DESIGN OF LONG WALL PANEL – A CASE STUDY
FOR NO.2 SEAM OF RAMAGUNDAM AREA, SCCL
ABSTRACT: Singareni Collieries Company Limited (SCCL) is a jointly owned Coal
Company by govt. of Andhra Pradesh and govt. of India. In view of its strategic location
and being the only coal producing company in South India, SCCL has the onerous
responsibility of catering to the coal requirements of consumers within the Godavari
GDK.10A Incline is one of the most mechanized underground mines in SCCL.
There are total 7 seams (No.1A, 1, 2, 3B, 3A, 3 & 4) present within the mine boundaries
out of which No.1A & 3B are proved inconsistent. No.1 & 2 seams are considered for
extraction from GDK.10A Incline and seam no.3& 4 are being worked by GDK.10.
Incline. No.1 seam having 2 clay bands has been worked by Long wall technology. No.2
seam is 18-20m below No.1 seam, This seam was developed near the out crop and
abandoned due to the presence of thick clay band.
With the experience of working No.1 seam with two clay bands and development
in scientific estimation of proper roof supports, the authors are of the opinion that the
No.2 seam can be extracted by mechanized Long wall technology with an extraction
height of 2.0m. The present paper explores the possibility of working No.2 seam of
GDK.10A Incline with Long wall Technology by thorough study of Geo-technical data
and Physico-mechanical properties of overlying roof rocks to estimate the caving and
required support resistance.
The Singareni Collieries Company Limited is operating 58 underground mines
and 12 opencast mines catering to the needs of coal consumers in South India. SCCL has
introduced suitable mechanization in mines wherever conditions favour to improve
production capacity, productivity and percentage of extraction.
GDK.10A Incline and GDK.10 Incline mines are the glittering examples of
successful underground mines mechanization in SCCL. Long wall technology was
introduced in No.1 seam of GDK.10A Incline in 1994. Since then six panels have been
extracted with total output of 3.63 Million tones.
* Dy.GM (5Group of Mines) ** Dy.Mgr (Project Planning) *** GME, No.5 Incline
The Singareni Collieries Company Limited, Kothagudem –507119
Blasting Gallery technology was introduced in No.3 seam of GDK.10 Incline in
the year 1989. The project is considered as trendsetter in thick seam underground mining
in India. No.3 seam lying below GDK.10A Incline property is being proposed for
Blasting gallery. No.1 Seam is worked successfully by Long wall method even though it
contains two clay bands.
2. EXPERIENCE OF WORKING NO.1 SEAM:
No.1 seam in GDK.10A Incline of Ramagundam area block is intercalated with
two distinct clay bands. These clay bands have restricted the development and extraction
by Bord and Pillar where percentage of recovery was poor and created strata control
problems. These seams have been developed by Road headers and extracted by Long
wall for the past 8 years in GDK.10A Incline. Nearly 10Km of roadways have been
developed and 3.5 Million tones of coal has been extracted. But for Long wall system this
seam could not have been recovered much.
Experience of development in top section, bottom section and extraction by Long
wall and allowing both clay bands to fall in goaf is ensuring ‘E’ grade from the No.1
seam. With all this a definite procedure is established in dealing with Clay bands in
No.1 seam and extraction of the same safely.
3. POSSIBILITY OF WORKING NO.2 SEAM:
With the valuable experience gained while working No.1 seam. It is proposed to
work No.2 seam with Long wall technology. In Ramagundam region of SCCL this No.2
seam is developed by Bord and Pillar in the past with heights as low as 1.5m to 2.0m in
GDK.3 Incline, GDK.2A Incline and GDK.5A Incline. In GDK.6B Incline this 2 seam is
being worked presently. In opencast mines, it is in completely worked.
Presently seams thinner than 1.5m are worked in OC mines and in underground
mines they are declared non-vendible5, since they are not workable, by the preset mining
methods. This concept should be changed and all the thin seams of good quality have to
be exploited. UK/Germany/Poland which had no reserves in thick seam have developed/
worked Long wall in thin seams to sustain their coal mining industry at the fag end of
their reserves. Double face system and dual usage of gate roadways for simultaneous
working of two contiguous seams/thick seam with clay band in middle section of the
seam can be adopted with German Collaboration6.
The main problem in the working of No.2 seam is presence of clay band, which
created strata control and quality related problems. No.1 seam of GDK.10A Incline is
developed in top section with 1.0m clay band and the gate roadways are driven in bottom
section leaving 0.3 to 0.5m coal against the clay. This in turn supported by roof bolting.
Roof support was initially difficult but after studies conducted by scientific agencies, roof
support was designed and is well established now.
Keeping in view the extent of II-seam efforts were put in for the development of
No.2 seam. The studies conducted on the boreholes drilled from GDK.10A Incline
revealed the following.
1. Bore hole No.1038 drilled from surface for shaft sinking. This borehole seam
section shows that No.2 seam can be developed along stone floor with an
height 1.8-2.0m. The grade of coal would be ‘D’ grade.
2. Bore holes (2 No.s) have been drilled from No.1 seam floor to No.II seam
floor at 35L/3D & 40L/2D. The borehole section and Lithology shows that
No.2 seam can be comfortably developed along floor with a height of 2.0m.
3. Further No.2 seam is being developed from 48L X-cut by drivage of level
tunnel. The seam section of various boreholes in deep shaft block indicate its
workability with a height of extraction 2.0m with low ‘D’ grade.
Internal studies conducted and proposals made by various scientific agencies
suggested extraction of II-seam by Long wall. No.II Seam was finally considered to be
worked with only Long wall technology2.
4. DESIGN OF LONG WALL PANEL IN NO.2 SEAM:
For proper understanding of caving behaviour an estimation was made basing on
the Plate theory of failure proposed by Prof. Qian Ming-gao and Prof. He Fulian, China.
PHYSICO-MECHANICAL PROPERTIES OF ROOF ROCK
Depth from BoreHole Thickness Density Tensile Str. Youngs Mod
Surface(m) 637 (m) (gr/cc) (kg/sq.cm) x105(Kg/sq.cm)
163.4 0.1 1.4
164.57 1.17 2.12 15.92 0.23
10.43 2.12 17.07 0.35
8.2 2.21 25.31 0.41
4.13 1.56 36.72
2 1.4 23.93
BORE HOLE LITHOLOGY
Depth from BoreHole Thickn Lithology Bulking Bulk-up Cumu. Cumu.
Surface(m) 637 (m) Factor(m) Height Bulk-up Ht. Thickn
163.4 0.1 Coal
164.57 1.17 Carb sandy Shale 1.4 1.638
10.43 (Medium - 1.15 11.9945 27.04 24.76
8.2 Grey Sandstone 1.13 9.266 15.048 14.33
(Fine &Medium -
4.13 Shaly Coal 1.4 5.782 5.782 6.13
2 COAL 2
189.33 Working Sec.
Caving Height = 14.33m
Working Sec. = 2.0m
Immediate Roof = 4.13m
( Which caves in as the supports are advanced)
SSt which is expected to cave = 8.2m
4.1. CALCULATION FOR FIRST FALL DISTANCE FOR A FACE LENGTH OF
1. Vertical Pressure (Pv) = e1 x t1 + e’ x H
e1 – Density of bed which is expected to cave.
t1 - thickness of bed which is expected to cave
e’ – Density of the bed which is lying above the expected cavable bed
H – Depth upto the bed.
Pv = 2.21 x 8.2*+ 2.12 x 175
= 389.122 t/sq.m (* from Table.2)
= 3.89 Mpa
2. m : Virgin Horizontal Stress:
= 175/d + 0.3
3. Horizontal Stress on (σh) = m x Pv
= 1.255 x 3.89
= 4.881 Mpa
4. Weight per Unit Thickness of Beds w = e1 x t1
= 2.21 x 8.2
w = 18.122 t/sq.m
5. Instiu Tensile Strength σt = 0.9 x 2.531
= 2.278 Mpa
BY TRAIL ERROR PROCESS…
a) Let a= 66m b=150m t = Thickness of Sandstone expected to cave in m
= 8.2 m (from Table.2)
a/b = 0.44
f(a/b) = 0.01991
Bending Stress (σ’) = f(a/b) x w x 1502 x 6 / t2
= 0.0199 x 18.122 x 1502x 6 / (8.2) 2
= 7.262 Mpa
σt = σ’ – σh
= 7.262 – 4.881
= 2.385 Mpa
The tensile Strength of the Rock is 2.278Mpa. Hence it can be concluded the first
fall will occur after a retreat of 66m.
4.2. PERIODIC FALL :
Thickness of Bed1 (t1) = 8.2m
Tensile strength σt = 2.278 Mpa
Density e1 = 2.21 t/sq.m.
Acceleration due to gravity(g)= 9.81 m/sec2
L12 = t1 x σt / 3 x e1 x g
= 8.2 x 2.278 x 103 / 3 x 2.21 x 9.81
L1 = 17 m
4.3. ESTIMATION OF RESISTANCE REQUIRED:
a. AT MAIN FALL:
Weight of immediate Roof Wi = ei x 4.9 x ti x Sp
= 1.56 x 4.9 x 4.13 x 1.5
= 47 T
Weight of bed 1 W1 = e1 x t1 x 33 x Sp
= 2.21 x 8.2 x 33 x 1.5
= 897 T
a.1. TAKING MOMENTS ABOUT FACE LINE:
Pxp = Wi x [4.9/2] + W1 [33/2]
P x 3.7 = 47 x [4.9/2] + 897 [33/2]
P x 3.7 = 115.15 + 14800.5
P = 4031 T
This is very momentary (just at the moment of break of main bed). There will be bleeding
of supports and the 33m of block will rotate about face line and will touch goaf waste.
This overhang of 33m can be treated as simply supported beam with one end on goaf and
the other end on rear of support with a length of (33-4.9) = 28.1
28.1m = e1 t1 x 1.5
= 2.21 x 8.2 x 1.5
W = 27 t/m
Maximum Bending movement = W l2 /8
B.M. = 27 x (28.1)2 /8
= 2665 tm
M = f
F = (M / I) y
= B.M. x 6 / Sp x t12
= 2665 x 6 / 1.5 x (8.2)2
= 158.53 t/sq.m.
= 1.59 Mpa.
The tensile strength of rock is 2. 278Mpa as this bending stress is 1.59 Mpa. It can be
concluded that there is no further break in the middle of block of 28.1m length.
a.2. TAKING MOMENTS ABOUT GOAF LINE:
P x (33-3.7) = 47 x [ 33- (4.9/2) ] + 897 [ 33/2 ]
P x 29.3 = 1435.85 + 14800.5
P x 29.3 = 16236.35
P = 554 T
b. AT PERIODIC FALL:
Weight of immediate Roof Wi = ei x 4.9 x ti x Sp
= 1.56 x 4.9 x 4.13 x 1.5
= 47 T
Weight of Periodic weight block W1 = e1 x t1 x (17+4.9) x Sp
(17m length) = 2.21 x 8.2 x 21.9 x 1.5
= 595 T
b.1. TAKING MOMENTS ABOUT FACE LINE:
Pxp = Wi x [ 4.9 / 2 ] + W1 [ 4.9+17 / 2 ]
P x 3.7 = 47 x [ 4.9 / 2 ] + 897 [ 21.9 / 2 ]
P x 3.7 = 115.15 + 9822.15
P = 2686 T
This is momentary load and the over hang will touch the goaf waste after bleeding and
subsequent lowering of supports.
b.2. TAKING MOMENTS ABOUT GOAF LINE:
P x [ (4.9+17) - 3.7 ] = Wi x [ (4.9+17) - (4.9/2) ] + W1 [ (4.9+17)/2 ]
P x [ (4.9+17) - 3.7 ] = 47 x [ 21.9 - (4.9/2) ] + 595 [ 21.9/2 ]
P x 18.2 = 914.15 + 6515.25
P x 18.2 = 7429.4
P = 408 T
4.4. SUMMARY OF ALL THE ABOVE CALCULATIONS:
The following points can be drawn from above calculations.
1. The main fall will occur after a retreat of about 66m for a face length of 150m
2. The periodic fall will occur at an interval of 17m
3. The required support resistance at the time of main fall is 554 t
4. The required support resistance at the time of periodic fall is 408 t
In view of the experience gained while working under settled goaf at JK-5 Incline
of SCCL and Jhanjra mine of ECL4, it is most likely that the capacity of support required
would be less compared to the calculations made treating the strata above as virgin.
Further work is in progress in this regard.
It is concluded that,
No.2 seam that is lying 18-20m below the No.1 seam can be worked by Long wall
method comfortably with better control of strata.
For economic viability and conservation of coal it is essential that the extraction
of II-seam is taken up though there are some difficulties in regard to low height
Working of II-seam will be better in regard to strata control as the upper seam is
distressed after liquidation of I-seam.
In II-seam, Anchorage with resign capsules at the top of the hole can be done for
immediate anchorage and avoid bed separation. Fore-poling bolts with cement
capsules and W-straps in conjuction with linked wire mesh of 50mm x 50mm x
8mm gauge should be used. In case of bed separation shot-create over the linked
wire mesh should be rested. With this type of support development can be done
below the goaf, which is the distressed zone.
The support capacity of around 4 x 600 t is sufficient for easy working of the
seam with Long wall technology with out keeping in-view the effects of
The authors are grateful to the SCCL management for permitting to publish this
paper. The views expressed by the authors in this article are of their own and not
necessarily of the organization to which they belong.
1. Prof. Qian Ming-gao, Prof. He Fulian – technical paper on “ The behaviour
of the main roof in Long wall mining – weighting span, fracture and
2. Goutham Benarjee, Scientist & Head Long wall & Short wall Division,
CMRI, Dhanbad – Report on possibility of working II-seam at GDK.10A
3. Peng.S - Long wall Strata Control.
4. S.K.Varma, P.K.Mandol, S.Dasgupta, a paper on “ Fire at AW1 Long wall
panel in 1&2 Incline, Jhanjra area, ECL an unique experience”, Journal of
CMTM, pg.no.5 to 14,Vol.6, No.5 May, 2001,
5. D.L.R.Prasad, M.S.Vanka Ramayya, a paper on “Sustainable Mining
Technology- past, present and future of Long wall mining in Godavari valley
coalfield, Andhra Pradesh”, National Symposium on “Sustainable Mining
Technology: Present and Future”, conducted by Dept. of Mining, Anna
University., pg.no.143 to 151, March 14-15, 2002,
6. DBT Mining Engineers (2001), Double face system and Dual usage of gate
roads, Paper on “The experiences of simultaneous working of two seams at
Cayirhan (Turkey), Saar Brucken, Germany.