MASTER'S THESIS
A New Concept for Timing Double RingBlasts
Results from small-scale blasting tests
Hasnain Iqbal2013
Master of Science (120 credits)Civil Engineering
Luleå University of TechnologyDepartment of Civil, Environmental and Natural resources engineering
A NEW CONCEPT FOR TIMING DOUBLE RING BLASTS
Results from small-scale blasting tests
Hasnain Iqbal
Masters of Science in Civil Engineering
Division of Mining and Geotechnical Engineering
Department of Civil, Environmental and Natural Resource Engineering
Luleå University of Technology, Sweden
Dedication
Dedicating this thesis to my late Father who always wanted me to achieve the highest position
of my career. To my Mother, her encouragement, support and countless love made me sustained
throughout my life.
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PREFACE
This thesis work is a final contribution towards the Master’s degree and submitted to the Department
of Civil, Environmental and Natural Resources Engineering at Luleå University of Technology,
Sweden in conformity with the requirements for the degree of Master of Science in Civil Engineering
with specialization in Mining and Geotechnical Engineering.
I am highly grateful to my external supervisor Anders Nordqvist Manager R&D mining engineering
Luossavaara-Kirunavaara mine (LKAB) for accepting me as a student for this master’s thesis and
giving me a chance to study blasting in detail, which is one of the most interesting areas of rock
engineering. He was the source of inspiration for this thesis work, without his encouragement and
technical support it would not have been possible for me to complete this work.
I would like to express my sincere gratitude to my academic supervisor Daniel Johansson (PhD)
Director at Swebrec, Lulea University of Technology and assistant supervisor Nikolas Petropoulos,
PhD Student, Luleå University of Technology, Sweden. Your encouragement, advice and support
throughout this thesis period made it possible to accomplish my goal and to complete this work in
time.
I like to thanks my friends, class fellows, teachers and other technical staff who assisted, advised and
supported my work and writing efforts over the last few months. Especially, I need to express my
gratitude and deep appreciation to Lars Åstrom and Hans Olof for providing access to underground
laboratory at Lulea University of technology, to support during practical work and providing necessary
help whenever it was required.
I am thankful to Jonny Olofsson and Leif Keskitalo, technical staff at LKAB for providing their
technical support and guidance during the blasting tests at LKAB Kiruna.
Special thanks to my mother, my sisters and my brothers for encouraging me to finish this Master’s
program and providing me mental support and all necessary help during completion of this thesis
work.
I will always appreciate the experience of working for a Master’s thesis at LKAB mining company
and studying at Lulea University of Technology in Northern Sweden has been a wonderful experience
for me.
Finally I thank Allah Almighty for enabling me to work through all conditions in my master’s studies.
Hasnain Iqbal
Luleå, Sweden
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ABSTRACT
Sub-level caving (SLC) is an important mass mining method which is based upon the utilization of
gravity flow of waste material and blasted ore. The method function on the principle that ore is
fragmented by blasting, while the overlying host rock fractures and caves by the action of mine
induced stresses and gravity. The caved rock or debris from the previous blasted rings reduces the
fragmentation and the swelling of the blasted ring as it absorbs some of the explosive energy and
preventing all energy of the explosive to break the ore.
The main objective of this thesis is to investigate a new concept for timing double ring blasts in terms
of fragmentation. For this purpose, a series of tests has been made in small-scale SLC blocks. The idea
is to blast two rings at the same time, but with a short delay time between the rings. In this case, the
second ring will be blasted first which will create a slot between the blasted burden and the remaining
rock which will eventually provide a free face for the first ring. This may result in improved
fragmentation.
In order to complete this thesis work, a literature study on sub level caving mining, shock wave
interactions in blasting, effect of delay timing and a study on fragmentation models has been done.
The overall process involved a literature study, construction and preparation of small-scale models,
test blasts and finally sieving analysis of the blasted material.
The models were made of magnetite mortar in ring shape (drilling of bore-holes in fan shape upwards,
currently in practice by LKAB Kiruna) for single blasts and in rectangular shape for double blast. The
model design was based on actual geometrical specifications used by LKAB with a scale factor of
1:54. For the single blast tests each ring in the model had 8 holes with a diameter of 11mm. To create
confined conditions, the blocks were confined in a 1x1x1m steel chamber with one adjustable side that
made it possible to open the chamber after the blast. The gap between the front of the chamber and the
free face was filled with confining material .By using different PETN cord strength and burden size,
the specific charge was varied from 1.63 to 4.6 kg/m3.
A total of 6 tests have been made and 5 of these were single blast tests and 1 double row blast test.
After each test the blasted material was collected, sieved and analyzed in terms of fragmentation. The
analysis has been based on confinement and specific charge i.e. free versus confined condition and x50
versus specific charge.
Results from single blasts tests shows that with increasing specific charge under same confined
conditions gives finer fragmentation. The specific charge varied from 1.63 to 4.54 kg/m3,
giving x50
from 12.6 - 11 mm respectively.
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Two single blast tests were made under free face conditions with a specific charge of 1.16 kg/m3 and
1.89 kg/m3. The results showed a minimum value of x50 (24.9mm) at q=1.89 and 30.9 mm at q=1.16
kg/m3 i.e. the x50 was proportional to .
A double row blast has been made and results have been compared with single row blasts. The results
from this thesis work shows improved fragmentation in terms of x50 for double row blast as compared
to single row. The specific charge was 4.6 kg/m3 and the inter row delay time was 10 μsec. The test
was made under free face conditions. The result has been compared with three single blast tests made
by earlier research (Petropoulos, 2011) with the same setup and type of explosive. Though, the
specific charge was different (4.16 kg/m3).
From the analysis it shows that double ring blast give value of x50 12.1 mm whereas values of x50 for
single row tests made by Petropoulos (2011) were 33.02, 21.56 &13.34 for R1, R2 & R3 respectively.
Confinement material has been analyzed by comparing the confined material for free and confined
shots. The specific charge for the tests varied from 1.63 to 4.54 kg/m3, giving value of x50 from 4.8 -
7.4 mm.
The results and conclusions presented in this thesis work can provide a better understanding of small
scale double row SLC blasts, selection of proper blasting material and delay timings between the two
rings. The analysis of the results focused on the influence of double row blast on fragmentation and
amount of explosive used in both rows.
Fragmentation analysis has been done both for single rows tests and for one double row test. All the
results have been analyzed and compared with previous work and discussed within this thesis work.
Keywords: Fragmentation, small scale blasting tests, sublevel caving, double ring blasting.
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LIST OF ABBREVIATIONS, SIGNS AND SYMBOLS
BeFo Rock Engineering Research Foundation
LKAB Luossavaara Kiirunavaara Aktie Bolag
LTU Luleå University of Technology
PETN Pentaerythritol tetranitrate
q Specific charge, (kg/m3)
SLC Sub level caving
Swebrec Swedish Blasting Research center
UCS Unconfined Compressive Strength, (MPa)
VOD Velocity of detonation, (m/s)
x50 Average fragment size, (mm)
Symbols:
A Rock mass factor
B Burden, (m)
cp P-wave velocity,(m/s)
cs S-wave velocity, (m/s)
E Elastic modulus, (Pa)
P Porosity, (%)
S Spacing, (m)
ρ Density, (kg/m3)
σΒΤ Strength of magnetite, (MPa)
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SOME IMPORTANT TERMINOLOGY IN MINING ENGINEERING
Burden (B): The distance from a blasthole to the nearest free face.
Back breakage: Rock broken beyond the limits of the last row of holes marking the outer boundary in
a blast.
Delay time: Time interval between the initiation and detonation of a detonator.
Detonator: A device containing a small detonating charge that is used for detonating an explosive,
including, but not limited to, blasting caps, exploders, electric detonators, and delay electric blasting
caps.
Coupling: It is defined by the volume of explosive in relation to the total volume of the blast hole.
Decoupling ratio: The ratio between the diameter of the blasthole and the diameter of the charge.
Drilling and blasting: The process of using a drill to create long, narrow cylindrical holes in the
rock, and filling these holes with explosives which are then detonated to fragment the rock.
Free face: This is an exposed rock surface towards which the explosive charge can break out.
Explosive: Any rapidly combustive or expanding substance. The energy released during this rapid
combustion or expansion can be used to break rock.
Hanging wall: The wall rock on the upper side of an inclined vein or bedded deposit.
Ore Dilution: The contamination of ore with waste rock
Powder factor or specific charge or blasting ratio: This is the ratio between the mass of explosives
required to break a given quantity of rock and is normally expressed in kg/m3 or kg/ton.
Pre splitting: A blasting method used to create a crack along the contour before the actual round. The
tensile cracks for the first contour are created by a single row of closely spaced holes blasted
simultaneously prior to the initiation of the remaining holes in the round.
Spacing (S): This is the distance between adjacent blast holes and measured perpendicular to the
burden.
Sub-Level: Drifts opened at different levels to exploit ore beds.
Waste: The barren rock in a mine which is too low grade to be of economic value.
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Table of Contents
PREFACE ................................................................................................................................................ i
ABSTRACT ............................................................................................................................................ iii
LIST OF ABBREVIATIONS, SIGNS AND SYMBOLS ....................................................................... v
SOME IMPORTANT TERMINOLOGY IN MINING ENGINEERING ............................................. vii
CHAPTER 1- INTRODUCTION ........................................................................................................... 1
1.1 Background ................................................................................................................................... 1
1.2 Research Objective ........................................................................................................................ 1
1.3 Methodology ................................................................................................................................. 2
1.4 Thesis Outline................................................................................................................................ 2
1.5 Limitation of Thesis work. ............................................................................................................ 3
CHAPTER 2- LUOSSAVAARA-KIIRUNAVAARA MINE (LKAB) .................................................. 5
2.1 Introduction ................................................................................................................................... 5
2.2 Mining method at LKAB in Kiruna .............................................................................................. 6
CHAPTER 3-LITERATURE REVIEW ................................................................................................. 9
3.1 Sub Level Caving .......................................................................................................................... 9
3.2 Confined Blasting in sublevel caving .......................................................................................... 10
3.3 Findings from previous studies ................................................................................................. 10
3.4 Evaluation of fragmentation ...................................................................................................... 14
3.4.1 Sieving Analysis ................................................................................................................... 14
3.4.2 Oversized boulder counting method ..................................................................................... 14
3.4.3 Visual analysis method ......................................................................................................... 14
3.4.4 Digital Image processing and analysis ................................................................................. 14
3.5 Fragmentation prediction models ................................................................................................ 15
3.5.1 The Kuz-Ram model (Cunningham, 1987) .......................................................................... 15
3.5.2 The KCO model ................................................................................................................... 17
3.5.3 The JKMRC models ............................................................................................................. 18
CHAPTER 4-METHODOLOGY ......................................................................................................... 19
4.1 Methodology ............................................................................................................................... 19
4.2 Geometrical design ...................................................................................................................... 20
4.3 Model Material ............................................................................................................................ 21
4.4 Mechanical and Physical properties of magnetic mortar ........................................................... 21
4.5 Manufacture of model block ....................................................................................................... 22
4.6 Confined material ........................................................................................................................ 23
x
4.7 Test set-ups in model block ......................................................................................................... 24
4.8 Model block for single row test: .................................................................................................. 24
Figure 19: Set-up for the ring shape block model. ............................................................................ 25
4.9 Model Block for double row test. ................................................................................................ 25
4.10 Firing Procedure ........................................................................................................................ 27
CHAPTER 5-RESULTS ....................................................................................................................... 29
5.1 Fragmentation Analysis ............................................................................................................... 29
5.2 Fragmentation measurement process .......................................................................................... 30
5.3 Fragmentation result .................................................................................................................... 31
5.3.1 Combination of all tests. (Single blast tests) ........................................................................ 31
5.3.2 Specific charge versus x50 (magnetite material) ................................................................... 34
5.3.3 Results (confined material) ................................................................................................... 37
5.3.4 Double rows blasting test result ........................................................................................... 39
5.3.5 Comparison of double row test with single row tests ........................................................... 42
CHAPTER 6- DISCUSSION ................................................................................................................ 47
CHAPTER 7- CONCLUSION .............................................................................................................. 49
CHAPTER 8- RECOMMENDATIONS FOR FUTURE RESEARCH ................................................ 50
REFERENCES ...................................................................................................................................... 51
APPENDIX- SIEVING DATA & VOD MEASUREMENT ................................................................ 55
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CHAPTER 1- INTRODUCTION
1.1 Background
Sublevel caving (SLC) is a mass mining method based upon the utilization of gravity flow of blasted
ore and caved waste rock (Kvapil, 1992). This mining method involves blasting under confined
conditions. The debris in front of the blast ring acts as a wave trap i.e. it prevents to reflect back all
energy from the blast holes as a tensile wave because some energy will be transmitted out into the
caved material resulting in coarser fragmentation (Johansson, 2011). This phenomenon may cause
immobilization of the blasted ring, causing ore losses. There are two major factors that influence the
mobilization of the blasted ring, fragmentation and swelling of the blasted material.
Janelid (1972) indicates, in the first application of sublevel caving, the ore was not drilled and blasted
completely between two sublevels, but certain parts were broken by induced caving (hence sublevel
caving).
1.2 Research Objective
This thesis work was offered by LKAB mining company and is a part of their research and
development activities.
The main objective of this thesis work is to evaluate a new concept for timing double ring blasts in
terms of fragmentation of the blasted burden. For this purpose, a series of blast tests has been made on
small scaled blocks. The idea is to blast two rings in the same shot but with a short delay between
them. In this case, the second ring will be blasted first which can create a slot between the blasted
burden and the remaining rock which will eventually provide a free face for the first ring providing
better fragmentation.
The results from this study would further improve the understanding of confined blasting as in SLC
which may have a significant impact on extraction and recovery of ore, and provide direction for
future research.
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1.3 Methodology
The thesis work consists of a series of small-scale blast tests. The literature review shows that small
scale tests are in many ways comparable with large scale tests (Oucherlony & Moser, 2006).
However, it is of great importance to link the results from small-scale to full scale.
‘‘It is important to point out already in the beginning that complete static, dynamic and geometric
model similarity cannot be achieved” (Rustan, 1990).
Two different types of model set-ups have been used to evaluate the fragmentation. The set-up is a
ring shaped block, used for single row blast tests. To simulate the confined blasting environment, as in
sub-level caving crushed granite (0-16mm) has been used as confining material.
For the double row blasts a rectangular set-up has been used. Both model blocks were manufactured
using the same material.
The blasted material for each test has been collected directly after blasting and later transported to
sieving analysis lab for further analysis. The blasted material was separated from the confining
material by using magnetic separator and all the material larger than 20 mm was sieved at LKAB
whereas material smaller than 20 mm was sieved in a lab at LTU.
The ring shape model has been designed based on the real ring layout which is currently in practice at
LKAB. The ring consists of 8 holes in fan shape. The model has been scaled down to 1:54 to limit the
height of the model to 1 m for handling purposes.
1.4 Thesis Outline
This thesis can be divided into 8 Chapters.
Chapter One is about the introduction, main objective and scope of performed research work.
Chapter Two is an introduction about LKAB mine and the method used by LKAB for mining
activities i.e. sublevel caving.
Chapter Three is a literature review regarding small scale blasting tests, blasting and evaluation of
fragmentation and understanding of SLC. Topics like confinement in SLC, fragmentation prediction
models.
Chapter Four is a detailed description of preparation of test samples (model blocks), methodology
used to prepare the block samples. As well the firing procedure and test set-ups are described in this
chapter.
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Chapter Five discusses the main results.
Chapter Six, Chapter Seven and Eight summaries discussion, conclusion and recommendation for
future research work respectively.
1.5 Limitation of Thesis work.
This thesis is limited to small-scale blasting tests using models made up of magnetite mortar and
covers only the investigation of double ring blasts in terms of fragmentation.
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CHAPTER 2- LUOSSAVAARA-KIIRUNAVAARA MINE (LKAB)
2.1 Introduction
LKAB’s underground mines are located in Kiruna and Malmberget in the northern part of Sweden.
The mines are owned and operated by Loussavaara- Kiirunavaara AB, LKAB. LKAB has been mining
iron ore for more than 120 years. In the early days, mining was done in open pits. Today, the entire ore
body is mined using sublevel caving. This means that the blasted ore fall down under gravity during
mucking. Mucking is carried out using large LHD machines, and the material is dumped into
orepasses. Transportation of the material at the main level is carried out with trains in the Kiruna mine
and by trucks in the Malmberget mine. The material is transported to crushers and then hoisted to the
surface using skips.
Figure 1: Schematic diagram of Sub level caving.
The ore body in Kiruna is about four kilometers long and the average width is approximately 80 m.
The depth of the ore body is unknown but ore has been proven at depths more than 1500 m. To date,
more than one billion tonnes of ore has been mined out. Parts of a new main haulage level at 1 365
meters will be operational in 2014 and secures the mining operation for an additional 15–20 years.
LKAB is currently also operating one open pit at Gruvberget close to Svappavaara which is located
about 50 km south of Kiruna. LKAB also plans to open another two open pits in the Svappavaara area
(Mertainen and Leveäniemi) 2014-2015.
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2.2 Mining method at LKAB in Kiruna
Today at LKAB, the primary mining method used is sublevel caving at large scale, independent of
ore-body size, shape, dip, and geographical location. The SLC mining method is cost effective, and
allows large scale mechanization, increasing the ore extraction rate (Howard & Jan, 2002).
Sublevel caving mining method can be summarized in following steps.
Drifting development
In order to mine the ore it is necessary to excavate drifts. Development drifts are excavated through
the ore body, the length is normally about 100 m (depends on the width of the orebody). The drilling
during development is carried out using hydraulic rigs. The length of each round is about 3.6-5.2 m
(14-18 feet). The roof and the walls are reinforced in the drift.
Production drilling
After the completion of drifting work, 22-55 meters long fan shaped production holes are drilled
upwards, a so called ring. Each ring consists normally of eight drill holes and one drift will take about
25 rings (depends on the width of the ore body), the burden is 3 m. Production drilling are remote
controlled, the water-driven hammer technology developed by Wassara (LKAB’s subsidiary) are used
enabling drilling of long straight holes.
Blasting of sublevels
The actual production starts after completing production drilling in a production area. A production
area is a 300-400 m long part of the ore body. Charging is done with bulk emulsion and special
charging trucks are used. The microballon sensitized bulk emulsion is pumped into the boreholes, the
density is about 1.2 kg/l. Precharging and prepriming is used, 2-4 rings are normally
precharged/preprimed in each drift.
Production loading
The blasted ore is loaded out of the drifts into orepasses using large LHD machines. LKAB uses both
driver-operated and remote controlled LHD machines.
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Transportation, crushing and Hoisting
At the main level the ore is transported to huge crushers with trains. After that the ore is hoisted up to
the surface and the mineral processing plants. The main end product is pellets as shown in figure 3.
Figure 2: Sub Level caving with stages of development and mining.
Figure 3: Example of pellets, one end product made by LKAB after all the stages of mining and
processing.
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CHAPTER 3-LITERATURE REVIEW
3.1 Sub Level Caving
Sublevel caving (SLC) is a mass mining method based upon the utilization of gravity flow of blasted
ore and caved waste rock (Kvapil, 1992). The method functions on the principle that ore is fragmented
by blasting, while the overlying host rock fractures and caves under the action of mine induced
stresses and gravity (Bull & Page C H, 2000). The caved material from the overlying rock mass fills
the void created by ore extraction. The original application of the SLC mining method was in soft
ground at the Minnesota and Michigan iron ore mines in the early 1900’s (Hustrulid, 2000).
The method was later adapted to stronger ore bodies (requiring blasting) enclosed by weaker overlying
and wall rock masses. In the last 40 years SLC geometries have increased significantly, resulting in
increases of scale and extent of industrial application, and decreases in production costs (Brady &
Brown, 2004).
Current SLC geometries (Figure 4) consist of a series of sublevels created at intervals between 20 m
and 30 m, beginning at the top of the ore body and working downward (Hustrulid, 2000). A number of
parallel drives are excavated on each sublevel, with drives being offset between sublevels. From each
sublevel drive, vertical or near vertical blast hole fans are drilled upward to the overlying sublevel
(even up to the second level above).
The burden between blasts fans are in the order of 2 m to 3 m (Hustrulid, 2000). Beginning typically at
the footwall, drifts are excavated through the ore body. Drilling during development is carried out
using hydraulic rigs. After that, 22-55 meters long holes in a fan shape are drilled as called rings. The
holes in the rings are charged and blasted one by one against the front-lying material, consisting of a
mixture of ore from overlying slices and caved rock waste. Extraction of the ore from the blasted slice
continues until total dilution or some other measure reaches a prescribed level (Hustrulid, 2000). The
next slice is then blasted, and the process continues.
One of the main disadvantages of the Sublevel caving mining method is high dilution of the ore body
by caved waste (Just,1981;Kvapil, 1992). The main factor influencing this dilution is the flow
behavior of the ore and waste material (Janelid & Kvapil, 1966; Just, 1981; Kvapil, 1982). Despite its
importance on SLC performance, the mechanics of gravity flow of blasted and caved material is not
well understood (Brady & Brown 2004). SLC material flow behavior is controlled by the interaction
of a wide range of factors (Janelid & Kvapil, 1966; Kvapil, 1992; Just, 1981; Bull & Page C H, 2000;
Hustrulid, 2000). These factors are related to geometric design considerations, draw control practices
and cave and ore material properties.
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Figure 4: Sub level caving mining method at LKAB Kiruna. (Source LKAB Kiruna).
Early small and full scale experimental results and theoretical calculations were conducted to partly
investigate the influence of these factors on flow behavior (Janelid & Kvapil, 1966).These factors
were related to geometric design considerations (sublevel height, crosscut spacing, drive geometry,
ring inclination, and ring burden), draw control practices (excavation strategy and depth of bucket
penetration into the blasted material), and ore material properties (friction angle, fragment size, and
bulk density). It was clearly demonstrated that these factors had a significant impact on the test results.
3.2 Confined Blasting in sublevel caving
The term confined blasting has been defined by Cullum AJ (1974) as the action of blasting a ‘‘slice of
rock against either previously blasted material or caved material or fill’’. A successful flow of
fragmented ore, as in SLC, is dependent on how well the material is broken up and the confinement
before blasting (Johansson, 2008). Results from the previous researcher’s shows that blasting in
confined conditions gives much coarser fragmentation then free face conditions.
3.3 Findings from previous studies
Several small-scale blast tests have been made to investigate the different parameters that influence the
fragmentation. One of the important factors is how small scale results can be related to full-scale
blasting. “It is important to point out already in the beginning that complete static, dynamic and
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geometric model similarity cannot be achieved” (Rustan, 1990). Many researchers used dimensional
analysis as a tool to scale down the full scale blasting conditions. However it is impossible to scale
down all parameters, but there should be given consideration to the most important ones.
Several researches investigated the confined conditions in sub level caving. Several small scale tests
have been made by Johansson (2008) and Petropoulos (2011) to determine the effect of confinement
on fragmentation. Some tests were made on magnetite cylinders. For this purpose different magnetite
samples provided by LKAB were tested, both confined and free face shots were made. To simulate the
confined environment the cylinder specimens were surrounded by a steel cylinder in which the
annulus between the two cylinders were packed with different confined material. The explosive source
was PETN cord with varied strength (3 to 40 g/m) giving different specific charges from 0.2 to 2.6
kg/m3. Four different confining materials were used during these tests: crushed granite (0-16 mm),
crushed granite with plaster of Paris (0-16 mm) and crushed non-magnetic mortar (0-16 mm).
Johansson (2011) made a series of small scale tests by using small rectangular blocks of magnetic
mortar. The main purpose of this setup was to investigate the influence of short delay times i.e. to
evaluate shock wave interactions. The block size was 650/660x205x300 mm (LxWxH). Burden and
spacing was 110 mm and 70 mm respectively. Average fragment size x50 was plotted versus delay
times under free face condition and under confined condition (Figure 5-6).
Figure 5: Mean fragment size (x50) versus delay time and row under free face condition. (Johansson,
2011).
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Figure 6: Mean fragment size (x50) versus delay time for different rows and confinement. (Johansson,
2011)
Johansson (2008) concluded that confinement gives coarser fragmentation compared with a free shot.
The properties of the confined material have also a significant influence on the fragmentation of the
blasted material.
Johansson (2011) made confined shots by installing a steel plate in front of the free face of a block
model. A total of 15 tests were made, 11 tests without confinement and 4 with confinement. All the
tests were made in a blast chamber and the broken material was collected after each shot, separated
and later sieved to measure the size distribution. The main objective was to investigate the influence of
delay time on fragmentation. The explosive used was decoupled PETN-cord with a strength of 20
g/m; giving a specific charge of 2.6 kg/m3. The nominal delay time was varied from 28 to 140 µs.
Figure 7: Set up for the free face shot. (Johansson, 2011)
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Figure 8: Set up for the confined shots. (Johansson, 2011)
It was concluded from these tests that the confinement makes the fragmentation coarser and x50
increases by nearly 100 %.
Olsson (1987) made half scale tests of confined bench blasting in LKAB Malmberget mine. The main
purpose of the research was to determine an optimum void ratio which could give improved
fragmentation. These half scale tests were made in three different campaigns made with different
void ratio, location and geology. Different charging and initiation were used during these tests. The
setup was a standard half-scale bench design. Two concrete walls were made against the side and in
front of the bench. To avoid fly rock and to make more confined environment, an iron plate was used
on the top.
Material was collected after blasting and sieved to get average fragmentation and then plotted against
the void ratio. Results from these tests indicated an optimal fragmentation when the allowable swell
was around 40 to 50 % (See Figure 9). Though, the number of tests was limited and the scatter in the
data was large.
Figure 9: Mean fragment size x50 versus void ratio. (Olsson, 1987)
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The conclusion of these tests made by Olsson was that the fragmentation could be improved in
confined conditions, as the energy released during blasting is better directed for the crushing work.
3.4 Evaluation of fragmentation
The term fragmentation refers to size distribution of rock. Quality (good or bad) of fragmentation
depends on the end use of the product being mined. Literature review shows that in most of the cases
reference is made to largest boulder size, oversized boulder from the blast and median size of
fragmented rock material known as x50.
The primary requirement of a good blast is the production of desired fragmentation, so that it can be
easily handle for remaining processes. The fragmentation is said to be optimum if one get the
maximum amount in a desired range so that it could be utilized effectively for further crushing
processes (Mohanty et al., 1996).
A number of methods, models and tools have been developed. Some of them as listed below.
- Sieving Analysis.
- Oversized boulder counting method.
- Visual analysis method.
- Digital image processing and analysis.
3.4.1 Sieving Analysis
The average fragment size can be obtained by sieving analysis; both dry and wet sieving can be made.
After sieving all the material, the fragment size distribution curve is obtained and the median size (x50)
and maximum size (xmax) can be determined.
3.4.2 Oversized boulder counting method
Manual counting of oversized boulder in a muck pile is done in this method. It gives an oversize index
with respect to total in-situ rock mass blasted. This is a simple method and commonly used where the
number of boulders including oversized boulders are important to monitor.
3.4.3 Visual analysis method
In this method assessment is made by reviewing the post blast immediately after blasting.
3.4.4 Digital Image processing and analysis
This is a method to measure blast fragmentation by using digital photography. The advantages of
image analysis (Maerz & Zhou, 1998) are that it is cost effective, and a number of experiments can be
made to reduce the sampling errors. There are many software programs developed for digital image
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Figure 10: An example of image captured by digital camera.
processing. One example is SPLIT software which is used to find the particle distribution of rock
fragments.
3.5 Fragmentation prediction models
Throughout the years, a number of different models have been developed to describe the size
distribution of the fragments after blasting.
There are many models developed which describes fragmentation distribution. Some of the most
common fragmentation distributions models are as follows:
3.5.1 The Kuz-Ram model (Cunningham, 1987)
Kuz- Ram Model is the most widely used fragmentation model for prediction of rock fragmentation by
blasting. This model consists of following main equations:
- Kuznetsov’s Equation
- Rosin – Rammler Equation
- Uniformity index
The Rosin –Ramler distribution is as follows
( ) (
)
(I)
The average fragmentation is given by
16
(
)
⁄⁄ (II)
The uniformity exponent is given by
n = (2.2-0.014·B/Ø)· (1-SD/B)·√[(1+S/B)/2]·[(Lb-Lc)/Ltot+0.1]0.1
·(Ltot /H) (III)
where,
x50 = median fragment size ,(cm)
n = uniformity index
SANFO = weight strength of the explosive used: % ANFO equivalent
Q = total charge mass (kg) per hole.
q = specific charge (kg/m3)
B = burden (m)
S = spacing (m)
Ø = drill-hole diameter (m)
Lb = length of bottom charge (m)
Lc = length of column charge (m)
Ltot = total charge length (m)
H = bench height (m)
SD = std deviation of drilling accuracy (m)
A = rock mass factor i.e. A=0.06·(RMD+RDI+HF) (IV)
where,
RMD (Rock mass description): 10, if rock is friable or powdery
JF, if joints are vertical
50, if rock is massive
JF = Joint factor = JPS+JPA (V)
17
JPS = Joint plane spacing = 10,if average joint spacing Sj<0.1m (VI)
20, if Sj<0.1x0 oversized fragment
50, if Sj>0.1x0 oversized fragment
JPA = Joint plane angle = 20,if the joints dip out of the face (VII)
30,if strike is perpendicular to the face
40, if the joints dip into the face
RDI (Rock density influence) = (0.025.ρ)-50 (kg/m3) (VIII)
HF = Hardness factor = E/3 if E< 50 GPa (IX)
c(MPa)/5 if E >50 GPa
3.5.2 The KCO model
The KCO model (Ouchterlony, 2005a) is an extended version of Kuz – Ram model. This model
replaces the Rosin – Rammler function used to describe the fragmentation curve in Kuz – Ram model
with a new function, the Swebrec function. Swebrec function includes 3 main parameters, maximum
size (xmax), 50 % passing (x50) and undulation parameter b.
The Swebrec function is defined as:
( )
{ [ ( )
]
}
(X)
[ (
)] (XI)
Where:
P(x) = percent of material passing sieve size x (%)
b = curve undulation exponent
x = sieve size (mm)
x50 = 50 % passing size (mm)
xmax = maximum in situ block size
n = uniformity index
18
3.5.3 The JKMRC models
The JKMRC model is based on two fragmentation models, the two component model (TCM) and the
crushed zone model (CZM). These two models are based on assumption that fragmentation is caused
separately by two different mechanisms i.e. the fine part and the coarser part. According to the
assumption the finer material are generated within crushed zone while the coarser material is
generated by tensile fracturing and preexisting fractures in the rock mass as shown in the Figure 11.
Figure 11: Schematic diagram showing crushing zone, fracture zone and fragment formation zone.
19
CHAPTER 4-METHODOLOGY
4.1 Methodology
It is quite difficult to investigate fragmentation and movement of burden in confined blasting in full-
scale sublevel caving. For this reason, a small-scale test setup has been prepared since earlier findings
have shown that small-scale tests in many ways are comparable with large-scale tests (Oucherlony &
Moser, 2006).
Two different types of materials have been used in the small scale tests i.e. model material and
confining material. Magnetic mortar has been used as a model material to simulate actual ore in the
field. Crushed granite (0-16 mm) has been used as confining material (act as blasted material or caved
waste rock in full-scale). It has been shown by (Johansson, 2008) that crushed granite (0-16 mm)
follows the Swebrec function with its properties x50 = 8.0 mm, xmax = 16.0 mm and b = 2.1.
After each shot, both materials have been separated using magnetic separator and analyzed.
The broken material was collected and transported to a sieving lab. Material larger than 20 mm was
sieved at LKAB and material < 20 mm has been sieved in a lab at LTU. Material separation has been
done using a magnetic separator in order to investigate both magnetic material and confining material.
Figure 12: Magnetic separator used to separate magnetic material & confined material.
The model was designed based on a real ring layout and which is currently used at LKAB Kiruna. The
ring consists of 8 holes in ring shape with different spacing. The model has been scaled down to 1:54,
since the height limit of the model.
20
4.2 Geometrical design
To make the model more realistic, it has been considered that the neighboring rings at the upper level
have been blasted out whereas the neighboring rings at the same level are not blasted. Half portion of
both neighboring drifts has been considered to make the model symmetric as shown in Figure 13. The
proposed cross-section of the model is shown in the Figure 14.
Figure 13: Selected area to simulate.
Figure 14: Cross-sectional area of block model showing different parts of the test setup.
YZ-snitt
3 2703 2603 2503 2403 2303 2203 2103 200
960
955
950
945
940
935
930
925
920
915
910
905
900
895
890
885
880
875
870
865
860
855
850
845
21
4.3 Model Material
Magnetic mortar is used as a model material, as in the Less Fines project (Moser, 2005). A model
material made of mortar (Table 1) mixed with magnetite fines has showed to have good repeatability
between different batches, the standard deviation of x50 for the free face shots with 20 g/m PETN cord
was less than 1 mm, x50 = 15.2 ± 1.0 mm over 19 shots (Johansson, 2008).
Table 1: Composition of magnetic mortar.
Ingredients %
Cement 26.62 %
Water 12.64 %
Glenium 51 0.25 %
TBP 0.13 %
Magnetite powder 29.65 %
Quartz sand 31.71 %
Glenuim 51 water reducing admixture used in pre-cast industry to gain early strength and durability.
Whereas TBP is abbreviation of Tributylphosfate (defoamer).
4.4 Mechanical and Physical properties of magnetic mortar
The composition of the magnetic mortar is identical with the magnetic mortar used by (Johansson,
2008). It is assumed that the physical properties of the magnetic mortar are identical with (Johansson,
2008).
The measured mechanical properties of the magnetite mortar are shown in Table 2. Uniaxial
compression test and Brazilian test has been done to measure the properties of magnetic mortar.
Table 2: Mechanical properties of magnetic mortar. (Johansson, 2008)
Properties value
Unconfined compressive strength (MPa) 50.7 ± 4.8
Young’s modulus (GPa) 21.9
Tensile strength (MPa) 5.23 ± 0.34
P-wave speed (m/s) 3808 ± 73
Density (kg/m3) 2511 ± 25
22
4.5 Manufacture of model block
The design was made by using the AutoCAD software and the moulds were manufactured by using
plywood with the help of hinges and screws (See Figure 15). Plastic sticks were fixed in the moulds
and later pulled out after curing.
Figure 15: Manufacturing process of moulds.
Figure 16: Arrangement of plastic sticks to create holes for the PETN cord.
23
After manufacturing the mould, the magnetite mortar was poured into it and after 8 hours of curing
time the plastic sticks were pulled out with the help of a mechanical jack. The model has been left at
room temperature (20-25) Celsius for 28 days to get the desired strength (Figure 17).
Figure 17: The mould filled with magnetite mortar and left for hardening.
4.6 Confined material
Crushed granite (0-16 mm) with a mean size of 8 mm (x50) was used as a confining material and
tamped in front of each burden. The properties of the crushed granite are shown in Table 3.
As the model was based on the assumption that the neighboring rings at the same level was not
blasted, two triangular shaped block of concrete were manufactured and used during the tests. (See
Figure 18).
Table 3: Properties of crushed granite. (after Johansson, 2008)
Description Porosity (%) Cp
(m/s)
Average
density(kg/m3)
Swebrec
distribution
parameters.
Crushed
granite
36 1168 1696 x50 =8 mm
xmax =16 mm
b=2.2
24
Confined material Magnetite portion
4.7 Test set-ups in model block
To simulate confined conditions for each test, the model was fixed in a steel box with confining
material from the sides and back (See Figure 18). For confined shots the gap between the free face of
the model and steel gate was filled with crushed granite (0-16 mm) and tamped for each test. After
each blast the broken material was collected and transported for further analysis.
Figure 18: Small scale model after scaled down.
4.8 Model block for single row test:
Two different ring shaped blocks (Figure 19) have been used for all the single row blasting tests. The
first model simulating 3 m burden and the second 3.5 m. This corresponds to 55 and 64 mm
respectively in model scale. For each blast test the block was placed in a steel box of size 1x1x1m.
Sand bags were used as a wave trap during blasting at the back side of the model, the side walls of the
model were covered with crushed granite (0-16mm) and tamped.
Cemented portion
25
For confined shots the gap between the free face of the model and steel gate in front of it was filled
with same confining material. After blasting the confining and the blasted material have been
separated and sieved for further analysis.
The first test was a free face shot using instantaneous initiation while the second test was a confined
shot with inter row delay time, both with 55 mm burden.
Figure 19: Set-up for the ring shape block model.
4.9 Model Block for double row test.
Petropoulos (2011) performed small scale blasting tests with small rectangular magnetic mortar blocks
in order to investigate fragmentation at different delay times and also to investigate the burden
movement under confined conditions. A block of the same dimensions has been used in this thesis
work and results are compared with Petropoulos (2011) data.
26
The block had the dimensions of 660 x270 x 215mm (length x height x width). The burden was 58.3
mm, spacing 82.5mm and hole diameter was 11mm. The model had 3rows and 7 holes in each row
(Figure 20). The model was manufactured with the same material and the method was same as
discussed in section 4.5 earlier.
Figure 20: Set-up for the rectangular shape block model. (Petropoulos, 2011)
Figure 21: Block model in final position after fixing in big cemented U-shaped block. (Petropoulos,
2011)
27
The model has been fixed by placing it into a reinforced U shaped concrete block. The reinforced
concrete block covers the model from back and sides and acted as wave trap during the blasting tests
as shown in Figure 21 above.
4.10 Firing Procedure
All the tests were done at LKAB Kimit AB’s blasting test site in Kiruna. An electric detonator was
used to initiate the PETN cord. Different strength of PETN cords were used during the tests. The VOD
has been measured using the DATA TRAP II instrument. The results are presented below.
Cord Strength (g/m) 3.6 5 8.9 20
VOD (m/s) 7155 7080 7016 *7540
* VOD for 20 g/m PETN cord has been taken from Petropoulos (2011).
Table 4: Measured VOD for different strengths of PETN cord.
28
29
CHAPTER 5-RESULTS
5.1 Fragmentation Analysis
Blasting is the first step in the rock comminution process and has a major influence on the downstream
processes in the mining industry such as loading, hauling, crushing and grinding, (Demenegas,
2008).The amount of oversized boulders produced by a blast defines how much resources will be used
to further decrease the size in order to be effectively handled by the equipment. The size distribution
of the blasted material is the most important parameter to be considered. In most types of blasting, the
fragmentation is the primary quality demand.
Fragmentation both in full – and model scale blasting generally follow Swebrec function extremely
well: usually r2 >0,995 in 95 % of cases (Ouchterlony, 2009a). Model scale tests have been carried out
to understand the mechanism of rock breakage and fragmentation under confined conditions.
The model scale tests carried out does not fully replicate the conditions in full scale but they should
give some valuable insight into possible mechanism of confined blasting and its impact on
fragmentation and compaction (Johansson et al., 2007).
In order to investigate the influence of confinement on fragmentation both free face and confined
blasting have been carried out. In the free face tests the gap between the first row and the steel plate in
front was kept empty while for the confined tests it was filled with crushed granite (0-16mm) and
compacted well.
All the tests have been carried out by placing the model blocks in a special steel chamber at LKAB
Kimit AB’s blasting test site.
Five different tests have been carried out, with different amount of explosive, giving a specific charge
between 1.16 and 4.54 kg/ m3.The specific charge was varied by using different PETN cord strengths
ranging from 3.6 to 12 g/m.
Table 5: Specific charge for different strengths of PETN cord.
Strength (g/m) 3.6 5 5 9 12
Specific charge(kg/ m3) 1.16 1.63 1.89 2.92 4.54
30
5.2 Fragmentation measurement process
Figure 22: The fragmentation measurement process, from Johansson (2011)
Collection of blasted material and
transportation to sieving lab at LKAB
Dry sieving of material above 20 mm
Transportation of material less than 20 mm to LTU for
further analysis
Magnetic separation at the mineral technology lab at LTU
Magnetic Mortar Confined material
Dry sieving
11.2 – 0.063 mm
Dry sieving
11.2 – 0.063 mm
31
5.3 Fragmentation result
Size distribution curves for the model block made of magnetite and the confining material (crushed
granite) are presented below. Figure 23 shows the size distribution curves for the different tests.
Details of burden, specific charge and boundary conditions are presented in Table 6.
5.3.1 Combination of all tests. (Single blast tests)
Table 6: Parameters for different test setups (magnetic mortar).
Test
No
Burden in small
scale(mm)
Cord Strength
(g/m)
Specific charge
(kg/m3)
Condition
T1 55 5 1.89 Free
T2 55 12 4.54 Confined
T3 64 3.6 1.16 Free
T4 64 5 1.63 Confined
T5 64 9 2.92 Confined
Figure 23: Fragmentation curves for 5 different tests with different specific charge and burden.
0,1
1,0
10,0
100,0
0,010 0,100 1,000 10,000 100,000
% M
ass
pas
sin
g
Sieve size , mm
T1 Free - PETN 5 g/m
T2 Confined- PETN 12 g/m
T3 Free- PETN 3.6 g/m
T4 Confined- PETN 5 g/m
T5 Confined- PETN 9 g/m
32
The effect of specific charge can be seen in Figure 23, when the specific charge increases the
fragmentation becomes finer for the same confinement condition. One example is test 1 (5 g/m, free
shot) and test 3 (3.6 g/m, free shot). Another example is test 5 (9 g/m, confined shot) and test 4 (5 g/m,
confined shot).
On the other hand it can also be seen the effect of specific charge for the different conditions.
Fragmentation becomes finer for free shot as compared to confined shot at the same specific charge (5
g/m PETN). Example can be seen by comparing test1 (5 g/m, free shot) and test 4 (5 g/m, confined
shot). Test 2 resulted in excessive back breakage and the rest of the model was collapsed during the
tests. The block is shown before and after blasting test 1 in Figure 24.
Figure 24: To the left; the model after first shot of the model. To the right the model from top after
first shot.
Test 2 was a free shot (without filling the gap between free face and steel chamber) with confining
material. Figure 25 below shows test set up for T2. The inter hole delay time was 30µsec and the
PETN cord strength was 12 g/m.
33
Figure 25: Test setup for test 2 with confinement from all sides.
Figure 26: Damaged parts of model after blasting test T2.
34
5.3.2 Specific charge versus x50 (magnetite material)
Table 7: Specific charge and x50 for all tests.
Test No Specific charge
(kg/m3)
x50
(mm) Condition
T1 1.89 24.9 Free
T2 4.54 11 Confined
T3 1.16 30.9 Free
T4 1.63 29.6 Confined
T5 2.92 29.2 Confined
Figure 27: x50 versus specific charge.
From Figure 27 it is clear that by comparing test 1 and test 4 x50 increases in confined shots compared
to free shots. This is because of the confinement condition i.e. confinement act as a wave trap during
1
10
100
1 10
X 5
0, m
m
Specific charge,q (kg/m3)
T1 Free-PETN 5g/m
T2 Confined-PETN 12g/m
T3 Free-PETN 3.6 g/m
T4 Confined-PETN 5 g/m
T5 Confined-PETN 9 g/m
35
blasting test and absorbs some explosive energy preventing fully utilization and resulting in coarser
fragmentation.
It is also concluded that the fragmentation becomes finer (x50 decreases) when the specific charge
increases under the same confinement. There is a significant difference between x50 for test 1 and test
3; both test setups have same burden and confinement (free shots) but different specific charge. x50 for
test 1 is 24.9mm while x50 for test 3 is 30.9mm.
By comparing confined shots it is concluded that the fragmentation becomes finer with increasing
specific charge. x50 is 11mm for test 2, 29.2 mm for test 5 and 29.6 mm for test 4, the specific charge
is 4.54, 2.93 and 1.63 kg/m3 respectively.
The Swebrec function fit parameters for all the confined tests are given in Table 8 below.
Table 8: Swebrec function fit parameters for T2, T4 & T5 (magnetite mortar).
Test
No
xmax
(mm)
x50 (mm) b r2 q (kg/m
3) Condition
T2 181.9 11 2.712 0.995 4.54 Confined
T4 80 29.6 1.586 0.997 1.63 Confined
T5 99.7 29.2 2.015 0.997 2.92 Confined
It can be seen from table 8 that the variation of x50 is caused by the variation of specific charge. For
example by comparing x50 for all confined shots i.e. T2,T4 and T5 it can be concluded that increasing
specific charge gives finer fragmentation.
The Swebrec function fits parameter for all the tests without confinement are given in Table 9 below.
Table 9: Swebrec function fit parameters for T1&T3 (magnetite mortar).
Test
No
xmax
(mm)
x50 (mm) b r2 q (kg/m3) Condition
T1 181.9 11 2.712 0.995 1.89 Free
T3 80 29.6 1.586 0.997 1.16 Free
When comparing x50 for all free shots i.e. T1 and T3 it can be seen that a higher specific charge gives
finer fragmentation.
The slopes for both free face and confined conditions has been analyzed with respect to normal value
proposed by Kuz-Ram model i.e
36
x50 ⁄ (XII)
Where,
x50 = mean fragment size (mm)
q= specific charge (kg/m3)
It can be seen from Figure 28 that the slope for free face condition (0.449) seems not subjected to the
Kuz-Ram equation (equations II & XII) where the exponent for the specific charge is 0.8.
Figure 28: Comparison between free face and confined condition.
For confined conditions the slope seems to be subjected to the Kuz –Ram Equation (equation VIII),
since the exponent for the specific charge is 0.9.
y = 33,129x-0,449 R² = 1
y = 47,461x-0,966 R² = 1
1
10
100
1 10
Free
Confined
Ave
rage
fra
gmen
t si
ze X
50
(m
m)
Specific charge ,q (kg/m3)
37
0,1
1
10
100
0,01 0,1 1 10 100
% m
ass
pas
sin
g
sieve size,mm
T2
T4
T5
5.3.3 Results (confined material)
Crushed granite (0-16mm) has been used as confined material.
Table 10: Parameters for all confined state tests.
Test No Burden in small
scale(mm)
Cord Strength (g/m) Specific charge
(kg/m3)
Condition
T2 55 12 4.54 Confined
T4 64 5 1.63 Confined
T5 64 9 2.92 Confined
Figure 29: Size distribution curves for confined material in different tests.
Figure 29 shows a comparison of fragment size distribution for the confined material used during the
confined shots test 2, test 4 and test 5. Table 18 below shows x50 for each test.
38
Table11: Values of x50 versus specific charge for confined material.
Test No Specific charge (kg/m3) x50(mm) Condition
T2 4.54 6.9 Confined
T4 1.63 7.4 Confined
T5 2.92 4.8 Confined
Figure 30: Specific charge versus x50 for confined tests.
Figure 30 shows different values of x50 versus specific charge for confined material. The average
fragment size is 6.3 mm when measured after the blast test i.e. the average fragment size of the
confining material has been reduced to some extent. Before blasting the average size of the confined
material (0-16 mm crush granite) was x50=8 mm as it follows the Swebrec function parameters i.e. x50
= 8 mm.
1
10
100
1 10
X 5
0, m
m
Specific charge,q (kg/m3)
T2 Confined
T4 Confined
T5 Confined
39
5.3.4 Double rows blasting test result
Double row blasting tests has been carried out by using a block model manufactured with the same
material and procedure as discussed in chapter 4. The burden between two rows was 58.1mm. Details
about test set-up are shown in Figure 31.
Before the actual double row blast a single row was blasted with instantaneous initiation to make the
conditions more realistic for double row blasts as shown in Figure32.
Figure 31: Test set up for first row with instantaneous initiation.
Figure 32: The model block after blasting row 1.
40
We can see from the Figure 32 that the instantaneous shot was successful and the model was ready for
the double row shot. The test setup for the double row blast was to blast two rows in the same shot but
with a small delay between the rows. Row 1 was blasted instantaneously with 3.6 g/m PETN cord and
row 2 blasted after a delay of 10µsec, the inter hole delay was 60 µsec. The model block before and
after blast are presented in Figures 33 and 34.
Figure 33: Test setup for double row blasts.
Figure 34: Model block after double row blast.
41
Figure 35: Broken magnetite material after double row blast.
Figure 36: Top view of model block after double row blast.
We can see from Figure 35 and 36 that the back row did not break out, only some portion from the
bottom has been extracted during the test. It can be concluded that the amount of explosive was too
low for row 1 (3.6 g/m PETN) to break out of the burden. However further conclusions has been
drawn by comparing the results with previous single blasts tests carried out with the same setup by
Petropoulos (2011) during his thesis work in 2011.
42
Table12: Parameters for double row blast.
Double
row test
Inter hole
delaytime,
μsec
Inter row
delaytime,
μsec
Cord
Strength
(g/m)
Specific
charge
(kg/m3)
x50
(mm)
Condition
R1 Instantaneous 10 3.6
4.6
12.1 Free
R2 60 20
5.3.5 Comparison of double row test with single row tests
Due to some design problems in model blocks of ring shape double row blast was not possible to carry
out due to excessive back breakage after the single row tests. Though the results for both the tests
(singles versus double blasting tests) cannot be compared directly because of very limited test results
obtained from double row blast and based on some other facts i.e. the difference in specific charge and
confinement condition, but by comparing it with previous work done with the same setup can give
some general ideas of blasting using different delay times and confined condition for single row and
double row blasts.
A double row blast test has been carried out using a small scale model. Due to limited no of rows in
the block only one double row test was made possible. The results are compared with single row test
carried out by Petropoulos (2011) using the same model specification and amount of explosive during
his work.
Petropoulos (2011) performed three single blasts test with the same setup of the model. One major
difference between these tests is the confinement. Petropoulos used confined shots whereas the double
row blast was not confined. We can see from Table 20 below that x50 varied between (13.34 to 33.02
mm). x50 for double row blast is 12.1mm.
Figure 37: Small scale mode Test setup. From Petropoulos (2011).
43
Table13: Values of x50 versus specific charge.
Test No Specific charge (kg/m3)
x50 (mm) Condition
Single Row 1 4.16 33.02 Confined
Single Row 2 4.16 21.56 Confined
Single Row 3 4.16 13.34 Confined
Double Rows 4.6 12.1 Free
*Results for Single Row 1, Row2 and Row 3 have been taken from Petropoulos (2011).
The graphical presentation of x50 versus specific charge is shown in Figure 38.
Figure 38: Values of x50 versus specific charge for double and single row tests.
From Figure 38 x50 for the double row test is 12.1 mm (free shot) while x50 for single row test lies
within 13.34 to 33.02 mm (confined shots). One of the reasons for coarser fragmentation in the single
row test is the confinement.
An attempt has been made to compare the results with Johansson (2011). x50 for free face blasting tests
and under confined conditions are compared with the double row test. The Swebrec function
parameters for double row test are shown in Table 14.
1
10
100
1 10
X 5
0, m
m
Specific charge,q (kg/m3)
Sinlge Row 1 Single Row 2 Single Row 3 Double Rows
44
0
10
20
30
40
50
60
70
80
0 20 40 60 80 100 120 140
Me
an f
ragm
en
t si
ze, X
50
,mm
Inter hole Delay time, µ sec
Single Row (Free state)
Double Row (Free state)
Table 14: Swebrec function fit parameters for double row test.
Test No Inter hole delay
time (µ sec)
xmax (mm) x50 (mm) b r2 State
T6 60 80.294 12.15 2.74 0.999 Free
Figure 39 below shows the average fragment size x50 versus inter hole delay time for single row tests
and double row test for all free shots. From the diagram it is clear that fragmentation is coarser for the
entire single row tests compared to double row test. From the results of both tests (single versus
double blasting tests) conclusion can be made is that longer delay times give coarser fragmentation.
Some fragment size can be considered as dust and boulders.
It can be concluded that for the same delay times for both single and double row tests the mean
fragment size x50 is coarser for single row tests compared to double row test. The number of double
row test is only one so more tests with double row blasts can give more reliable results.
Figure 39: x50 versus delay time for single and double row test in Free State.
All single row tests data has been taken from earlier research (Johansson, 2011)
Comparison has been made also with the results of single row blasts test in confined state versus
double row blast in Free State and presented in Figure 39.
45
0
10
20
30
40
50
60
70
80
0 20 40 60 80 100 120 140
Me
an f
ragm
en
t si
ze, X
50
,mm
Inter hole Delay time, µ sec
Single Row (Confined Condition)
Double Row (Free state)
Figure 40: x50 versus delay time for double row tests(free shot) and confined single row tests.
The nominal delay times for the single row test were 73 and 146 µs respectively. By comparing Figure
39 and 40 it is clear that confined conditions increases the mean fragment size for single row tests. The
mean fragment size x50 for single and double row tests at a delay time of 60µsec are different. Single
row tests gives 100 % increase of x50 compared with double row tests. Due to the limited amount of
data and drawbacks in the testing, no distinct conclusions can be drawn.
46
47
CHAPTER 6- DISCUSSION
Sub level caving mining method involves blasting under confined environment. The importance of
studying the behavior of confining material such as in sub-level caving cannot be overlooked.
For this purpose a study of fragmentation in Sub-level caving was made using small-scale model block
tests. This thesis work introduced a non-conventional blast tests by blasting double rows in the same
shot using small-scale block models and the results have been analyzed and compared with single
blast tests in terms of fragmentation. Both confined and free face blast tests were made and addressed
during the work. Before blasting the actual row for the tests the first row from the blocks has been
blasted simultaneously without any delay time under free face condition to make the block more
realistic for the actual shots. The blasting of first row with zero delay time under free face condition
gives a finer fragmentation for the next rows. A low strength of PETN cord (3.6 g/m) has been used
which resulted in form of dust and big fragments.
Crushed granite (0-16 mm) has been used as confining material. The selection of crushed granite was
based on previous results by Johansson (2011). Johansson studied the properties of different materials
during his work. The crush granite follows the Swebrec function, the parameters are x50=8 mm,
xmax=16 mm and b=2.2
In the same way the first row from the model block for the double row blast was also made. For this
purpose magnetite block with 3 rows has been used. The first row was blasted using a lower strength
of PETN cord (3.6 g/m).
Results from this thesis work shows a difference for x50 under free face and confined conditions. The
results for the 5 single row tests indicate that increasing specific charge results in finer fragmentation
for both free face and confined conditions. x50 decreased from 29.6 mm to 11 mm when the specific
charge increased from 1.63 to 4.54 kg/m3.
Early small-scale blasting experiments made by Petropoulos (2011) with the same set-up (specific
charge= 4.16 kg/m3) indicates a large increase of x50 for row blasts under confined conditions.
Johansson (2011) made a series of blasting tests with cylindrical specimens using magnetic mortar for
both confined and free-face conditions. Results from the tests show a large difference by giving the
value of x50 (13.2 – 28.3 mm) for free face condition tests and x50 (21.9 – 34.6 mm) for confined
condition blast tests. The fragmentation was coarser for confined shots compared with free shots. The
difference was an average of 37%. More than 160 blast experiments with cylinders were made.
Results from these tests shows that the confinement gives a coarser fragmentation compared with free
cylinders. Also that the properties of the confining material have a strong influence on both
fragmentation and swelling.
48
Wimmer (2008) made a full-scale sieving experiment on magnetite material from a blasting ring in the
Kiruna mine. Average x50 was 86 mm for the whole sieving campaign. However Johansson (2008)
analyzed that the tests made with small scale on the same magnetite material shows the value of x50
varied from 32.9 to 34.1 mm (average 33.5 mm) under confined condition.
Small-scale tests made during this thesis work such as double row blast contributes to understanding
the complex behavior of blasting in sublevel caving which involve confined conditions.
The use of small scale block models in this thesis work gives some results in terms of fragmentation
which are compared with earlier small-scale tests.
49
CHAPTER 7- CONCLUSIONS
An attempt has been made to investigate a new concept of timing double ring blast by performing
small scale blasting tests. The blasting tests have been carried out at LKAB Kimit AB’s blasting
testing site. The fragmentation from results from single row blasts has been compared with double row
blasts. The models were manufactured using magnetite mortar in order to simulate the real situation in
sublevel caving. The models were confined with crushed granite (0-16mm).
The main objective of this thesis research was to evaluate a new concept of timing double ring blast in
terms of fragmentation of blasted burden. The idea behind the concept was to blast two rings in the
same shot with a shot delay time between the rings and later compares the results with single ring
blasts by creating size distribution curves. In this case the second ring has blasted first without any
delay time between the ring holes (simultaneously) and then the first ring with a short delay time
between the rings. The idea was to create a slot by blasting second ring first which will act as a free
face for the first ring resulting in a finer fragmentation.
The initial step for this thesis work was to manufacture the model blocks in small scale. For this
purpose real ring geometric specifications were used. The models were constructed using scale factor
of 1:54 giving model height of 1 m.
A total of six blasting tests have been performed during this thesis work. The specific charge varied
for all the tests by changing burden and amount of explosive. Both free face and confined shots were
performed and the results have been compared. The test setup for the first five tests was single row
and the last test was double row blast.
Due to some drawbacks in the test setup, blasting of double rows in ring shape model was not possible
to carry out. However double rows test was performed with a block model in small scale with the
same test set-up as for ring shape to get the size distribution curve and to compare the results with
previous investigations made by Petropoulos (2011) and Johansson (2011).
Laboratory sieving analysis was performed both for blasted burden and for confined material; the
results were plotted as fragmentation distribution curves. Swebrec function parameters x50, r and b has
been presented and discussed in the report.
Size distribution curves were plotted for different tests. The size distribution curves for confined and
free face shots were also investigated.
One of the conclusions drawn from this thesis work is that the fragmentation decreases (becomes
finer) with increasing specific charge. Another conclusion is that confinement results in coarser
fragmentation compared with free shots. This is because in a free shot 100 % of the wave is reflected
50
back at the free face. In a confined situation a part of the wave is transmitted into the caved material in
front of the blasted burden which acts as wave trap and absorbs some of the explosive energy and
prevents the utilization of all energy from the explosive source to break the rock mas.
One of the important aspects of the thesis work was to construct a model in small scale in order to
perform double ring blasts that would give some valuable data of fragmentation in order to compare it
with single ring blasts.
In spite of all this a single test has been performed with double rows and results have been compared
with previously conducted single blast tests. The number of blast test for double row was only one ,
therefore the results to compare with single blast tests are very limited however the results from this
thesis works shows an improvement in fragmentation for double row blast, giving more fine fragments
as compared to single row blasts.
CHAPTER 8- RECOMMENDATIONS FOR FUTURE RESEARCH
There are important areas that can be highlighted for future work:
An investigation of the movement of the blasted burden was not carried out during this thesis
work. Future small scale model test can be performed in order to investigate the burden
movement.
During small scale blasting test for Sublevel caving consideration must be given to simulate a
real confined situation.
Investigation of double ring blasts by numerical analysis and comparison of results with small
scale blasting tests could give valuable results.
Further investigations can be carried out using small scale models in order to investigate shock
wave interaction.
Different delay times in small scale blasting test can give valuable information concerning
optimal delay time in terms of fragmentation and burden movement.
51
REFERENCES
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Academic Publishers, Dordrecht, Netherlands.
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2000,ed.G.Chitombo, AusIMM ,Melbourne.
Cox A J. (1967). Latest development and draw in sublevel caving. In Institution of Mining and
Metallurgy Section A,London, England.
Cullum A J. (1974). The effect of confined blasting on rock fragmentation and how flow
characteristics in sublevel caving flow.Master's Thesis. Queensland, Australia: University of
Queensland,Brisbane.
Cunningham, C V B. (1987). Fragmentation estimations and the Kuz-Ram model-four Years On. In
Proc 2nd Int. Symp on Rock Fragmentation by Blasting. pp 475-478, W L Fourney & R D Dick (eds)
Bethel CT, USA: SEM.
Cunningham, C. (2005). The Kuz-Ram fragmentation model. In Proceedings 3rd EFEE world
conference on Explosive and Blasting.
David, I. (2009). The impact of blasting on sublevel caving material flow behavior and recovery.
Master's thesis. WH Bryan mining and geology research centre,University of Queensland.
Demenegas, V. (2008). Fragmentation analysis of optimized blasting rounds in the Aitik mine.
Master's thesis. Luleå University of Technology.
Gour, C. (1995). Blasting technology for mining and civil engineers. University of New South Wales
Sydney Australia.
Gustafsson, P. (1998). Waste rock content variations during flow in sublevel caving:analysis of full
scale experiments and numerical simulation. Phd thesis 1998: 10, Div of rock engineering. Luleå
University of Technology, Sweden.
Gustafsson, R. (1973). Swedish Blasting Technique. SPI ,Gothenburg, Sweden.
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Jersey.ISBN0-471-34851-1.
Hustrulid, W. (2000). Method selection for large scale underground mining. In Massmin 2000,ed,G.
Chitombo, AusIMM, Melbourn.
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Janelid, I. (1972). Study of gravity flow process in sublevel caving. In International sublevel caving
symposium,Atlas Copco, Stockholm.
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compaction.Results from small scale blasting tests. Doctoral Thesis. Luleå University of Technology
Luleå, Sweden,pp 11-31.
Johansson, D & Ouchterlony, F. (2011). Fragmentation in small-scale confined blasting.In
International Journal of Mining and Mineral Engineering,Vol 3,No 1.
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scale’.In:Schunnesson Nordlund (eds)MassMin 2008.Proc. 5th International Conference and
Exhibition on Mass Mining. Balkema, Rotterdam.
Johansson, D., Ouchterlony, F. & Nyberg, U. (2007). Blasting against aggregate
confinement:fragmentation and swelling in model scale. In EFEE Vienna Conference
Proceedings.Moser,P.(ed.): European Federation of Explosives Engineers p.13-26.14 p.
Johansson, D., Ouchterlony, F., Edin, J., Martinsson, L., & Nyberg, U. (2008). Blasting against
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Operation of Caving and Sublevel Stoping Mines. ED. DR. Stewart, SME-AIME,New York.
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53
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189-199.
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movement. Master's thesis. Luleå,Sweden: Luleå University of Technology Luleå,Sweden, pp51-68
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Brookfield,Netherlands.ISBN 9054104414.
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Luleå Sweden.
1,000
10,000
100,000
0,010 0,100 1,000 10,000 100,000
% M
ass
pas
sin
g
Sieve size , mm
T1
APPENDIX- SIEVING DATA & VOD MEASUREMENT
Test No 1
Table 15: Size distribution for magnetic mortar.
Sieve size (mm) Mass passing (%)
80 100
65 93.73
50 83.25
45 82.63
32 68.32
25 50.09
20 37.18
16 30.35
11.2 23.04
5.6 15.14
2 10.21
1 8.52
0.5 4.80
0.25 3.21
0.125 2.04
0.063 1.28
Figure 41: Size distribution curve for magnetic mortar.
Test 1 (Magnetic mortar)Eqn 8001 (a,b,c)
r 2̂=0.99487827 DF Adj r 2̂=0.99359784 FitStdErr=2.7684307 Fstat=1262.6031
a=2.3269818 b=3.6004189
c=89.840807
0.01 0.1 1 10 100
Mesh size [mm]
1
10
Ma
ss P
assin
g [
%]
1
10
Ma
ss P
assin
g [
%]
-3
-1
1
3
5
7
Re
sid
ua
ls [
5]
-3
-1
1
3
5
7
Re
sid
ua
ls [
5]
Figure 42: Fitted Swebrec function curve for magnetite mortar.
Test No 2
Table 16: Size distribution for magnetic mortar.
Sieve size (mm) Mass passing (%)
80 100
65 100
5 85.50
45 85.50
32 77.33
25 71.09
20 66.06
16 61.37
11.2 50.99
5.6 34.60
2 22.30
1 17.30
0.5 12.28
0.25 8.23
0.125 5.28
0.063 3.82
Table 17: Size distribution for the confined material.
Sieve size (mm) Mass passing (%)
20 100
11.2 56.68
5.6 49.03
2 38.23
1 30.68
0.5 16.21
0.25 5.81
0.125 2.48
0.063 1.24
1
10
100
0,01 0,1 1 10 100
% m
ass
pas
sin
g
sieve size,mm
T2
Figure 43: Size distribution curve for magnetite material.
Figure 44: Size distribution curve for confined material.
1,000
10,000
100,000
0,010 0,100 1,000 10,000 100,000
% m
ass
pas
sin
g
sieve size,mm
T2
1,000
10,000
100,000
0,010 0,100 1,000 10,000 100,000
% m
ass
pas
sin
g
sieve size,mm
T3
Test No 3
Table 18: Size distribution for magnetic mortar.
Sieve size (mm) Mass passing (%)
80 100
65 84.68
50 77.93
45 67.89
32 54.39
25 40.78
20 31.39
16 27.51
11.2 20.64
5.6 11.93
2 7.14
1 5.65
0.5 4.29
0.25 3.12
0.125 2.03
0.063 1.41
Figure 45: Size distribution curve for magnetite material.
Test 3 (Magnetic Mortar)Eqn 8001 (a,b,c)
r 2̂=0.99676141 DF Adj r 2̂=0.99595176 FitStdErr=2.0350134 Fstat=2000.5443
a=2.2148631 b=3.3563067
c=103.89066
0.01 0.1 1 10 100
Mesh size [mm]
1
10
Ma
ss P
assin
g [
%]
1
10
Ma
ss P
assin
g [
%]
-4
-2
0
2
4
Re
sid
ua
ls [
9]
-4
-2
0
2
4
Re
sid
ua
ls [
9]
Figure 46: Fitted Swebrec function curve for magnetic mortar.
Test No 4
Table 19: Size distribution for magnetic mortar.
Sieve size (mm) Mass passing (%)
80 100
65 93.91
50 78.29
45 68.82
32 52.64
25 41.51
20 36.09
16 30.60
11.2 25.07
5.6 18.18
2 13.89
1 11.22
0.5 8.05
0.25 5.54
0.125 3.35
0.063 1.62
Table 20: Size distribution for the confined material.
Sieve size (mm) Mass passing (%)
20 100
11.2 56.59
5.6 46.41
2 35.47
1 27.97
0.5 15.20
0.25 6.59
0.125 2.11
0.063 0.96
1,000
10,000
100,000
0,010 0,100 1,000 10,000 100,000
% m
ass
pas
sin
g
sieve size,mm
T4
0,1
1
10
100
0,01 0,1 1 10 100
% m
ass
pas
sin
g
sieve size,mm
T4
Figure 47: Size distribution curve for magnetite material.
Figure 48: Size distribution curve for confined material.
Test 4(Magnetic mortar)Eqn 8001 (a,b,c)
r 2̂=0.99752762 DF Adj r 2̂=0.99690952 FitStdErr=1.7519108 Fstat=2622.5417
a=1.5861084 b=2.6819599
c=80.014749
0.01 0.1 1 10 100
Mesh size [mm]
1
10
Ma
ss P
assin
g [
%]
1
10
Ma
ss P
assin
g [
%]
-2
-1
0
1
23
Re
sid
ua
ls [
3]
-2
-1
0
1
23
Re
sid
ua
ls [
3]
Test 4 (Confined material)Eqn 8001 (a,b,c)
r 2̂=0.9437626 DF Adj r 2̂=0.91002016 FitStdErr=8.7919604 Fstat=50.34528
a=1.3371967 b=2.947666
c=22.000612
0.01 0.1 1 10 100
Mesh size [mm]
0.1
1
10
Ma
ss P
assin
g [
%]
0.1
1
10
Ma
ss P
assin
g [
%]
-7.5
-2.5
2.5
7.5
Re
sid
ua
ls [
3]
-7.5
-2.5
2.5
7.5
Re
sid
ua
ls [
3]
Figure 49: Fitted Swebrec function curve for magnetic mortar.
Figure 50: Fitted Swebrec function curve for confined material.
Test No 5
Table 21: Size distribution for magnetic mortar.
Sieve size (mm) Mass passing (%)
80 100
65 88.03
50 76.78
45 67.09
32 55.13
25 44.87
20 37.06
16 32.11
11 21.28
5.6 15.53
2 10.97
1 6.87
0.5 3.28
0.25 2.08
0.125 1.51
0.063 0.96
Table 22: Size distribution for the confined material.
Sieve size (mm) Mass passing (%)
20 100
11.2 58.93
5.6 52.71
2 42.68
1 34.52
0.5 18.60
0.25 7.16
0.125 3.72
0.063 2.48
1
10
100
0,01 0,1 1 10 100
% m
ass
pas
sin
g
sieve size,mm
T5
0,100
1,000
10,000
100,000
0,010 0,100 1,000 10,000 100,000
% m
ass
pas
sin
g
sieve size,mm
T5
Figure 51: Size distribution curve for magnetite material.
Figure 52: Size distribution curve for confined material.
Test 5 (Magnetic Mortar)Eqn 8001 (a,b,c)
r 2̂=0.99707043 DF Adj r 2̂=0.99633804 FitStdErr=1.9360112 Fstat=2212.2585
a=2.0152821 b=3.4023786
c=99.715843
0.01 0.1 1 10 100
Mesh size [mm]
0.1
1
10
Ma
ss P
assin
g [
%]
0.1
1
10
Ma
ss P
assin
g [
%]
-3
-1
1
3
Re
sid
ua
ls [
7]
-3
-1
1
3
Re
sid
ua
ls [
7]
Test 5 (Confined material)Eqn 8001 (a,b,c)
r 2̂=0.91969498 DF Adj r 2̂=0.87151197 FitStdErr=10.504996 Fstat=34.357567
a=2.2417089 b=10.723283
c=51.2164
0.01 0.1 1 10 100
Mesh size [mm]
1
10
Ma
ss P
assin
g [
%]
1
10
Ma
ss P
assin
g [
%]
-10
-5
0
5
1015
Re
sid
ua
ls [
3]
-10
-5
0
5
1015
Re
sid
ua
ls [
3]
Figure 53: Fitted Swebrec function curve for magnetic mortar.
Figure 54: Fitted function curve for confined Material
Test No 6:
Table 23: Size distribution for magnetic mortar.
Sieve size (mm) Mass passing (%)
80 100
65 100
5 100
45 98.22
32 86.84
25 77.78
20 69.07
16 61.08
11 47.69
5.6 27.60
2 12.86
1 9.49
0.5 7.60
0.25 5.26
0.125 2.26
0.063 0.46
Figure 55: Size distribution curve for magnetic material.
0,100
1,000
10,000
100,000
0,010 0,100 1,000 10,000 100,000
% M
ass
pas
sin
g
Sieve size,mm
T6
Test 6 (Magnetic mortar)Eqn 8001 (a,b,c)
r 2̂=0.99908819 DF Adj r 2̂=0.99886024 FitStdErr=1.3107781 Fstat=7122.1635
a=2.7430568 b=6.6056098
c=80.294336
0.01 0.1 1 10 100
Mesh size [mm]
0.1
1
10
Ma
ss P
assin
g [
%]
0.1
1
10
Ma
ss P
assin
g [
%]
-2
-1
0
1
23
Re
sid
ua
ls [
5]
-2
-1
0
1
23
Re
sid
ua
ls [
5]
Figure 56: Fitted Swebrec function curve for magnetic mortar.
VOD Measurements
Figure 57: VOD test for 3.6 g/m PETN cord
Figure 58: VOD test for 5 g/m PETN cord
Figure 59: VOD test for 8.91 g/m PETN cord