Longwall Top coal Caving is going to be the significant method of thick seam mining at higher depths in India. Limiting depth of present opencast mining is about 300m. In this paper concepts of LTCC were discussed for Indian application.

1. 1
Int. Conf. on Deep Excavation, Energy Resources and Production DEEP16
24-26 November 2016, IIT Kharagpur, India
A STUDY INTO THE FEASIBILITY OF APPLICATION OF LONGWALL
TOP COAL CAVING (LTCC) METHOD IN INDIAN GEO-MINING
CONDITIONS
Nasina Balasubrahmanyam a
* and Dr. G.Budi b
a
Deputy Director, Directorate General of Mines safety, Dhanbad, India
b
Assistant Professor, Department of Mining Engineering, ISM, Dhanbad, India
*nasinabalasubrahmanyam@gmail.com
ABSTRACT
Nearly 40% of the proven Indian coal reserves are thick and their extractions by underground mining
methods are ever posing technological challenge for mining engineers. Despite severalconcerted efforts,
so far no clear cut solutions nor any breakthrough in extraction techniques under the widely varied Indian
geo-mining condition have emerged. The conventional underground method of multi stage pillar extraction
was the only proven technology so far for thick coal seam extraction in the country. The percentage of
extraction in this method is well known to be less than 30%. Over the past three decades numerous research
projects were carried out on operation of thick seam mining in various challenging geo-mining conditions.
Bord and Pillar method (or its modification with deployment of Continuous Miner or Blasting Gallery
method), High reach Single Pass Longwall, Multi-slicing Longwall Method, Hydraulic Mining and
Longwall Top Coal Caving method are mainly used to extract thick seams with their own limitations.
The LTCC method is considered the most appropriate method for efficient extraction of thick seams in
which lower section of the coal is extracted while caving coal from the upper section for the most seams
with suitable caving behaviour and flow characteristics. This method is used extensively in China with
more than 100 faces producing over 200 MT in conditions ranging from soft (<10 MPa UCS) to hard (>50
MPa UCS) coals. Compared to High reach Single Pass Longwall mining, the LTCC method offers a lower
face height, which results in smaller and less expensive equipment, and better face conditions.
In this paper a brief review of Indian experiences of thick seam underground mining methods is made. A
brief study is made on extraction thickness vis–a-vis total seam thickness of longwall panels extracted in
India. Applicable conditions for successful operation by LTCC method are detailed. A bird's–eye view
study is made on geological and physico-mechanical properties of coaland immediate roof of selectedthick
seams is made for application of LTCC method in Indian which shown that several Indian coal seams are
suitable for adoption of the method.
In the current Indian economic scenario, expensive longwall mining is being practiced in Jhanjra Project
Colliery and Adriyala Longwall Project in collaboration of global pioneers and it is the right time to work
on techno-economic feasibility of LTCC for thick seam underground. In this paper LTCC method is
projected as appropriate technically feasible thick seam mining method for Indian geo-mining conditions
KEYWORDS: Indian Geo-Mining Conditions, Thick seam mining, Hardness of coals, flow
characteristics,Caving behaviour, LTCC.
1. INTRODUCTION
Most of the about 300 underground coal mines in India operate with Bord and pillar mining method
using drill and blast cyclic operations. Output perman shift from underground mines has beenstagnant
at from 0.45 to 2.7 tonnes per man year (Bucyrus, 2010) since decades and a cause of concern. Output
per Man Shift (OMS) in coal is more than 20 in other developed countries. Introduction of continuous
miner technology is considered as an appropriate technology to boost productivity from already
developed coal mining reserves,which are not suitable for longwall technology. Over 89% of the coal

2. 2
production comes from open pit mining within 300m depth and has its own limitations due to depth
and environment pollution issues, whereas huge reserves of coal is locked up in underground as
standing pillars, in thick seamsandin depths beyond 300m. Too much opencastmining, due to its lower
costs and reduced losses, has stagnated underground mining. In India, seams more than 4.8m thick are
considered as thick seams. There is an urgent need for development and implementation of bulk
production technologies for deep seated thick deposits in the depth range of 300m – 600m. In India,
Jharia coalfields about 500MT of coalin seamsmore than 4.8m in thickness are locked in pillars. About
9000MT virgin coal in seamsmore than 4.8m in thickness is available considering the combined seams.
In Raniganj coalfields also 6 seams of Raniganj formation are up to 24m thick and some seams of
Barakar formationare 45-48m thick like Ramnagar or salanpur seams. In Karanpura coalfield of CCL
some of the seams are quite thick like Argada(22m), Dakra(19m), Bukabuka(18m), Karakata(18m),
Sirka(15m) seams.In eastBokaro feild seamslike KaroTop (45m), KaroBottom (15m), Bermo (17m),
Kargali (31m) Top are thick seams. In Singareni coalfields, king seam, Queen seam Top, 3 seam,
salarjung seam are thick. In Mahanadi coalfields, seams are quite thick like Jagannath seam (50m),
Rampur seam (42m), Lajkura seam (17-34m) and Belpahar seam (25-28m). Singrauli coalfield has the
thickest deposit, Jhingurddah top seam (154m) and other seams like Tura, Jingurdah Bottom and
Purewa seams ranging from 12 to 15m in thickness. In WCL some of the seams are thick like
Chandrapura (28m) and seam 1 of Chirimiri area (13m).
The coal seams thickness-wise and their percentage of share in India1
are 0.5-1.5m(15%), 1.5-
3.5(15%),3.5-5.0(12%),5.0-10.0(20%),10-20m(19%) and above 20m (19%).Though there is lack of
precise statistical information of thick coal reserves in India, M.M. sen and A.K Sural(1986) estimate
is as follows:
Table 1: thickness wise coal reserves (Depth Range: 0-600m) in million tones with seam thickness
5m and above. The figures relate to gross reserves (total of proved, indicated and inferred)
Seam thickness
Type
5-10m 10-20m 20-30m 30m total
Quarriable 4751 7262 3989 8567 24659
Non-quarriable 15873 12216 4505 874 33468
Grand Total 20624 19478 8494 9441 58127
Over the past two decades numerous research projects were carried out to make it evident that thick
seam mining operations are a challenge in various geo-mining conditions. Sarkar and Chatterjee
(1992) researched the potential application and related issues of the High reach Single Pass Longwall
technique in the extraction of thick coal seams. A literature review of international thick seam mining
practice undertaken by Ghose (1984) and Cai (1997) identified that at different times, the following
methods were mainly used to extract thick seams:
i. Room and Pillar method (or modification of this method like Blasting Gallery),
ii. High reach Single Pass Longwall,
iii. Multi-slicing Longwall Method,
iv. Hydraulic Mining and
v. Longwall Top Coal Caving method.
1.3 The Longwall Top Coal Caving (LTCC) method is basically a combination of the traditional longwall
method and the caving of top coal during the process of mining operations. The original name of the
LTCC method was the “Soutirage" method (Nath, 1979; Proust, 1979).
In the LTCC method, the panel is created by a set of headings (gate roads), the same as in the
conventional longwall panel (usually retreating longwall method), but the roadways are driven in the
lower section of the coal seam. The shields with caving function, coupled with other equipment are
then installed to create the longwall face. During mining operations, the lower section of the coal seam
is extracted by the conventional longwall method. The remaining upper section of the coal seam will

3. 3
be drawn through the window of the shields aftercaving behind the supports in parallel with the process
of longwall operations. The following Figure illustrates the principle of the LTCC method.
Figure 1: Conceptual Model of LTCC System (after Xu, 2001)
The LTCC method was first introduced in China in 1982, and then developed rapidly over the next two
decades. The first successfulLTCC face was achieved at face No.8603 of Yangquan coal mine with an
output of 140,000 tonnes per month in 1990, and a recoveryratio at the working face of over 80% (Jian,
Xianrui and Yaodong, 1999). Currently, production from the LTCC method accounts for nearly 10%
of China's underground production (Tien, 1998). By improving technology, mining equipment and
operation management, significant development and an impressive performance has been achieved in
China with the application of this mining method. After5 yearsof applying the LTCCmethod to extract
the 5.6 - 6.5m thick coal seams with a gradient of 3 - 80 in Dontan mine, Yazhou coalfield, the
maximum monthly output increasedfrom 151,786 tonnes in 1994 to 501,068 tonnes in 1999, and annual
productivity increased from 2,821 tonnes to 14,306 tonnes per man. The maximum annual production
of a face has reached up to 5.1 million tonnes per year (Yingdi, Tianzhi, Guishan and Weiqing, 1999).
Now the LTCC method is being studied for deployment in more difficult geo-mining conditions.
Presently, the LTCC method has been experimented in China to extract thick coal seams, dipping up
to 450
. Output from one such mining face was 97,100 tonnes per month, productivity was 45 tonnes per
man-shift, and the recovery rate was 82.27% (Xie, Gao and Shangguan, 2005).
The LTCC method is advantageous compared to the multi-slice longwall method since it is more
economical, easierto be applied in thick seamsand requires less labour. Compared to High reachSingle
Pass Longwalling, the LTCC method offers a lower face height, which results in smaller and less
expensive equipment, and better face conditions. The following are the reasons for switching over to
LTCC from multi-slice longwall method:
i. Less number of gateroads:One top coal caving face needs only two gateroads but in the multi-slice
mining, the number of gateroads will be at least double.
ii. Higher Production: Because coalis not only extracted by the shearer loader, but also produced by
simultaneous direct caving of top coal behind the powered supports.
iii. Less energy consumption: In the LTCC method, the top coal is forced to be cave by ground
pressure. Therefore, this method uses less electricity than the multi-slice mining method.
iv. Less consumption of supplies/materials: Because of the lower number of gate roads required, this
method will need less supplies/materials.
2. BRIEF RETROSPECTION OF INDIAN LONGWALL MINING
2.2 India too followed the world trend in 1975 in adopting mechanized longwall mining. ‘Project Black
Diamond’ envisaged introduction of 130 Power Support Longwall (PSLW) faces by the year 2000.
Initially, the first fully mechanized self- advancing PSLW face was introduced in Moonidih mine in
Jharia Coalfield in 1978. Subsequently, in between 1978 to 1985, more mines were planned with
PSLW in the eighties, namely, East Katras ( BCCL), Seetalpur, Dhemo-Main, Jhanjra, Khottadih (
ECL), Patharkhera (WCL) and Churcha (SECL). First long wall in SCCL was introduced at GDK 7
incline in 1983 followed by a few other mines in that Company. In the process about 30 PSLW sets
had been imported from different sources in different countries like UK, Poland, Russia, Germany,

4. 4
France and China. Most of the Longwall faces were far from the desired level of production and
productivity on sustainable basis. In addition, large scale introduction of longwall technology received
severe setbacksdue to its successive failures at Churcha (SECL)and Khottadih (ECL) mines. Churcha
Longwall face failed due to dynamic loading. In Jhanjra the shallow depth Longwall working faces
ran into acute sparesproblem. Kottadih face failed aftersuccessfulcompletion of two Longwall panels
due to dynamic loading and underrated capacity of supports. GDK.11A failed due to underrated
capacity of supports. Longwall technology was introduced in seven mines of SCCL. GDK-10A, JK-5
and VK-7 Incline gave consistently good results, and the other four mines GDK-7, GDK-9, GDK-
11A and PVK suffered mainly due to non-availability of sufficient geological data. At present,
longwall mining accounts for a meager production of about 4% of the total underground production.
In India, Extended height Single Pass Longwall system was introduced at Jhanjra Project Colliery of
M/s ECL in R-VI Seam with maximum extraction height 5.5m. Extraction was commenced on
18.08.2016 and it produced 2,89,740 tonnes of coal with a face retreat of 426.50m as on 30.11.2016.
No significant strata control issues were faced.
2.3 It is noteworthy that like India, China introduced longwall mining in the late seventies and early
eighties .Within a span of 20 years it has not only emerged as the world leader in coal production, but
has established itself as the largest user of longwall technology in underground mines and has created
for itself an international market for export of the technology, expertise and equipment. It has
constructed a number of new highly productive and efficient mines with different capacities based on
seam/geological conditions by identifying suitable coal blocks in advance. It has improved its
metallurgy for indigenous manufacture of powered supports with higher support resistance, more
powerful shearer,AFC and belt conveyor and started achieving 6-10mt coal from a longwall face per
annum.
3 A BRIEF REVIEW OF THICK SEAM MINING EXPERIENCES
3.1 Room and Pillar method: In almost all Indian coalfields thick seams abound. Such reserves have been
and are being developed on Bord and pillar system. In the past, coal seams in India, with a thickness
of up to 8.5m, were extracted in one lift, but this had to be abandoned due to the difficulty of roof
support (Singh, 1992). Multi-lift room and pillar mining in ascending order, with hydraulic sand
stowing, prevailed in the extraction of No.14 seam with a thickness of 8.4m in the Tisco collieries of
Jharia coalfield, India (Trehan, 1992). Multi-lift room and pillar mining with hydraulic sand stowing
was also practiced to extract the King seam, Singareni Collieries Company Limited (Vyas and
Benjamin, 1992). According to Vyas and Benjamin (1992), this method yielded extraction of up to 60
- 65% of the coal seam. Continuous Miners introduced in Anjan Hill Mine, Chirimiri (SECL)
commissioned in May 2002, Tandsi Mine (WCL-June 2003), VK No.7 Incline (SCCL-Aug, 2006),
Jhanjra (ECL-June, 2007) and GDK 11A Incline (SCCL-Dec,2008). CIL and SCCL, apart from are
planning to introduce CM in several other mines. These methods are quite suitable for complicated
geo-mining conditions where longwall mining is not feasible.
3.2 High reach Single Pass Longwall method: With the development of technology, the height of the
shearer and the supports of the High reach Single Pass Longwall (HSPL) method have already
gradually increased to 5m and above. Some of the advantages of the HSPL method are:
 A simple operation and ventilation system, high production and productivity, and high coal
recovery rate.
 The low rate of gate road development per tonne of coal production.
Besides the obviously advantageous HSPL method, some of the following challenges are there to face
when applied to the Indian coalfield:
 Due to the appearance of many faults, the coal seams are separated into small coal blocks.

5. 5
 The complications in transportation of the heavy roof supports and other equipment in the mine:
Roadway developments for underground coalmines in India were mostly driven by the drilling and
blasting method, supported by steelarches with a small cross sectional area ranging from 6 - 10m2
.
 Gate roads in longwall panels in many underground coal mines are generally driven at a height of
2 - 3.5m. With a cutting height on the longwall face of up to 5 or 6m, there will be a sudden step
between the gate roads and the longwall face. The free face of the step that exceeds the height of
the gateroads could cause spall on the longwall face,resulting in unsafe conditions for equipment
and personnel working at the face or the roadways.
 Spalling, especially of high longwall faces,may cause many difficulties in mining operations, such
as overloading the armoured face conveyor (AFC) or causing danger to the personnel working
along the longwall face.
 To guarantee stability, the centre of gravity of the support must be maintained as low as possible.
As a result, the width of the supports should be wider. Due to the greater height of extraction, the
transport of longwall equipment would consume more time and labour than the traditional
longwalling.
 The stability issues of the supports due to the Inclination of the coal seam: Extraction heights being
the same, the higher the seam dip, the more instable the supports, as illustrated in Figure below.
Thus, for extracting inclined seams, HSPL is certainly not suitable in terms of maintaining the
stability of the supports.
Figure 2: The effect of extraction height on stability of support
As mentioned, extended height Single Pass longwall retreating with caving method at Jhanjra Project
Colliery of M/s ECL was introduced in 2016 in R-VI Seam, deploying 2 Legged 11000 KN capacity
Powered shield Support (type ZY 11000/26/ 56) and DERDshearer (MG650/1630-GWD) both
manufactured by M/s China Coal Beijing Coal Mining Machinery Co.Ltd, P.R.China. The face length
of the panel is 145 m and panel length is 1666 m. Maximum height of extraction is 5.5m with a rated
support resistance of 121 T/m2
capacity. The experiences of this project are quite motivating and this
may open new avenues in Indian coal mining industry for full extraction of seams up to 5.5m.
3.3 Multi-slicing Longwall Methods like inclined slicing, horizontal slicing, diagonal slicing, and
transversely inclined slicing in ascending/ descending/both were applied. These methods are suitable
for those thick seams which need assistance in fracturing the immediate roof. However, the main
disadvantage is in extraction of thick seams of high variation in thickness. Another challenge is the
arrangement and maintenance of entry systems (the gate roads in different slices). In general, a set of
main gate and the tailgates are required for each slice. Driving and protecting those gate roads would
be difficult and costly. Table-2 summarizes the brief details of thick seam extraction by longwall
method.
Table-2: Brief Summary of thick seam extraction by longwall method.
Name of
the
mine
Seam Thickness
of seam
(m)
Height
of
extrac-
tion
Method of working Remarks

6. 6
Gidi’A’
Colliery
Sirka 12m
140
inclination
2.4m
slices
Multi slicing with
sub-level caving in
1967-70
In the I slice roof had to be
blasted down initially to induce
caving. After a 40m advance of
face from barrier, the first fall
took place and thereafter roof
caved regularly. Sub levels had
to blast to break. This
experiment proved to be
Technically Success.
Sudamdihi
Colliery
XI/XI
I
seam
35o
in
clined
7.5 6.0m
slices
Jankowice method
(inclined slicing in
ascending order
with sand stowing)
in 1969
Satisfactory from ground
control point of view. But
average production was only
100TPD.
Sudamdihi
Colliery
IX/X
seam
27o
inclin
ed
22m 33
slices
Kazimierz method
(horizontal slicing
in ascending order
with sand stowing)
in 1974
The working conditions
aggravated in upper slices and
the panel was abandoned after
seven slices had been extracted.
Khottadih Saml
a
5.4 2.4m
slices
Decending Slicing
with artificial roof
in 1980
Laying the artificial roof was
arduous and labour-intesive.
Poor productivity-100 to
120TPD.
Banki G-III 3 3 Knife edge with
timber props
The maintenance of large face
span and high convergence
under weak shale roof became
problematic and the method
discontinued.
Dhemoma
in
Barac
- hak
3 3 Single lift
extraction
Technically Success.
GDK-7
Incline
No.3
seam
3 3 Single lift
extraction
Technically Success.
For the obvious reasons, the MSL methods were not proven viable
3.4 Hydraulic mining involves the use of high pressure water to break and transport coal from the seams.
The broken coal, mixed with water, is transported hydraulically in flumes of suitable dip by gravity.
High pressure water is created by pumps, carried through a network of pipes and applied to break out
the coalthrough a monitor. Previous hydraulic mine operations have existed in placessuch asGermany,
Canada and Japan. The case study of South Island of New Zealand is a considerable success.
A trial application of hydraulic mining was also carried out to extract pillars developed in X (flat, less
than 7°, compressive strength270 kg/cm2
) seam of Gopalichak colliery of BCCL, where 80 bar
hydraulic monitor was used in three different phases of the trial which was not encouraging. Hydraulic
mining found to have a significant potential in a limited range of suitable mining conditions with limited
large scale production potential and not considered to be a universally applicable option.
4 LONGWALL TOP COAL CAVING (LTCC)
There are three types of top caving method according to coal reserve condition and the relative mining
technical process:
Table 3: types of top caving method as per coal reserve condition and the relative mining technical
process

7. 7
Method criteria
Full-seam Extraction Top Caving Gently inclined thick coal seam with height less than 12~14 m.
Top Layer Pre-cutting Top Caving
Under Net
Suitable to coal seam height more than 12~14m .The
immediate roof is stiff, or high gas content in coal seam. The
pre-exhaling in gently inclined coal seam.
Inclined Layer Top Caving Mining Suitable to coal seam height more than 12-14m.
For the extraction of very thick seams or thick seams which have a strong, competent roof, the LTCC
method can be modified to a technique named “sub-level caving". In this method, the thick seam is
divided into two slices. The top slice is extracted by the conventional longwall method, and the bottom
slice is extracted by the conventional longwall method combined with caving the remaining coal layer
between the two slices. Another variation of the LTCC method in very thick coal seams is that both
slices are extracted by the longwall method with the caving of the top coal. If a seam is too thick to be
divided into two slices, three slices are used. In this case,the top slice can be extracted by the traditional
longwall method, and the middle and the bottom slices can be mined by the longwall method combined
with winning caving coal between slices. Another principle of the LTCC method is illustrated in the
following Figure.
Figure 3: The sub-level caving method (after Bewick, 1983)
The sub-level caving method has been widely practiced in the former Soviet Union, the former Yugoslavia,
France,and China. An early application of the sub-level caving method was in the Kuzbass coal_eld of the
former Soviet Union to extract the at and 6 - 12m thick coal seams with the help of exible steel mats
(Vorobjev, 1962). In this mining system, the thick seam was divided into two slices. A 1.5 - 1.8m thick
slice was extracted by longwalling from the top of the coal seam. Flexible steel mats, which consist of
interlacing steel strips, were laid on the oor of the top slice during mining operations. The bottom slice was
extracted to a height of 2.5m, supported by KTU shields, advancing down the dip. The coal layer between
the two slices was fractured by blasting and won though the windows of the shields.
The sub-level caving method has also been deployed at Blanzy coal mine, France,to exploit its 9.9 - 14.8m
thick coal seam, dipping at up to 260
, with a maximum monthly output, in 1975, of 69,456 tonnes, and a
productivity per man-shift of 15.7 tonnes (Adam, 1976). And also practiced widely in China to extract the
at (dip ranging from 00 to 250) and medium to steep (dip ranges from 260 to 450) thick seams during the
1970s (Tian et al., 1979).
In India , the sublevel caving mining method was applied at East Katras colliery (Singh et al., 1993) to
liquidate a 7.5 m thick coal seam ( avg.comp. strength 280 Kg/cm2
) at 147 m depth by mechanized
longwalling (in collaboration with Cdf,France).The 210 m long panel wasworked by a retreating longwall
face of 100 m length. The total mining operation within the panel was divided into three phases.
i. Longwalling of the 2.5 m thick top section along the roof for the first 90 m of the panel under the
intact multilayered immediate roof strata.
ii. Extraction of the 2.5 m bottom section along the floor for the first 90 m of the panel with sublevel
caving of the remaining 2.5 m thick middle section parting (lying directly below the broken
overlying strata caused by top section longwalling).
iii. Extraction of a 2.5 m thick bottom section for the remaining 120 m length with integral caving of
the 5.0 m thick top coal bed under intact strata.

8. 8
During top section working, the face was just a normal longwall with undisturbed 30-33m thick roof
followed by settled goaf of old overlying seam workings. At the time of sublevel caving, the sublevel
section, after 12m advance oprated under broken debris of 2.4m thick coal band as only roof. Caving of
sub-level coal was very ggod but had frequent mixing of stone and heavy load on supports. During integral
caving, the coal flow wasnormal from the very beginning because of extended regular caving of immediate
roof.
Chock shields of 0.556 MPa setting load density (at 32 MPa leg pressure)and 0.567 MPa yield load density
(at 38 MPa leg pressure) were used. However, the chock shields did not perform well. Field monitoring
showed a rapid increase in setting load density of the support in relation to the yield load density. This was
followed by a large amount of leg closure during mining cycles of the sublevel caving face under the broken
rock strata. This behavior/performance of the chock shield was deemed to be critical. However, estimation
of the load on the shield was difficult without knowing the behavior of the overlying rock mass. Self-
sustaining strength and cohesion among the strata caused a blocky nature of roof caving in different
locations during integral caving. Multilayered parting in the roof strata causing complete packing of the
goaf during integral caving resulted in a reduction in face problems except during periodic roof weighting.
5 Applicability of LTCC to Indian Geo-Mining Conditions
There are numerous intrinsic and non-intrinsic parameters which govern the feasibility of LTCCin any
mine, whichshouldbe evaluated suitably. The intrinsic parameters are thickness of the coalseam,
coalstrength and deformation properties, inclination of the coal seam, roof sandstone strength and
deformation properties and coal geology. The non-intrinsic parameters existequipmentsupport for the
normal longwall extraction, life of the mine, financial health of the mine and a detailedgeological study of
the mine(Khanal et al., 2014). In addition to these parameters,coal seam cavability and fragmentation and
horizontal stresses can have significant influences on LTCC safety and effective application (Hebblewhite
and Cai, 2004) as shown in the table:
Table 4: The geological conditions applicable to top caving mining.
Conation Description
Coal Seam Reserve
Condition:
Stable coal seam reserve of between 5~10 mtrs, a coal seam inclination 0-15°,
coal seam Protodyaknov coefficient f =3. (Uni-axial compressive strength from
10MPa to 25Mpa.
The Nature of Roof
and Floor:
The roof can collapse down with roof caving, the filling height of roof collapsing
should be equal to the height of shearer cutting and roof caving and the nature of
floor lithology should be strong.
Geology Structure: Geology Structure: The geology structure should be simple with no big coal
seam fluctuation or folds, karst collapse pillar and igneous intrusive free, no big
fault throw. There should not be any hard thick balk in top coal, and the stable
thickness of single layer balk should normally be less than 300 mm.
Danger due to
inundation
Standard Longwall Mining hydrology practices and risk assessment should be
carried out.
Danger of
spontaneous heating
&fire
Besides accelerating the advancing speed of longwall face to complete within the
incubation period of the seam, all other standard measures including correct
ventilation by pressure balancing, etc. should be taken to prevent any risk of
spontaneous heating and fire.
Longwall Face
Reserve
Normally the top caving face length is 150-350m, the panel length is
1000~3000m, face reserve preferably 1-20 million tons.
Thickness, compressive strength of some of Indian thick coal seams were collected from various sources
like publishes papers,visits to mines, etc. area given in the following table:-

9. 9
Table 5: Strength parameters of some of Indian coal seams
Name of the seam Thickness
Name of the colliery
UCS(MPa) Pd
Rebound No.of
Schmidh hammer
Raniganj coalfields (mostly covered by Eastern Coalfields Limited and IISCO)
Raniganj formations:
Hatnal(R-III) 2.0-4.0m Seetalpur 43.3 1.65 42
Koithee(R-III) 2.0-4.0m Sripur 43
Samla(R-II/III) 1.0m-6.0m Kottadih 31.2 1.27 47
R-VI 2.1-6.1m Kottadih 30.43
Disergarh(R-IV) 1.0-5.0m Chinakuri 36.3 1.40 37
R-VI 2.4 Satgram 37
R-VII 1.5-4.9m Jhanjra 35.8 1.40 44
R-VII 3.6 Bankola 28
R-VII 3.6 Shyamsunderpur 29
R-VII 4.2 Sankalpakhani 28
Borachak(R-VIII) 5m-14m Dhemomain 32.5 1.35 44
Nega(R-VIII) 5m-14m Nimcha 50MPa
Lower Kajora(R-
VIII)
5.0-14m Lachipur 33Mpa
Jambad (R-VIII) 5.0-14m Bankola 35Mpa
Lower Kajora(R-
VIII)
5.0-14m Lachipur 33Mpa 1.36 52
Jambad Top (R-
VIIIT)
5.0 Bankola 35Mpa
Kajora top
seam(R-IX)
6.5-7.5m
Madhusudanpur
Colliery
Barakar formations
MAHIDA TOP 2.85 MURALDIHI 27.8
VII/VIII
East
Bhuggatdih,BCCL
18.0 1.33 20
X 3.1-18.3 N.Salanpur 21MPa
Salanpur –A 1.5m-45m Bonjimeheri, Dabor
Salanpur –D 1.2-21.5m
Ramnagar 4.8m Ramnagar 28MPa
Jharia Coalfields ( mostly Barakar measures covered by BCCL,CCL IISCO, TISCO)
G-1 Surakacchar 29MPa
XVI top 1.8-3.0m Moonidih 22.0 1.38 23
XIV 9.06 Jitpur 19MPa
X 3.1-18.3m East Katras 27.0 1.34 26
X 3.1-18.3m Gopalchak 27.7 1.49 28
I 4.5 Gorawari 28
MECIII(T) 4.4 Nandan Mine-II 30
IV 4.8 Saoner Mine-1 23
UW 3 Satpura-II Mine 31
GIII 2.5 Surakachchar 24
UPPER
PATPAHARI
2.8 Bhatgaon 26.5
PASANG 2.8 Jaigar 22.1
4A 2.2 Jhimar 30
Seam V Churcha mine 30.00
LAJKURA 2.4 ORIENT MINE-3 30

10. 10
4Aseam 2.6m Rajnagar Colliery 41.09MPa
Jhagrakand 4A
seam
2.6m
South Jhimar
Colliery
40.36MPa
Johilla topseam 3.5m Nowrozabad East 30MPa
No.V seam 3.0m Chucha West
0 seam 12m thick Chirimiri Colliery 62.72MPa
Pranahita Godaveri Valley Coalfields (The Singareni Collieries Company Limited)
I 6.0m GDK 11 50
No.1 seam 6.0m SRP 3A Inline 9.81MPa
1 2.1 GDK 5A 27
1A 4.5 KK 5A 17.3
I 4.2 GDK 8A 19.5
III seam - 9.0 RG OCP-I 95
III seam 9.0 Vakilpalli block 31.26
III 9.0 GDK 8 Incline 56
IIIseam 9.0
Ramagundam shaft
block I
68.60MPa
IV seam 4.0 RG OCP-I 83
3B seam 2.2m SRPI Incline 27.05MPa
3Aseam 2.5m SRP 3 Incline 43.86 MPa
No. 4 seam 2.10 RK 8 Incline
17.93MPa-
53.214MPa
Ross 2.1m Bellampalli 48MPa
Salarjung 8.2m
Morgan Pit,
Bellampalli
46MPa
The study of physic mechanical properties and other pre-requisites of LTCC application criteria shows that
various coal seamsin different Indian coalfields canbe suitably extractedby LTCCwith high conservation,
economy and safety.
In this aspect,the Singareni Collieries Company Limited, India has taken initiation and has undertaken a
projectof comprehensive analysis of geological and geophysical data of the mine site and developed
detailed geotechnical frameworks for the assessment of LTCC technology in Ramagundam area in
collaboration with CISRO, Australia. III Seam is the thickest seam with an average thickness of around 8
to 10m and hence requires advanced thick seam mining methods for optimum extraction. Presently , III
Seam is being extracted by Bord and pillar in two sections and Blasting Gallery (BG) method.
A first pass assessment of LTCC in III seam of Adriyala mine was made using already established caving
indices (Chinese index and CSIRO index) for LTCC. The seam is about 10m thick and is dipping at 8 to
10deg. The seam depth is ranging from 300 to 400 m. A Parameter study on cavability and recovery rate of
top coalwas conducted after detailed investigation. Chinese advocated Cavability Index(Y) based on study
of 23 faces in China (Theory and Technology in Top coal Caving Mining, Prof. Jin Zhongming, 2001):
Y=0.704+0.0006338H-0.00786Rc+0.238C-0.1797Mj+0.01434Md;
where Mining depth(H),m; UCS of Coal seam (Rc),MPa; Top Coal thickness(Hd), m; Stone band
thickness(Hj),m; Coal fracture index(C).
Immediate roof thickness is known to influence cavability in practice, however,it was shown to have
little effect in numerical modelling studies completed by Chinese.
Table 6: Relationship between Chinese caving index ‘Y’ and success of LTCC

11. 11
LTCC
Classification
1 2 3 4 5
Mining
Conditions
Very good Good Medium Bad Very Bad
Caving
Index(Y)
>0.9 0.8-0.9 0.7-0.8 0.6-0.7 <0.6
Top Coal
recovery
>80% 63-80% 50-65% 30-50% <30%
For Singareni, Chinese index was evaluated by considering the above parameters including average
laboratory UCS of 25.5MPa C=0.3 and Mj=0.1 and Md = 7m. The caving index ranged from 0.84 to 0.91
for depths between 300 m and 400 m; which could be categorized into classification 2 yielding "good"
rating for LTCC with predicted coal recovery of about 70 to 80 %.
CSIRO conducted a parametric study [13] with COSFLOW and identified depth of mining, coal strength
and top coal thickness as the three most important parameters that influence the degree of fracture in the
top coal and hence the caveability of top coal, which indirectly governs the success of LTCC. The caving
index (CI) developed by CSIRO using multi variant regression of the parametric study is shown below:
CI = ‐2.64 + 0.0395 H – 0.72 CS + 0.191 TC
Where H is depth of mining in meters, CS is coal strength at test scale in MPa,TC is top coal thickness in
meters
The CSIRO's caving index for the same material properties yielded a rating between ‐7.5 and ‐3.5 or depths
between 300m and 400m. This yields a "good to moderate" rating for LTCC with predicted coal recovery
of about 56 and 67%. However,it is important to note that both of the above methods are based on Chinese
geological conditions, thus it is necessary to investigate caveability of top coal at SCCL through numerical
modelling using site specific in situ stress conditions and rock mass geotechnical parameters.
Taking only the three most important parameters based on the size of their regression coefficients, a
multivariate regression was undertaken to develop a new simplified equation:-
CI=-2.64+0.0395H-0.72CS+0.191TC and
Percentage of top coal recovery =2.72 CI+78
As damage in top coal is directly related to the caving result, hence the success of LTCC mining is largely
determined by depth, coal strength and top coal thickness.
6.CHALLENGES OF LTCC IN INDIAN GEO-MINING CONDITIONS
High strength of coal seam is the major problem. As per the experiences, coal seamshigh
strengthCoalcannot cave naturally and lead to dangerous conditions like rock burst and air blast or coal
break in large blocks and form stable arch. To overcome these problems due to high strength of coal, three
approaches including Pre-blasting, Hydraulic Fracturing and vibrationcan be adopted.
In Omerler underground mine in Turkey, 1.5 m of coal was properly cavedand thereafter, caving process
was hindered. Based on numerical modeling by FLAC3Dof Itasca,a pre-blasting in 3.5 m of coalseam was
suggested to obtain a suitable coal flow (Unver and Yasitli, 2006, Yasitli and Unver, 2005).
In XinzhouyaoCoal Mine located in north China, pre-blasting was resorted to improve coal recovery (Xie
et al., 1999).Hydraulic fracturing is another way to overcome problems. This method was experimented
successfully in Liuxiang coal mine in which a linear multi-hole control of hydraulic fracturingwith 20 MPa
pressure was applied (Huang et al., 2015).
Vibration System: Using vibration technology in LTCC wasstudied to solve technical challenges like large
blocks locking(Xie et al., 2006). If caved coal with large blocks (particles about 30 percent of dropout)
formed a stable arch, vibration is useful and can decrease archstability and improve coal flow.

12. 12
7. CONCLUSIONS
There is a lot of scope to gain from the China and Australia experiences in thick coal seamtop coal caving.
In India, comprehensive database of thickness, depth, geological disturbances, geotechnical data, reserves,
etc., deciding appropriate technology for winning the thick seams is required to be formulated. Further,
specific guidelines in deciding winning technology with optimum conservation of each coalblock from the
regulatory authorities may be required which require thorough exploration, research and geotechnical
analysis. A high level expert group is to be constituted at national level to promote, coordinate and discuss
different aspects related to Longwall technology and in particular LTCC. Concrete efforts are required by
the mining inspectors, policy makers,coal companies, researchorganizations and equipment manufacturers
to translate the ideas into concrete action and reap the benefits of LTCC in the years to come.
8. ACKNOWLEDGEMENTS
The authors are thankful to the Directorate General of Mines Safety, Dhanbad for providing opportunity
to work on the subject and permitting to submit the same for seminar. The views presented in this paper are
those of the authors only and not necessarily of the institution to which they belong and also express their
sincere gratitude to all those who have directly or indirectly helped in preparing this manuscript.
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