longwall experience in SCCL india introduction of longwall technology in India, comparision of longwall performance with China and measures for improvement, success in implementation of longwall technology

1. 3rd Asian Mining Congress
22 - 25 January 2010, Kolkata, India
The Mining, Geological and Metallurgical Institute of India (MGMI)
A RETROSPECTIVE ASSESSSMENT OF LONGWALL MINING WITH A FOCUS
ON SUCCESSFUL MECHANISED UNDERGROUND MINING TECHNOLOGY
V. N. S. Prasad1
, M. U. Siva Sankar2
, Prof. S. K. Mukhopadhyay3
and Prof. Debasis Deb4
ABSTRACT
The global demand for energy continues to grow at a rapid pace, driven by both developed and developing
countries. Coal has major role to play in meeting this demand and it must be ensured that it remains
available and competitive with other energy sources.
Coal occupies the centre-stage in the energy economy of both China and India; coal has a share of more
than 70% of the primary consumption of energy in the current mix of commercial energy. Under ground
mined coal accounts for more than 50% of total global hard coal production and in China, 95% of hard
coal production comes from underground mining.
Surface mined coal alone can not meet the huge growth in demand that is forecast for India. Some
import of coal will be necessary, the amount dependent on how successful the Indian underground
coal industry is in stepping up to the challenge.
In order to keep pace with the growing Indian economy at the rate of 8 to 9%, the coal industry requires
narrowing down the supply-demand gap at a competitive price. Mechanised Longwall mining is a
sustainable option to achieve higher production and productivity.
This paper looks at the retrospective assessment of production performance and short comings for
under rated performance of Longwalls in India, particularly of Singareni Collieries Company Ltd
(SCCL), in comparison with other countries especially China. The authors also expressed thrust areas
to be addressed for successful implementation of Indian Longwall mining to meet the global standards.
Keywords : Longwall; SCCL
1
M.Tech Student IIT Kharagpur, Under Manager, SCCL, shyam.pragadaiitkgp@gmail.com
2
M.Tech, Under Manager, SCCL, Kothagudem – 507101, A.P. India e-mail: uss_7@yahoo.com
3
Professor, Department of Mining Engineering, IIT Kharagpur – 721302,subirmin@gmail.com.
4
Associate Professor, Department of Mining Engineering, IIT Kharagpur – 721302, deb@mining.iitkgp.ernet.in
INTRODUCTION
India has vast natural resources with the world’s fifth
largest coal reserves. The depth wise coal reserves of
India as on January 2005 are as given in Table 1. At
present rates of growth it will soon be the world’s third
largest coal producer. It is worth noting that India is also
presently the world’s fifth largest importer of coal, and
unless major steps are taken the amount of imported coal
will need to grow drastically1
. Total annual hard coal
production in India is about 450 Million tonnes (Mt), out
of which nearly 83% is from opencast mines. At present
percentage of contribution to the underground mining

2. 160 A Retrospective Assesssment of Longwall Mining With A Focus on Successful Mechanised Underground Mining Technology
production by mechanized Longwall mining in India is less
than 4%. The expected demand for coal by 2011-12 is
about 707 Mt; where as coal production would be around
550 Mt, leaving a gap of about 157 Mt, which needs to be
met by imports or private mining2
.
The production from underground coal sector has
remained practically stagnant for the last three decades.
The technological up gradation in underground mining
methods in India during this period was very marginal
due to inadequate investment and lack of any serious
approach for its development. To cope up with the fast
growing demand of coal, entire attention was given to the
comparatively easily available option of opencast mining
which proved to be more productive and economical. With
economic liberalization and consequent reduction of
import duty on coal, the coal mining industry in India is
facing a new challenge and India can no longer rely on
opencast mining alone. For bulk production of coal at
faster rate from underground coal mining particularly at
depth the proven technology world over is Longwall.
Table 1 : Coal reserves in India
Depth(m) Proved Indicated Inferred Total
(in Bt) (%)
0-300 71 66.5 15 152.5 61.5
300-600 6.5 39.5 17 63 25
0-600(Jharia) 14 0.5 - 14.5 6
600-1200 1.5 10.5 6 18 7.5
0-1200 93 117 38 248 100
(Source: GSI Report, Jan’2005) (Bt: Billion tonnes)
GENESIS AND EVOLUTION OF
LONGWALL TECHNOLOGY
The seventeenth century innovation of ‘Longwall’
system in Shropshire in England has made giant strides
over the past three centuries to emerge as the
predominant bulk production system in global coal
industry today with a share of nearly 70% of aggregate
production and is recognized as the safest, the most
productive and cost effective method as well as for
extraction of coal seams by underground mining3
.
In India first mechanized powered roof support (PRS)
face, the new-age Longwall, was launched in August 1978
at Moonidih Colliery4
. In India, 33 Longwall packages have
been deployed to date in Coal India Ltd (CIL) and
Singareni Collieries Company Ltd (SCCL) in collaboration
with U.K, Russia, China, France mostly funded by GOI.
During these three and half decades of Longwall
experience powered roof supports of capacity varying
from 280 to 800 tonnes have been used at many mines
in India under varying geo-mining conditions5
. Majority of
the Longwall faces in India have been worked under
relatively shallow cover (< 200m) and significant problems
on the cavability of the roof have been experienced6
. The
overall performance has fallen short of expectations
despite the above experiences. Only a few of the faces
could yield planned production level for initial three to
four years of support life. A number of reasons have been
attributed to the lower performance of such Longwall
operations6 - 9
. Severe strata control problems at face
resulting in damage of supports and increased downtime
of equipments substantiated by improper matching of the
sub systems are understood to be two prime reasons for
such poor performance. An unsuitable locale selection
incompatible with the selected supports due to improper
pre-investigation studies while planning worsened the
situation in few cases.
In China, first fully mechanized face using chock
type supports was introduced at Meiyukou colliery in 1963.

3. V. N. S. Prasad, M. U. Siva Sankar, Prof. S. K. Mukhopadhyay and Prof. Debasis Deb 161
Since then introduction of fully mechanized faces in coal
fields of China have been a classic case of large-scale
diffusion, using both imported and indigenously developed
equipment. The Chinese coal industry made a near-
quantum jump with massive implementation of Longwall
technology, especially the new generation of Longwall
equipment10
.
Through sustained R&D efforts over the fast three
decades, China has made a major break through in
Longwall technology for thick seams using sub level
caving (Soutirage) has emerged as the world leader in
this area with record production levels and manufacture
of equipment packages for sub-level caving6, 11, 12
.
Coal production in China soared to two Bt per annum
from one billion, and in excess of 95% of coal is being
produced by underground mining technology, in which
Longwall technology is contributing major share. By
careful selection of the geological conditions and
equipment, several Longwalls are now producing at
around 9 Mt per annum and have achieved one Mt per
month1
.
The coal measure formations of India and Australia
are similar as both belong to the lower Gondwana.
Australian coal mining industry have achieved a great
success in mechanized coal production, while in India,
the strata control and rock mechanics problems created
havoc for the mechanization in the beginning itself. A
review of support capacity of two countries shows that
support capacity of Australian Longwall faces is almost
double that of our Indian Longwall mining faces13
. Annual
average of around 3 Mt with a commensurate OMS has
been reported from Australia with 24 Longwall faces giving
an annual production of 72 Mt14
.
The national average production from a Longwall
face in the USA was less than a million tonne in mid 80s;
recent statistics indicate that the country produced around
270 Mt of coal from 52 Longwall faces, which means an
annual average of more than 5 Mt from a face with an
average OMS exceeding 10014
.
EXPERIENCE OF LONGWALL MINING AT SCCL
Longwall mining was introduced in SCCL for the first
time in GDK-7 Incline in the year 1983 and after successful
completion of two faces equipment was shifted to GDK-9
Incline in 1986, where the Longwall face collapsed due
to inadequacy of the support capacity. Two more Longwall
packages were introduced in VK-7 and JK-5 Inclines in
1985 and 1990 respectively. There after three more
Longwall packages were introduced in GDK-11A during
1992-93. Capacity of powered roof supports in the above
mines is of 4x360 tonnes (t) and 4x450t. Later higher
rated supports one set in each GDK-10A, GDK-9 Inclines
and two sets in PVK 5 Incline were introduced. The
support capacity in the above mines is of 4x800t and
4x760t with a support density of 110 to 120 t/m2
respectively.
So far, 10 Longwall packages have been introduced
in seven mines with collaboration of foreign countries like
UK, and China, details of which are as given in Table 2.
Presently two Longwall units are working in GDK-10A
and GDK-9 Inclines, while the units in other mines were
surveyed off /not in working condition.
The faces at SCCL in GDK-7 and VK-7 Inclines did
well in comparison with other faces, which experienced
caving difficulties. In early nineties with the introduction
of higher rated supports the performance of Longwalls
improved to some extent. Barring the catastrophic failure
of Longwall faces of Churcha, Kottadih and Dhemomain
of Coal India Ltd., faces at GDK-10A, PVK, JK-5 and VK-
7 gave consistently good results. The production
performance of Longwall faces from SCCL and CIL is as
shown in Fig.1.
Fig.1: Longwall production in CIL and SCCL

4. 162 A Retrospective Assesssment of Longwall Mining With A Focus on Successful Mechanised Underground Mining Technology
So far, nearly 68 Longwall panels of varying face
lengths 60m to 150m have been worked at a depth range
of 45 to 400m. The production performance of five
Longwall units viz; JK-5(1 unit), VK-7(1 unit), GDK-10A
(1 unit) and PVK (2 units) is as shown in Fig.2. History of
Longwall mining in SCCL reveals that performance of
almost all the Longwall units was better for first two to
three years when compared to later. The average
production at GDK-10A and PVK is about 4 Lakh tonnes
(Lt) and 3 Lt per annum respectively, while other Longwall
units were below 3 Lt per annum. In JK-5 Incline
production above 3 Lt per annum obtained after successful
working under caved Longwall goaves. This reflects that
numerous high productive Longwall faces that have been
installed did not perform to the level as envisaged. It can
also be observed that high capacity support faces
performed better than other faces in respect of production
and strata control point of view. These Longwall units,
apart from working creditably, have provided an
opportunity for SCCL engineers to study the equipment
and support parameters vis-à-vis the geo-mining
conditions prevailing in the SCCL mines. Presently Sccl
is planning high capacity longwalls at Adriyala shaft
blocks, Jallaram shaft blocks of Ramagundem region and
Kakatiya longwall projects of Bhupalapalli area. The
Kakatiya longwall project is undergoing a process of TPO(
Technology Provider cum Operator)for longwall mining.
Table 2 : List of Powered roof supports (PRS) deployed at Longwall faces, SCCL, India.
Mine Initial / Date of Capacity Rated
Shifted Commission Make of PRS TPD
GDK.7 Incline Initial 02-09-1983 Gullick Dobson, UK 4 x 325t to
4 x 360t
GDK-11A Incline
Unit-I Initial 01-04-1991 Gullick Dobson, UK 4 x 430t
Unit-II Initial 10-10-1991 MECO, UK 4 x 450t
Unit-III Initial 16-12-1992 Gullick Dobson, UK 4 x 450t
VK-7 Incline
Unit-I Initial 13-06-1985 Gullick Dobson, UK 4 x 360t
Unit-II From GDK-11A 13-07-1994 MECO, UK 4 x 450t 1600
PVK
Unit-I Initial 21-08-1995 CME, China 4 x 760t 2200
Unit-II Initial 22-06-1996 CME, China 4 x 760t 2200
JK-5 Incline Initial 06-06-1990 Gullick Dobson, UK 4 x 450t 2000
GDK-9 Incline
Unit-I From GDK-7 31-01-1986 Gullick Dobson, UK 4 x 360t
Unit-II Initial 05-02-1996 MECO, UK 4 x 750t to4 x 800t 1900
Unit-III From PVK Unit -I 21-08-1995 CME, China 4 x 760t 2200
GDK-10A Incline Initial 18-10-1994 MECO, UK 4 x 800t 2200
TPD : Tonnes per day
Fig. 2 : Production performance of different Longwall units, SCCL

5. V. N. S. Prasad, M. U. Siva Sankar, Prof. S. K. Mukhopadhyay and Prof. Debasis Deb 163
The availability and utilization of the Longwall
equipment at different mines of SCCL is depicted in Fig.3.
It was obvious that, the average availability of all the units
is 65 to 75% of scheduled shift hours (SSH), where as
their utilization is only 17.5% to 22.5% of SSH. The
average utilization of the equipment of all the above units
is only 28 to 38% of machine available hours. The
utilization and availability of Longwall equipment is far
below the world Longwall equipment standards. From the
analysis, the down time percentage was on the higher side in
which major causes were breakdowns in outbye transport,
shearer, AFC, Powered supports, stage loader/gate belt
conveyor, electrical, frequent movement and shifting of
equipmentatfaceandotherreasons.Thebreakdownanalysis
of powered support Longwall (PSLW) face, CME make, at
PVK from 1996 to 2000 is given in below Table 3.
Table 3 : Breakdown analysis of PSLW face at PVK, SCCL.
Year Shearer AFC PRS Power BSL Crusher Gate Electrical others Total BD Worked Hours lost
pack belt hours hours due to
other
reasons
96-97 370.25 121.25 5.10 2.00 29.10 1.30 11.55 34.60 10.45 586.20 1742.20 972.00
97-98 358.25 161.00 31.10 15.20 207.25 0.25 27.00 20.00 39.00 861.30 2147.35 531.00
98-99 127.30 224.00 15.40 2.50 62.25 - 47.15 2.35 127.45 612.35 1260.50 777.00
99-2K 569.15 240.00 88.20 10.45 160.00 3.40 120.45 27.00 523.00 756.55 2042.25 1402.00
Fig. 3 : Comparison of Percentage of Availability and Utilization of
different Longwall units, SCCL

6. 164 A Retrospective Assesssment of Longwall Mining With A Focus on Successful Mechanised Underground Mining Technology
FACTORS RESPONSIBLE FOR LOW
UTILIZATION AND HIGH DOWNTIME OF
LONGWALLS
Minor geological disturbances like faults, erratic
appearance of sandstone modules affected the Longwall
operations to a large extent. Prominent cavities, roof
breakage or roof collapse due to dynamic loading over
supports caused bad roof/face conditions under coal or
sandstone as immediate roof.
Bad face/roof conditions also cause breakdown in
face machineries, like damages in shearers while
negotiating various geological disturbances, overloading
of shearer drive, damage of legs of powered supporters,
chain snapping of AFC, etc. Frequent shifting of
equipment from one panel to another panel, i.e., salvaging
and installation of face equipment also led to low utilization
and high downtime.
However, general views of the problems faced by
various types of face machineries in SCCL are described
as under.
Shearer
Some of the common and major breakdowns in the
shearers observed are haulage breakage, main and
auxiliary hydraulic system malfunctioning, bearing of the
first and second motion shafts in the gear head gear boxes
getting damaged, failure of the oil seals in the trunion
shaft of the ranging arms and in the motor, failure of gear
pumps for lubricating oil for ranging arms, gears and
bearings, scouring in the ranging arm cylinder liner, failure
of pick holders, failure of the hinge pins connecting the
ranging arms with under frame sprocket tooth. The
downtime due to breakdowns increased from 3% to 6%
with indigenous spares in comparison with original
equipment (OEM)15
.
AFC (Armored Face Conveyor) & BSL (Beam
Stage Loader)
Indigenization of all parts of AFC resulted in frequent
break downs. OEM supplied gave life of 3.0 Mt. Where
as Indigenous AFC gave a life of 0.7 to 0.8 Mt only. In
comparison with OEM the breakdowns increased from
3.5 % to 8 %15
.
The major problems faced are failure of rigid section
fastening at two drive ends, failure of blind shaft bearings
and oil seal journals at oil seals, jamming of chain in the
bottom race of the line pan, snapping of chain in the top
and bottom of the AFC, failure of AFC flight bars, failure
of chain connectors, breakage of AFC pans, failure of
fluid couplings of the drives and excessive chain
elongation
As BSL is almost similar to AFC, only problems
unique to stage loader are frequent breakdown of the tail
end idle sprocket and its bearings, elongation of the TOB
chain, sometimes due to creep of AFC and weak fastening
of the lump breaker over stage loader, fast wearing of the
convex and concave pans of the bridge section.
Powered Supports and Power pack
Some of the common and major breakdowns in the
powered supports and power pack are frequent troubles
with the control valves, frequent failure of hydraulic hoses
and connectors, leakage of leg seals, premature operation
of the bleed valves, damage of reverse thrust rams, failure
of relay bar piston fixing brackets due to less collar
thickness, pumping of hydraulic fluid at a pressure below
the required level, frequent failure of the unloader valve,
improper functioning of the accumulators, excessive
leakage in the system owing to the use of locally made
components as no original spares are normally available
causing excessive pressure drop. Improper maintenance
of emulsion resulted in rusting and failure of hydraulic
valves and increased bypasses in the system.
However, high breakdown times of face machineries
can be summarized as non-availability of imported spares,
lack of proper quality of indigenous spares, absence of
planned maintenance and reporting, apart from
unexpected geological features and disturbances.
Reasons for Slow Progress of Longwalls
Main reasons for under rated performance of Indian
Longwalls particularly at SCCL include technical as well
as financial constraints. They are;
• Long walls were introduced mostly in the blocks left
over by working Bord and pillar method. Clean and
extensive blocks have not been identified. Even the

7. V. N. S. Prasad, M. U. Siva Sankar, Prof. S. K. Mukhopadhyay and Prof. Debasis Deb 165
smaller blocks, which were identified, were of inferior
grade coal.
• Long wall had to co-exist with the conventional
mining in most of the mines, which caused
management problems.
• There were some deficiencies in the imported spares
management and the supplies were not reaching in
time.
• Development could not keep pace with the extraction
of Long wall panels; slow progress in the formation
of Long wall panels affected the performance.
• Large expansion in opencast mining in the past two
decades provided cheaper and safe method for bulk
coal production and as a result long wall had to take
back seat.
• Coal companies were sensitive to the failures of a
few long wall faces and were not prepared to risk
huge investments.
• Infrastructure was not suitable to support the higher
production.
• Geological and geotechnical conditions were more
difficult than expected.
• Problems in the maintenance of the equipment.
By and large contributory factors that have been
identified for the not so successful operation of Longwall
systems in India converge on the following;
• Inadequacy of geological and geotechnical
assessment of the Longwall locales.
• Flawed equipment selection with inadequate rating
of supports, shearer and coal clearance systems.
• Management failure in planning, operation, provision
of service back-up and spares availability.
• Absence of a viable manufacturing capacity for
Longwall equipment.
• Equipment sourced from many suppliers with no
accountability.
• Bureaucracy of end user regarding availability of
spares supply.
• Lack of suitably trained management.
SAGA OF SUCCESSFUL LONGWALL
MINING OF CHINA
In the recent decade, remarkable progress has been
made in realization of high output and high efficiency in
coal industry, especially in state-owned key coal mines
in China. The reasons are:
China from the very beginning as a policy adopted
wholesome approach for large scale Longwall
mechanization in their UG mines. Their approach was
very methodical and it took into account their own social
and economic conditions. Instead of instantaneously
jumping into hi-tech mechanization only in some isolated
mines, they introduced Longwall technology stage by
stage with incremental technology development.
The economy in China has been developed rapidly
under the new economic system; the continuously
increased demand for coal promoted coal mines to
increase production. Coal mines have become
independent enterprises, assuming sole responsibility for
profits and losses. State is no way responsible for
financing. On the other hand, the state-owned coal mines
have a relatively unwieldy organization, with higher value
of fixed assets, over staff members and workers.
The Chinese government has worked out policies
for reforming the existing underground mines and
construction of new mines, preferential terms can be given
to any project which can meet with the principle of high
output and high efficiency. This has promoted the
development of high output and high efficiency in coal
mines.
The number of working Longwall faces in state-
owned key coal mines is reduced from 2313 in 1984 to
1499in1994,andthetotaloutputofarelevantfaceisincreased
from 320 Mt per annum to 370 Mt per annum, which depicts a
great progress in Longwall mining in China 16
.
The development of science and technology in
recent years has delivered equipment and technology with

8. 166 A Retrospective Assesssment of Longwall Mining With A Focus on Successful Mechanised Underground Mining Technology
more varieties and better performances, which has made
it possible for coal mines to realize a high-output and high-
efficiency.
Based on the reasons mentioned above, various
measures have been taken in coal mines, especially in
state-owned key mines in China, to realize a high output
and high efficiency. Manufacturers concerned for coal
mines and department of scientific research have been
very active to take part in this work, delivered a lot of new
technology and new equipment to promote the
development of high output and high efficiency in coal
mines, and a remarkable success has already been
achieved.
For achieving high production and productivity lot
of work have been done in the field such as such as:
increasing the length of a working face, selecting
equipment used on a working face with a large power
and high performance, improving the mechanization of
auxiliary procedures, (e.g. Auxiliary haulage system and
supports on ends of a face, etc), popularizing the
communication control system used underground and
strengthening control system used underground,
improving the reliability of equipment and strengthening
the technical training to staff members and workers of
the mine9
.
Based on the statistics, during 15 years, i.e., till the
middle of 1995, a total of 820 kinds of equipment of ten
categories with different performances, models and
specifications used in coal mines had been developed
with a tendency to satisfy the demands of coal mines of a
high output and high efficiency. The capacity of the
equipment, such as shearer, scraper conveyor, and
emulsion pump has been increased substantially to
negotiate unforeseen circumstances too.
AREAS TO BE ADDRESSED
Based on the past experience of Longwall mining in
India in comparison with China, the following thrust areas
are also to be addressed for successful implementation
of Longwall mining in India to meet the global standards:
• Indigenous development of qualitative Longwall
equipment is to be encouraged for introduction of
Longwall faces at several mines.
• The manufacturing companies of India such as
MAMC and Jessop which have been planned for
infrastructure development of Longwalls have to be
reconstructed. Private sector participation in
infrastructure development must be encouraged.
• More number of Longwall blocks to be identified to
encourage manufacturing of equipment in India.
• Approval process from Government of India, for
implementation of new projects should be fast to
bring projects on stream at the earliest.
• Rigid quality control and performance testing should
be done for the spares manufactured indigenously.
• Use of high capacity supports of up to 1280 tonnes
providing a load density of 135 to 140 t/m2
are to be
used under Indian geo-mining conditions.
• Even with the use of high capacity supports may
not give satisfactory roof condition during impending
roof weighting. In such cases artificial means of
induction of caving by hydraulic fracturing or other
means is to be considered.
• Orientation of Longwalls correctly with respect to
horizontal stress is critical for strata control during
development and Longwall extraction.
• Effective monitoring of strata and support behavior
and meticulous maintenance of equipment are the
keys for the success of Longwalls.
• Interactive evaluations of mine plans with integrated
geological data have to be established for Longwall
workings. Automation should be implemented for
planning and monitoring Longwall workings.
• Collieries should develop a highly competent
maintenance group with suitably defined
responsibilities and a good team leadership. The
members should be properly trained by experts both
at site as well as in the manufacturer’s works.
CONCLUSIONS
Mechanised Longwall mining has emerged as the
most successful production technology in the global coal
mining scenario. The effective application of enabling

9. V. N. S. Prasad, M. U. Siva Sankar, Prof. S. K. Mukhopadhyay and Prof. Debasis Deb 167
technologies of hydraulics and electronics coupled with
the use of heavy duty supports and equipment during
last three decades have helped Longwall technology to
scale new heights of production and productivity.
Introduction of fully mechanized Longwall technology
was made in China and India almost simultaneously. No
comparison between these two developing nations can
be made in terms of the success parameters. The basic
factor is the difference in attitude and determination to go
ahead with this globally accepted technology.
Many factors contribute to preventing most Longwall
installations from producing anything but a fraction of their
theoretical capacity. Longwall should be promoted as a
technology mission, thrust areas are to be given due
consideration to succeed Longwall technology as in other
developing country like China. A high level expert group
is to be constituted at national level to promote, coordinate
and discuss different aspects related to Longwall
technology. Training with regard to the problems
anticipated in the countries in which such problems are
already overcome so as to prepare guidelines for future
Longwalls. Concrete efforts are required by the mining
inspectors, policy makers, coal companies, research
organizations and equipment manufacturers to translate
the ideas into concrete action and reap the benefits of
Longwall technology in the years to come.
ACKNOWLEDGEMENTS
The views expressed in the paper are those of the
authors only and should not be attributed to organization
they belong.
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