“New Technology and Challenges for Underground Coal Mining”
1.
Coal Production from Underground Mines
India has emerged as the third largest coal producer in the world after China and USA. With global
total coal production of 6.2Bt, the share of China, USA & India is about 51%, 15% and 9% (8.7%),
respectively. About 76% of global hard coal production is from these 3 countries. Other major contributors
with coal production of more than 100Mt are Australia (6%), South Africa & Russia (about 4% each)
Indonesia (3%) and Kazakhstan (around 2%). Most of global coal production is consumed locally, i.e. within
domestic market. Only about 15% of this coal production is destined for international coal market. (source :
World Coal-International Energy Agency, 2011).
Coal mining is carried by
Surface or ‘opencast’ mining;
Underground or ‘deep’ mining
Around 60% of this world coal production is from underground mines while 40% from surface mines.
However, the proportion of coal production from underground coal mines varies widely in various countries.
China accounts for about 95% of its production from underground mines, while corresponding figures for
USA and India stands at about 33% & 10%, respectively. In South Africa, production underground mines is
about 50% while in Australia, it is 20%.
While the choice of mining method is largely determined by the geology of the coal deposit, but the
statistics above illustrates that leading coal producers have significant contribution from underground mines.
The question is what plagues or afflicts Indian Scenario?
2.
Coal Production from CIL Mines
Coal production from CIL mines (surface as well as underground) has been over a period of 19742011 is shown in Fig. 1. The growth of coal production from mines of CIL is linked to growth of coal
production from surface mines. Further, it shows a gradual but consistent decline of coal production from
underground mines in CIL since nationalization of coal mines in 1973-75. It reflects focus, dominance and
reliance on surface mining in meeting coal/energy demand of the country.
Fig. - 1 : Trend Coal Production from CIL mines (1974-75 to 2011-12)
500.00
70.00
450.00
60.00
Coal Production
400.00
50.00
350.00
300.00
40.00
250.00
30.00
200.00
150.00
20.00
100.00
10.00
50.00
Year
3.
TOTAL
OC Mines
20
10
-11
20
04
-05
20
06
-07
20
08
-09
19
98
-99
20
00
-01
20
02
-03
19
92
-93
19
94
-95
19
96
-97
19
86
-87
19
88
-89
19
90
-91
0.00
19
80
-81
19
82
-83
19
84
-85
19
74
-75
19
76
-77
19
78
-79
0.00
UG Mines
Underground Mining Technology scenario in CIL
There are two main methods of underground mining: room-and-pillar and longwall mining.
Bord / Room & Pillar Mining,
In room-and-pillar mining, coal deposits are mined by cutting/driving a network of 'rooms/bords' into
the coal seam and leaving behind 'pillars' of coal to support the roof of the mine. These pillars can be up to
40% of the total coal in the seam - although this coal can sometimes be recovered at a later stage.
Longwall Mining
Longwall mining involves the full extraction of coal from a section of the seam, or 'face' using
mechanical shearers. A longwall face requires careful planning to ensure favourable geology exists
throughout the section before development work begins. The coal 'face' can vary in length from 100-350m.
Self-advancing, hydraulically-powered supports temporarily hold up the roof while coal is extracted. When
coal has been extracted from the area, the roof is allowed to collapse. Over 75% of the coal in the deposit
can be extracted from panels of coal that can extend 3km through the coal seam.
The mining methods with associated technologies in vogue in UG mines of CIL are as under :
(i)
(ii)
(iii)
(iv)
(v)
(vi)
Conventional Bord & Pillar (B&P) system with manual loading of coal onto tubs.
Semi-mechanised B&P system with loading by Side Discharge Loaders (SDLs) or Load Haul
Dumpers (LHDs) or mechanised drilling by Universal Drilling Machines (UDMs).
Mechanised Bord & Pillar/ Room & Pillar system with Continuous Miners (CMs).
Mechanised Powered Support Longwall (PSLW) mining system.
Methods with hydraulic stowing technology in conjunction with sand or alternative filling.
Special methods (i.e. site specific methods), like Blasting Gallery (BG) method, Cable bolting
method, wide-stall method, steep mining methods, etc.
Technology-wise break-up of underground coal production has been shown in Fig. 2.
Fig.-2 : Technology-wise Underground Coal Production in CIL (2011-12)
0.32, 1%
1.79, 5%
0.18, 0%
3.54, 9%
0.15, 0%
0.1, 0%
32.31, 85%
B&P Intermediate technology
Roadheader (LW Dev.)
PSLW
Highwall Mining
Conventional B&P (& Others)
Continuous Miner
Shortwall (in B&P)
Some ‘Special Methods’ with specific technology application in one or more mining operations or
specific seam conditions, which have found application in CIL mines are :
(a)
(b)
(c)
(d)
(e)
(f)
(g)
(h)
(i)
Shortwall Mining with reduced face length
High pressure water jet mining (Hydro-mining) for winning of coal
Integrated sub-level caving for thick seams
Short longwall method for extraction of standing pillars
Jankowice Method (for Steeply dipping seams)
Sub-level caving (retreat) (for Steeply dipping seams)
Scraper assisted chamber method (for moderately dipping seams)
Highwall (HW) mining (actively under consideration in one CIL block)
Underground Coal Gasification (UCG) for coal/ lignite deposits which are conventionally not
workable (actively under consideration in three CIL blocks).
Alternative technologies for extraction of resources by underground mining in geologically disturbed
areas and deep seated coal resources will depend primarily on the intensity of geological disturbances and
depth of occurrence. The prevailing technologies will also find their applicability in most cases with or without
modifications.
4.
Application of New Mining Technologies
Worldwide, technological advancements have made coal mining today more productive than it has
ever been. To keep up with technology and to extract coal as efficiently as possible modern mining
personnel must be highly skilled and well-trained in the use of complex, state-of-the-art instruments and
equipment. Significant technological development has taken place both the systems of underground mining,
i.e.
(i)
Continuous Miner Technology (Bord/Room & Pillar);
(ii)
Powered Support Longwall Technology
In both the systems, the technology has developed manifold in terms of
size & capacity of equipment,
customization : variety of equipment to cater to different needs,
sophistication and automation
ever growing actual production and productivity levels
Features of enhanced safety and hazard management system with the technology, etc.
These technologies are competing to achieve to still higher level of production and productivity. In
line with the world-wide development in underground mining, continued efforts are being made in CIL to
bring home the world-wide technological developments in underground mining.
The main focus in CIL has been for application of Continuous Miner technology as the system is
comparable to the existing underground mining system. First modern Continuous Miner was introduction in
SECL in the year 2001 in association with JOY Machinery. Its success has paved way for its wide application
in underground in CIL. The present status of projects with application of Continuous Miner technology is
briefly enumerated as under :

In operation
 Jhanjra, ECL – Joy Continuous Miner
 Sarpi, SECL – Joy Continuous Miner
 Tandsi, WCL - Joy Continuous Miner
 Kumberkhani, WCL- Sandvik LCCM
 NCPH, Chirimiri, SECL- Joy Continuous Miner
 Sheetaldhara-Kurja, SECL- Bucyrus Continuous Miner
 Pinoura, SECL- Bucyrus Continuous Miner
 Rani Atari- Sandvik LCCM

Proposed
 Jhanjhra, ECL- MOU has been signed
 Tilaboni, ECL - Under tendering
 Kottadih, ECL- Under tendering
 Block-II, BCCL- LOA has been issued
 Lohapatti, BCCL- Bids under scrutiny
 Saoner-I,WCL- Under re-tendering
 Churcha, SECL- LOA has been issued for two sets
Power Support Longwall (PSLW) technology has been in operation in India since 1978 at several
mines in BCCL, ECL, WCL, & SECL. The technology has been rated as mixed bag with limited success. The
collapse/damage of powered supports in SECL (Churcha West) & ECL (Kottadih), in the year 1990 and
1997, respectively, has set in a sense of apprehension about its profound applicability and success in coal
mines of CIL. Further, Chinese PSLW sets were procured for 3 mines in SECL, which operated with a fair
degree of success in early years. Later, production dropped significantly due to poor equipment maintenance
& other unrelated problems.
However, since then, significant technological development has taken place in powered support
longwall technology with respect to equipment specifications as well as methodology to mitigate other related
problems, which werefaced during its implementation in early years. Again, initiatives have been taken for its
application in CIL mines. The status of longwall projects in CIL mines is as under :
5.

In operation
 Jhanjra, ECL
 Rajendra, SECL

Proposed
 Jhanjhra, ECL- Agreement has been signed
 Moonidih seam XVI, BCCL- Bids under scrutiny
 Moonidih seam XV, BCCL- LOA has been issued
 Muraidih, BCCL- Agreement has been signed with L1
 Kapuria, BCCL- LOA has been issued
Challenges of Underground Mining in CIL mines
The reasons for decline in coal production from underground mines may be attributed to :
-
UG operations at shallow depth has given way to quarry or surface mining
Closure of number of underground mines due to exhaustion of coal reserve or losses
Reduction or stagnation in production due to attrition of workforce or natural retirement
Reduced production and productivity due to old, long & arduous mines
Low technological, R&D or skill-development input in underground mines
A number of underground mining operations or processes involve human effort or drudgery
Low productivity of manpower
Geological disposition and exploration of coal seams has also affected indirectly
Besides reasons enumerated above presents, underground mining presents in CIL present several
other constraints and challenges, which have been briefly elaborated as under :
(a)
Size of the Mine / block
Selection of comparatively small size of a mine or block with limited reserve available. It restricts
overall dimensions of a mine, thereby further constraining economic dimensions of mineable panels or coal
sub-block, thus limits production capacity and life of the mine. The mine/block area of most of the
underground mines in CIL is generally less than 5sq. km. The extractable reserve in these mines rarely
exceeds 15-20Mt. Hence, it presents a challenge to plan and operate a large mine block consisting of
extractable reserve in excess of 20Mt so that an underground mine with a capacity of 1.0Mt or more can be
planned or operated.
(b)
Geological Complexities and Exploration
Indian coal deposits present varieties of attributes to coal deposit – multi-seam (upto 30 coal
horizons), seams thickness (upto 35m), proximity of seams (parting <3m), gradient (from flat to upto 45deg.),
quality of coal, low rank or maturity of coal, etc. The deposit has been further complicated presence of
structural disturbances, like multiple faults, occurrence of intrusive bodies, burning of coal, etc. Such
disturbances further constrained economic dimension of working panels or coal sub-sub-blocks for mining.
The role of exploration is to facilitate complete exploration for delineation of all structures and other deposit
attributes.
(c)
Mine Approach & Development : high gestation period
Drivage of mine entries and further mine development & construction have been pathetically
sluggish. Typically, it takes about 6-12years to develop an underground mine. Of this, drivage of main mine
entries, inclines or shafts, takes about 50-60% of total gestation period due to slow rate of drivages through
stone/rock or coal. Rates of drivages in underground are as low as 20-30m per month in stone/rock
(single/twin roads) and about 30-60m per month in coal (two or more roadways). It is no way near the rates
achieved elsewhere in the world. It presents a challenge to match the international benchmark.
(d)
Technological Development & Implementation
Technological Innovation in underground mining did not exist in our country. The problems in
technology or operations are being managed through in-house supportive efforts (Indian ‘Jugaad’).
Dependence on overseas technological development and its adoption has been the way of up-gradation of
technique and technology in underground mines. Regarding its implementation, most of the projects have
missed its deadline and have been delayed by varied period of time, generally 3-10 years.
(e)
Absorption of Technology – Skill development
Measures need to be taken to indigenise the technological import by suitable in-house manpower
and skill development and promote such efforts through appropriate policies at corporate and operation
level. It a challenge to maintain, upgrade and utilize trained persons at its appropriate and needed locations.
(f)
Strata Management & Control
The most important component of success of underground mining technology is strata management
and control during mining operation. It is required to develop appropriate understanding of its various
aspects and trained, manpower for success of technology. Further, an appropriate system & organization are
required to record, monitor and manage such system in underground mines.
Mechanization – Productivity Enhancement Needs
The current status of technology and productivity reflects urgent need for mechanization of
underground mines. Still many of the underground mines, mining operations & processes are carried out
manually without any automation or understanding to minimize human effort and enhance productivity. This
aspect needs to absorbed with respect to every mining activity to improve overall productivity of the mines.
(g)
Equipment Supply & Maintenance – Vendor Development
The technological upgradation in mines is taking place without any focus on indigenous development
of either equipment or its spare parts sourcing. Procurement from overseas is costly as well as time
consuming (longer gestation). It is necessary to insist on local vendor development to cut down future
procurement or maintenance costs indigenous vendor development. This would help in cutting down cost of
mining and technology implementation.
(h)
Long & Arduous Travel / tramming routes – Man-riding / Material Supply
Travelling of the work persons to their work places and timely material supply at required places are
very pertinent for success of technology and effective utilization of work force efforts. A large number of
mines are still operating without any man-riding system or any effecting system for timely conveying of
materials to required work places. It is a challenge to select an appropriate to select and provide a mine with
such effective system.
(c)
(i)
Mining hazards
Underground mining is fraught with hazards, like fire, inundation, subsidence, explosion, roof fall, air
blast, etc. Large area in BCCL has been on fire. Several mines are connected through underground. Roof
does not collapse easily during extraction of coal posing threat of air plast or overriding. The threat
perception of such hazards holds enormous impact on production operations and other related processes in
an underground mine, Active mitigation and management of such hazards is a challenge to Coal Mining
Industry. It requires quality technical & training input to persons working in underground mines.
Technological Gap – Focus on Specific R&D
Understanding of the Indian mining conditions required to be understood in right earnest with regard
to technological requirements and prevailing geo-mining conditions. Precious little effort has been made to
further the cause underground mining problems. Specific R&D input is required from research interface
developing a better understanding of the Indian geo-mining conditions.
(j)
Besides above, there are several other problems specific to a mine or coalfield, at macro and micro
level, which require proper analysis and identification and seek a justifiable solution in Indian context. The
problem identification is a bigger problem in underground mines, as a difficulty in any operation or process is
considered as inherent and part of the operation or process rather than identifying it as a suitable problem
and then try to seek appropriate solution.
6.
Renewed Focus on Underground Mining
With the increase in coal demand and growing awareness towards sustainable development, the
coal industry has drawn a consensus over the need for increased production from underground coalmines.
From the current share of about 10 per cent, the industry aims to reach a total coal production of 30 per cent
from underground mines by 2030.
With just 10 per cent share of coal production from UG mines in India, there is a need for a quantum
jump in production and productivity from such mines as there are more opportunities in productivity
improvement and cost benefits in underground mining. This is more relevant considering the likely
exhaustion of shallow depth coal reserves and hurdles in surface land acquisition in future.
This fact was highlighted by erstwhile CMD, CIL at a recent conference in New Delhi. It was stated
that there had been a persistent decline in underground coal production over the years with more emphasis
on open cast mining. The decline was arrested in the last fiscal year and a nominal growth was registered in
all CIL subsidiary companies, except Bharat Coking Coal Ltd and Central Coalfields Ltd. The improvement is
a result of the combined impact of a number of actions taken to increase production from the existing mines
and also through the introduction of new technology in some cases.
At the conference it was agreed by the coal industry stakeholders that the large increase in coal
production envisaged now could be achieved only by focusing on technology and productivity in both
underground and opencast mines. This called for increasing the level of mechanisation, introduction of stateof-the-art machines, and ensuring their optimal utilisation as per international standards.
Speaking at the conference, erstwhile CMD, SCCL (presently CMD, CIL) said that the challenges in
underground mechanisation for the increased production and productivity with safety could be met if the
projection planning was guided by a realistic approach considering all important components like suitable,
productive and safe methods, increased machine utilisation, inventory management, reduction in cost due to
accidents through improved health and safety standards, improved work culture, and discipline through
efficient management. Training of workforce for underground mechanisation to enable increased production
would be an essential input. The application of research and development for scientific exploitation is also
another input in meeting the challenges in increased mechanisation for higher productivity with profitability.
Policy guidelines may also be drawn for replicating the Chinese model of developing suitable technologies
for higher percentage of extraction under our geo-mining conditions.
At present, multiple clearances are required from the government for commencement of new
opencast projects like site clearances for mining lease, forestry clearance and environment clearance. The
process would also be much simpler for UG mining as the forest land and environment clearances in respect
of underground mines are relatively uncomplicated.
As part of Coal India's attempts to reverse the trend of mining from opencast mines, the public sector
company has awarded a longwall mining contract to Zhenghou of China for its coking mine at Moonidih in
BCCL. Apart from this CIL has already taken action to reopen 18 abandoned underground mines having
cumulative reserves of 1,647 million tonnes through a joint venture. CIL has also identified seven new highcapacity underground mines with vast reserves of coal to be operated contractually.
The largest coal producing countries like China, USA and Australia are producing coal from underground
mining at 95 per cent, 33 per cent and 20 per cent, respectively.
7.
Alternative Underground Coal Mining Technologies
CIL has revived focus development of alternative technique for underground extraction of energy
from through research and development initiatives. Project have been undertaken for :
a.
b.
Underground Coal Gasification
Coal bed Methane