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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 Plan view

x

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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 e xtent 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 shie lds have beenthe most widely used.

� Several mines in India like Kottadih, Churcha and Dhemomainhad 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 c ontact roofs, viz; coal and sand stone roofs were analyzed.

Lt: Chock,1950 Rt: Frame, 1951

4 - Leg Shield

6 - Leg Chock Shield

4- Leg Chock Shield (1962)

2 - Leg Shield

Types of Powered Roof Supports

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�

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Powered Roof Supports - Design

Complete CanopyAssembly

Complete Base Assembly

Complete Rear Shield Assembly

�Earlier Caliper Canopy design was replaced with lemniscatedesign to maintain uniform tip to face distance

�Rigid canopy are replaced with extensible canopy to control friable roof geologies

Powered Roof Support Canopy Designs

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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 IFS

Name of the Project Make Support Capacity (tonnes) & Type

Working Range (m)

Depth of 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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�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

S C C L

Historical overview of increasing shield capacities

World’s Biggest and Highest Rated Roof Support

Capacity: 2x1750 tonnes

Weight: 62 tonnes

Range: 2.40 to 5.0m

Leg Dia: 480mm

Life: 90,000 cycles

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Longwall supports used in Australia (Source: Cram,2007)

�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

Factors Affecting Support Selection

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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

(After Peng, et. al.,1988)

Load Ratio = Rear leg to Front leg

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1. Massive Main roof with Weak Immediate Roof

�Caving and bulking up of immediate roof supports ma in roof leads to less weighting on face

� In the above higher capacity support is not require d

2. Massive Main Roof with Strong Immediate Roof

�Does not cave properly and does not support upper s trata quickly leads to intense loading of longwall face

� In the above higher capacity support is required

�Under massive roof conditions, Supports having resi stance of 120 tonnes/Sq.m., are desirable under above cond itions based on Australian’s Experience.

Case-1 Case-2

Main Roof

� Detached Block theory (Wilson, 1975) � Empirical Nomograph based method (Peng, Hsiung and J iang,

1987)� Load cycle analysis (Park et al, 1992, Peng 1998)� Neural networks (Chen, 1998, Deb) � Various Numerical models (Gale, 2001, Klenowski et a l, 1992,

UK Singh, G. Benerjee, Deb )� Ground response curves (Medhurst, 2003)� Convergence Vis–a-Vis Support Resistance (CMRI Appr oach)� Roof Separation Index, After U.K.Singh, e.t.al. � Plate Theory Proposed by Quan Ming Gao(1989)

METHODS USED FOR SUPPORT CAPACITY DETERMINATION

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Fig. Impact of shield capacities (setting pressures) on convergence.

Fig. Ground Reaction Curve and support response.

SUPPORT CAPACITYINSITU STRESS

Bigger the Better ����

Pressure Arch Concept

Performance of Shields under Unstable or Poor or weak Roof Conditions

�With inclined legs, 2 leg shields create compressiv e forces in the immediate roof with which the roof is held in place .

�Thus the stability of the roof can be maintained an d 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

After Barczak T.M., (1992)

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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 the roof

minimum distance to the coal face

due to construction 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 operation extremely low insufficient setting of

the rear props Cycle time < 12 sec > 15 sec Requirement of hydraulics relatively small larger

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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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 Heig ht of Extraction

SCCL GEO MINING CONDITIONS

Geo Engineering properties of roof and floor strata of ALP (SCCL, 2007)

SCCL GEO MINING CONDITIONS

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Layout of Longwall Panels in Top seam of PVK 5 Incline

CASE 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

85.0 Maximum 206 Minimum 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 seam, i.e., Middle Seam

Depillared Depillared

Panel 1A Panel 21

Salient features of Longwall Panels under Study

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Specifications of Chock Shield of PVK

20.50 tonnesSupport weight

633 KNForce to advance support

360KNForce to advance conveyor

3.10 MPaFloor specific pressure

110 t/sq.mSupport density

760 tonnesYield load

6.30 Sq.mRoof coverage

2.50Canopy ratio

3.87mSupport length

1.50 mSupport width

2.20 to 3.40m Support Range

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21

23

25

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34 95 145 212 279 355 429 498Average face progress (m)

Leg

pres

sure

(M

Pa)

Front

Rear

0 5 0 1 0 0 1 5 0 2 0 0 2 5 0 3 0 0 3 5 0 4 0 01 8

2 0

2 2

2 4

2 6

2 8

3 0

3 2

Leg

Pre

ssur

e(M

Pa)

D i s t a n c e F r o m B a r r i e r ( m )

F r o n t R e a r

Average pressure distribution between front and rear legs under

shaly coal roof (Panel No.1) – shallow short longwall panel

Average pressure distribution between front and rear legs under stone

roof conditions (Panel No.21)

Pressure Distribution between Front and Rear legs

Stone Roof Coal Roof

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Performance of 4-leg Chock Shield at PVK mine under varying roof conditions

0.90 to 1.000.70 to 0.76Load Ratio Rear to Front

IntenseModerateWeighting Intensity

10 to 1215 to 25Periodic Weighting Interval (m)

ModerateFrequent (crumbled)

Cavities

80 to 85%60 to 65%Capacity utilization (MMLD/RMLD)

70008000 to 12500Main Weighting Exposure (Sq.m)

75%65%Setting Pressure (% of Yield Pressure)

16 to 21 MPa9.3 to 11 MPaCompressive Strength (MPa)

Stone RoofCoal RoofParameter

MMLD: Measured Mean Load Density RMLD: Rated Mean Load Density

Conclusions

� The desirable type and capacity of the powered roof support mustbe selected based on the site specific geo-mining c onditions.

� While deploying longwall technology with foreign co llaborations,sufficient scientific study regarding suitability o f powered roof support under existing geo-mining conditions should be done.

� Under immediate weak and strong roof conditions, co ntaining overlain massive sandstone beds, high capacity 2- le g shields of same capacity are desirable over 4-leg chock shield s.

� 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 stra ta control problems.

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THANK YOU