selection of longwall powered roof supports with a case study of Singareni Collieries company limited.

1. Selection of Powered Roof Supports
for Longwall Face
U Siva Sankar, U.Mgr
Project and Planning Department
SCCL, ANDHRA PRADESH
Layout of Longwall Face
Sectional view along x-x
x
x Plan view
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2. Close View of Longwall Face
Purpose of Powered Roof Support in Longwall Face:
To ensure the Safety of face Crew
To ensure Controlled Roof Caving
To Prevent flushing of Goaf material into the face, and
To facilitate Smooth Functioning of Longwall face
Face length decides the number of supports to be
installed in the face
Cost of Supports is nearly 70% of longwall package cost
and this cost increases or decreases w.r.t. face length.
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3. The success of a longwall face depends to a large extent on the
Type and Capacity of the Powered Roof Supports.
In India, different types of Powered Roof Supports of various
capacities were tried earlier, but 4 leg chock shields have been
the most widely used.
Several mines in India like Kottadih, Churcha and Dhemomain
had experienced catastrophic failures of long wall faces due to
ground control problems and inadequate capacity and design of
powered roof supports.
A case study summarizing the experiences of working Longwall
faces with IFS, 4-leg chock shields under varying contact roofs,
viz; coal and sand stone roofs were analyzed.
Types of Powered Roof Supports
4 - Leg
Shield
Lt: Chock,1950 Rt: Frame, 1951
6 - Leg Chock Shield
2 - Leg
Shield
4- Leg Chock Shield (1962)
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4. Powered Roof Supports - Design
Complete Canopy
Assembly
Complete Rear
Shield Assembly
Complete Base
Assembly
Earlier Caliper Canopy design was replaced with lemniscate
design to maintain uniform tip to face distance
Rigid canopy are replaced with extensible canopy to control
friable roof geologies
Powered Roof Support Canopy Designs
4

5. Caliper Shield Support
4 legged Chock Lemniscate Shield Support ,
Legs –V orientation
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6. 4x410 Tonne ,I.F.S , Chock Shield with rigid roof bar
4x410 Tonne ,I.F.S , Chock Shield with articulated
forward bar
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7. Conventional IFS
Name of the Project Make Support Capacity Working Depth of
(tonnes) & Type Range (m) Working(m)
BCCL
Moonidih Dowty, UK 4x280, Chock 1.24 - 1.82 400
Moonidih Kopex, Poland 6x 240, Chock 1.25 - 1.98 400
Moonidih Dowty, UK 4x280, Chock 1.49 - 2.90 400
Moonidih MAMC, Dowty 4x325, Chock Shield 1.90 - 3.20 400
Moonidih MAMC, Dowty 4x400, Shield 1.27 - 2.40 400
Moonidih Jessop/Gullick 4x400, Chock Shield 0.70 - 1.65 400
Moonidih Kopex, Poland 4x400, Chock Shield 2.00 - 3.50 400
ECL
Sheetalpur Gullick, UK 4x240 Chock Shield 1.40 - 2.09 420 - 450
Dhemomain Gullick, UK 4x360 Chock Shield 2.02 - 3.20 300
Dhemomain & Jhanjra Jessop/Gullick 4x550, Chock Shield 1.70 - 3.05 40 - 100
Jhanjra KM -130,USSR 2x320, Chock 2.50 - 4.10 40 - 90
Churcha & Jhanjra, Joy 4x680 Chock Shield 1.65 - 3.60 90 - 200
Kottadih, CDFI, France 2x470 Shield 2.20 - 4.70 180 - 220
Pathakera, MAMC, Dowty 6x240 Chock 1.11 - 1.74 110
SECL
Balrampur CMEI&E,China 4x650, Chock Shield 1.40 - 2.70 45 - 55
New Kumda CMEI&E,China 4x450, Chock Shield 1.40 - 2.70 45 - 55
Rajendra CMEI&E,China 4x450, Chock Shield 1.70 - 3.10 50 - 90
SCCL
GDK 7 & 9 Gullick, UK 4x360, Chock Shield 2.10 - 3.21 100 - 350
JK5 Gullick, UK 4x450, Chock Shield 2.0 - 3.20 138 - 265
VK 7 Gullick 4x360, Chock Shield 2.0 - 3.20 93-272
VK 7 Gullick 4x450, Chock Shield 2.0 - 3.20 38-382
GDK-11A Gullick, UK 4x430, Chock Shield 1.50 - 3.00 70 - 200
GDK-11A MECO&Gullick 4x450, Chock Shield 1.50 - 3.00 70 - 200
GDK-10A MAMC 4x750, Chock Shield 1.65 - 3.60 240
GDK-9 Extn. MECO 4x800, Chock Shield 1.65 - 3.60 225
PVK & GDK 9 CME, China 4x760, Chock Shield 2.20 - 3.40 54 - 297
List of Powered Roof Supports deployed in India.
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8. Historical overview of increasing shield
capacities
SCCL
Powered roof supports of 1750 tonnes was also Manufactured by Joy
International, and DBT Bucyrus, 2008
World’s biggest powered roof supports used at Anglo Coal’s
Moranbah North mine in Queensland, Australia, 2008
Capacity: 2x1750 tonnes
Weight: 62 tonnes
Range: 2.40 to 5.0m
Leg Dia: 480mm
Life: 90,000 cycles
World’s Biggest and Highest Rated Roof Support
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9. Longwall supports used in Australia (Source: Cram,2007)
Factors Affecting Support Selection
Thickness and Strength of immediate roof above the
supports (easily caving or massive)
Upper Main Strata Competency (including
strong/massive units) – thickness and strength of upper
roof, especially information on any units that may bridge
Floor strength
Support Design and Capacity to prevent spalling of the
face or weakness of roof between tip to face area
Alignment of jointing or cleating in the face area
Cutting height
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10. CLASSIFICATION OF LONGWALL ROOF STRATA
Vertical Stress Distribution in Longwall
Panel & Immediate Roof
Vertical stress Distribution in Immediate
roof
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11. Vertical Stress Distribution Immediate Roof
When the load in the front leg is higher, the vertical stress
distribution on the front portion of the canopy is the
largest and the horizontal force acts towards the face.
As a result, there is no tensile stress in the immediate roof
of unsupported area between the canopy tip and face line
and consequently the roof will be stable.
Conversely, when the load in the front leg is smaller, the
vertical stress distribution on the front portion of the
canopy is also smaller
The horizontal force acts towards the gob resulting in
development of tensile stress in the immediate roof of
unsupported area, causing roof failure.
Magnitude and type of Horizontal stress in
Immediate Roof
Load Ratio = Rear leg to Front leg
(After Peng, et. al.,1988)
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12. Main Roof
Case-1 Case-2
1. Massive Main roof with Weak Immediate Roof
Caving and bulking up of immediate roof supports main roof
leads to less weighting on face
In the above higher capacity support is not required
2. Massive Main Roof with Strong Immediate Roof
Does not cave properly and does not support upper strata
quickly leads to intense loading of longwall face
In the above higher capacity support is required
Under massive roof conditions, Supports having resistance
of 120 tonnes/Sq.m., are desirable under above conditions
based on Australian’s Experience.
METHODS USED FOR SUPPORT CAPACITY
DETERMINATION
Detached Block theory (Wilson, 1975)
Empirical Nomograph based method (Peng, Hsiung and Jiang,
1987)
Load cycle analysis (Park et al, 1992, Peng 1998)
Neural networks (Chen, 1998, Deb)
Various Numerical models (Gale, 2001, Klenowski et al, 1992,
UK Singh, G. Benerjee, Deb)
Ground response curves (Medhurst, 2003)
Convergence Vis–a-Vis Support Resistance (CMRI Approach)
Roof Separation Index, After U.K.Singh, e.t.al.
Plate Theory Proposed by Quan Ming Gao(1989)
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13. INSITU STRESS
SUPPORT CAPACITY
Bigger the Better �
Fig. Ground Reaction
Curve and support
response.
Fig. Impact of shield
capacities (setting
pressures) on
convergence.
Pressure Arch Concept
Performance of Shields under Unstable or
Poor or weak Roof Conditions
After Barczak T.M., (1992)
With inclined legs, 2 leg shields create compressive forces in the
immediate roof with which the roof is held in place.
Thus the stability of the roof can be maintained and support
efficacy can be improved under weak roof conditions
Positive setting of legs is not advisable in 4 leg chock shields
under weak roof conditions
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14. Operational characteristics
2 Leg and 4 Leg shields
Parameter 2- Leg shield 4-Leg Chock shield
Canopy ratio optimum at approx. 2 : 1 > 2:1
Canopy length short and compact longer canopy design
Supporting force into minimum distance to the due to construction
the roof coal face larger distance
Range of adjustment up to approx. 3 : 1 <3:1
Travelling route in front of / behind the props between the props
Handling very easy and quick more complicated
Possibility of faulty insufficient setting of
extremely low
operation the rear props
Cycle time < 12 sec > 15 sec
Requirement of
relatively small larger
hydraulics
Toe loading High Low
(Ground Pressure)
Floor penetration can be overcome with the use of Base lifting
device with solid base or with use of split base
Powered Roof Supports - Longwall
The illusion of chock shields helps in inducing
caving of goaf was ruled out with numerical
modelling studies.
There is an increasing trend of usage of 2 leg
shields all over the world.
The life of the PRS was also increased from
earlier 10,000 cycles to nearly 70,000 to 1 Lakh
cycles based on manufacturer and cost of
longwall package.
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15. SCCL GEO MINING CONDITIONS
1. EXTRACTION THICKENESS: 1.70 to 4.50 m (>4.50m WITH LTCC)
2. IMMEDIATE ROOF:
SHALY COAL OR SAND STONE
3. IMMEDIATE FLOOR:
SHALY COAL OR SAND STONE
4. COMPETENCY OF MAIN ROOF: Fg to Cg Sand stone
MASSIVE IN NATURE, with less Strength values
THICKNESS RANGE: 12 to20 m
MODERATELY CAVABLE to CAVABLE WITH DIFFICULTY
CAVING HEIGHT is 30 to 45m, i.e., 10 times of Height of Extraction
SCCL GEO MINING CONDITIONS
Geo Engineering properties of roof and floor strata of ALP (SCCL, 2007)
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16. CASE STUDY
Panel 1A
Panel 21
Layout of Longwall Panels in Top seam of PVK 5 Incline
Salient features of Longwall Panels under Study
Panel 1A Panel 21
Panel - A Panel - B
Dimensions (m x m) 62.5 x 500 150 x 420
Height of extraction (m) 3.0 3.0
Depth of workings (m) 48.0 Minimum 206 Minimum
85.0 Maximum 239 Maximum
Face Gradient 1 in 8.9 1 in 8.9
Support capacity 4 x 760 t 4 x 760 t
No. of Supports at face 43 102
Contact Roof Shaley coal Partially stone &
partially Shaley coal
Contact Floor Shaley coal Shaley coal
Setting pressure (Mpa) 25 28
Status of Underlying Depillared Depillared
seam, i.e., Middle Seam
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17. Specifications of Chock Shield of PVK
Support Range 2.20 to 3.40m
Support width 1.50 m
Support length 3.87m
Canopy ratio 2.50
Roof coverage 6.30 Sq.m
Yield load 760 tonnes
Support density 110 t/sq.m
Floor specific pressure 3.10 MPa
Force to advance conveyor 360KN
Force to advance support 633 KN
Support weight 20.50 tonnes
Pressure Distribution between Front and Rear legs
27
Front
25 Rear Average pressure
distribution between
Leg pressure (MPa)
23
front and rear legs under
21
shaly coal roof (Panel
19 No.1) – shallow short
17 longwall panel
15
34 95 145 212 279 355 429 498
Average face progress (m )
32
F ro n t
R ear
30
28 Average pressure
distribution between front
Leg Pressure(MPa)
26
24
and rear legs under stone
roof conditions (Panel
22
No.21)
20
Stone Roof Coal Roof
18
0 50 100 150 200 250 300 350 400
D is t a n c e F r o m B a r r ie r ( m )
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18. Performance of 4-leg Chock Shield at PVK
mine under varying roof conditions
Parameter Coal Roof Stone Roof
Compressive Strength (MPa) 9.3 to 11 MPa 16 to 21 MPa
Setting Pressure (% of Yield 65% 75%
Pressure)
Main Weighting Exposure (Sq.m) 8000 to 12500 7000
Periodic Weighting Interval (m) 15 to 25 10 to 12
Cavities Frequent Moderate
(crumbled)
Weighting Intensity Moderate Intense
Load Ratio Rear to Front 0.70 to 0.76 0.90 to 1.00
Capacity utilization (MMLD/RMLD) 60 to 65% 80 to 85%
MMLD: Measured Mean Load Density RMLD: Rated Mean Load Density
Conclusions
The desirable type and capacity of the powered roof support must
be selected based on the site specific geo-mining conditions.
While deploying longwall technology with foreign collaborations,
sufficient scientific study regarding suitability of powered roof
support under existing geo-mining conditions should be done.
Under immediate weak and strong roof conditions, containing
overlain massive sandstone beds, high capacity 2- leg shields of
same capacity are desirable over 4-leg chock shields.
Numerical modeling studies are to be conducted for better
understanding of the interaction between the shield and the
strata.
Faster rate of extraction and continuous monitoring of the shields
are the sine-qua-non for effectively combating strata control
problems.
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19. THANK YOU
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