge at Askari Cement Nizampur

Sr. No. Entity Quantity Cost Per Unit Total Cost (Rs)

1 Dynamite 133.44 kg 380.16 Rs/kg 50728.55

2 Watergel 160 kg 247.22 Rs/kg 39555.2

3 ANFO 784 kg 151.07 Rs/kg 118438.88

4 Detonating cord 232 m 31.88 Rs/m 7396.16

5 Delay Relay 15 281.86 Rs/unit 4227.9

6 Safety fuse 1m 5.13 Rs/m 5.13


Total Cost 220370.95 Rs

0.00

20.00

40.00

60.00

80.00

100.00

0.0 0.1 1.0 10.0 100.0

Pe

rce

nt P

as

sin

g

Size [in]

Size Distribution

141


= 3024 m3

Total tonnage blasted= 3024 x 2.7

= 8164.8 tonnes


Explosives Consumed= Dynamite + Watergel + ANFO

=133.44+160+784=1077.44 kg


=1077.44/3024

=0.36 kg/m3

Cost of explosives per tonne of rock blasted = Total cost of explosives/Tonnes of rock

blasted

=220370.95/8164.8

= 25 Rs/tonne

5.2.2 Modified Blast using 20% Airdeck Length at Middle of the Explosive Column at

Askari Cement Nizampur

In order to determine the effect of airdeck on fragmentation, all blast design

parameters like bench height, hole length, stemming length, hole dia, burden, spacing, type of

rock and type of explosive were kept constant for conventional and airdeck blast other than

introducing a wooden plug or spacer at the middle position of the explosive column in case of

modified 20% mid-airdeck blast.

In this test, in each blasthole a wooden plug of 2 m length was introduced at the

middle of the explosive column to create an air space equivalent to 20% of explosive charge

length. This airdeck at the middle of the explosive column reduced the consumption of

explosive by 20%. The wooden plug used in the experimentation is shown in the Figure 5.8.

142

Figure 5.8 Wooden plug used for airdecking at Askari Cement Nizampur

The next 16-holes in the same specific bench at Askari cement Nizampur, as shown

in Figure 5.1 were blasted in a single row. The drilling and firing pattern used in this

experiment was kept same as was in the conventional blast and is shown in Figure 5.10 and

Figure 5.11 respectively. It is important to note that the amount, type and sequence of

explosives above and below the airdeck was kept same for each blasthole as shown in Figure

5.9, because when both explosive columns are initiated at same delay they produce gases at

the same time which meet at centre of airdeck to produce further shock waves thus aiding

fragmentation.


Charge loading was done by putting 4.17 kg of Dynamite in the cartridge form with

first cartridge tied to detonating cord as primer charge in the bottom of the blasthole followed

by one cartridge of Watergel weighing 2.5 kg. The diameter, length and weight of each

explosive cartridge were same as that in the conventional blast. The bottom charge was then

followed by 20 kg of ANFO which was overlain by half cartridge of Watergel. Wooden

spacer of 2 m length which was equivalent to 20% of explosive charge length was introduced

at mid of explosive column as shown in Figure 5.9. The wooden spacer overlain by half

cartridge of Watergel followed by 20 kg of ANFO which was then followed by a cartridge of

143

Watergel weighing 2.5 kg and one and a half cartridges of Dynamite weighing 4.17 kg. The

stemming of length 3 m was maintained at the top with drill cuttings. The different stages

involved in preparing the bench at Askari Cement Nizampur for blasting is shown in Figure

5.12 to Figure 5.22.

5.2.2.2 Design parameters of modified blast with 20% airdeck length at middle of

explosive column at Askari Cement Nizampur

The details of the modified blast design with 20% airdeck length at middle of

explosive column are presented in form of Table 5-4.

Table 5-4Modified blast design parameters with 20% airdeck length at middle of explosive

column at Askari Cement Nizampur


2 Spacing 4.5 m

3 Burden 3.5 m

4 Sub-drilling 1 m

5 Stemming 3 m

6 High explosive (3 Dynamite + 3 Watergel cartridges) (8.34 + 7.74) = 16.08 kg

7 ANFO 36 kg

8 No. of holes 16

9 No. of rows 1



12 Airdeck length 2 m

144

Figure 5.9 Loading scheme of each blasthole with 20% airdeck length at mid of


5.2.2.3 Drilling pattern of modified blast with 20% airdeck length at the middle of the


The drilling pattern of modified blast with 20% airdeck length at mid of explosive

column at Askari Cement Nizampur is shown in Figure 5.10.

Figure 5.10 Drilling pattern of modified blast with 20% airdeck length at mid of explosive

column at Askari cement Nizampur

5.2.2.4 Firing pattern of modified blast with 20% airdeck length at the middle of the

explosive column at Askari cement Nizampur

The firing pattern of modified blast with 20% airdeck length at the middle of the

explosive column at Askari cement Nizampur is given in Figure 5.11.

145

Figure 5.11 Firing pattern of modified blast with 20% airdeck length at mid of explosive

column at Askari cement Nizampur

Figure 5.12 Bench before mid-airdeck blast at Askari Cement Nizampur

Figure 5.13 Measuring hole depth Figure 5.14 Measuring burden distance

146

Figure 5.15 Measuring spacing between the holes Figure 5.16 Loading of Dynamite cartridge as primer

Figure 5.17 Loading of Watergel at Askari Cement Figure 5.18 Loading of ANFO at Askari Cement

Figure 5.19 Loading of wooden plug at Askari Cement Figure 5.20 Firing circuit at Askari Cement

147

Figure 5.21 Surface delay detonator at Askari Cement

Figure 5.22 Fragmentation after blast with mid-airdeck at Askari Cement Nizampur

5.2.2.5 Fragmentations results

Digital image analysis of the fragmentations after blast with 20% airdeck at the

middle of the explosive column at Askari Cement Nizampur was done with Split Desktop

software. The results of the fragmentation analysis in terms of cumulative percentage passing

are presented in Figure 5.23.

148

Figure 5.23 Size distribution of fragmentations of 20% mid-airdeck blast at Askari Cement


blast at Askari Cement Nizampur is under the sieve size of 50 inches.

5.2.2.6 Cost per tonne of limestone extracted by modified blast design with 20% airdeck

length at middle of explosive column at Askari Cement Nizampur

Table 5-5 shows the total quantity and cost of the explosive used in the blast with

20% airdeck length at the middle of explosive column.

Table 5-5Total quantity and cost of the explosive used in the blast with 20% airdeck length at

middle of explosive column at Askari Cement Nizampur

Sr. No. Entity Quantity Cost per Unit Total Cost (Rs)

1 Dynamite 133.44 kg 380.16 Rs/kg 50728.55

2 Watergel 120 kg 247.22 Rs/kg 29666.4

3 ANFO 576 kg 151.07 Rs/kg 87016.32

4 Detonating cord 232 m 31.88 Rs/m 7396.16

5 Delay relay 15 281.86 Rs/unit 4227.9


7 Plain detonator #

8

1 19.13 Rs/det 19.13

8 Air plugs 16 250 Rs/plug 4000

Total cost of explosives 179059.59 Rs

Total cost of explosives + Air plugs = 183059.59 Rs

0

20

40

60

80

100

0.0 0.1 1.0 10.0 100.0

Pe

rce

nt P

as

sin

g

Size [in]

Size Distribution

149


= 3024 m3

Total tonnage blasted =3024 x 2.7

= 8164.8 tonnes


Explosives Consumed = Dynamite + Watergel + ANFO

= 133.44 + 120+ 576

= 829.44 kg


= 829.44/ 3024 = 0.27 kg/m3

Cost of explosives per tonne of rock blasted = Total Cost of explosives/Tonnes of rock

blasted =179059.59 / 8164.8 = 22 Rs/tonne

Total cost per tonne= cost of explosives + air plug cost / tonnes of rock blasted

= 183059.59 / 8164.8 = 22.4 Rs/tonne

5.2.3 Comparison of Performance of all Blasts Fired at Askari Cement Nizampur

Blast performance of conventional with full column charge and 20% mid-airdeck

blast was evaluated on following parameters: degree of fragmentation, muckpile

displacement, over break, toe, floor level and ground vibrations.

5.2.3.1 %age reduction in fragment size with respect to FXO series by using 20%

airdeck length at mid of explosive column at Askari Cement Nizampur

Fragmentation results of conventional and 20% mid-airdeck blast in terms of

cumulative percent passing at Askari Cement Nizampur are shown in Table 5-6.

150

Table 5-6Fragmentation results of conventional and 20% mid-airdeck blast at Askari Cement

Nizampur

Description of %

age Passing

Conventional Blast

Size(in)

20% Mid-Airdeck

Blast

Size(in)

%age Reduction

with 20% Mid-

Airdeck Blast

F10 0.01 0.01 0

F20 0.17 0.02 88%

F30 0.71 0.15 79%

F40 1.96 0.57 71%

F50 4.35 1.59 63%

F60 8.35 3.71 56%

F70 15.90 7.69 52%

F80 22.22 13.99 37%

F90 30.03 22.75 24%

Top size measured 60.92 48.49 20%

Comparison of %age passing between the fragmentation of conventional and 20%

mid-airdeck blast at Askari cement Nizampur is further shown by bar and cumulative passing

graph in Figure 5.24.

Figure 5.24 Comparison of %age passing of fragmentation between conventional and 20%

mid-airdeck blast at Askari Cement Nizampur

151

It can be observed from Figure 5.24 that the blast with 20% airdeck length when

placed at the middle position of explosive charge produces a small and uniform fragment size

distribution as compared to blast when full column explosive charge was used. Moreover

50% passing of fragments was achieved at 1.59 inch with 20% mid-airdeck blast and 4.35

inch with conventional blast.

It may also be observed from Table 5-6 that in 20% mid-airdeck blast the fragment

size reduction of approximately 88% for F20 passing size, 79% for F30 passing size, 71% for

F40 passing size, 63% for F50 passing size,56% for F60 passing size,52% for F70 passing

size,37% for F80 passing size, 24% for F90 passing size and 20% for top size was found.

Thus, there was no significant difference found for sizes of F10 or below.

5.2.3.2 Muckpile displacement

Muckpile distances were measured for both conventional and mid-airdeck blasts as

presented in Table 5-7. The throw was significantly reduced in case of mid-airdeck blast as

compared to conventional blasting with full column charge as shown in Figure 5.25. The

muckpile was scattered in case of conventional blast with full column charge showing

inefficient use of energy.

Figure 5.25 Muckpile profile of 20% mid-airdeck blast at Askari Cement Nizampur

152

Table 5-7 Muckpile distances

Entity Conventional Blast 20% Mid-Airdeck Blast

Throw(m) 24 12

The mid-airdeck showed efficient use of explosive energy even though the blast

used 20% less explosive.

5.2.3.3 Over break

There was no back break found in case of mid-airdeck blast and clean face without

any crack was available for the next round. The conventional blast on the other hand

produced some back crack as shown in Figure 5.26 which showed not only wastage of energy

but uneven face for the next round.

Figure 5.26 Back crack due to conventional blast

5.2.3.4 Level of floor

In both modified mid-airdeck and conventional blast without airdeck at Askari

Cement Nizampur bench the floor level was analyzed very carefully to check for any toe or

disruption of floor after the blasted material was removed. The floor was smooth and no toe

was found in both cases. It was very significant because mid-airdeck blast used 20% less

explosive.

Back Crack

153

CHAPTER 6.

ECONOMIC ANALYSIS

6.1 GENERAL

Experiments were conducted at DG. Cement, Chakwal Pakistan, on three relatively

homogeneous limestone benches. First, blasting experiments were conducted on these

benches by conventional method, then the experiments were repeated on the same benches

by introducing an airdeck in the middle of explosive column. The airdeck length was kept at

20% of the explosive column length. The subsequent results from both the blasts were

compared in terms of economics and fragmentation.


AND MODIFIED BLAST WITH 20% AIRDECK LENGTH OF EXPLOSIVE

COLUMN AT DG. CEMENT CHAKWAL

The details from the full-scale conventional and modified blast design at DG. Cement

Chakwal for comparison are shown in Table 6-1.

Table 6-1 Comparison of cost of explosive used for conventional and modified blast with

20% airdeck length of explosive column at DG. Cement Chakwal

Sr.

No. Entity

Conventional Blasts with Full

Column Charge

Modified Blast with 20%Mid -

Airdeck Length

Quantity Cost

per Unit

Total

Cost (Rs) Quantity

Cost

per Unit

Total

cost (Rs)

1 Dynamite 71.40

kg

415.90

Rs/kg 29695.26

71.40

kg

415.90

Rs/kg 29695.26

2 Watergel 357.00

kg

242.19

Rs/kg 86461.29 285.60

242.19

Rs/kg 69169.04

3 ANFO 1500.00

kg

48.70

Rs/kg 73024.54

1000.00

kg

48.68

Rs/kg

48,683.0

3

4 Nonel

(20 m)

20

Nonel

367.65

Rs/nonel 7353.00

20

Nonel

367.65

Rs/nonel 7353.00

5 Nonel

inst.

(10m)

5

Nonel

174.33

Rs/nonel 871.65 5 Nonel

174.33

Rs/nonel 871.65

154

Sr.

No. Entity


Column Charge

Modified Blast with 20%Mid -

Airdeck Length

Quantity Cost

per Unit

Total

Cost (Rs) Quantity

Cost

per Unit

Total

cost (Rs)

6 Safety

fuse

1

m

8.14

Rs/m 8.14 1.00 m

8.14

Rs/m 8.14

7

Plain

Detonator

# 8

1 13.60

Rs/det 13.60 1.00

13.60

Rs/det 13.60

8 Air plugs - - - 20 250.00

Rs/plug 5000.00

9 Nonel (10

m) - - - 20 nonel

260.50

Rs/nonel 5204.00

Total Cost of Explosive =

197,427.49 Rs

Total Cost of Explosive

=160,997.71 Rs

Total Cost of explosives + Air

plugs = 165,997.71 Rs

Figure 6.1 Comparison of cost of full scale conventional and modified blast with 20%

airdeck length of explosive column at DG. Cement Chakwal

The Figure 6.1 presents the overall cost comparison of each explosive and

accessories used in the form of bars for full scale conventional and mid-airdecked blast. It is

155

clearly visible that the total cost of explosive used for conventional blast is greater than that

in the case of airdecked blast. Table 6-2 represents cost comparison of explosive used per

tonne of rock blasted between full scale conventional and 20% mid-airdecked blast at DG.

Cement Chakwal.

Table 6-2 Cost per tonne of full scale conventional and modified blast with 20% airdeck

length at mid of explosive column at DG. Cement Chakwal

Entity Conventional Blast 20% Mid-airdeck Blast

Cost of Explosive per Tonne

(Rs.) 15.70 13.20

As presented in Table 6-2 savings in explosives cost/tonne of rock blasted by using

20% mid-airdeck length in explosive column is 2.50 rupees per tonne (15.70 – 13.20).

Moreover, the analysis of estimated cost of limestone extracted by modified blast

design with 20% airdeck length at middle of explosive column and conventional blast with

full column charge at DG. Cement Chakwal, suggests that up to 2.5 rupees per tonne can be

saved for the explosive only by adopting 20% mid-airdeck length in the explosive column.

The current production of limestone per month at DG. Cement Chakwal is 300,000 tonnes.

As per the calculation up to 16% saving can be achieved and 750,000 rupees can be saved at

the DG. Cement quarry monthly and annually 9 million rupees can be saved.


AND MODIFIED BLAST WITH 20% MID-AIRDECK LENGTH OF

EXPLOSIVE COLUMN AT ASKARI CEMENT NIZAMPUR

The details of cost of explosive incurred on conventional and modified blast with

20% airdeck length of explosive column at Askari Cement Nizampur are given in Table 6-3.

156

Table 6-3 Comparison of cost of explosive used for conventional and modified blast with

20% airdeck length of explosive column at Askari Cement Nizampur

Sr.

No

.

Entity


Column Charge

Modified Blast with 20%

Airdeck at Mid of Explosive

Column

Quantity Cost per

unit

Total cost

(Rs) Quantity

Cost

per unit

Total

cost (Rs)

1 Dynamite 133.44 kg 380.16

Rs/kg 50728.55 133.44 kg

380.16

Rs/kg 50728.55

2 Watergel 160.00 kg 247.22

Rs/kg 39555.2 120.60

247.22

Rs/kg 29666.4

3 ANFO 784.00 kg 151.07

Rs/kg 118438.88 576.00 kg

151.07

Rs/kg

870,16.3

2

4 Detonating

cord 232 m

31.88

Rs/m 7396.16 232m

31.88

Rs/m 7396.16

5 Delay Relay 15 281.86

Rs/unit 4227.9 15

281.86

Rs/unit 4227.9

6 Safety fuse 1

m

5.13

Rs/m 5.13 1.00 m

5.13

Rs/m 5.13

7 Plain

Detonator # 8 1

19.13

Rs/det 19.13 1.00

19.13

Rs/det 19.13

8 Air plugs - - - 16 250.00

Rs/plug 4000.00

Total Cost of Explosive = 220,370.95 Rs

Total Cost of explosives

=179059.59 Rs

Total Cost of explosives + Air

plugs = 183059.59 Rs

Figure 6.2 Comparison of cost of conventional and modified blast with 20% airdeck

length at Askari Cement Nizampur

157

The Figure 6.2 represents the overall cost comparison of each explosive and

accessories used in the form of bars for full scale conventional and airdecked blast. It is

clearly visible that the total cost of explosive used for conventional blast is greater than that

incurred in the case of airdecked blast.

The cost per tonne of both blasts fired at Askari Cement Nizampur is given in Table

6-4.

Table 6-4 Cost/tonne of conventional and modified blast with 20% mid-airdeck length of


Entity Conventional blast 20% Mid-airdeck Blast

Cost of Explosive per

Tonne (Rs) 25 22.4

As given in Table 6-4 saving in explosives cost/tonne of rock excavated by 20%

mid-airdecked blast is 2.6 rupees ( 25 – 22.4) .

The cost analysis conducted from blasting results of Askari Cement Nizampur,

clearly suggests that up to 2.6 rupees per tonne can be saved by adopting 20% mid-airdeck

length in the explosive column, instead of the conventional blast. Now production of

limestone per month at Askari Cement Nizampur is 180,000 tonnes. Therefore, using 20%

mid-airdeck length in explosive column, saving per ton can be increased by 10.4%. If it is

converted into nominal values, Rs. 468,000 rupees can be saved at the Askari cement quarry

monthly and an annual saving of 5.6 million rupees can be achieved.

6.4 DISTRICT/MINERAL WISE LIMESTONE PRODUCTION IN MINING

INDUSTRY OF PUNJAB

Table 6-5 presents the annual production of limestone for various districts of

Punjab.

158

Table 6-5 District/Mineral wise limestone production in mining industry of the Punjab

Districts of Punjab Limestone (Tonnes)

Attock 3029757

Rawalpindi 982495

Jhelum 487970

Chakwal 6120377

Sargodha 0

Khushab 1487688

Mianwali 2890400

D.g. Khan / Rajan pur 2387188

Total 17385875

The total production of limestone as given in Table 6-5 is 17385875 tonnes. The

average cost/tonne saved at DG. Cement Chakwal and Askari Cement Nizampur is 2.55

Rs/tonne.

If the calculation based on statistical data as given in Table 6-5 were to be projected

for limestone production in Punjab (province of Pakistan), 44.33 million rupees

(=17385875x2.55) can be saved annually, just for the explosive used, by adopting 20%

airdeck length in explosive column. Similar calculations can be estimated for other provinces

of the country as well. As there are many other minerals is Pakistan which require blasting

for their production. If airdeck blasting technique is used for the production of those minerals,

millions of rupees can be saved annually.

To sum it up, the efficiency of all downstream processes: loading, hauling, crushing

and grinding, depends upon the optimum size of fragmentation from the blast. As the 20%

mid-airdeck blasting gives even fragmentation with negligible amount of boulders and fines,

machinery can easily handle even fragmentation with least power consumption and wear and

tear, increasing the overall efficiency and production of the entire process. The cost analysis

of all these downstream processes could lead to billions of rupees being saved annually.

159

CHAPTER 7.

CONCLUSIONS AND RECOMMENDATIONS

7.1 CONCLUSIONS

After comprehensive experimentation and analysis of the results from blasted

fragmentation, following conclusions can be drawn:

Airdeck blasting technique was found to be significantly effective in homogeneous

concrete block, as the rock fragments produced by this method were either better or as

good as those produced by using full column charge ,but with reduced expense.

Furthermore, it was also established that the type of fragmentation produced by

airdecked charge depends on the location and size of airdeck in the explosive column.

In this regards it was learned, that the mean size of blasted rock fragments increase with

the increase in airdeck size. While airdecks, when placed in middle position of an

explosive columns produced more uniform blasted rock size distribution, with

minimum fines and oversized material, compared to those produced when same airdeck

length and explosive loadings used at top and bottom positions. The reason that

explains this finding is that when the airdeck is placed in the middle position it creates

multiple series of shock waves which lead to efficient transfer of explosive energy in

the surrounding rocks. For the model materials and explosive used in this research

work, the combination of 20% airdeck length and the center position of airdeck in the

explosive column were produced optimum results.

Comparison of performance of all the shots fired at DG. Cement Chakwal on bench

number-1 was done for following parameters: fragmentation, muckpile, throw and back

break at the toes or at the collars. For this purpose the Split Desktop software was used

at bench number-1, the analysis established that 20% airdeck length at top, middle and

bottom of the explosive column produced better fragmentation as compared to when

conventional blasting method was employed with full column charge without any

airdeck. The results of the test blasts at bench number-1 of DG. Cement quarry were in

accordance with the test blasts performed on concrete blocks. It was also very clear that

20% airdeck, when placed at middle position of the explosive column produced more

160

uniform blasted rock size distribution compared to that at other positions and full

column charge without any airdeck. Moreover, there was no back break and toe

problem. The degree of muckpile formed by fragmentation of the blast with 20%

airdeck at middle of explosive column was better than that produced by conventional

blast with controlled throw and the scattering of material was also nonexistent to make

it easy for the loading equipment. The more significant aspect was that in the airdeck

blast 20% less explosive was used.

For the full scale blast at DG. Cement quarry on bench number-2, the fragment size

reduction with 20% mid-airdeck blast as compared to conventional blast of

approximately 45% for F10 passing size, 49% for F20 passing size, 52% for F30

passing size, 54% for F40 passing size, 56% for F50 passing size, 58% for F60 passing

size, 59% for F70 passing size, 55% for F80 passing size, 60% for F90 passing size and

63% for top size was observed. Mid-airdeck produced even and no oversized

fragmentation, which has significant economic effect on downstream processes.

Muckpile distances were measured for both conventional and mid-airdeck blasts. The

throw was significantly reduced in case of mid-airdeck blasting compared to that in the

case of conventional blasting with no airdecking and in which muckpile was scattered

because of inefficient use of energy. Furthermore, there was no back break or end break

found in case of mid-airdeck blast and clean face without any crack was available for

the next round. Conventional blast on the other hand produced some back cracks, not

only did it waste energy but also produced uneven face for the next round.

With regards to the quarry floor no significant difference was found between modified

mid-airdeck and conventional blast without airdeck at bench number-2. It was very

significant because airdeck blast used 20% less explosive.

The full scale blast at Askari cement Nizampur yielded significant difference in degree

of fragmentation and muckpile displacement by using 20% airdeck at middle of

explosive column as compared to that produced in the case of conventional blast with

full column charge. In 20% mid-airdeck length blast the fragment size reduction of

approximately 88% was found for F20 passing size, 79% for F30 passing size,71% for

F40 passing size, 63% for F50 passing size,56% for F60 passing size,52% for F70

161

passing size,37% for F80 passing size, 24% for F90 passing size and 20% for the top

size. There was no significant difference found for sizes of F10 or below.

Muckpile distances were measured for both conventional and 20% mid-airdeck blasts

conducted at Askari Cement Nizampur. Throw was significantly reduced in case of

mid-airdeck blasting as compared to that in the case of conventional blasting with no

airdecking, in which muckpile was scattered showing inefficient use of energy. The

mid-airdeck showed efficient use of explosive energy even though the blast used 20%

less explosive. Moreover, there was no back break found in case of mid-airdeck blast

and clean face without any crack was available for next round. Conventional blast on

the other hand produced some back cracks which showed not only wastage of energy

but also uneven face for the next round.

With regards to the multiple airdecks, double airdecks equivalent to 20% of explosive

column when placed at middle of explosive columns achieved the same results, in

terms of fragmentation, muckpile, throw and back break at the toes with 20% less

explosive, as was achieved in other benches with 20% middle airdeck in the explosive

column.

From the analysis of estimated cost of explosive used per tonne of limestone extracted

by modified blast design, with 20% airdeck at middle of explosive column and

conventional blast with full column charge at DG. Cement Chakwal, it can be

concluded that up to 2.5 rupees per tonne of explosive can be saved by adopting 20%

mid-airdeck length in the explosive column. In other words saving can be increased by

16% per tonne of rock excavated. This way 750,000rupees can be saved at the DG.

cement quarry monthly while annually 9 million rupees can be saved.

Similarly, the cost analysis conducted from blasting results of Askari Cement

Nizampur, it can be concluded that up to 2.6 rupees per tonne of rock excavated can be

saved by adopting 20% mid-airdeck length in the explosive column, instead of the

conventional blast. Therefore, using 20% mid-airdeck length in explosive column

saving can be increased by 10.4 % per tonne of rock excavated. This way 468,000

rupees can be saved at the Askari cement quarry monthly and an annual saving of 5.6

million rupees can be achieved. If the calculation based on statistical data were to be

162

projected for limestone production in Punjab (province of Pakistan), 44.33 million

rupees can be saved annually only for explosive by adopting 20% airdeck length in

explosive column. Similar calculations can be estimated for other provinces of the

country as well. As there are many other minerals is Pakistan which require blasting for

their production. If airdeck blasting technique is used for the production of those

minerals, millions of rupees can be saved annually.

The airdeck blasting technique was used for the first time in Pakistan at industry level.

In fact the workforce at DG. Cement Chakwal and Askari Cement Nizampur were so

impressed with the effectiveness of the airdeck blasting technique that they have

already started using it in their routine blasts. The teams there have also verified the

cost saving that they are achieving by airdeck blasting technique.

To sum it up, the efficiency of all downstream processes: loading, hauling, crushing

and grinding, depends upon the optimum size of fragmentation from the blast. As the

20% mid-airdeck blasting gives even fragmentation with negligible amount of boulders

and fines, machinery can easily handle even fragmentation with least power

consumption and wear and tear, increasing the overall efficiency and production of the

entire process. The cost analysis of all these downstream processes could lead to

billions of rupees being saved annually.

7.2 RECOMMENDATIONS

The following recommendations are being made to further enhance this study and to

take full advantage of the airdeck blasting technique.

The scope of the study was to deal with the homogenous material but the work can be

safely extended to limestone having variation in geological properties. Thereby, in case

of a particular rock formation, a relationship can be developed between airdeck length

& fragment size. This relation will serve as guideline to select optimum airdeck length

for a certain rock type.

The size distribution of blasted rock fragmentation depends on the extent of geological

discontinuity in the area to be blasted. Therefore, in order to find out precisely the

163

discontinuities within the blasthole a borehole Camera is recommended for the future

work.

While drilling it is recommended that the drilling rate for the blastholes drilled with the

machine should be monitored. This would allow to extract information about the

variation in strata, presence of cavities and voids within the borehole for making

necessary adjustment in blast design.

As widely believed that the size distribution of blast fragments mostly depends upon

the discontinuities present in the rock. Moreover, ease or difficulty of blasting a rock

depends on its strength. Keeping this in mind it is recommended that a relationship be

developed between the rock condition, its strength and airdeck length. In this regard,

rock condition can be quantified by using RMR system of classification of rocks,

whereas rock strength can be expressed in terms of ultimate compressive or tensile

strength. This relationship can help the engineers working in the cement quarries or in

any other surface mine to select the airdeck length for their blast design conveniently.

The plug used in this study was made of wood with fixed diameter, due to which in

cracked and soft holes it got stuck. So there is a need to design a plug locally which

should be adjustable according to hole dia. Also the cost of wood is high, therefore it is

recommended to manufacture a plastic plug which will reduce the cost of plug thus

increasing profits. Moreover, it was also learned that the use of gas bags could help in

achieving better airdecking, increasing the efficiency of this method and resulting in

more effective use of airdeck blasting technique.

In the present research work up to two airdecks in the explosive column were used, but

it will be more beneficial to check if more than two airdecks are used in the explosive

column, allowing for better and economic fragmentation.

It would be better to make use of Seismograph for monitoring blast induced vibrations

and air blast for both conventional and airdecked blast because it has been reported that

with the inclusion of airdecks in explosive column the magnitude of ground vibration

are reduced from 10% to 75%. This reduction will allow mining engineers to use larger

quantity of explosive per delay while maintaining the same vibration level.

164

A cost analysis of all downstream processes like secondary blasting, hauling, crushing,

grinding etc, should be conducted for conventional and 20% mid-airdecked blast. This

will allow for a comprehensive analysis of cost saving from mine to mill.

Moreover, it is recommended that test blasts should be conducted at different cement

quarries of Pakistan using airdeck in the explosive column, so that all mine operators in

Pakistan can adopt this technique, which will help them to solve a lot of blasting related

problems.

165

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