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Journal of Geological Resource and Engineering 1 (2015) 28-36 doi:10.17265/2328-2193/2015.01.004
Punch Multi-slice Longwall Mining System for Thick
Coal Seam under Weak Geological Conditions
Takashi Sasaoka1, Akihiro Hamanaka1, Hideki Shimada1, Kikuo Matsui1, Nay Zar Lin2 and Budi Sulistianto3
1. Department of Earth Resources Engineering, Kyushu University, Fukuoka 819-0395, Japan
2. Mine Planning Section, Ministry of Mines, Nay Pyi Taw, Myanmar
3. Department of Mining Engineering, Institute Technology Bandung, Bandung 40116, Indonesia
Abstract: Most of coal is produced from open-cut mines in Southeast Asian countries. However, the conditions of their surface mines are worsening each year: the stripping ratio is increasing, approaching economic ratio and the regulation of environmental protection. To meet the demand for coal, underground mines have to be developed in the near future. Under these circumstances, the development of new coal mines from open-cut highwalls are being planned in Southeast Asian Countries. Moreover, some of the Southeast Asian mines have thick coal seams. However, if the conventional mining systems and designs introduced in US, Australia and European Countries are applied, several geotechnical issues can be expected due to the mines’ weak geological conditions. From these backgrounds, this paper proposed a punch multi-slice mining system with stowing for thick coal seam under weak geological conditions and discussed its applicability and suitable design by means of numerical analysis. Key words: Punch multi-slice longwall mining, thick coal seam, weak strata, stability of highwall.
1. Introduction
The surface mining method is generally considered
to be more advantageous than the underground method,
especially in recovery, grade control, production
capacity, economics, flexibility, safety and working
environments. Therefore, the surface mining method is
common in major coal producing countries [1, 2]. Most
of coal is produced from open-cut mines in Southeast
Asian countries. However, the conditions of their
surface mines are worsening each year: the stripping
ratio is increasing, approaching economic ratio, the
regulation of environmental protection, and poor
infrastructure for coal from inland mining areas [3]. To
meet the demand for coal in Southeast Asian Countries
and the rest of the world, underground mines have to be
developed in the near future. Under these
circumstances, the development of new coal mines
from open-cut highwalls are being planned in several
Corresponding author: Takashi Sasaoka, assistant
professor, research fields: ground control in mining, blasting and mining system. E-mail: [email protected].
mines in Southeast Asian Countries including Thailand,
Indonesia, etc. Moreover, some of the Southeast Asian
mines have thick coal seams [4, 5]. However, if the
conventional mining systems and designs introduced in
US, Australia and European Countries are applied,
several geotechnical issues can be expected due to the
mines’ weak geological conditions [6]. From these
backgrounds, a punch multi-slice top coal caving
method with stowing was proposed as a mining system
for thick coal seam and weak geological conditions.
This paper discusses the applicability of punch
multi-slice top coal caving method to the mines in
South-East Asian Countries and its suitable design and
measures by means of numerical analysis.
2. Punch Mining System
One of the major mining system for final highwall of
surface coal mine is highwall mining system.
Conventional highwall mining systems extract coal
with an auger machine or continuous miner. However,
less coal recovery is a problem in these systems,
D DAVID PUBLISHING
Punc
because man
maintain the
mined length
of the sy
introduction
alternative.
concept [7].
Archveyor s
shown in Fi
leave a lot o
Rapid ac
practiced in
mining oper
conventiona
blocks deve
highwall [8
longwall min
Beltana is
which achie
producing 6
considered
operation in
system of m
requires no t
ventilation sy
Fig. 1 Punch
ch Multi-Slice
ny coal pilla
e highwall/mi
h is limited b
stems. Con
n of undergrou
The punch m
. The first pu
system was pr
ig. 1. Howev
f coal as pilla
ccess punch
Australia. Au
ration comme
al longwall e
eloped direc
]. Fig. 2 sho
ning system.
s a highwall
ved its first f
6 Mt (ROM
to be the m
n Australia
mining are: h
transport, con
ystems or mai
h mining syste
Longwall Mi
ars have to be
ined openings
by the inhere
nsidering the
und mining s
mining syste
unch mining
roposed and t
ver, this minin
ars.
longwall m
ustralia’s firs
enced in the
equipment to
ctly from an
ows the sche
access longw
full year of op
M: Run-of-M
most cost-ef
[9]. The adv
high producti
nveyor drifts
in headings as
em.
ning System
e left in orde
s stability and
ent characteri
ese issues,
systems is als
em is not a
system using
tried in the U
ng system ha
mining has b
st punch long
late 1990s u
mine coal f
n open-cut f
ematic of pu
wall punch m
peration in 2
Mine) coal. I
fficient long
vantages in
ivity; the sys
, shafts, com
s in conventio
for Thick Co
er to
d the
stics
the
o an
new
g an
US as
as to
been
gwall
using
from
final
unch
mine,
004,
It is
gwall
this
stem
mplex
onal
Fig.
und
prov
com
requ
reta
thro
its
pro
high
incr
How
the
slop
con
3. MSto
W
min
less
leng
may
extr
divi
mul
arou
stab
bee
issu
con
oal Seam und
. 2 Punch lon
derground m
vides cheap
mmencement
uired proper
ain and maint
oughout the l
advantages
ductivity, an
hwall mining
reasingly imp
wever, the de
mining pane
pe and the m
ndition have n
Multi-slice owing
While conside
nes, an applic
s potential du
gths. It is see
y be conside
raction of the
iding the sea
lti-slicing me
und the mini
bility of slop
en made clea
ues such as hi
nventional thi
er Weak Geo
ngwall mining s
mining metho
per, faster,
of longwall
mine plann
tain the open
life of underg
of high p
nd competit
g system, this
plemented in
esign and the
el/face and its
mining opera
not been made
Top Coal
ering the situ
cability of hig
ue to their l
en that punch
ered for the
e thick coal s
ms into mult
ethod is appl
ing panel/fac
pe and the m
arly yet. In
ighwall instab
ck seam mini
ological Cond
system.
ods, hence
simpler
l mining. Ho
ning and min
cut surface i
ground operat
production c
tively lower
s system is ex
n Australian
e ground beh
s impact of th
ation in wea
e clearly.
Caving M
uation of Sou
ghwall mining
limitations in
highwall min
mines. How
eam, it must
ti-slicing. Ho
lied, the grou
e and their im
mining operati
case, the gro
bility can be
ing method is
ditions 29
this benefit
access and
owever, it is
ne design to
infrastructure
tions. Due to
capacity and
r cost than
xpected to be
coal mines.
havior around
he stability of
ak geological
ethod with
utheast Asian
g systems are
n penetration
ning systems
wever, as for
be mined by
wever, when
und behavior
mpact of the
ion have not
ound control
expected if a
s introduced.
9
t
d
s
o
e
o
d
n
e
.
d
f
l
h
n
e
n
s
r
y
n
r
e
t
l
a
Punch Multi-Slice Longwall Mining System for Thick Coal Seam under Weak Geological Conditions 30
A new multi-slice top coal caving mining method
based on the concept of punch longwall and top coal
caving methods is proposed. The concept of the new
multi-slice top coal caving mining method is illustrated
in Fig. 3. First, the coal seam is developed along the
mine roof with conventional cut. Then stowing
material is injected into gob area in order to have better
mine roof condition. After the stowing material is
consolidated, the next slice is begun by leaving
appropriate thickness of coal parting beneath the first
slice and it is recovered by applying a top coal caving
method in the second slice. After the second slice is
extracted using a top coal caving method, stowing
material is injected into the gob area in the second slice.
Next slices are also extracted by applying a top coal
caving method and stowing is conducted after each
slice is mined out and mining and stowing are repeated
until the whole coal seam is mined out as the same
manner. By applying this method, the number of slices
required for the extra-thick coal seam and the burden
for excessive costs for development of gate roads
required for extra-thick seam can also be overcome
compared with an application of the conventional
multi-slice mining method. It will be also useful to
reduce the impact on ground/slope due to extraction of
extra-thick coal seams and can also be useful to
minimize the amount of waste rocks managed on
surface.
4. Numerical Analysis
When an underground mine is developed from an
open-cut highwall, the design of panels and safety
pillars such as boundary pillar and inter-panel pillar in
the transition area have great influenced on the
highwall stability as well as the amount of resource
recovery around the final highwall. If the pillar and
panel sizes are inadequate, it is possible for slope
instability or sliding of slope due to insufficient support
to the highwall. On the other hand, if the pillars are
over-sized, the amount of resource recovery around the
highwall will be decreased. Therefore, careful planning
and designing of panels and pillars around the final
highwall. In order to make the criteria for the
applicability and the design of a punch multi-slice top
coal caving method around the final highwall, the
response of ground/slope under weak geological
conditions and different operational conditions are
investigated by means of FLAC3DVer.5.
4.1 Numerical Model
In surface mining, as the bench design is usually
based on economic reach of the mining equipment used
in the mine, characteristics of deposit, production
strategy and geological and geotechnical condition of
the mine. In this study, therefore, the following
assumptions are made based on the typical bench
design for open-cut coal mining practices [10]. The
height of the each single bench is designed as 20 m, and
the bench slope angle is 65 degrees. The width of the
bench is set as 36 m whereas the safety berm is 6 m
wide in the models. The angle of overall slope is 37
degrees. The geometry, meshes and group of zones and
dimension of the 200 m deep pit model employed in the
analyses are illustrated in Fig. 4. In this study,
mechanical properties of rock obtained from one
Indonesian surface coal mine are used in this study as
represented in Table 1.
The design of panels and pillars in transition area
from surface to underground mine for thick seam
under weak and strong geological condition are
discussed. Due to the advantages of highest efficiency
Fig. 3 Concept of multi-slice top coal caving with stowing method (longwall mining system).
Punch Multi-Slice Longwall Mining System for Thick Coal Seam under Weak Geological Conditions 31
Fig. 4 Numerical model (Pit depth = 200 m).
Table 1 Mechanical properties of rock mass and coal used in this analyses.
Rock mass Coal
Density (kg/m3) 1,950 1,430 UCS (Uniaxial compressive strength) (MPa)
11.36 5.0
Bulk modulus (MPa) 6.67 × 103 3.79 × 102
Shear modulus (MPa) 4.0 × 104 1.95 × 102
Tensile strength (MPa) 0.1 0.1
Cohesion (MPa) 1.75 0.5
Friction angle (deg.) 25 22.3
and productivity among the methods available for thick
seam, a longwall top coal caving method is primarily
considered in this study. In longwall top caving
practices, although the method allows for more than 10
m thick seam in one pass and up to 80-90% recovery of
additional coal, coal recovery is less than expected in
practical situation due to coal seam and strata
conditions, about 70-80% of coal can be recovered in
practical situation. Operational issues also limit top
coal recovery and can often account for a greater
percentage of the reduce recovery than geological
conditions alone. In this study, therefore, two slice
system is considered for the 10 m thick coal seam,
where the first slice is cut conventionally and next slice
is extracted by top coal caving method. Basically, the
height of mining for conventional cut for the first slice
was considered as 3 m and next slice is set as 7 m,
where 3 m thick of coal is cut along the floor of coal
seam and 4 m thick of coal is recovered. The scheme of
multi-slice top coal caving mining method performed
in the analyses is illustrated in Figs. 5a-5b.
The panels and pillars were initially designed based
on the results of preliminary analysis that the
conventional longwall mining system is applied for the
extraction of 3 m thickness of coal under weak
geological condition. The panel of 100 m width and the
inter-panel pillar of 60 m width are initially taken and
the ground behavior is investigated. The boundary
pillar of 100 m width for 200 m and 300 m deep pit and
that of 150 m width for 400 m deep is initially taken.
Layout of the initial mining panel is shown in Fig. 6.
4.2 Results and Discussions
4.2.1 Punch Multi-slice Longwall Mining System
without Stowing System
Figs. 7a-7b and 8a-8b show failure states and contours
of induced displacement after extracting second slice in
Punc32
Fig. 5 Schem(without stow
Fig. 6 Layou
200 m and 3
case of 200
slope is ob
boundary pil
can be said
maintained u
other hand, i
the vertical d
in both ca
boundary pil
ch Multi-Slice
(a) The Firs
(b) The secome of multi-sl
wing).
ut of panel mo
300 m deep p
0 m pit depth
bserved 6.5-7
llar is also in
that the stab
under these p
in the cases of
displacement
ses, large f
llars. In this s
Longwall Mi
st slice extractio
nd slice extractlicing perform
delled in the a
pit slopes, res
h, as the disp
7 cm in ma
stable condit
bility of over
anel and pilla
f 300 m pit de
at the slopes
failures are
situation, if th
ning System
on
tion med in the ana
nalyses.
spectively. In
placement at
aximum and
tion. Therefor
rall slope can
ar designs. On
epth, even tho
is about 6.5-7
occurred at
he condition a
for Thick Co
alyses
n the
t the
the
re, it
n be
n the
ough
7 cm
the
at the
toe
who
Con
incr
larg
F
con
m d
con
slop
of 4
and
slop
mai
mod
pan
T
m t
100
and
of d
disp
Fig.extrpillawidt
oal Seam und
of the slope
ole slope inst
nsequently, t
reased into 2
ger than 300 m
Figs. 9a-9b an
ntours of displ
deep pits. In
ndition of bou
pe can be mai
400 m deep p
d the large di
pe, the stabi
intained. Th
deling with
nel width is di
The width of
to 100 m and
0 m to 60 m.
d Figs. 12a-12
displacement
placement at
. 7 Failure stracting 2nd slar width = 100th = 100 m).
er Weak Geo
is worsen an
tability and/or
the widths
00 m in the c
m.
nd 10a-10b sh
lacement in th
the case of 3
undary pillar
intained. On t
pit, as the bou
isplacement
ility of over
herefore, the
larger inter-
iscussed in th
inter-panel p
d the width o
Fig. 11 illus
2b shows the f
in this condi
the slope is
(a) Failure
(b) Displactates and conlices in 200 m0 m, inter-pane
ological Cond
nd the pillar
r slide would
of boundary
cases that the
how the failu
he cases of 30
300 m deep p
can be impro
the other han
undary pillar
can be recog
all slope sti
e ground b
-panel pillar
he case of 400
pillar is increa
f panel is dec
strates the lay
failure states
itions. It is fo
decreased fro
e state
cement tours of displ
m deep pit sloel pillar width
ditions
is failed, the
d be occurred.
y pillars are
e pit depth is
ure states and
00 m and 400
pit depth, the
oved and the
nd, in the case
is still failed
gnized in the
ll cannot be
behavior by
and smaller
0 m pit depth.
ased from 60
creased from
yout of panel
and contours
ound that the
om 4.5-5 cm
lacement afterope (boundary
= 60 m, panel
e
.
e
s
d
0
e
e
e
d
e
e
y
r
.
0
m
l
s
e
m
r y l
Punc
Fig. 8 Failuextracting 2npillar width =width = 100 m
Fig. 9 Failuextracting 2npillar width =width = 100 m
into 3.5-4 c
boundary pi
ch Multi-Slice
(a) F
(b) Diure states and nd slices in 30= 100 m, inter-m).
(a) F
(b) Diure states and nd slices in 30= 200 m, inter-m).
cm. In addit
illar is impro
Longwall Mi
ailure state
isplacement contours of d
00 m deep pi-panel pillar w
ailure state
isplacement contours of d
00 m deep pi-panel pillar w
tion, the failu
oved and its
ning System
displacement it slope (boun
width = 60 m, p
displacement it slope (boun
width = 60 m, p
ure condition
stability can
for Thick Co
after dary
panel
after dary
panel
n of
n be
mai
ord
400
4
A
that
also
prop
larg
Fig.extrpillawidt
Fig.deep60 m
oal Seam und
intained. How
er to maintai
0 m deep pit.
4.2.2 Applicat
According to
t punch mul
o be applica
per panel an
ge amount of
. 10 Failure sracting 2nd slar width = 200th = 100 m).
. 11 Layout op pit slope (boum, inter-panel
er Weak Geo
wever, a plent
in the stabilit
tion of Stowi
the results di
lti-slice top
able around
nd pillar des
coal have to
(a) Failure
(b) Displacstates and conlices in 400 m0 m, inter-pane
of panel modelundary pillar wpillar width =
ological Cond
ty of coal hav
ty of slope in
ing System
iscussed abov
coal caving
the final hig
sign. Howeve
be left as the
e state
cement ntours of displm deep pit sloel pillar width
led in the analywidth = 200 m,100 m).
ditions 33
ve to be left in
n the case of
ve, it is found
method can
ghwall by a
er, since the
pillars, coal
lacement afterope (boundary
= 60 m, panel
yses for 400 m, panel width =
3
n
f
d
n
a
e
r y l
m =
Punc34
Fig. 12 Failextracting 2npillar width =width = 60 m)
Fig. 13 Sche(with stowing
ch Multi-Slice
(a) F
(b) Diure states and
nd slices in 40= 200 m, inter-p).
(a)The Firs
(b) The secoeme of multi-sg).
Longwall Mi
ailure state
isplacement d contours of d00 m deep pipanel pillar wi
st slice extractio
nd slice extractslicing perform
ning System
displacement it slope (bounidth = 100 m, p
on
tion med in the ana
for Thick Co
after dary
panel
alyses
reco
of
stow
T
with
gob
slic
app
top
seco
adv
Fig
In
des
bou
pit,
is ta
T
use
rati
0.5
resp
A
in th
con
with
foun
to
dec
sub
effe
or s
F
disp
dee
and
3-3
from
60
syst
but
oal Seam und
overy will be
multi-slice t
wing method
The first slice
h 3 m mining
b immediately
e, next slic
plying longwa
coal 4 m th
ond slice. S
vance as the s
s. 13a-13b).
n the analyse
igned as 100
undary pillar w
whereas 200
aken as the sl
The mechanic
d in the analy
o 0.23, Youn
MPa, cohesi
pectively.
At first, the p
he 200 m dee
ntours of disp
h multi-slice
nd that failur
be small dr
reased from
sidence at th
ect of subside
sliding of slop
Figs. 15a-15b
placement af
ep pit. No fai
d the displace
.5 cm after s
m 60 m to 10
m to 100 m
tem can not o
also increase
er Weak Geo
e decreased. T
top coal cav
is investigate
is also extrac
g height and s
y. After extrac
ce extraction
all top coal ca
hickness and
Stowing is f
same manner
s, the panel a
m and 60 m a
width is taken
0 m for 400 m
lurry stowing
cal properties
yses are: densi
ng’s modulus
on 0.5 MPa,
performance o
ep pit. Fig. 14
placement aft
e top coal ca
re zone aroun
ramatically a
6.5-7 cm in
he slope is ve
ence at the sl
pe will not be
b show failur
fter extracting
lures are fou
ement at the
stowing even
00 m and the
m. Hence, th
only improve
e coal recover
ological Cond
Therefore, th
ving in conju
ed and discus
cted with con
towing is inje
cting and stow
ns were co
aving method
cutting heigh
followed afte
r as in the fi
and pillar size
as shown in F
n as 100 m fo
m deep pit. A f
g material.
s of this stow
ity 1,000 kg/m
617 MPa, ten
friction angle
of stowing is
4 shows failu
er extracting
aving with st
nd the mine r
and the disp
nto 2.5-3 cm
ery small, th
ope such as f
e expected.
re states and
g second slic
und in the bou
slope is sma
n the panel s
panel size in
e application
e the stability
ry.
ditions
he application
unction with
ssed.
nventional cut
ected into the
wing the first
onducted by
d with leaving
ht of 3 m in
er each face
irst slice (see
es are initially
Fig. 6 and the
r 200 m deep
flyash cement
wing material
m3, Poisson’s
nsile strength
e 26 degrees,
s investigated
ure states and
second slice
towing. It is
roof becomes
placement is
m. Since the
e subsequent
failure, crack
d contours of
ce in 400 m
undary pillar
all and about
ize increases
ncreases from
n of stowing
of slope and
n
h
t
e
t
y
g
n
e
e
y
e
p
t
l
s
h
,
d
d
e
s
s
s
e
t
k
f
m
r
t
s
m
g
d
Punc
Fig. 14 Failextracting 2npillar width =width = 100 m
Fig. 15 Failextracting 2npillar width =width = 100 m
From the
the stowing
ch Multi-Slice
(a) F
(b) Dilure states andnd slices in 20= 100 m, inter-m).
(a) F
(b) Diure states and
nd slices in 40= 200 m, inter-m).
above discus
is effective m
Longwall Mi
ailure state
isplacement d contours of 00 m deep pi-panel pillar w
ailure state
isplacement d contours of d00 m deep pi-panel pillar w
sions, it can b
method for pr
ning System
displacement it slope (boun
width = 60 m, p
displacement it slope (boun
width = 60 m, p
be concluded
revent the fai
for Thick Co
after dary
panel
after dary
panel
d that
ilure
of p
com
bou
be i
pit.
100
inte
eve
has
can
dee
pill
How
pan
whe
extr
be h
5. C
T
cav
dep
app
pill
pap
cav
seam
coa
is f
pill
at t
imp
H
of p
wea
con
stow
sequ
Re
[1]
oal Seam und
pillars and co
mparison with
undary pillar w
in stable and
If stowing is
0 m is enou
er-panel pillar
en though the
to be left, the
n be increased
ep pit, the rat
ar is approxim
wever, if stow
nel to inter-p
en stowing i
raction length
higher.
Conclusion
The applicab
ving method
pths under
propriate des
ars and panel
per. Moreover
ving in conjun
m is proposed
al recovery an
found that sto
ar failure and
the slope. As
proved.
However, in o
punch multi-
ak geological
nducted includ
wing materi
uence, etc.
ferences
Oya, J., ShimPertiwi, R., a
er Weak Geo
ontrol the disp
h previous res
width 200 m
to have safe
s applied, the
ugh although
r sizes are the
e boundary p
e panel width
d. For examp
io of the wid
mately 0.60 :
wing is applie
anel pillar is
is applied. I
h can be set,
ns
bility of pun
for thick co
weak geol
ign of boun
ls are investig
r, the applicat
nction with st
d and discuss
nd improveme
owing is quit
d to control th
s the results,
order to devel
-slice top co
l condition, th
ding the cont
ial, sizes o
mada, H., Sasaokand Fajrin, A. M
ological Cond
placement at
sults without
need to be le
e operation in
e boundary pi
h the size o
e same. In 40
illar of 200 m
to inter-pane
ple, in the ca
dth of panel t
: 1 when with
ed, the ratio of
s approximat
In addition,
the productiv
nch multi-sli
oal seams in
logical con
ndary pillars
gated and disc
tion of multi-
towing for we
sed in order to
ent of stabilit
te effective to
he stability an
the coal reco
lop the appro
oal caving m
he more stud
trol of top coa
of panel/pil
ka, T., Ichinose,M. 2009. “Fund
ditions 35
the slope. In
stowing, the
eft in order to
n 300 m deep
illar width of
of panel and
0 m deep pit,
m width still
el pillar ration
ase of 400 m
to inter-panel
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Punch Multi-Slice Longwall Mining System for Thick Coal Seam under Weak Geological Conditions 36
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