A Report on Mine Opening and Development

1. 1
REPORT ON
MINE OPENING AND DEVELOPMENT
BY
ANURAG KUMAR JHA

2. 2
CONTENTS
FINAL TERM APPRAISAL 2019.......................................................... Error! Bookmark not defined.
MINE OPENING AND DEVELOPMENT............................................................................................1
CONTENTS............................................................................................................................................2
LIST OF TABLES..................................................................................................................................4
LIST OF FIGURES ................................................................................................................................5
1. Introduction.....................................................................................................................................6
2. Box cut............................................................................................................................................7
2.1. Objective and type of box cut:-...............................................................................................7
2.2. Types and applicability...........................................................................................................7
2.2.1. Internal boxcut ................................................................................................................7
2.2.2. External boxcut ...............................................................................................................7
2.3. Box cut parameters and methods ............................................................................................8
2.3.1. Parameters:- ....................................................................................................................8
2.3.2. Methods:-........................................................................................................................8
2.4. Theoretical Calculation of cut volume of box cut...................................................................9
2.5. Practical calculation of cut volume of box cut......................................................................11
2.6. Factors affecting the Selection of Box-Cut Site....................................................................11
2.6.1. Site accessibility:...........................................................................................................11
2.6.2. Minimum excavation requirement:...............................................................................12
2.6.3. Availability of dumping space:.....................................................................................12
2.6.4. Pit haulage plan:............................................................................................................12
2.6.5. Overall mine plan:.........................................................................................................12
2.6.6. Water condition:............................................................................................................12
2.6.7. Geological disturbance:.................................................................................................12
2.6.8. Reclamation requirement:.............................................................................................12
3. Production bench ..........................................................................................................................13
3.1. Formation of bench...............................................................................................................13
3.1.1. Formation of benches by establishing additional cut....................................................13
3.1.2. Formation of benches by extending the existing box cut..............................................14
3.2. Bench Parameters and their selection ...................................................................................14
3.2.1. Bench height .................................................................................................................14
3.2.2. Bench width ..................................................................................................................15
3.2.3. Bench length .................................................................................................................16

3. 3
3.2.4. Bench face slope ...........................................................................................................17
3.2.5. Bench floor slope:.........................................................................................................17
4. Preparation Of Bench Material For Excavation............................................................................18
4.1. Ripping..................................................................................................................................18
4.1.1. Applicability and Limitations of Rippers......................................................................19
4.1.2. Ripping is considered due to various reasons as stated below:.....................................19
5. Estimation of Number of Blast-hole Drills required in a Mine:-..................................................20
5.1. Estimation of Number of Drills required in a Surface Coal Mine ........................................20
5.1.1. Estimation of Number of Drills required for Coal Bench/Benches ..............................20
5.1.2. Estimation of Number of Drills required for O/B Bench/Benches ...............................21
6. Conclusion ....................................................................................................................................23

4. 4
LIST OF TABLES
Sl. No. Title Page No.
1 Table of content 2-3
2 List of figures 5
3 Parameters to calculate
number of drills
18
4 Estimation of number of
coal drills required
20
5 Estimation of number of
O/B drills required
21
6 Conclusion 23

5. 5
LIST OF FIGURES
Sl. No. Title Page No.
1 Box cut 7
2 Types of box cut 7
3 Method of opening of
box cut
8
4 Longitudinal section of
box cut
9
5 Formation of bench by
additional cut
12
6 Formation of bench by
extending the existing
cut
13
7 Bench parameters 14
8 Preparation of bench
material
16

6. 6
1. Introduction
Mining industry plays a very crucial role in the development of any country
or the society. Aim of mining is maximum extraction of minerals keeping in
view of enviroment,economic and lease constrants.Earlier, mining aimed at
maximum extraction of minerals and fules without involving of any other
factor. But now a day mining totally concern with health,safety, and
environment. With the growing demand of different minerls, there is an
upsurge in intrest and action in opencast mining because of improvment of
productivity,recovery and safety of mining oerations . There has been
observed an improvement in production.
1. Large capacity open cast mines
2. Continuous mining system
3. Explosive and accessories
4. New inovation involving information technology
As we know that our nation need energy and the best way to full fill the need
of energy is to generate the electric energy. In our case, we are fully depends
on thermal power plant that needs coal to produce the electricity for this we
need a large amount of coal.
As we know that we have two mining method
underground and open pit mining method in which underground has a huge
restriction in mechanisation ( presently longwall and continues miner is
performing well ) and it is very costly also so if possible we are preferring
open pit mining method in which can produce a huge amount of coal and the
scope of mechanisation is also very high so that it makes the cost of
production minimum .
In this report we have discussed the different
parameters of bench and the calculation of volume of box cut and calculation
of number of drill required in the overburden.

7. 7
2. Box cut
Box cut is the initial/first cut given for the physical development of a mine. The name ‘Box cut’
has been attributed to this cut as this cut generally looks like a top open box having an inclined
floor and walls on three sides (front wall and two side walls) in case of opening up of subsurface
deposits. However, in today’s surface mining terminology the initial cut given for the physical
development of a mine is called a box cut whether it looks like an open box or not.
Box cut
2.1. Objective and type of box cut:-
The main objective of box cut are:
 To reach the ore body / coal seam
 To provide a smooth entry to the pit
 To provide space for development of working / production benches
2.2. Types and applicability
Box cuts are of two types:
 Internal boxcut
 External boxcut
2.2.1. Internal boxcut
When the box cut is located fully or partially on the mineralized zone, it is called an
internal box cut. This is applicable for all types of deposit. The cut follows a direction
that is usually oblique to both the strike and dip direction. Generally, the direction is so
chosen that the haul road ramp formed by this cut and subsequent cuts will not have
unnecessary steep turning at any position.
2.2.2. External boxcut
When the box cut is placed totally outside the mineralized zone, it is called an external
box cut. This is applicable only for shallow and gently dipping bedded deposits. The cut
is generally located at the middle of the rise-most side.
A A′
B
B′
Section A - A′
SectionB-B′
ORE BEARING ZONE
ORE BEARING ZONE
INTERNAL BOX CUT EXTERNAL BOX CUT

8. 8
2.3. Box cut parameters and methods
2.3.1. Parameters:-
The main parameters of box cut are:
 Maximum level difference (H) or the height of the box cut is generally equal
to the proposed bench height
 Width of the floor (W) of the box cut should such that the movement of the
machinery is smooth. If shovel – dumper combination is used for the box cut,
then there should be sufficient space for the shovel movement for excavation
& loading and the width should be at least three times the width of the
dumper being used.
 Longitudinal inclination of the floor (θ) of the box cut depends on the
intended use of it at later dates. If it is planned that the box cut will form a
part of the haul road ramp, then the cut is generally made with an inclination
between 4.086 deg. (1in 14) and 4.764 deg. (1 in 12).
 Front slope angle (α) and side slope angles (β1 & β2) are generally dependent
on the rock-mass properties (physico-mechanical) and the pore pressure
condition at the cut site, and the maximum height of the cut. The front slope
angle is generally steeper than the side slope angles. The side slope angles are
generally same, but under certain conditions they may be different.
2.3.2. Methods:-
For establishing box cut shovel – dumper combination or backhoe – dumper
combination is generally used. However, in certain cases dragline can also be used for
the purpose. The schemes for establishing box cut by shovel – dumper combination,
backhoe – dumper combination and dragline are shown below.
For establishing box cut in some situations (in hard rocks), it may be necessary to adopt
drilling & blasting to loosen the rock mass to facilitate its excavation & loading. For
this, holes of different depths are required to be drilled and blasted to form the inclined
floor of the cut.
BOX CUT BY SHOVEL BOX CUT BY BACKHOE
BOX CUT BY DRAGLINE DRILLING PATTERN FOR BOX CUT

9. 9
2.4. Theoretical Calculation of cut volume of box cut
The points O and O1 are the projections of points B and B1 respectively on the surface.
Considering the longitudinal section and the transverse section,
OB = O1B1 = H (height of the cut)
From Δ ABO, tanθ = OB / AO => AO = OB / tanθ = H / tanθ
From Δ OBC, tanα = OB / OC => OC = OB / tanα = H / tanα
AC = AO + OC => AC = H [(1 / tanθ) + (1 / tanα) => AC = H [( tanα+tanθ) / (tanα tanθ)]
From Δ OBN, tanβ1 = OB / ON => ON = OB / tanβ1 = H / tanβ1
From Δ O1B1N1, tanβ2 = O1B1 / O1N1 => O1N1 = O1B1 / tanβ2 = H / tanβ2
Again considering the surface projections of surfaces ABCMNA and A1B1C1M1N1A1,
From Δ AON and Δ ACM, MC / ON = AC / AO = (AO + OC) / AO = 1 + (OC / AO)
MC = ON  [1 + (OC / AO)]
MC = (H / tanβ1)  [1 + (H / tanα) / (H / tanθ)] = (H / tanβ1)  [1 + (tanθ / tanα)]
MC = (H / tanβ1)  [(tanα + tanθ) / tanα] = H  [(tanα + tanθ) / (tanα tanβ1)]
A
A1
M1
B
B1
N
C
C1
N1
M N
N1
O
O1
A O C
θ
α
β1
β2
H
H
W
B
Longitudinal Section
TransverseSection
B
B1
N1
O1
M1
C1
A1
A
N M
CO

10. 10
Similarly from Δ A1O1N1 and Δ A1C1M1,
M1C1 / O1N1 = A1C1 / A1O1 = (A1O1 + O1C1) / A1O1 = 1 + (O1C1 / A1O1)
=> M1C1 = O1N1  [1 + (O1C1 / A1O1)] => M1C1 = H  [(tanα + tanθ) / (tanα tanβ2)]
MM1 = MC + M1C1 = H  [(tanα + tanθ) / (tanα tanβ1)] + H  [(tanα + tanθ) / (tanα tanβ2)]
MM1 = H  [(tanα + tanθ) / tanα]  [(1/ tanβ1)+(1/ tanβ2)]
If β1 = β2 = β, then MM1 = 2H  [(tanα + tanθ) / (tanα tanβ)]
For calculation of the cut volume, the whole volume has been divided into three segments –
segment ABCC1B1A1, segment ABCMN and segment A1B1C1M1N1. Of these, the segment
ABCC1B1A1 is an inverted triangular prism of width W, and when the other two segments
ABCMN and A1B1C1M1N1 are joined together they form an inverted pyramid with a
triangular base AMM1A1 as shown below.
Let,
V1 be the volume of the prism ABCC1B1A1 and V2 be the volume of the pyramid MM1BA.
So, the total cut volume, V = V1 + V2
V1 = W  Area of Δ ABC = W  (1/2)  AC  OB = (W/2)  [H  (tanα+tanθ) / (tanα tanθ)] 
H
V1 = H 2
 (W/2)  [( tanα+tanθ) / (tanα tanθ)]
V2 = (1/3)  H  Area of Δ AMM1 = (1/3)  H  (1/2)  (MC + M1C1)  AC
V2 = (H/6) H [(tanα+tanθ) / tanα][(1/ tanβ1)+(1/ tanβ2)] H [(tanα+tanθ) / (tanα tanθ)]
V2 = H 2
 (H/6)  [(tanα+tanθ) / (tanα tanθ)] [(tanα+tanθ) (tanβ1+tanβ2)/( tanα tanβ1tanβ2)]
If β1 = β2 = β, V2 = H 2
 (H/3)  [(tanα+tanθ) / (tanα tanθ)] [(tanα+tanθ) (tanβ)/( tanα tanβ)]
V = V1 + V2 = H 2
[(tanα+tanθ)/(tanα tanθ)] [(W/2)+(H/6)(tanα+tanθ)(tanβ1+tanβ2)/(tanα
tanβ1tanβ2)]
If β1 = β2 = β, V = H 2
 [(tanα+tanθ) / (tanα tanθ)] [(W/2) + (H/3)  (tanα+tanθ)/( tanα tanβ)]
A C
A1 C1
B
B1
W
H
A B C
M
A1
M1
B1 C1

11. 11
2.5. Practical calculation of cut volume of box cut
These are the following parameters that we need to calculate the volume of box cut:-
Height of the box cut ( H )
Width of the floor ( W )
Longitudinal inclination of the floor ( ϴ )
Front slope angle (α )
Side slope angle ( β1 & β2 )
Theoretical formula for calculation of volume:
If ,
Β1 = β2 = β
V = volume of box cut
Now ,
These are the following given data from mines
Height of box cut ( H ) = 13m
Width of box cut ( W ) = 60m
Longitudinal inclination of the floor ( ϴ ) = 1 in 16 or 3.5760
Front slope angle ( α ) = 800
Side slope angle ( β ) = 750
Now,
Hence as we see that from the above calculation
Volume of initial cut box cut is 94894.26 m3
2.6. Factors affecting the Selection of Box-Cut Site
Selection of location of box cut for any surface mine is of utmost importance as it has far
reaching effects on the economy of the mine. The location should be so chosen that there is a
minimum of foreseeable trouble with uncovering the coal seam and a maximum of economy.
In selecting the optimum box cut location, the following factors are necessary to be taken
into consideration.
2.6.1. Site accessibility:
The site for establishing the box cut should be easily accessible/reachable for
men and machinery.

12. 12
2.6.2. Minimum excavation requirement:
The location of box cut should be so chosen that the material to be excavated to
reach the ore body will be as less as possible. This will ensure early production
of ore from the mine, and this is very important from the view point of the
economics of mine operation.
2.6.3. Availability of dumping space:
The cut material should preferably be handled only once and stacked off the
mineral bearing zone. For dumping the excavated material, sufficient space
should be available nearby. This will improve the economy of transport of the
cut material.
2.6.4. Pit haulage plan:
If the box cut is planned to be a part of the pit haulage system, it must match
with the haulage plan for the complete pit. The roads, as far as practicable,
should be put in but once and used as much as possible.
2.6.5. Overall mine plan:
The box cut location should be so chosen that it matches with the overall mine
plan including the waste dump locations, sites for infrastructural facilities and
sites for other facilities. It should not hinder the pit expansion at a later date.
Also the location should be such that the overall economy of coal and waste
transport over the whole mine life is maintained.
2.6.6. Water condition:
Drainage is one of the most important aspects for the box cut. Surface drainage
must be diverted, preferably by gravity. If possible, the location of the cut should
be so chosen that the problems of accumulation of water from surface water and
ground water are not there or minimum.
2.6.7. Geological disturbance:
The box cut location should preferably be free of any geological discontinuities
and structural disturbances.
2.6.8.Reclamation requirement:
The reclamation requirements may dictate that the box cut material should be
dumped/emplaced at particular location. This may affect the location of the cut
in order to satisfy such requirements most economically.
If the box cut is a part of the pit haul road system, particularly in case of external
box cut for a bedded deposit, preferably the cut should be placed at the middle of
the rise-most side of the deposit for the economy of transportation provided that
the location is not dictated otherwise by some other factors.

13. 13
3. Production bench
3.1. Formation of bench
Once the box cut is established upto the 1st
bench floor level, the development of the 1st
bench is started. Once the 1st
bench is developed over a considerable area, the development
of subsequent benches are done by two methods – by establishing additional cuts or by
extending the existing box cut after widening the same.
3.1.1. Formation of benches by establishing additional cut
In this method, the first bench (I – Bench) is developed by extending the initial box-cut.
Proper working face is established and the bench of designed height and slope is
advanced sufficiently. This is followed by establishing the next cut (second cut), a
separate one from the first cut, leaving sufficient gap/space between the two cuts to
allow unrestricted movement of dumpers between the first bench and the surface. The
second cut is generally established oblique to the first cut. Once the second cut is
established fully, the development of the second bench of designed height and slope
starts; and the same process continues for development of subsequent benches.

14. 14
3.1.2. Formation of benches by extending the existing box cut
In this case, the first bench (I – Bench) is developed by extending the initial box-cut.
Proper working face is established and the bench of designed height and slope is
advanced sufficiently (figures i to iii). This is followed by establishing the next cut
(second cut) by extending the first cut after widening the same so as to leave sufficient
gap/space to allow unrestricted movement of dumpers between the first bench and the
surface. The second cut effectively becomes as an extension of the first cut. Once the
second cut is established fully, the development of the second bench of designed height
and slope starts; and the same process continues for development of subsequent
benches.
3.2. Bench Parameters and their selection
A surface mine bench is characterized by the following bench parameters – Bench
height, Bench width, Bench length, Bench face slope and Bench floor slope.
3.2.1. Bench height
Bench height is the vertical distance between the crest and toe of a bench. As
specified by the Directorate General of Mines Safety (DGMS), it shall not be
more than the -
o maximum digging height of the excavator excavating the bench in case
of hard formation
o maximum digging height of the excavator excavating the bench + 3m
in case of soft formation.
From the operational point of view, the bench height is decided based on the
following criteria – optimum digging height of the excavator for efficient

15. 15
excavation, one pass drilling length should preferably be more than the bench
height, and the blending requirement dictated by the geological parameters.
For benches worked by rope shovels and draglines, the bench height is
generally selected on the basis of optimum digging height of the excavator. In
case of hydraulic excavators, the bench height is generally selected on the
basis of maximum digging height. In case of bucket wheel excavator (BWE)
workings, the bench height depends on – the height of the cutting boom pivot
point, the effective length of cutting boom including the cutting wheel and the
allowable maximum angle of inclination of cutting boom in the vertical plane
limited by the dynamic angle of repose of the cut material.
H - Bench Height, W - Bench Width, L – Bench Length,  - Bench Face Slope
3.2.2. Bench width
Bench width is the horizontal distance between the crest of a bench and the toe
of the immediately upper bench. As specified by the DGMS, it shall be more
than –
o the bench height
o the maximum width of the largest machine + 2m
o three times the width of largest size dumper that is plying on the bench
H - Bench Height W – Bench Width L – Bench Length  - Bench Face Slope
BENCH PARAMETERS

16. 16
o From the operational point of view, minimum width of a working bench
should be equal to
= 0.8 X bench height + dumper width + shovel dimension + 4m
Now according to the practical calculation of mines
Bench height = 9m ( can be 3m more than the boom height )
Dumper width = 2.49m
Shovel width = 3.44m
Now
Working bench = 0.8 x9 + 2.49 + 3.44 +4
= 17.13m
3.2.3.Bench length
Bench length in a surface mine is the length (straight or curve as the case may be)
measured along the floor of the bench between its two extremities. It is generally
decided based on the operational requirements and conveniences. The minimum
bench length required is generally dictated by the frequency of primary blasting and
the advancement of the face along the length of the bench per blast, and also on the
type of excavator used.
In a mine that is being worked by shovel – dumper combination with full scale
blasting, minimum bench length required may be calculated as follows.
Let,
The frequency of primary blasting in the bench is once per week
The volume of material to be handled per week from the bench is V
The height and width of the bench are H and W respectively
The length of broken material required per week, l = V / (H  W)
The minimum bench length, L = 3  l
The minimum bench length, L shall be equal to 3l as an additional length of l will be
required for drilling while the blasted material is being handled by the excavator and
another extra length of l for maintaining the flexibility.
For dragline benches, the minimum bench length should be 300m to 500m in view of
marching requirements and operational conveniences.
For the mines being worked by bucket wheel excavator (BWE) – conveyor
combination, the minimum bench length should be decided on the basis of the
production requirement, the method of work of BWE (full block or half block), shift
able belt conveyor shifting frequency and other operational conveniences.

17. 17
The maximum bench length is generally selected on the basis of depositional features
and/or transport requirement.
Now bench length calculation from the practical data of mines
Given data,
Annual coal production = 1 x 106
ton
Stripping ratio = 5.9 m3
Volume of OB handled per year = 1 x 106
x 5.9
= 5.9 x 106
m3
Volume of OB handled per week = 5.9 x 106
/ 52
= 113461.58 m3
Length of broken material required per week =113461.58 / (9 x 17.13 )
= 735.95 m
Minimum bench length = 3 x 735.95
= 2207.85 m
Additional 735.95 m will be required for drilling while the blasted material will be
handled and the rest 735.95 required for maintaining the flexibility.
3.2.4. Bench face slope
Bench face slope is the slope of a line (in the vertical plane) that joins the toe
and the crest of the bench. It is generally selected considering the requirements
of slope stability and inclined hole blasting, and criterion of complete removal
of blasted material by the excavator excavating the bench.
Now in our case
Bench face slope = 800
3.2.5. Bench floor slope:
Generally 1% to 2% longitudinal slope is provided on the bench floor to
facilitate the drainage of water to the sump area.

18. 18
4. Preparation Of Bench Material For Excavation
Preparation of bench material involves the processes of changing the mechanical state of
in-situ rock-mass of the bench, wherever necessary, so that it becomes amenable to easy
extraction by the excavators.
The purpose of preparing the rock-mass for extraction is to ensure safety in mining, the
production of raw material of the required quality, and the possibility of using means of
mechanization in the best possible operating conditions.
The methods used for bench material preparation are mainly by Ripping (mechanical
loosening by actuating members) and Drilling & Blasting.
The method of bench material preparation is chosen based on the in-situ state of the rock-
mass (state of aggregation, strength, presence and orientation of weakness planes, etc),
capacity of the mining plant, the available technical means, and the mining system
adopted.
When the material is soft enough, it does not require any preparation as it can be directly
excavated and loaded onto transport equipment by excavators. If the material is
marginally strong, limited drilling and blasting (without any throw) may be used to loosen
the ground. For moderately strong rocks, limited drilling and blasting followed by ripping
is used sometimes as means of material preparation. Full scale drilling and blasting is
used in rock-mass that cannot be excavated directly or cannot be loosened effectively/
economically by ripping (with or without limited drilling and blasting).
4.1. Ripping
Ripping is a method used for preparation of bench material / rock-mass that are soft
to marginally hard to facilitate subsequent loading and transport through mechanical
loosening. Ripping with dozers as a means of loosening the rock-mass came into
existence in late 1950s and has become a popular method. Ripping is usually
economic than drilling and blasting as a means of bench material preparation. But as
the rock mass becomes harder drilling and blasting becomes cheaper.
Ripping is done by ripper that is basically an attachment having single tooth or
multiple teeth (up to five teeth) fitted to a shank. Ripper is generally attached at the
rear of a dozer (tractor-mounted) and operated hydraulically. Weathered igneous and
metamorphic rocks are generally prepared with the use of single tooth-rippers. For
loosening the dense rocks generally multi-teeth rippers are used to raise their output.
The depth of ground penetration of tractor-mounted rippers is varied by means of
hydraulic control system. Low or medium jointed weathered igneous and
No
Preparation
Ripping
Limited
Drilling &
Blasting
Limited Drilling &
Blasting followed
by Ripping
Full -scale
Drilling &
Blasting
Very Soft Soft Marginally/Moderately Strong
Strong to
Very Strong

19. 19
metamorphic rock-mass are ripped with tooth/teeth having straight uprights. Heavily
jointed and/or brittle rock-mass are ripped with tooth/teeth of intricate shape.
With the evolution of high power ripper-dozers, the rock-mass that were considered
earlier to be non-rippable now comes under rippable category. As it stands today
ripping, while taking care of environment and safety, have become competitor to
drilling and blasting for bench material preparation.
4.1.1. Applicability and Limitations of Rippers
Rippers are generally used in soft to marginally hard rock-mass. It is mostly used to
excavate overburden, but can also be used for soft to marginally hard ore body. If the
rock-mass is bit more hard, some times it is first weakened by limited drilling and
blasting followed by ripping. The rippers do not find much application in hard or very
hard rocks.
4.1.2. Ripping is considered due to various reasons as stated below:
1. Increased Productivity:
In ripping process there is continuous work going on. This reduces idle time. It
also eliminates shifting of machines which is present in blasting operation.
2. Minimized ground vibration:
Drilling and blasting operation includes large ground vibration which affect
nearby inhabitation and creates cracks on ground and structures. Ripping and
dozing minimizes ground vibration.
3. Safety:
There are chances of generation of fly rocks during blasting. Also chances of
misfires are more in blasting operation. Ripping eliminates the chances of
generation of fly rocks and misfires, thereby increasing safety of life and
properties.
4. Noise and dust reduction:
Drilling and blasting creates a lot of noise and dust which is eliminated by
use of rippers.
5. Product size:
Blasting sometimes result in oversize boulders which may require secondary
blasting which is a costly affair. But selection of right kind of ripper results in
right size of material.
6. Slope stability:
Blasting may result in slope failure. But ripping provides better safety and
slope stability.
7. Quality control:
In blasting there are chances of dilution of ore. But in ripping operator can
easily distinguish between ore and waste. Ripping is helpful in selecting
mining .
8. Cost economics:
Ripping doesn’t involve involvement of various machineries as in drilling
and blasting thereby making the process economical.
9. Environmental friendly:
Ripper provides a pollution free environment to work.

20. 20
5. Estimation of Number of Blast-hole Drills required in a Mine:-
The method of estimation of number of blast-hole drills required in a surface mine mining
bedded deposits with sharp contact differs from that in case of a surface mine mining
massive / vein / pipe type deposits where the ore-body grade change is gradual.
5.1. Estimation of Number of Drills required in a Surface Coal Mine
In a surface coal mine (dip of coal seam ≤ 1 in 8) the coal and the overburden and/or
inter-burden are excavated in separate benches. Hence, the number of blast-hole
drills required for coal bench / benches and that for overburden and/or inter-burden
bench / benches are required to be estimated separately.
Some of the following data will be given and the rest are to be assumed calculation
for the number of drills required for the mine.
Given Conditions / Assumptions
Required production of coal – T te / year Stripping ratio – SR m3
/ te
or
Overburden thickness – THob m
In-situ density of coal – Cd te / m3
Coal seam thickness – THc m
Coal bench height – BHc m O/B bench height – BHob m
Blast-hole pattern for coal bench – Bc  Sc m2
Blast-hole pattern for O/B bench – Bob  Sob
m2
Drilling hours / year – Hr Sub-grade drilling for O/B bench – SG %
Drilling rate in coal bench – dc min / m Drilling rate in O/B bench – dob min / m
Length of feed in coal bench – fc m Length of feed in O/B bench – fob m
Time to move the drill in coal bench – lc min
Time to move the drill in O/B bench – lob
min
Time to set the drill in coal bench – gc min Time to set the drill in O/B bench – gob min
Time to change a drill rod in coal bench – ec
min
Time to change a drill rod in O/B bench – eob
min
Overall utilization of drill in coal bench – Ec Overall utilization of drill in O/B bench – Eob
5.1.1. Estimation of Number of Drills required for Coal Bench/Benches
Height of the coal bench is selected from the given coal seam thickness and the
shovel capacity intended to be used. The coal bench height (BHc) should be so
selected that THc is an integer multiple of BHc.
Volume of coal to be produced / year = (T / Cd) m3
Volume handled / hole = Bc  Sc  BHc m3
Total number of holes to be drilled / year = (T / Cd) / (Bc  Sc  BHc) = Nhc
(say)
Depth of blast-hole = BHc m, as there is no sub-grade drilling for coal bench

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Number of feeds required for a hole = BHc / fc = Nfc (say)
Actual number of feeds required for a hole = Nfc, Nfc is integer
= (Integer part of Nfc) + 1, otherwise
Number of feed change required (Ncc say) = Nfc - 1, Nfc is integer
= Integer part of Nfc, otherwise
Total time to drill one hole = ((lc + gc + (BHc  dc) + (Ncc  ec)) min = tc min
(say)
Actual number of holes drilled per hour per drill = (60 / tc)  Ec
Actual number of holes drilled per year per drill = (60 / tc)  Ec  Hr
Total number of drills required = Nhc / ((60 / tc)  Ec  Hr) = Ndc (say)
Actual number of drills required = Ndc, Ndc is integer
= (Integer part of Ndc) + 1, otherwise
5.1.2. Estimation of Number of Drills required for O/B Bench/Benches
The stripping ratio is given by –
If the overburden thickness is given, then the stripping ratio is calculated from the above
relation.
SR = THob / (THc  Cd)
If the stripping ratio is given, then the overburden thickness is calculated as –
O/B thickness = Stripping ratio  Coal seam thickness  Density of coal
THob = SR  THc  Cd
Height of the O/B bench is selected from the given O/B thickness (when it is given) or
from the calculated O/B thickness (when stripping ratio is given) and the shovel
capacity intended to be used. The O/B bench height (BHob) should be so selected that
THob is an integer multiple of BHob.
Volume of O/B to be excavated / year = (T  SR) m3
Volume handled / hole = Bob  Sob  BHob m3
Total number of holes to be drilled / year = (T SR) / (Bob  Sob  BHob) = Nhob (say)
Depth of blast-hole, DHob = BHob  (1 + SG/100) m for sub-grade drilling of SG%
Coal seam Thickness (THc)  Density of Coal (Cd)
Stripping Ratio (SR) =
Overburden Thickness (THob)

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Number of feeds required for a hole = DHob / fob = Nfob (say)
Actual number of feeds required for a hole = Nfob, Nfob is integer
= (Integer part of Nfob) + 1, otherwise
Number of feed change required (Ncob say) = Nfob - 1, Nfob is integer
= Integer part of Nfob, otherwise
Total time to drill one hole = (lob + gob + (DHob  dob) + (Ncob  eob)) min = tob min
(say)
Actual number of holes drilled per hour per drill = (60 / tob)  Eob
Actual number of holes drilled per year per drill = (60 / tob)  Eob  Hr
Total number of drills required = Nhob / ((60 / tob)  Eob  Hr) = Ndob (say)
Actual number of drills required = Ndob, Ndob is integer
= (Integer part of Ndob) + 1, otherwise

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6. Conclusion
As per the study of practical mine , and taking some of the assumed data and
trying to find out the different parameters required for operation of the mine
and we found that
In mine
This the conclusion table
Sl No. Parameters Result
1. Box cut volume 94894.24 m 3
2. Bench height 9 m
3. Bench width 17.13 m
4. Bench length 2207.85
As per the present condition of our project this is the following this that we
need to operate the mine.