MINISTRY OF EDUCATION AND TRAINING
UNIVERSiTY OF MINING AND GEOLOGY nguyen dinh AN
RESEARCH ON DETERMINING POWDER FACTOR
TO ENSURE A PROPER FRAGMENT SIZE FOR
LIMESTONE QUARRIES IN VIETNAM
Branch: Mining Engineering
Code: 62520603 SUMMARY OF DOCTORAL DISSERTATION ha noi - 2014
The dissertation was completed at: Surface Mining Department,
Mining Faculty, University of Mining and Geology


In mining industry in general and open pit mining in particular,
blasting is an important which influences directly loading, haulage
and milling phase.
Nowadays, there are many achievements in research of blasting
theory and blasting material in mining industry, especially of blasting
parameters for improving rock fragmentation efficiency.
Powder factor is very important in blasting. Explosive cost used
to break a volume unit of rock according to requirement and blasting
mission is called as powder factor. Powder factor is a blasting
parameter which depends on physical and mechanical characteristic
of blasting, size requirement of rock fragmentation, explosive type,
blasting technology, other blasting parameters and so on.
Some equations of powder factor have been applied in Vietnam.
However, they are not close to practice in mines due to factors
influencing powder factor are determined not accurately.
According to mining experiences from overseas and
disadvantages of blasting in open pit mines, especially in quarries in
Vietnam, research on determining powder factor to ensure a proper
degree of rock fragmentation for some quarries in Vietnam is very
urgent. Annually, there are millions m
3
of rock blasted and hence, if
good calculation of powder factor can be done to decrease 1÷2%, the
amount of explosive used will be reduced considerably. Research
results will assist mining companies being more active in blasting and
improving their business and production which contributes to ensure
investment efficiency for new technology and more safety for
humans and surrounding environment.
Therefore, the PhD dissertation “Research on determining
powder factor to ensure a proper fragmentation size for

6. Scientific and real significance
Powder factor is an important blasting parameter affecting and
relating closely to other blasting parameters. Accurate determination
of blasting parameters plays the decisive role in quality and efficiency
of blasting in mines.
Research result is creating a method to determine powder factor
based on a scientific foundation and a relation between powder factor
and impact coefficients, ensuring it is employed favorably in quarry
mining. 3

Research result can be applied in quarries in Vietnam and
guarantee efficiency and reduction of impacts on environment.
7. Theoretical points to defend
1. Powder factor is a basic one which plays an important role in
blasting in quarries. Impact coefficients of powder factor are divided
into two groups: group of variables and group of coefficients.
2. Technical powder factor (q
cn
) determined according to
required degree of rock fragmentation (d
tb
) and degree of crack (d
max
)
is a foundation to determine powder factor for any blasting
conditions. Relation between q
cn

4

Chapter 3 - Relation between powder factor and explosive degree
and degree of rock fragmentation
Chapter 4 - Research on determining powder factor to ensure a
proper degree of rock fragmentation in some quarries in Vietnam.
9. Publications
Based on research trend shown in the dissertation, I have 15
research works which are published in journal of mining industry and
domestic and international conferences.
CHAPTER 1: OVERVIEW OF RESEARCHES OF POWDER
FACTOR AND OTHER BLASTING PARAMETERS
1.1. OVERVIEW OF BLASTING TECHNOLOGY IN MINING
Valuable deposits are often extracted by open pit or underground
method in which mostly rock with hardness degree of f = 6÷14 and
70% of valuable materials are necessary to break into desired size.
Currently, rock fragmentation methods are done mainly by
blasting using boreholes and small holes.
1.2. ROLES OF POWDER FACTOR IN MINING
One of the most fundamental standards used in evaluating
efficiency of rock fragmentation is size of blasted rock or degree of
rock fragmentation. This degree depends on mining equipment
dimension (bucket capacity, haulage method, and milling). Whereas,
powder factor is a key parameter to determine the degree of rock
fragment.
1.3 SOME DIFINITIONS OF POWDER FACTORS
1.3.1 Calculated powder factor, q
This powder factor is used to calculate and for initial design or
carrying out initial blasting in specific conditions according to
requirements of blasting. Some other authors treat it like powder

minimized.
1.4. OVERVIEW OF BLASTING PARAMETERS IN SURFACE MINING
There are two types of blasting parameters in open pit mining
including: parameters of drilling pattern and parameters of explosive
charge.
1.5. OVERVIEW OF RESEARCHES ON POWDER FACTOR
Relevant researches on powder factor includes as followings:
- Method of determining powder factor according to required size
of rock fragmentation (Kuznetsov, B.N Kutuzov).
- Method of determining powder factor according to power of
explosive (I.P.Oxanhit and P.X. Mirônov).
- Method of determining powder factor according to standard
powder factor (V.V. Rjevxki).
- Method of determining powder factor according to the rule of
size distribution within blasted rock heap.
1.6. EVALUATION OF RESEARCHES ON POWDER FACTOR
1.6.1. Comments about researches published on powder factor
1. All researches admit that powder factor is a fundamental
parameter which affects directly the quality of rock fragmentation
and cost of mining product.
2. Almost researches evaluate accurately about factors in
qualitative aspect which affects the determination of value of powder 6

factor. Impact coefficients can be divided into some groups as
followings:
Group 1: Factors characterize environment of blasting such as
physical and mechanical properties of rock, degree of hardness,

1935) and non - electric facility (1970 ÷ 1973) has been brought a big
efficiency in open pit mining. Millisecond delay non-electric blasting 7

using modern firing facilities is better than others because of some
advantages as followings :
- Being able to control the degree of rock fragmentation due to
increase impact time of explosion and crushed control zone on rock.
- Being able to widen drilling pattern (due to create a large free
face) and simultaneously, ensure the quality of fragmentation. Hence,
it contributes to decrease drilling cost.
- Reducing power factor whereas improving quality of
fragmentation.
- Being able to increase blasting scale and control ground
vibration.
- Millisecond delay non-electric blasting improves quality of
fragmentation and reduces harmful effects on environment
(especially ground vibration). However, scientific foundation of
efficiency of rock fragmentation of millisecond delay non-electric
blasting is researched not comprehensively in Vietnam.
c. Rock broken by blasting is a complex environment in which it
is non-identical and isotropic. Explosion process occurs very quickly
so that determining stress state of each point is very difficult. Using
equivalent materials to model explosion samples and experimental
factors to converse it into practical environment in blasting are often
make a large error.
d. Equations established are often complicated or contain lots of
experimental factors which reduce ability to apply in practice.

- Economic and technical factors include blasting parameters,
type of explosive being used, and firing method.
2.3. COMMENTS AND EVALUATION OF RELATION BETWEEN
POWDER FACTOR AND IMPACT COEFFICIENTS
Coefficients affecting powder factor can be divided into two
groups:
Group of variables includes coefficients that affect directly and
change powder factor continuously. They are:
+ Chemical and physical properties of rock include hardness
factor f and degree of crack.
+ Required degree of rock fragment that is grain size of blasted
heap rock and characterized by average size of rock.
Group of coefficients includes factors which influence powder
factor in a certain level, depending on explosion condition, as
followings:
+ Type of explosive
+ Method of firing control
+ Technology and technique of carrying out blasting. 9

CHAPTER 3: RELATION BETWEEN POWDER FACTOR AND
ROCK BLASTABILITY AND DEGREE OF ROCK
FRAGMENTATION
3.1. RELATION BETWEEN POWDER FACTOR AND DEGREE OF
EXPLOSION
Blasting considers rock as a main object to impact. Degree of
explosion characterizes how difficult to fire explosive are and is
determined by powder factor under a standard condition. The larger

( )
max
0
12
2
1
21
0
L
X
lgqq
P
P
lgqq
q
−
=
, kg/m
3
(3.1)
Where: P
1
, P
2
are percentages of grain size corresponding to x ≤
x
0
in two courses of blasting q
1
và q

Average
q
0
= 0,39 ÷ 0.46
Difficult
q
0
= 0,47 ÷ 0,55:
Very
difficult
q
0
> 0,56 Extreme difficult
3.2.3. Designing a software to rock classify of blastability Fig 3.1- Block diagram

for determining standard
powder factor
Fig 3.2- Interface of software used
to determine rock classification of
blastability
3.3. RELATION BETWEEN POWDER FACTOR AND DEGREE OF
ROCK FRAGMENTATION
In order to evaluate efficiency of fragmentation, degree of lump
(D
tb
)is used. In case of the same blasting condition, the larger powder
factor is the smaller (D

size within blasted heap as follow:
100
D
D
ii
tb
∑
γ
=
(3.4)
Where: D
i
– average size of grain size of “i”;
i
γ
- percentage of
grain size of “i”, %.

3.3.1.2. Determining degree of rock fragmentation
Degree of rock fragmentation can be determined by methods as
followings:
- Determining average size of blasted rock D
tb
by statistical power
method.
- Determining average fragment size of blasted rock D
tb
by semi-
experimental method of V.M. Kuzonhetxov.
- Determining average fragment size of blasted rock D

i
– basic cost of one m
3
of rock 12

according to phases including: drilling; loading, hauling and milling,
đ/m
3
; E – coefficient of investment efficiency.
3.3.1.4. Proper degree of rock fragmentation for quarries
In order to determine a proper degree of rock fragmentation
according to technical conditions of quarries, it is possible to use
some method as followings:
- According to bucket capacity:
3
tb
E)2,015,0(d ÷=

(3.6)

Where: E – bucket capacity, m
3

- Determining average size of blasted rock according to method
of B.N. Kutuzov
3
o

cp
is determined based on milling condition. Maximum size of blasted
rock depends on type and capacity of milling machine.
CHAPTER 4: DETERMINATION OF REASONABLE POWDER
FACTOR FOR LIMESTONE QUARRIES IN VIETNAM
4.1. Research to the relationship between powder factor with element
affect.
Determination of reasonable powder factor for limestone quaries
in Vietnam to have research to relationship between powder factor
with affecting element to blasting.
4.1.1. Research to relationship between powder factor with
explosives 13

For the selection explosives based on:
- The first is characteristic of explosives
- The second is the cost of explosives
When determining powder factor by using other explosives, it is
different from standard explosives must mention the conversion
coefficient because the explosive energy is different
4.1.2. Research to relationship between powder factor with rock
properties
According to experimental and theory of blasting, the rock
properties is the most important and directly affect to calculate
powder factor.
4.1.3. Research to relationship between powder factor with
blasting parameters
4.1.3.1. Relationship between powder factor with charge diameter

4.1.6. The relationship for the
determination of Powder factor
- environment
To protect the environment
when blasting in limestone
quarries as follows:
- Using suitable types of
explosives
- Using suitable powder factor

Fig 4.1- Powder factor depend
on Fragmentation size
- Using appropriate blasting parameters
- Using reasonable blasting methods
4.2. DETERMINATION OF REASONABLE POWDER FACTOR
FOR LIMESTONE QUARRIES IN VIETNAM
4.2.1. Analysis, assessment and classification of the elements
affecting to powder factor
Powder factor depends on rock properties, explosive types,
blasting methods, blasting parameters, and required fragmentation.
The influence of each factor to powder factor is different, based on
these properties it can be divided into two groups.
Group one: The factors
directly influencing to reasonable
powder factors:
- Rock properties, (rock
strength, rock fracture);
- Required fragmentation,
(average fragment size);
These factors are variables

1
, x
2
,….) (4.2)
4.2.2. Definition of optimum explosives
Based on the requirements and characteristics of limestones
quarries in Vietnam, using standard explosives are ANFO to
calculation
4.2.3. Method of determination of powder factor for limestone quarries
4.2.3.1. Powder factor depends on blasting requirements
The research results indicated the distribution law of particle size
and the function of powder factor with average fragment size is linear
function:
q
cn
= ad
tb
+ b (4.3)
Where- q
cn
is technical powder factor, kg/m
3
; d
tb
is average
fragment size, m; a, b is empirical coefficients, it found from
empirical blasts.
For determination relationship between power factor -
Fragmentation size, author carry out blasting test at Ninh Dan
limestone quarry, Thuong Tan limestone quarry, Yen Duyen

Fig 4.6- Powder factor -
Fragmentation size relationship at
Thuong Tan IV limestone quarry

Fig 4.7- Powder factor -
Fragmentation size relationship at
Yen Dunyen limestone quarry 17

Base on results blasting test, if other affecting factor is not
changing as rock hardness, type of explosives, fracturing, then only
changing fragment size, to realize:
- When d
tb
≈ 0 then q
cn
= q
max
= b
- When q
cn
= 0 → 0 = ad
max
+ b
→
max
max
d

= 0,8kg/m
3
→ b = 0,8, The equation (4.3) becomes:

8,0
d
d
8,0q
max
tb
cn
+−=
(4.5)
4.2.3.2.
Powder factor depends on rock hardness f
The rock strength is estimated by hardness coefficient f, (M.M.
Protodiaconov's classification). When hardness coefficient
increasing, Powder factor also increasing. When mentioning the
hardness coefficient, the formula of Powder factor is determined as
follows:
q
1
= k
1
.q
cn
(4.6)
According to the statistics, blasting test determination relationship
between rock hardness power factor q
cn

0,46
5
0,53
5
0,58
2
q
1
/q
cn

1 1,07 1,10 1,13 1,16 1,18 1,21 18

From data in table 2 determine the relationship between quotient
q
1
/q
cn
and rock hardness such as:
q
1
/q
cn
= 0,635.f
0,262
(4.7)


(4.10)
For the limestons quarries in Vietnam, average rock density is 2,6
t/m
3
. According to the theory of blasting and blasting test coefficient
k
2
determined by the following formula:

6,2
k
đ
2
γ
=
(4.11)
Replace (4.10) in (4.9) and equation (4.9) then is becomes:

cn
4đ
2
qf635,0
6,2
q ×××
γ
=
(4.12)

4.2.3.4.
Powder factor depends on type of explosives

quarries in Vietnam because of its many advantages. The most
common value of k
4
when using delay initiation method will
generally lie in the range of 0.85 to 0.95. Powder factor can be
determined by the following formula:

cn
4đ
343
qf635,0
6,2
kkq ×××
γ
××=

(4.15)
4.2.3.6. Powder factor - blasting parameters and environment
relationship
The relationship between powder factor - blasting parameter and
environment is indirectly. Method of determination of reasonable
powder factor (q
hl
, kg/m
3
) does not take into account this relationship
and also not shown in this formula.
From the results of the formulas (4.4 ÷ 4.14) to establish the
final formula of determination of reasonable powder factor is
becomes:

, kg/m
3
(4.16)
The formula determination of reasonable powder factor shows
full factors of influence on powder factor and meets the requirement
and purposes of the blast as when changing fragment size, rock
property, explosives type and condition of blasting for limestone
quarries in Vietnam.
The results of calculations for a number of limestone mines are
suitable with actual results. The problems of this formula need to be
more multiple blasting experimental to determine exactly influence
coefficient.
4.3. Build program calculates powder factor, blasting parameters
and blasting patterns
From the study, author have built the software calculates powder
factor, blasting parameters and blasting patterns. Programs written by 20

VBA / Excel language help engineers easy to use for calculating
blasting parameters, blast log quickly, exactly and reliably.
4.3.1. Software structure
Software including 4 parts:
- Part 1: General Information
- Part 2: Determination of reasonable powder factor
- Part 3: Determination of blasting parameters
- Part 4: Drawing blasting patterns
4.3.2. Introduce some interfaces and results calculated by the
software


.
Fig- 4.14. Interfaces of blast log
GENERAL CONCLUSION
1. Rock blasting is the first step in mining, especially in
limestone quarries. One of the most important blasting parameters
needs caring is powder factor. This parameter has considerable
influence on other blasting parameters and the environmental
impacts.
2. There are various natural and technological factors that
influence on the powder factor. Two groups classify the elements:
fluctuation factors and constant factors. In different condition, the 22

powder factor is calculated based on the quantitative relationship of
the mentioned factors.
3. The most factors influencing on powder factor is blasting
index and
- Blasting index is specified by the standard powder factor q
0
.
then the size of blasted rock is a linear distributed). Software by the
author can help to classify the blasted rock by blasting index in
different in limestone quarries.
- Required fragment size in the limestone quarries can be
calculated under different technical condition (by the formular of
Prof. Kutuzov, in which D
cp

. Some factors, such as the strength, the fracture, the
density, fragment size, are set in the technical powder factor as
fluctuation factors; the others are mentioned constant factors.
7. From the suggested formular of the powder factor, other
blasting parameters and blasting log can be solved in the software
that the author mentioned in the dissertation.
PUBLICATIONS
1. Nguyen Dinh An (2004), Determination of reasonable powder
factor for surface mining in Vietnam, Proceedings of mining science
and technology conference 19
th
, Hanoi University of Mining and
Geology. p 37-41. 23

2. Nhu Van Bach, Nguyen Dinh An, Nhu Van Phuc (2006).
Blasting design for obtaining desired fragmentation at Apatite mine
in Lao Cai, Journal of mining and geology in science and technology,
Hanoi University of Mining and Geology. p 11-14.
3. Nguyen Dinh An, Bui Xuan Nam (2006). Computer simulations
of delay blasting, Journal of mining and geology in science and
technology, Hanoi University of Mining and Geology. p 74-75
4. Nhu Van Bach, Lê Văn Quyển, Bui Xuan Nam, Nguyen Dinh
An, Nhu Van Phuc (2006). Reduce of ground vibration in blasting at
Nui Beo surface coal mines. Journal of mining and geology in
science and technology 14th edition, Hanoi University of Mining
and Geology. p 58-62
5. Nguyen Dinh An, Tran Khac Hung (2010). Determination of

10. Nguyen Dinh An, Tran Khac Hung (2011). Reduce of ground
vibration in blasting at Nui Beo surface coal mine. Proceedings of
The International Symposium on Earth Science and Technology
2011, 6-7 December 2011, Kyushu University, Fukuoka, Japan
11. Nguyen Dinh An , Nhu Van Bach, Nguyen Van Sang, Tran
Khac Hung, Tran Dinh Bao (2012). Determination of reasonable
powder factor for Vietnam limestone quarries. The 2nd International
Conference on Advances in Mining and Tunneling. Hanoi, August
23-25, 2012, Publishing House for Science and Technology, p 350-
352 (ISBN 978-604-913-081-6).
12. Nhu Van Bach, Nguyen Dinh An, Le Qui Thao (2012).
Analyzing the factors affecting to the vibration when blasting with
non-electric detonators. The 2nd International Conference on
Advances in Mining and Tunneling. Hanoi, August 23-25, 2012.
Publishing House for Science and Technology. P. 338-340 (ISBN
978-604-913-081-6).
13. Nhu Van Bach, Nguyen Dinh An, Lê Qui Thao, Tran Dinh Bao
(2012), Developing technology of large hole drilling diameter for
limestone quarries in Vietnam, Proceedings of mining science and
technology conference 20
th
, Hanoi University of Mining and
Geology. P. 141.
14. Nhu Van Bach, Nguyen Dinh An, Bui Xuan Nam, Tran Khac
Hung (2012), Reduce of ground vibration in blasting is the use of
none electric blasting, Journal of mining and geology in science and
technology 38
th
edition, Hanoi University of Mining and Geology. p
25 - 28.