Selection of Powered Roof Supports2-Leg Shields vis-à-vis 4-Leg Chock               Shields             B Ramesh Kumar, CG...
Historical overview of increasing shield                        capacities•Powered roof supports of 1750 tonnes was also d...
Powered Roof Supports - longwall The illusion of induced caving of goaf with the use of chock shields was ruled out with t...
Vertical Stress Distribution Immediate                          RoofWhen the load in the front leg is higher, the vertical...
Magnitude and type of horizontal stress in  Immediate Roof                        (After Peng, et. al.,1988)      Performa...
Operational characteristics of 2-leg and 4 –leg                                              Powered roof supports        ...
Performance of 4-leg Chock Shield at PVKmine under varying roof conditions     Parameter                     Coal Roof    ...
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2leg vs4leg

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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

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  1. 1. Selection of Powered Roof Supports2-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, ANDHRAPRADESHPresented 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. 2. Historical overview of increasing shield capacities•Powered roof supports of 1750 tonnes was also developed by Joyinternational, 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. 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 packageVertical Stress Distribution in Longwall Panel & Immediate Roof Vertical stress Distribution in Immediate roof 3
  4. 4. Vertical Stress Distribution Immediate RoofWhen the load in the front leg is higher, the vertical stressdistribution on the front portion of the canopy is the largest andthe horizontal force acts towards the face.As a result, there is no tensile stress in the immediate roof ofunsupported area between the canopy tip and face line andconsequently the roof will be stable.Conversely, when the load in the front leg is smaller, thevertical stress distribution on the front portion of the canopy isalso smallerThe horizontal force acts towards the gob resulting indevelopment of tensile stress in the immediate roof ofunsupported 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. 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 inthe immediate roof with which the roof is held in place.Thus the stability of the roof can be maintained and supportefficacy can be improved under weak roof conditions 5
  6. 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 frontLeg 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. 7. Performance of 4-leg Chock Shield at PVKmine 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 RecommendationsThe desirable type and capacity of the powered roof support must be selectedbased on the site specific geo-mining conditions.While deploying powered roof supports with foreign collaborations, sufficientscientific study regarding suitability of powered roof support, under aparticular geo-mining condition should be conducted by both Indianresearchers and foreign researchers like Australia, china, and USA wherelongwall technology was well proven.Under immediate weak and strong roof conditions, containing overlain massivesandstone beds, high capacity 2- leg shields of same capacity are desirableover 4-leg chock shields.Numerical modeling studies are to be conducted for better understanding ofthe 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
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