HIGH WALL MINING IN INDIA : A Case study By Tikeshwar Mahto, Dy. Director of Mines Safety, Bilaspur Region(India)

1. TIKESHWAR MAHTO
DY. Director of Mines Safety,
Bilaspur Region
07898033693, 08982493361
tikeshwarmahto@yahoo.co.in
HIGHWALL MINING – A NEW APPROACH IN INDIA
: - A Case study
Worldwide, there are two main High wall mining Technology being in operation in the
business of High wall Mining. In India, both technologies are in operation by the different
Agencies. There details are as follows.
 Add Car High Mining system: It`s details are covered in this case study. It is basically
an US Company marketed by ICG ADDCAR System LLC, No.1, HWM Drive, Ashland, KY
41102, USA, http://www.addcarsystem.com. In India it is operated by a Hyderabad
based company named Advanced Mining Technologies Pvt. Ltd., Plot No.668, Road No.
33, Jubilee Hills, Hyderabad- 500 033, India, Tel: +91-4023548990, Fax: +91-
4023608565, Email: hari@amt.net.in . This Technology is highly productive and can be
achieved upto 1MT/Year. Only constraint with this technology is that, it is best suitable
for competent roof. Because Addcar conveyors are open and if, roof collapses it can
damage the conveying system.
 Auger High Wall Mining system: It is also an US based company ``BUCYRUS
Mining``. In India it is operated by CBL (Coopram Bagdoria Limited). Presently, it is
being operated in Sohagpur Area of SECL, a sub-sidiary of CIL. It is being operated on
the name of Sharda High wall mining. It is less productive in comparison to Add Car
Highwall Mining system, but it is safer. Because, it`s augers( conveying system) are
armoured and covered. It can be applied in any condition. Presently, this company in
India is headed by Sri B.N. Pan, a retired C&MD of SECL, whose contact No. +91-
9830024733
INTRODUCTION
Highwall mining is a method of mining, originated from auger mining that involves
the use of a remote controlled mining machine, which is driven into a coal seam to
extract the coal. This method is often used to access coal left behind from previous
mining operations or when difficult geological conditions restrict the use of other
mining methods. Coal is extracted from the base of a cliff (a highwall) using
horizontal or inclined drilling to create holes in the coal seam left in barriers of
highwall of opencast mine. Another primary difference in a highwall mining operation
is that it is carried out by remote control at the surface, where an operator located
in a cabin uses a television camera to monitor and control the progress of the
continuous miner machine. There are two main types of highwall mining: continuous
highwall mining and auger mining. Continuous highwall mining involves the use of a
continuous mining machine that creates rectangular openings into the coal seam of
a highwall. Coal is hauled to the surface using a conveyor system. In Auger mining,
coal is extracted using an auger mining machine. This machine operates like a drill,
with a cutter head rotating into the coal seam and creating circular holes to access
the coal. The extracted coal is returned to the surface using the auger machine and
a conveyor system. Auger has limitation of penetrating into the seam. It can go upto
60m, but Continuous mining machine can go upto 600m. Production capacity of
continuous mining machine is about 1MT per annum.

2. History
Historically, when an open-pit or open cut mine was excavated, a highwall remained
after excavation and was abandoned or covered up. This eventually provided an
incentive for coal miners to devise a means of extracting coal from an existing
highwall, as much labour had already gone into excavation and exposing an
accessible coal seam. The primary goal for establishing a highwall mining system
was therefore to increase the production life of an open-pit mine. Initial attempts to
mine high walls were met with very little success until the development of
coal auger mining in US in the 1940s. In this respect, highwall mining has largely
been viewed as an adaptation of auger mining. The problem with deploying just
augers to mine a highwall was their restriction to penetrate coal seams to a limited
depth. They were also unable to easily navigate over the rolls and dips of coal seams
because of the rigid structuring of auger flights.
Eventually, the continuous miners used in the underground mining of coal were
developed and outfitted to also recover coal from surface high walls. This spurned
the development of new highwall mining machine systems such as the Terex SHM,
the Highwall Hog, and the Addcar System developed in 1990. As on now, more than
60 highwall miners are in operation in US, and they may account for about 4% of
total U.S. coal production. This technology is also very popular in Australia. More
than 13 panels have been extracted till date in Australia. And now SCCL, the Indian
Mining Giant witnessed the successful implementation of first Highwall Mining in Asia
continent.
Machinery used for Highwall mining at RGOCP-II of SCCL are supplied by
Addcar Mining company of US based.
The key components of the system comprises
 A continuous miner
 A launch vehicle
 Conveyor cars (Addcars or screw conveyors)
 A stacker
 Rubber tyred loaders
 Dozer
1. The Continuous Miner
The continuous miner is a Joy 12 CM12, instructed to underground
specifications apart from a shortened and fixed tail. Additionally cameras
have been fitted to provide the remote operator with instantaneous pictures
of the face, machine instrumentation and methane detectors.
Specifications
Length of machine: 11 m
Width of the boom: 3.5 m
Weight : 72 T
Ground pressure: 1.95 kg per square cm
Height of extraction: 1.52 to 4.0 m
Electrical Details:
Cutter motors: 2 x 220 HP (1.1 KV)

3. Gathering head motors: 2 x 60 HP (1.1 KV)
Scrubber fan motor 1 x 35 HP (1.1 KV)
Pump motor 1 x 70 HP (1.1 KV)
Traction motors: 2 x 35 HP DC motors
2.The Launch Vehicle
The launch vehicle is the main platform from which the continuous miner
and conveyor cars enter the coal seam. A central “ belly belt” receives the
coal from miner and conveyor cars as added, and transports it to a stacker.
Additionally the launch vehicle houses the power centre and operator
control centre, plus hydraulic system to provide thrust force for mining
advance and retreat and machine positioning.
Specifications
Length : 29 m
Width : 9 m
Height : 8.5 m
Weight : 300 T
Motors: 2 x 200 HP, 1.1 KV ( operates hydraulic pumps)
Belly belt motor 75 HP , 1.1 KV
Ground pressure: 1.95 kg per square cm

4. 2. Conveyor Cars
Wheel mounted conveyor cars, known as Addcars are added as the
continuous miner advances under the highwall. It is also known as screw
conveyors.
Specifications
Length: 12.5 m
Width : 1.4 m
Motor : 40 HP
Weight: 12 T
3. Stacker
The stacker receives the coal from the launch vehicle belly belt and can
either discharge into trucks directly or stockpile coal to a height of 5.0
meter.
Specifications
Motor: 75 HP, 480 V
Production: On and average 3000 tones per day and 1 MTPA can be
achieved with this machine.

5. 4. Loader
Loader is used for loading and unloading of conveyor cars.
5. Dozer
It is required for leveling and compacting the platform used for the highwall
mining.
Safety Features of Equipment:
Miner:
 HORTA (Honeywell Ore Recovery and Tunneling Aid) ---
It provides real time horizontal guidance in conjunction with miner steering
system. The position of the miner head (heading, pitch, and roll) is
continuously monitored using the (HORTA) system. The HORTA system was
originally developed for the military in USA, and uses three-axis, ring-laser
gyroscopes and three-axis accelerometers. A monitor in the launch vehicle
shows the position of the miner relative to the planned heading, allowing
the operator to steer the miner and make adjustments in cutting height to
keep in seam. This ability is important to the overall safety of Highwall
mining, as the highwall miner holes can be mined to designed
specifications, ensuring that the web pillars are the correct size to carry
overburden loads. Stability of Highwall and web pillars depend upon the
accuracy & correct interpretation of HORTA by the operator sitting in the
operator’s cabin of H/Wall machine. Deviation of web holes from the
projected direction can lead to major disaster. There are many cases of
Highwall collapse due to failure of web pillars in U.S. One case of Highwall
slope failure is shown in figure below.

6. Figure 8-Site of massive web pillar collapse resulting in highwall slope
failure. Photograph was taken from adjacent spoil pile. Highwall is about
150 ft high. A 110-ton coal haulage truck is buried in rockfall debris.
 Inflammable gas Detector-----
Miner has fitted with CH4 detector. Automatic power cut off system when
inflammable gas is 1.25% or more.
 Inclinometer—It is fitted into Launch Vehicle and used for setting suitable
inclination (50
to 70
from horizontal) to miner and conveyor cars before
entering into inclined seam. If the seam is steeply inclined, the platform is
made sloping (50
to 70
) towards the Highwall toe, so that the total
inclination to the miner matches with the seam inclination.
 Gamma sensors—
It is used for vertical guidance to keep the miner within the seam to
eliminate dilution. The system uses gamma detectors at the miner
head/bottom gathering arm pan to avoid cutting into the roof or floor. This
allows the system to attain high penetrations from the highwall and
minimizes out-of-seam dilution.
 All electrical apparatus are Flame Proof.
 Interlock with water supply---
Miner stops working when water supply to the cutting head is not available.

7. Launch Vehicle:
 Rugged and robust canopy
 Pull chord
 Emergency buttons
 All electrical apparatus are FLP
 Metal halide lamps top down
 Cat walk with fencings and doors
Add Car:
 All electrical apparatus are FLP
Stacker:
 Pull chord
 Emergency button
LIMITATIONS:
 Miner penetration capacity is limited by seam gradient with a maximum
of 16 deg. It can penetrate to a length of about 600 m to 300 with flat
to 16 deg gradients, respectively.
 It is not suitable for soft roof and soft floor. Roof should be strong
enough to bear the strata load till the completion of entire length of web
cutting and retreating of machine.
 Geological disturbances, like fold, faults etc. in the path of cutter
creates problem in further advancement.
Ground Control Analysis of Highwall Mining
Ground control analysis is the very critical pre-mining activity for High wall mining.
This technology is new for India, but very popular in USA and Australia. Till now USA
has completed around 20 High wall mining projects with few cases of highwall
collapses due to webs failure.
The approaches to web and barrier pillar design involved three basic steps:
 Application of empirical pillar design formulas,
 Back-analysis of available information from past augering operations, and
 Numerical modeling analysis to confirm design performance and test its
robustness.
When designing a high wall mining, the mining engineer must specify
1) Web pillar width, 2) number of web pillars between barrier pillars and 3) barrier
pillar width. The other design parameters determined by the high wall miner are
hole width (or web cut), the mining height and the overburden depth. In
addition, the mine planner must estimate the pillar strength, the applied stress
on pillars and the pillar stability factor.

8. Design of Web pillar
Strength of Web Pillar
Numerous empirical formulas are available to predict coal pillar strength, but Mark-
Bieniawski formula for rectangular pillar is best suitable Web and Barrier pillar
design.
Bieniawski formula for square pillar design is;
SP = SI[ 0.64 + 0.36 W / h ] (1
Where:
Sp= strength of Square pillar
SI = in situ coal strength = 6.0 for US condition and > 6.0 for Indian condition.
W = width of square pillar, and h = mining height
Later Mark modified this formula to design the rectangular pillar, which is known as
Mark- Bieniawski formula. The Mark-Bieniawski formula applies best for web pillars,
which are very long, narrow rectangular pillars. By far, the most widely accepted
formula for web pillars design in the United States today is the Mark-Bieniawski pillar
design formula.
Mark- Bieniawski formula for rectangular pillar is;
SP = SI [0.64 + 0.54 W / h – 0.18 W2
/Lh] (2
Where:
Sp= web or barrier pillar strength
SI = in situ coal strength
W = web or barrier pillar width, h = mining height, and
L = length of the pillar.
t
Front view of Highwall mining face
HIGHWALL BENCHES
Web Cuts Web Pillars

9. In the case of high wall mining where the pillar length (miner penetration) is much
greater than either the pillar height or width, the last term may be omitted, and
Mark- Bieniawski formula (2) reduces to;
SP = SI [0.64 + 0.54 W / h] (3
In situ coal strength is normally taken as 6.2 MPa (900 psi, not for Indian Coal Mines).
For Indian Coal Mines, it is more than 20 MPa.
In India first high wall mining Technology was applied at RG OCP-II of SCCL and
completed successfully with little problem of roof collapses. Ground control layout
was formulated by CIMFR, Dhanbad. Web pillars strength was designed by using the
CIMFR`S formula, which is as follows.
Sp =0.27pc* h-0.36
+ (H/250 +1)(We/h -1) Mpa………………………………….(5)
Where, Sp = strength of web pillar (in Mpa)
Pc = compressive strength of sample of 25mm cube (23.8 Mpa);
h = height of extraction (in meter);
H = depth of cover(in meter) , and
We = equivalent width of web pillar (in meter)
= 4A/P
= 2W1*W2/W1+W2 (for rectangular pillar )
= 2W1 (W1+W2 ≈ W2 ,for long narrow web pillar of high wall)
Where, W1 is the width of web pillar
Stress on web pillar
Once web pillar strength is determined, an estimate of pillar loading is required to
calculate a safety factor. Pillar loading is estimated using tributary area load theory
as follows:
LP= SV(W + WE)(L)/W*L
Or, LP= SV(W + WE)/W ----------------------------------------(6
Where,
Lp = average vertical load on the pillar

10. SV = in situ vertical stress W
= web pillar width, WE = entry width (or web cut width) and L= length of web cut
The high wall mining equipment dictates the hole width, which varies from 2.7 to 3.6
m. In situ vertical stress depends on the overlying rock density and overburden
depth. Vertical stress gradient is typically 0.025 MPa/m. Overburden depth may be
taken as the average of maximum overburden depth and minimum overburden
depth on a high wall mining web pillar. 75% weightage is given to the maximum
overburden depth and 25% weightage to the minimum overburden depth, which is
as follows,
H = 0.75 * HMAX+ 0.25 * HMIN (7
Where:
HMAX = maximum overburden depth,
HMIN = minimum overburden depth, and
H= average depth of cover
And In-situ vertical stress,
SV = density of rock * overburden depth
Or, SV = 2.5 * H , t/m2
= 0.025 * H, Mpa
Hence, LP = SV(W + WE)/W
or, LP = 0.025 H (W + WE)/W Mpa
Finally, the safety factor of web pillar is calculated as:
SF = SP/LP (9
For design purposes, the stability factor for web pillars typically ranges from 1.3 to
2.0. CIMFR designed the FOS of web pillar of high wall mining at RGOCP-II in the
range of 1.5 to 2.0. FOS of 1.5 for top most seam (I-seam) , and 2.0 for lower
seams (II, IIIA, III and IV- seams)
Design of barrier pillar
Strength of barrier pillar
Strength of barrier pillar can be calculated by using `Mark- Bieniawski formula or
CIMFR formula.
Mark- Bieniawski formula is;
SBP = SI [0.64 + 0.54 WBP / h] (10
Where, SBP = strength of barrier pillar, SI = In-situ coal strength= 6.0 for US
condition and > 6.0 for Indian condition, WBP = width of barrier pillar and h= height
of barrier pillar.

11. If the number of web pillars in a panel is selected as “N”, then the panel width is
given by
WPN = N (WWP + WE) + WE (11
Where, WPN = width of panel , N = No. of web pillars in the panel, WWP = width of
web pillar and WE = width of web cut (or width of cutting machine). A sub- panel
may be created in the panel for more safety. Generally 10-20 web pillars are taken
in a panel or sub-panel.
Stress on barrier pillar
Neglecting the stress carried by the web pillars (i.e. assuming that they have all
failed), the average vertical stress on a barrier pillar using Tributary area method as
in equation (6) is,
LBP= SV (WPN+ WBP) / WBP (12
Where, LBP= stress on barrier pillar, SV = In-situ vertical stress, WPN = width of
panel or sub-panel and WBP = width of barrier pillar
Similarly, the stability factor for barrier pillars against strength failure is simply
SFBP = barrier pillar strength / barrier pillar stress
Or, = SBP / LBP (13
Because the stress carried by web pillars within a panel is neglected, the stability
factor for barrier pillars can be as low as 1
Barrier pillars with a W/h (width/height) ratio greater than 3 are superior for sound
geomechanics reasons. So, assuming safety factor of barrier pillar, the barrier width
can be calculated.
Numerical Modeling Analysis:
The empirical method used for the web and barrier pillar design should be confirmed
by mining experience in a wide variety of mining types and geological conditions by
using Numerical modeling technique.
First experience of High wall mining in India at RGOCP-II of
SCCL
Before 2005 no any Indian mining operators dared to think about this technology to
adopt in their mines. In 2005, SCCL tender was floated and at the end of year 2006,
the contract was awarded to a Hyderabad based company (Advance Mining
Technology). In tender 18 months time were given to the bidder to procure the
machinery and take permission from DGMS. The process included a visit of DGMS
and senior official’s of Labour Ministry to the equipment supplier (ADDCAR Highwll
System, USA) facility and mines in the US to witness and approve the concept and

12. its adaptability in Indian mines. After clearing all litigations, the High wall mining
equipment was transported to the project site (RG OCP-II) in July of 2010, but the
site preparation and equipment assembling took another 4 months and finally the
High wall mining was inaugurated on December 10, 2010.
Initially, High wall mining was proposed for four seams, viz. I, II , III and IV seams
respectively ( nomenclature from up to down ) having thicknesses 5.2- 6.0m, 3.1-
4m, 11 – 12.5m and 3.7- 4.1m respectively. There is clay parting of 1.0m in I and II
seams. III and IV seams are free from any contamination. Hence, major coal and
quality coal is blocked in III and IV seams. In the mine I and II seams have already
been extracted upto the boundary and open to air, but III and IV seams (bottom
seams) are partly extracted and backfilled and partly under extraction. Therefore,
High wall mining was not possible in III and IV seams. So, first high wall mining
witnessed II seam and then I seam. The Highwall mining block was generally divided
into Panel-A and Panel-B, the extraction cuts were planned in these panels along
apparent dip and full dip directions, respectively.
DGMS permitted the extraction of coal by High wall mining at RG OCP-II of
SCCL by putting the following terms and conditions.
1. The extraction seams shall be in ascending order i.e. starting from No. IV seam
and upwards.
2. The no. of galleries/entries, length and width of galleries, no. of web pillars,
height of extraction, its dimensions etc., shall be made in accordance with
conditions no. of Annexure I attached to this permission letter.
3. In this connection your special attention is invited to Regulation 117 of the
CMR,1957 regarding precautions against fire to be taken for strict compliance.
4. Regulation 112(1)(c) read with this Directorate’s circular no.11 of 1959 regarding
fencing of the surface area likely to subside.
5.0 Please note that, this permission is subject to the following conditions:
5.1 In the event of any change in the circumstances connected with this permission,
which is likely to endanger the life of workmen employed in the mine or
endanger the mine, the mining operations for which this permission has been
granted shall be stopped forthwith and intimation thereof sent to this
Directorate. The said mining operation shall not be resumed without express and
fresh permission permission in writing.
5.2 If at any time any of the conditions subject to which this permission is granted is
violated or not complied with this permission shall be deemed to have been
revoked with immediate effect. The above permission may be amended or
withdrawn at any time, if considered necessary in the interest of safety.
5.3 This permission is being issued specifically under the regulations mentioned
above, and without prejudice to any other provisions of law including the Mines

13. and Minerals (Regulation & Development) Act, 1957 and Mineral Concession
Rules 1960, which may be or may become applicable at any time.
5.4 The above permission may be amended or withdrawn at any time, if considered
necessary.
5.5 The Directorate shall be informed as soon as the mining operations are
commenced in accordance with the above permission and intimation about
completion of mining operations shall also b sent promptly and in any case not
later than one month thereof.
Annexure- I
Conditions governing extraction of coal by High wall mining Technology at
Ramagundem opencast II Mine of M/S SCCL.
1.0 Before commencement of extraction of coal:
1.1 Check survey and leveling of the area shall be made. If any discrepancy is
noticed, the extraction shall not commenced and the Directorate shall be
informed with a copy of correct plan/sections indicating the difference and
extraction shall not be commenced except with the prior approval of the
Directorate.
1.2 Adequate steps, including provision of suitable garland drains shall be taken to
prevent accumulation of flow of water on surface above the panel.
1.3 Since the drivages are proposed to be made from floor of the quarry, the
quarry bottom shall be kept free from water. Adequate pumping arrangement
shall be provided to deal with water, if any.
2.0 The manner of extraction shall be as follows:
(i) The total identified area for high wall mining shall be divided into
two blocks called A & B.
(ii) The extraction galleries/cuts shall be made in these locks along apparent dip in
blocks A and along full dip in blocks B.
(iii) The width of the galleries proposed to be driven in all the panels/seams shall
be kept at 3.5m(cutter width).
(iv) seams I and II shall be extracted in both blocks A and B.
(v) While extracting III and IV seams :
 The galleries /web pillars in both the seams shall be columnised.
 Long term stability of the pillars /wall shall be so designed as to ensure a
factor of safety of more than 2 in IV seam and III seam.
 Alternate long and short galleries as proposed shall be extracted due to wider
variation in depth.

14. (vi) The galleries/cuts and the remnant web pillars shall be made to ensure long
term stability of workings/slope etc. Seam I and Seam II shall be extracted in
such a way that a factor of safety of more than 2 for Seam II and more than
1.5 for seam I shall be achieved.
(vii) The galleries shall be driven along floor of in IV seam and along roof of III
seam, so that a minimum solid parting of more than 5.0m is left between III
and IV seams.
3.0 Keeping the conditions in view, the dimensions of galleries/web pillars etc. in
different seams/sections shall be made and maintained as given below:
3.1 seam No. I, a factor of safety :>1.5
Seam Parameters Panel-A (in mtrs) Panel-B (in mtrs)
I Seam
Seam height 6.7 6.7
Gallery width 3.5 3.5
Extraction height 4.0 4.0
Web pillar width 4.8 5.5
Barrier pillar width 15.0 17.0
No. of galleries/entries 35 38
Panel Avg.width 320 375
Panel Avg. Length 107 135
Sub panel width 78.2 93.5
No. of web cuts 10 11
Cover 15-140 115-140
Factor of safety 1.5 1.5
3.2 Seam No. II, a factor of safety :>2.0
Seam Parameters Panel-A (in mtrs) Panel-B (in mtrs)
II
Seam
Seam height 4.1 4.1
Gallery width 3.5 3.5
Extraction height 4.0 4.0
Web pillar width- L- 8.1 8.5
Web pillar width- S- 2.3 2.5
No. of galleries/entries L28, S28 L28, S28
Panel Avg. Width 315 325
Panel Avg. Length 145 145
Panel Avg. Length 35 40
Cover 60-170 140-170
Factor of safety 2.0 2.0
However, the stability analysis of the dimensions of the cut, web as well as barrier
pillars shall be reassessed by another/International Scientific Agency having
experience in design of cut & web pillars in High wall mining.
4. The high wall shall be monitored to detect any movement in any part of the
standing slope using continuous scanning system to ensure any instability in

15. advance any to protect any danger to persons at or near the High wall miner.
Ground movements from surface shall be monitored to find out the web pillar
failures, if any. The ground monitoring activities on surface and along slope of
high wall shall be carried out in association with a Scientific Agency.
(i) The area shall be worked after thorough loose dressing. Reinforced wire mess
shall be installed near the zone which may be vulnerable to rock fall.
(ii) A strong protective canopy shall be provided on the launch vehicle to ensure
safety of work persons deployed on the vehicle.
(iii) A protective bund shall be provided at the working level to arrest the small
boulders falling from the lower portion of the standing high wall slope.
(iv) A bund or g garland drain or a combination of the two shall be provided at the
Highwall crest to avoid inrush of surface rain water into the pit. The water diverted
along the garland drain/bund shall always be diverted away from the quarry.
(v) The existing tension cracks , if any shall be filled and sealed properly before the
onset of the Monsoon. The drain should be properly graded to prompt quick water
movement and minimize the chances of ponding.
(vi) High wall slopes shall be checked for loose rock and adequate precautions shall
be taken for a distance of 15m on either side of the equipment under operation.
(vii) Persons shall not work or travel between the equipment and the high wall,
where there is a likelihood of fall of rock or other injury.
(viii) A hand plan of 500:1 showing the sequence of extraction shall be prepared and
given to all Supervisory staffs/Officers.
(ix) The supervisory staff and officers shall be adequately trained for the operation
of high wall mining.
(x) Copy of the approved code of practice of high wall mining shall be given to all
officers/supervisory staff and the same shall be implemented.
(xi) Stacker conveyor shall always be positioned at the rear end of the launch
vehicle to receive coal from the belt conveyor and to transfer to a stock pile.
5.0 A proper navigation system shall be provided to constantly monitor the position
of the continuous miner using HORTA (Honeywell Ore Recovery Tunneling Aid ) or
similar equipment with facilities to give the coordinates of the cut/gallery. This
system shall ensure guiding of continuous miner according the planned headings.
This system shall also ensure horizon control of the miner, gradient, parting between
the seams, web pillar left between the galleries etc.
5.1 A steering system shall be provided to steer the continuous miner while
progressing and even crossing undulations. This system shall ensure that the rib
thickness is not compromised or reduced.
5.2 Continuous miner proposed to be used shall be of approved type by this
Directorate.

16. 5.3 No workings shall be made or extended when the % of inflammable gas exceeds
1.25 in the face. Sensors shall be provided on the machine for shutting off power
when the % of inflammable gas reaches 1.25%.
5.4 All electrical provided in addcars shall be flame proof and one such Addcar motor
shall be subjected for test for FLP features in India.
6.0 After extraction of lower/bottom seam, the out bye areas shall be filled upto the
level of the next higher seam to ensure complete packing of opening of the galleries
to prevent heating. The galleries shall be filled with incombustible materials/debris
within 72 hors of completion of drivages. The entire lengths of cuts/Galleries shall
also be filled with inert gases such as N2 or CO2 immediately before sealing off the
mouth/entries by the incombustible materials/debris.
6.1 The width of the bench formed against high wall shall not be less than the
maximum dimension of the launch vehicle plus 10m for movement of machinery,
like front end loaders, dozers , graders, tractors with or without attachments.
6.2 The width shall be suitably increased in case of any need for safe operation and
type of equipment in use and any other operational considerations.
6.3Bench formed by dump material shall be thoroughly consolidated prior to
installation for safe positioning and operation of equipment.
7.0 Sequence of seam extraction. The sequence of extraction of coal shall be as
follows:
7.1 Generally the extraction of seams shall be done starting from bottom in
ascending order with opening designed for stability.
7.2 Superimposition of galleries and pillars shall be maintained in workings of all the
seam.
8.0 Blasting operations shall not be carried out within 500m from the hog wall
equipment. No person shall be admitted in to the galleries made in high wall.
9.0 Adequate instrumentation shall be provided to monitor noxious or inflammable
gases at the machine face and a written record shall be maintained for the same.
9.1 In the gallery, coal cutting shall be done in conjunction with jet of water with
adequate pressure and the generation of inflammable gas shall be continuously
monitored, diluted or removed by air/inert gases.
9.2 Air born dust shall be suitably suppressed by adequate water spraying
arrangements.
9.3 Water spraying arrangement/wet cutting shall be provided with the continuous
miner to reduce coal dust concentration. A flow of 155-195 lit/min of water shall be
supplied to the machine.
9.4 On continuous miner inter-locking arrangement in the form of flow switch with
safety circuit shall be provided to trip the machine power centre stopping the

17. equipment completely in the event of dropping of water flow rate in the miner at or
below 160 lpm.
10.0 Adequate supply of water for all operations and dust suppression measures
shall be provided at the site by portable water tankers and necessary head shall be
created either by pumping or by sitting the tanks at an elevated platform to create
the desired head.
10.1 A strong blast shield shall be provided on the front side of the launch vehicle
to prevent propagation of fire/blast etc., if any from the gallery.
11.0 Supervision, control and Management:
11.1 The operation shall be carried out under the supervision and guidance of
representatives of M/s Advance Mining Technologies, who would be operating this
panel on contract basis complying with all statutory obligations.
11.2 Adequate no. of trained competent persons shall be provided for the operation
and maintenance of high wall machinery and other associated equipment and they
shall be duly authorized in writing by the Manager.
11.3 Extraction of coal by high wall mining technology shall be kept under overall
supervision of one exclusive First Class Assistant Manager, who shall place and
coordinate the work well in advance.
11.4 The entire operations in each shift of the high wall mining technology shall be
placed under the charge of a 2nd
Class Asst./Under Manager, who shall be assisted
by an engineer having adequate experience for carrying the maintenance operations
in each shift.
11.5 Overall maintenance, testing and repair operations shall be kept under the
supervision of a senior engineer possessing Degree in Engineering under the overall
incharge of Ist Class Asst. Manager. He shall also be provided with required facilities
and adequate trained manpower for the purpose.
11.6 Routine condition monitoring and performance monitoring of the high wall
mining face and associated equipments shall be kept under an Asst. Manager duly
authorized for the purpose, who shall be provided with adequate number of
competent persons and facilities for the purpose.
12.0 Standard Operating Procedures:
Code of Practice for high wall mining operations shall be framed and submitted to
this Directorate for approval.
12.1 Standard Operating Procedures (SOP) for installation and maintenance of face
machinery & equipment viz. Continuous Miner, Loader, Launch vehicle and
associated power equipments shall be framed based on the hazard apprehended. A
copy of the SOP shall also be submitted to the Directorate.

18. 12.2 Suitable lock out system shall be provided and maintained at Continuous
miner, in order to prevent self starting of the machinery inadvertently during repair
or maintenance work.
12.3 A contingency plan for withdrawal of continuous miner safely in case of
breakdown or stoppage de to fall or any other reason shall be formulated and
submitted to the Directorate.
13.0 Safety Management Plan:
A Safety management plan (SMP) on the manner of extraction, operation of
continuous miner, Launch vehicle and also for very principal activities during
extraction is required to be prepared based on the Risk Assessment conducted at the
mine and the suggestive control mechanism for each hazard/sub-hazard shall be
documented, which shall also to be reviewed periodically for addition, deletion or
modification as detailed in DGMS (Tech)(S&T) Circular No.13 of 2002.
14.0 Emergency plan: For dealing the situation, in the event of any abnormality
Emergency plan shall be made and submitted to this Directorate. All persons
working in the panel shall be appraised and trained in this regard.
Extraction of II Seam by Highwall mining at RG OCP-II
II Seam has a maximum thickness of 4.1m that can be extracted in Panel-A and
Panel-B. Alternate short and long cuts were designed in this seam for achieving
maximum recovery. Highwall mining in Panel-A was designed along apparent dip,
because mine barrier at this particular location was in dip direction and 4.1 m height
of coal seam was not sufficient for the machine to drive in apparent dip. That is why
proposal of Highwall mining in Panel-A was cancelled. And first Highwall mining
started in Panel-B of II seam then in I seam.

19. Extraction in Panel-B of II- Seam:
First Coal extraction by Highwall mining at RG OC-II was started in Panel-B of II
seam. Panel-B lies along dip-rise direction of the seam. The seam is having 0.75m
clay parting lying 1.0m below the roof. Initially 0.5m of coal seam was left to keep
intact the clay parting, but after some instances of roof collapses during web
drivages 1.0m thickness of coal was left below clay for roof stability. After that no
any cases of roof collapse was observed. In some holes, stone bands were observed
while driving (in mid-length), which forced the machine to retreat back. Panel-B was
designed for alternate long and short holes for better stability and maximum
recovery of coal. The pattern is shown in next page.
A VIEW OF HIGHWALL MINING MACHINE WORKING AT RG OCP-II OF SCCL

20. PLANE VIEW OF HIGHWALL AT OC-II
Panel-A
Panel-B
Active Quarry
Edge
Surface
Boundary Edge
Panel-A
Panel-B
Seam-II
Seam-I

21. Sectional View of Highwall panels
Pattern of Long and short web cuts Seam-II Characteristics
Empirical design parameters for Ground Control
Seam Parameters Panel-B (in mtrs)
II
Seam
Seam height 6.0
Extractable height 4.1
Extraction height 4.0
Gallery width 3.5
No. of Long galleries/entries 28
No. of short galleries 28
Panel Avg. Length 325
Web width of Long holes(WL) 8.5
Web width of short holes (WS 2.5
Avg. length of Long holes (LL) 145
Max. length of short holes(LS) 40
% of extraction 36.6
Cover 140-170
Seam gradient 1 in 4.9
Factor of safety 2.0
Web pillars were designed by using CIMFR`
s
pillar design formula. Factor of safety
was assumed 2.0 for long stability. Using CIMFR formula and data shown in above
table, the graph between depth of cover and width of web pillar has been drawn
here.
1.0m coal left
Against roof
Height of web cut
8.5m
Web Cuts Web Pillars
1.0m clay parting

22. Web Pillar Width for 3.5m wide hole and FOS-2.0 using CIMFR
formula
0.00
5.00
10.00
15.00
20.00
25.00
50 100 150 200 250 300 350 400 450 500 550 600 650
Depth of Cover(m)
WidthofWebPillar(m)
For 4m Gallery height
For 3m Galler height
Graph of web pillar vs. depth of Cover as per CIMFR formula
The comparative graph by using the above mentioned data and Mark- Bieniawski
formula of pillar design has been drawn as shown below.
Web Pillar Width for 3.5m Wide Hole with stability factor 2.0 using
Mark- Bieniawski formula
0.00
5.00
10.00
15.00
20.00
25.00
30.00
35.00
40.00
50 100 150 200 250 300 350 400 450 500 550 600 650
Depth of Cover (m)
WidthofWebPillar(m)
FOR 4m Gallery height
FOR 3m Gallery height
Graph of web pillar vs. depth of Cover as per Mark-Bieniawski formula
Design of barrier pillar :
Barrier pillar should be left at regular intervals. While designing barrier pillars
to ensure arresting of cascading web pillar collapse, following assumptions were
considered.

23. 1) Barrier pillars should be able to take additional load from the excavated
portion on both sides assuming complete collapse of the web pillars.
2) Wilson’s approach is used to find the abutment loading on to the barrier pillars
from the caved goaf. This approach is based on the theory that the full cover
pressure in the goaf occurs at 0.3xH distance from the edge of the barrier
pillar.
3) The barrier pillars should have a minimum safety factor of 2.0, when the web
pillars on one side of the barrier are fully crushed forming a caved zone; and a
minimum safety factor of 1.5 when both the sides are caved.
4) The spacing between the barrier pillar should be such that the width of each
sub-panel should not exceed the critical width resulting in the occurrence of
full cover pressure in the middle of the sub-panel, say WBP < 0.6 x H.
Re-design of web thickness in II Seam extraction from numerical modeling
analysis by CIMFR.
Earlier web thickness design was based on the theoretical vertical cover acting on
the web pillars based on the final slope angle and seam inclination. However the
numerical modeling studies show that the vertical stress at the seam level may be
considerably more than the cover pressure near the slope surface due to the induced
stresses caused by heavy blasting of open pit. However the vertical stress equals the
theoretical cover pressure after about 100-120m of whole length.
At 40m short hole length the actual cover pressure may be 70% higher which may
bring down the safety factors to about 1.2-1.4. At 85m hole length, there is still
about 20% increase in the vertical stress as compared to the theoretical cover
pressure. At 160m hole length, it is as per the theoretical cover pressure.
With this additional knowledge following points are strongly recommended:
1. For 85m long hole region, after considering hole deviation and 20% increase in
vertical stress, the web pillar thickness required is 5.5m; and all the holes
could be kept long, up to 85m length.
2. For region beyond the 100m face length, towards active workings of the mine,
where the long hole length will be 160m, the web pillar thickness should be
8.5m; all the holes could be long (160m) and the short holes (40m) as per
earlier design should not be driven.
3. The concept of an alternate short hole (40m) for improving recovery should
not be practiced for Seam II from now on.
The above change will result in about 4% less recovery, but considering better
stability and success of the first Highwall face, CIMFR strongly recommends the
above extraction pattern and suggests to change the current pattern with immediate
effect. Please do the needful to effect the above changes and may also discuss with
the SCCL officers on this matter if needed.

24. Extraction of I -Seam :
After completion of extraction by Highwall mining in Panel- B of II- seam,
overburden was filled upto Panel-B of I-seam to extract I-seam. Extraction in Panel-
A of I- seam was done after extraction in Panel- B of I-seam and back filled upto
Panel- A. The web and barrier pillars were designed by taking FOS= 1.5, considering
the short term stability of web cuts. The web pillars in this seam are designed only
for short-term stability; say a minimum safety factor of 1.5. All the extractions are
to the full length possible. However, this requires leaving barrier pillars at regular
intervals.
Design parameters for I-seam are shown below.
Seam
Parameters Panel-A (in mtrs) Panel-B (in mtrs)
I Seam
Seam height 6.7 6.7
Gallery width 3.5 3.5
Extraction height 4.0 4.0
Web pillar width 4.8 5.5
Barrier pillar width 15.0 17.0
No. of galleries/entries 35 38
Panel Avg. width 320 375
Panel Avg. Length 107 135
Sub panel width 78.2 93.5
No. of web cuts 10 11
Cover 15-140 115-140
Factor of safety 1.5 1.5
Plan view of Pattern of web cuts in I-Seam with sub- panel barrier

25. Drawing depth of cover vs. width of web pillar as shown in fig. below.
Sp =0.27pc * h-0.36
+ (H/250 +1)(We/h -1) Mpa
LP= SV(W + WE)/W
where, SV = 0.025H , WE = 3.5m and
H = Avg. depth of cover , FOS =1.5
Web Pillar width for 3.5m wide hole with stability factor of 1.5 using
CIMFR formula
0.00
5.00
10.00
15.00
20.00
50 100 150 200 250 300 350 400 450 500 550 600 650
Depth of Cover(m)
WidthofWebPillar(m)
For 4m Gallery height
For 3m Gallery height
Graph of web pillar vs. depth of Cover as per CIMFR formula
Problems faced while operating Highwall mining at RGOCP-II
 Lack of expertism in Highwall mining in India posed a problem in proper
operation of machine.
 Navigation system was not able to picturise clearly the parting being left
against the roof.
 Instance of roof fall for full length of hole while cutting the coal.
 Highwall mining along apparent dip was not successful in Panel-A, due to face
in dip- rise direction.
 Back filling upto the seam level for shifting the machine in another seam
caused delay in operation.
 Encountering stone bands in the face.
 Accumulation of water in the galleries due to intermittent delays in drivage
when m/c is under breakdown.

26. Post Highwall mining activities
 The entire lengths of cuts/galleries shall be filled with inert gases such as N2 or
CO2 immediately before sealing off the mouth/entries. At RG OCP-II,
atmospheric N2 was used, but in author’s view as N2 is lighter than air, so it is
not suitable for dip galleries.
 The galleries shall be filled with incombustible materials/debris within 72
hours of completion of drivages.
 Complete back filling of area with O/B, so that chances of accumulation of
rain water in the cuts/galleries will be less.
Suggestions for future Highwall Mining operations put by CIMFR
 When the open pit touches its boundaries and being worked with benches, the
Highwall operations may be planned in descending order. The working benches
will provide platform for the extraction of the remaining portion of the seams.
 The Highwall operations may go parallel with the open-pit final slope
formation in descending order.
 A suitable backfilling technology may be developed in order to improve the
recovery and ground condition.
 A suitable Highwall cutter may be used such that it takes a narrow cut while
entering and widens the cut while retreating by thinning down the web pillar
on both the sides. This can give better ground conditions and can also improve
the recovery.
CONCLUSIONS
Highwall mining is an efficient and economic means of surface mining. HWM requires
a thorough knowledge of the strength and physical properties of the immediate roof,
coal, and immediate floor strata. Engineering design and surveying the orientation of
each HWM cut is necessary to avoid ground control problems. Ground control is
critical in HWM because a significant portion of the project cost (i.e. cost of HWM
machine) lies beneath the hillside with virtually no easy access to resolve a roof fall
or pillar squeeze. The analytical design equations provided in this paper present the
base from which web pillar design should begin. However, as illustrated by the case
histories, site conditions and characteristics of the coal seam and immediate roof
strata frequently require deviation from the web pillar width calculated using the
Mark/Bieniawski equation or CIMFR equation. In author’s view Mark-Bieniawski
formula is more suitable for designing long web pillars of Highwall mining.

27. REFERENCES
1. Newman, David President ,Appalachian Mining and Engineering, Inc.
Lexington, KY and Zipf, R. Karl Mining Engineer, NIOSH-Pittsburgh Research
Laboratory Pittsburgh, P. Analysis of Highwall Mining Stability - The Effect of
Multiple Seams and Prior Auger Mining on Design.
2. Shen, Baotang and E. Duncan Fama, Mary. Review of Highwall mining
experience in Australia and a case study
3. Vandergrift, Tom. Associate Agapitos Associates, Inc.Golden, CO, USA and
Arcia,Juan, Senior Mining Engineer Kennecott Energy, Colowyo Mine Meeker,
CO, USA. Highwall Mining in a Multiple-Seam, Western United States Setting
Design and Performance. 24th International Conference on Ground Control
in Mining Morgantown, West Virginia, USA, August 2-4, 2005.
4. Mark, Christopher, PhD and E. Chase, Frank. Analysis of Retreat Mining Pillar
Stability (ARMPS).
5. Karl, R., JR, Zipf and Christopher Mark. Ground Control for Highwall Mining.
6. CIMFR, Extraction Strategy and Pillar Design for Highwall Mining at RG OCP-II
of SCCL.
7. Rao, Nageshwar, Gen. Manager, SRP, SCCL. Summary of Highwall Mining at
OC-II, of SCCL.
TIKESHWAR MAHTO
DY. Director of Mines
Safety, Bilaspur Region