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

11

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

Brady, B. H. & Brown, E. T. (2004). Rock mechanics for underground mining-third addition. Kluwer

Academic Publishers, Dordrecht, Netherlands.

Bull, G. & Page C H. (2000). 'Sublevel caving-today's dependable low cost ore factory'. In Massmin

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.

Howard, & Jan. (2002). Introductory Mining Engineering. Jhon Wiley and sons,inc.Hoboken, New

Jersey.ISBN0-471-34851-1.

Hustrulid, W. (2000). Method selection for large scale underground mining. In Massmin 2000,ed,G.

Chitombo, AusIMM, Melbourn.

52

Janelid, I. (1972). Study of gravity flow process in sublevel caving. In International sublevel caving

symposium,Atlas Copco, Stockholm.

Janelid, I., & Kvapil, R. (1966). Sublevel caving. In International journal of rock mechanics and

Mining Sciences,Vol 13.

Johansson, D. (2008). Fragmentation and waste rock compaction in small-scale confined

blasting.(Licentiate thesis;2008:30). Luleå: Luleå University of Technology, Luleå Sweden.

Johansson, D. (2011). Effects of confinement and initiation delay on fragmentation and waste rock

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.

Johansson, D. et al., 2008. ‘Blasting against confinement fragmentation and compaction in model

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

confinement fragmentation and compaction in model scale. Balkema,Rotterdam: In:Schunnesson

Nordlund (eds)MassMin 2008.Proc. 5th International Conference and Exhibition on Mass Mining.

Just, G. (1981). The significance of material flow in mine design and production. In Design and

Operation of Caving and Sublevel Stoping Mines. ED. DR. Stewart, SME-AIME,New York.

Kvapil, R. (1982). The mnechanics and design of sublevel caving systems. In Underground mining

methods handbook,ed, W.A Hustrulid, SME, AIME.

Kvapil, R. (1992). Sublevel Caving. In SME mining engineering handbook, Society for

Mining,Metallurgy and Explorations, New York.

Maerz, N., & Zhou, W. (1998). Optical digital fragmentation measuring systems-Inherent source of

error. Fragblast, In The International Journal for Blasting and Fragmentation.

Muhammad, A. (2009). The effect of fragmentation specification on blasting cost. Master's thesis.

Queens University.Kingston, Ontario, Canada.

53

Ouchterlony, F. (2003). Influence of blasting on size distribution and properties of muckpile

fragments, a state-of-art review. MinFo project P2000-10:Energy optimization in comminution.

Ouchterlony, F. (2005a). The Swebrec function: Linking fragmentation by blasting and crushing.

Mining technology (Trans of the inst of Mining and MetallurgyA) Vol 114,pp A29-44.

Ouchterlony, F., (2005b). What does the fragment size distribution of blasted rock look like?. In Proc

3rd EFEE World Conference on Explosive and Blasting.Roger Holmberg (ed.). England:EFEE. pp

189-199.

Oucherlony, F., & Moser, P. (2006). Likenesses and differences in the fragmentation of full scale and

model scale blasts. In Proc. Fragblast 8, Pro. 8th International Symposium on Rock Fragmentation by

blasting,Santiago,Chile SA.

Ouchterlony, F. (2009a). Fragmentation characterization;The Swebrec function and its use in blast

engineering. In Fragblast 9, Proc. 9th Intnl Symp. on Rock Fragmentation by Blasting. C Orlandi (ed).

Santiago, Chile : Editec SA.

Petropoulos, N. (2011). Influence of confinement on fragmentation and investigation of the burden

movement. Master's thesis. Luleå,Sweden: Luleå University of Technology Luleå,Sweden, pp51-68

Roy, P. (2005). Rock Blasting. Effects and Operation. A.A.Balkema Publishers, Leiden, The

Netherlands. ISBN 0415372305.

Rustan, A. (1990). The importance of using joints to achieve scaled fragmentation in magnetite

concrete used for sublevel caving blast models. In Engineering fracture mechanics, Vol 35.

Rustan, A. (1998). Rock blasting terms and symbols. A.A.Balkema,Rotterdam,

Brookfield,Netherlands.ISBN 9054104414.

Rustan, A., Vutukuri, V., & Naarttijärvi, T. (1983). The influence from specific charge, geometric

scale and physical properties of homogenous rock fragmentation. In First International Symposium on

Rock Fragmentation by Blasting.Holmberg, R & Rustan,A. Vol 1, Luleå University of Technology,

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