Selection of Powered Roof Supports for Longwall Face
U Siva Sankar, Sankar, U.Mgr Project and Planning Department SCCL, ANDHRA SCCL, ANDHRA PRADESH
Layout of Longwall Face
Sectional view along x-x
x
x
Plan view
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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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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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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
Caliper Shield Support
4 legged Chock Lemniscate Shield Support ,
Legs –V orientation
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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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Conventional
Name of the Project BCCL Moonidih Moonidih Moonidih Moonidih Moonidih Moonidih Moonidih ECL Sheetalpur Dhemomain Dhemomain & Jhanjra Jhanjra Churcha & Jhanjra, Kottadih, Pathakera, SECL Balrampur New Kumda Rajendra SCCL GDK 7 & 9 JK5 VK 7 VK 7 GDK-11A GDK-11A GDK-10A GDK-9 Extn. PVK & GDK 9
IFS
Make
Support Capacity (tonnes) & Type
Working Range (m)
Depth of Working(m)
Dowty, UK Kopex, Poland Dowty, UK MAMC, Dowty MAMC, Dowty Jessop/Gullick Kopex, Poland
4x280, Chock 6x 240, Chock 4x280, Chock 4x325, Chock Shield 4x400, Shield 4x400, Chock Shield 4x400, Chock Shield
1.24 - 1.82 1.25 - 1.98 1.49 - 2.90 1.90 - 3.20 1.27 - 2.40 0.70 - 1.65 2.00 - 3.50
400 400 400 400 400 400 400
Gullick, UK Gullick, UK Jessop/Gullick KM -130,USSR Joy CDFI, France MAMC, Dowty
4x240 Chock Shield 4x360 Chock Shield 4x550, Chock Shield 2x320, Chock 4x680 Chock Shield 2x470 Shield 6x240 Chock
1.40 - 2.09 2.02 - 3.20 1.70 - 3.05 2.50 - 4.10 1.65 - 3.60 2.20 - 4.70 1.11 - 1.74
420 - 450 300 40 - 100 40 - 90 90 - 200 180 - 220 110
CMEI&E,China CMEI&E,China CMEI&E,China
4x650, Chock Shield 4x450, Chock Shield 4x450, Chock Shield
1.40 - 2.70 1.40 - 2.70 1.70 - 3.10
45 - 55 45 - 55 50 - 90
Gullick, UK Gullick, UK Gullick Gullick Gullick, UK MECO&Gullick MAMC MECO CME, China
4x360, Chock Shield 4x450, Chock Shield 4x360, Chock Shield 4x450, Chock Shield 4x430, Chock Shield 4x450, Chock Shield 4x750, Chock Shield 4x800, Chock Shield 4x760, Chock Shield
2.10 - 3.21 2.0 - 3.20 2.0 - 3.20 2.0 - 3.20 1.50 - 3.00 1.50 - 3.00 1.65 - 3.60 1.65 - 3.60 2.20 - 3.40
100 - 350 138 - 265 93-272 38-382 70 - 200 70 - 200 240 225 54 - 297
List of Powered Roof Supports deployed in India.
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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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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) Main Strata Competency (including Upper 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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CLASSIFICATION OF LONGWALL ROOF STRATA
Vertical Stress Distribution in Longwall Panel & Immediate Roof
Vertical stress Distribution in Immediate roof
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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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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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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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Operational characteristics 2 Leg and 4 Leg shields Parameter Canopy ratio Canopy length Supporting force into the roof Range of adjustment Travelling route Handling Possibility of faulty operation Cycle time Requirement of hydraulics Toe loading
2- Leg shield optimum at approx. 2 : 1 short and compact minimum distance to the coal face up to approx. 3 : 1 in front of / behind the props very easy and quick
< 12 sec
4-Leg Chock shield > 2:1 longer canopy design due to construction larger distance <3:1 between the props more complicated insufficient setting of the rear props > 15 sec
relatively small
larger
extremely low
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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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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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
Dimensions (m x m) Height of extraction (m) Depth of workings (m) Face Gradient Support capacity No. of Supports at face Contact Roof Contact Floor Setting pressure (Mpa) Status of Underlying seam, i.e., Middle Seam
62.5 x 500 3.0 48.0 Minimum 85.0 Maximum 1 in 8.9 4 x 760 t 43 Shaley coal Shaley coal 25 Depillared
Panel 21
150 x 420 3.0 206 Minimum 239 Maximum 1 in 8.9 4 x 760 t 102 Partially stone & partially Shaley coal Shaley coal 28 Depillared
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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
Average pressure distribution between front and rear legs under shaly coal roof (Panel No.1) – shallow short longwall panel
Rear
25 ) a P
23 M ( e r u s 21 s e r p g e 19 L 17 15 34
95
145
212 279 Average face progress (m)
355
429
498
32
F r o n t Rear
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Average pressure distribution between front and rear legs under stone roof conditions (Panel No.21)
28 ) a P M 2 6 ( e r u s s 24 e r P g e L
22
20
Coal Roof
Stone Roof
18 0
50
100
150
200
Distance From
250
300
350
400
B a r r ie r (m )
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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 Pressure)
65%
75%
Main Weighting Exposure (Sq.m)
8000 to 12500
7000
Periodic Weighting Interval (m)
15 to 25
10 to 12
Cavities
Frequent (crumbled)
Moderate
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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THANK YOU
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