selection of powered roof support for longwall under weak and strong roof conditions, overview of increasing shield capacities, and comparision between 2 leg and 4 leg shields of longwall

1. Selection of Powered Roof Supports
2-Leg Shields vis-à-vis 4-Leg Chock
Shields
B Ramesh Kumar, CGM(CP&P)
U Siva Sankar, UM(P&P), uss_7@yahoo.com
VNS Prasad,Dy.Mgr(CP&P)
SCCL, ANDHRAPRADESH
Presented at International Conference on Underground Space
Technology, Jan 17-19, 2011, Bangalore, India
INTRODUCTION
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 the four legged chock shields
have been the most widely used supports.
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 type 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.
1

2. Historical overview of increasing shield
capacities
•Powered roof supports of 1750 tonnes was also developed by Joy
international, DBT Bucyrus
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.
2

3. Powered Roof Supports - longwall
The illusion of induced caving of goaf with
the use of chock shields was ruled out with
the use of 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
Vertical Stress Distribution in Longwall Panel &
Immediate Roof
Vertical stress Distribution in Immediate
roof
3

4. 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.
Forces on supports due to lateral strata movement.
(a) Weak roof -- horizontal force acting away from face.
(b) Strong roof -- horizontal force acting towards face.
Adapted from Peng et al. [1987].
4

5. Magnitude and type of horizontal stress in
Immediate Roof
(After Peng, et. al.,1988)
Performance of supports 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
5

6. Operational characteristics of 2-leg and 4 –leg
Powered roof supports
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
CASE STUDY -PVK No.5 INCLINE
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 )
6

7. 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 16 to 21 MPa
CapacityUtilization 60% - 65% 80% to 85%
(MMLD/RMLD)
Setting Pressure( as % of 65% 75%
Yield Pressure)
Load Ratio of Front to rear 1.3:1 to 1.4: 1 1:1 to 1.1:1.
legs
Main Weighting Exposure 8000 to 12500 7000
(Sq.m)Approx.
Periodic Weighting Interval 15-25 10-12
(m)
Cavities
Frequent(crumbled) moderate
Weighting Intensity Lightlyto Intensely loaded
moderately loaded
Conclusions and Recommendations
The desirable type and capacity of the powered roof support must be selected
based on the site specific geo-mining conditions.
While deploying powered roof supports with foreign collaborations, sufficient
scientific study regarding suitability of powered roof support, under a
particular geo-mining condition should be conducted by both Indian
researchers and foreign researchers like Australia, china, and USA where
longwall technology was well proven.
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 affects.
7

8. 8