Selection of powered roof supports – 2 leg shields vis-à-vis


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Selection of powered roof supports – 2 leg shields vis-à-vis

  1. 1. International Conference on Underground Space Technology Technical Papers Selection of Powered Roof Supports – 2-Leg Shields vis-à-vis 4-Leg Chock Shields B Ramesh Kumar CGM, Corporate Project and Planning,, U Siva Sankar Under Manger, Project Planning, VNS Prasad, Deputy Manager, Corporate Project and Planning SCCL, AP, IndiaABSTRACTThe success of a longwall face depends to a large extent on the type andcapacity of the Powered Roof Supports. In India, different types of Powered RoofSupports of various capacities were tried earlier, but the four legged chockshields have been the most widely used supports. An extensive literature reviewon Indian longwall mining scenario over the last few decades suggests thatmajority of the downtimes and or failures were mainly due to ground controlproblems and inadequate capacity and type of powered roof supports. In Indiaseveral mines Kottadih, Churcha and Dhemomain had experienced catastrophicfailures of longwall faces.In this paper, a case study was presented, summarizing the experiences ofworking Longwall faces with IFS, 4-leg chock shields under varying contact roofs,viz; coal and sand stone. Based on the field observations, conclusions weredrawn regarding the suitability of 2 leg shields over 4-leg chock shields underIndian geo mining conditions in general and particularly regarding longwall minesof Singareni Collieries Company Ltd (SCCL).Key words: Longwall, Powered Roof Support, Contact Roof CM - 05 - 117 – 19 January 2011, Bangalore, India
  2. 2. International Conference on Underground Space Technology Technical PapersIntroductionSCCL introduced mechanized longwall mining in 1983. The first few faces wereworked with 4x360 t (conventional) 4x450 t IFS supports. Failure of the supportwith regard to breakage of immediate roof between canopy tip and face resultedin formation of cavities in face and subsequent closure of chocks and facestoppages. The cavities were more frequent and negotiation of the same with IFSsupports was even more difficult.With the introduction of second generation longwall supports, the supportcapacity was increased to 4x760 t (PVK) and 4x800 t (GDK 10A & GDK 9E),there was a considerable improvement in strata control. Face stoppages due toproblems related to strata failures or closure of chocks were few, though nottotally eliminated.In SCCL, majority of the longwall faces are worked under weak immediate roofconditions. The strength of immediate roof coal/sandstone of worked Longwallswas of weak to moderate strong. In most of the above cases, it has beenobserved that the front legs were taking more load than rear legs of conventionalas well as IFS chock shield supports, due to crumbled and premature cavingnature of immediate roof [1-5].Studies conducted and analysis of performance of powered roof supportssuggests that above supports with higher capacity are able to deal most of theproblems of strata under the prevailing geo-mining conditions. However there isalways a scope for selection of correct type of support to reduce the facestoppages because of strata control problems, as high cost equipment installedshould generate revenue for long term financial requirements.2.0 Trend of development of Powered Roof Supports:Two fundamental changes in shield design have been made since theintroduction of the shield in 1975: (1) the caliper design was replaced with alemniscate-guided caving shield that maintains a constant tip-to-face distancethroughout its operating range; and (2) electro hydraulic control systems have CM - 05 - 217 – 19 January 2011, Bangalore, India
  3. 3. International Conference on Underground Space Technology Technical Papersreplaced manual systems to permit remote and automated operation of the shield[6, 9].In India first mechanized powered roof support face, the new-age Longwall, waslaunched in August 1978 at Moonidih Colliery. In India, 33 Longwall packageshave been deployed to date in both Coal India Ltd and SCCL in collaborationwith U.K, Russia, Poland, China and France mostly funded by GOI. The list of thepowered roof supports deployed at Indian longwall faces is as given in theTable.1.The basic shield structure has remained unchanged for the past 25 years,although the structures have grown dramatically in size and capacity. Earlygenerations of shields experienced several structurally related failures and had tobe strengthened to prevent premature failures and provide a reasonable workinglife. Through this evolution of improvements, the life expectancy has beenincreased by a factor of 7 from 10,000 loading cycles in the late 1970s to 70,000loading cycles. The support capacity has continued to increase throughout thehistory of longwall mining [7].There has been a steady increase in the use of two-leg shields in favour of four-leg shields during the past decade, and two-leg shields are becoming thefavoured support worldwide. The overview of trend of increasing shield capacitieswas as shown below Figure.1. However, a full range of roof supports areavailable suitable for mining heights from 5.50 to 7.50m with support capacities inexcess of 1750 tonnes [8]. In SCCL, powered roof supports were introduced inthe late 80’s and early 90’s, where the maximum capacity was only 800 tonnes,which was the state of the art. CM - 05 - 317 – 19 January 2011, Bangalore, India
  4. 4. International Conference on Underground Space Technology Technical PapersTable.1: List of Powered Roof Supports deployed at Longwall faces in India 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 CM - 05 - 417 – 19 January 2011, Bangalore, India
  5. 5. International Conference on Underground Space Technology Technical Papers Fig.1. Historical overview of increasing shield capacities [9]3.0 Ground control aspects of Long wall miningThe roof falls in unsupported area are mainly due to tensile failure. Generally, theweak roofs can not sustain a tensile stress. Therefore, an important function thatsupports should provide in order to secure a better or more stable roof conditionis to prevent possible roof falls at the face. In order to prevent roof falls at face, itrequires complete elimination of tensile stress in the unsupported roof betweencanopy tip and the face line.Roof stability is a function of lateral confinement, which is generated by thesupport resistance and the coal seam. In general, stability of the roof strata ishighly dependent on the span-to-thickness ratio of the roof beam [10]. Roofinstability along a longwall face is generally driven by one or both of twofundamental geo mechanisms. They are guttering type of failure of the immediateroof and formation and subsequent opening of sub vertical shear and tensilefactures, i.e., delineation of the large intact blocks via the propagation ofweighting induced sub vertical tensile/shear fractures. CM - 05 - 517 – 19 January 2011, Bangalore, India
  6. 6. International Conference on Underground Space Technology Technical PapersThe hydraulic legs orientation and distribution of load between front and rear legsare two very significant factors in the design of powered support in longwallmining [11]. The principal factors which influence the magnitude of load onsupports include setting load density, height of the caving block, distance offracture zone ahead of the face, the overhang of goaf, the support yieldcharacteristics, and the mechanical strength of the debris above the canopy andbelow the support base [12].The maximum tensile stress in the main roof occurs mostly 5m to 15m ahead ofthe longwall face and the deformation of main roof appears to be not only in goafarea, but also in the unmined area [13]. As the longwall face advances, theposition of high stresses very close to the face, moves with the face in such away that the entire roof over the opening is broken by vertical and horizontalfractures [14].A problem encountered in working under weak roofs is the break-up of the roofover the rear half of the canopy. If the caving line moves forward of the line ofaction of resultant thrust, then the back legs will tend to push upwards into thebroken roof. This will cause the front of the canopy to lower, leaving the roof overthe AFC essentially unsupported, and exacerbating roof condition, as shown inbelow Figure.2 [15]. Fig.2 Caving line moving forward of line of action of support resultant [15] CM - 05 - 617 – 19 January 2011, Bangalore, India
  7. 7. International Conference on Underground Space Technology Technical Papers3.1 Effects of load distribution in front and rear legsIn India and Overseas many experiments were conducted and numericalmodeling was done to study the effects of load distribution on front and rear legsof the chock shield. Distribution of vertical and horizontal stresses on the canopyof the support, for different load ratios of front to rear was analyzed [11].Vertical stress distribution on the canopy of the support is different for differentload ratios. When the load in the front leg is higher, the vertical stress distributionon the front portion of the canopy is the largest and the horizontal force actstowards the face. As a result, there is no tensile stress in the immediate roof ofunsupported area between the canopy tip and face line and consequently theroof will be stable. Conversely, when the load in the front leg is smaller, thevertical stress distribution on the front portion of the canopy is also smaller andthe horizontal force acts towards the gob resulting in development of tensilestress in the immediate roof of unsupported area. This is the main reason for rooffalls in unsupported area. The vertical stress distribution in the immediate roofunder varying roof conditions is as shown below in Figure.3 [5]. Fig.3: Vertical stress Variation [5]Horizontal stress distribution for different load ratios of rear to front legs of achock shield is as shown in Figure.4. When the rear to front load ratio increases,stress in unsupported area will change from compression to tensile stress. Inother words, the stresses in the unsupported area change from compression to CM - 05 - 717 – 19 January 2011, Bangalore, India
  8. 8. International Conference on Underground Space Technology Technical Paperstension, when the front leg load continues to decrease. When the ratio is 1.0, thatis, the magnitude of front and rear legs is the same; there is only a smallcompressive stress in unsupported roof area. After that, as the ratio decreasesfurther, the stress will become tensile and the unsupported roof area is unstable.This situation must be prevented in designing parameters of the powered roofsupport under the weak roof condition. Fig.4. Magnitude and type of horizontal stress [11]From the above, in general it is suggested thati. A smaller load ratio, i.e., the rated load of front leg is should be larger than that of rear leg is preferred for the weak roof condition.ii. If a stronger immediate roof exists, a larger load ratio (Rear to front) is preferable.iii. If the rear leg load is much smaller than the front one, it will act like and can be treated as 2 leg shield. When the small load ratio is, 0 to 0.5 is expected, 2 leg shields are preferable.iv. The load ratio of rear legs and front legs must be in the range of 0 to 1, under weak roof conditions. CM - 05 - 817 – 19 January 2011, Bangalore, India
  9. 9. International Conference on Underground Space Technology Technical Papers4.0 2 -Leg shields vs. 4- Leg Chock ShieldsFrom a support strata interaction perspective, the two-leg shield provides anactive horizontal force toward the coal face due to inclination of the leg cylinders.This active horizontal force improves overall strata stability by arresting slippagealong fracture planes or by prevention the expansion of highly jointed or friableimmediate roof geologies which may be further damaged by the front abutmentloading [6,7,9] (see Figure. 5. a.)In terms of the shield loading, this increase in active horizontal loading alsotranslates into proportionally higher lemniscate link loading. Caving shield /lemniscate assembly reaction to forward canopy displacement reduces activehorizontal roof loading caused horizontal component of the leg force [9].The unbalanced distribution of loading between front and rear legs makes 4-legchock shields less effective in cavity prone areas. As shown in Figure.5.b, theforce in the rear legs causes the canopy to rotate up into the cavity. Thiscondition ultimately results in further cavity formation and requires front legs ofthe supports to do all of the supporting work. since the front legs of a 4-leg chockshield is considerably smaller than they would be in two-leg shield of equivalentsupport capacity , the four leg shield provides much less support force thanwould a comparable two leg design [6]. 5. a. Active horizontal force provided by 2-Leg shield, and Fig. 5.b. 4-leg shield operation in cavity prone conditions [6].Another issue related to the two-leg concept is higher contact pressure on thecanopy and base. High toe loading, caused by the moment created by the line of CM - 05 - 917 – 19 January 2011, Bangalore, India
  10. 10. International Conference on Underground Space Technology Technical Papersaction of the resultant vertical forces acting on the canopy and base, can be aproblem in high capacity two-leg shields and should be a consideration in thesupport design. Base toe pressures of 800 psi or greater can be expected onhigh-capacity two-leg shields. Base toe lifting devices are now standard on mosttwo-leg shields to assist in the advancement of the shields particularly in softfloor conditions. There has also been a trend toward solid base designs toreduce floor-bearing pressures in two-leg shields [7].Advantage of 4 leg shield is that it provides resultant vertical force farther fromthe coal face than does 2-leg support. This is supposed to be more efficient incantilevered strata, since the support force acts at a mechanically more efficientlocation. 2-leg shields inferior to 4-leg type in this mine from structural stabilitypoint of view. However if a 2-leg shield of the same capacity is to be obtained, itis the preferred in most applications. The other operational characteristicdifferences between 2-leg and 4-leg powered supports in brief is given inTable.2.Table.2. Comparison of operational characteristic of 2-leg and 4 –legpowered supports Parameter 2- Leg shield 4-Leg shieldCanopy ratio optimum at approx. 2 : 1 > 2:1Canopy length short and compact longer canopy designSupporting force into minimum distance to the due to constructionthe roof coal face larger distanceRange of adjustment up to approx. 3 : 1 <3:1Travelling route in front of / behind the props between the propsHandling very easy and quick more complicatedPossibility of faulty insufficient setting of extremely lowoperation the rear propsCycle time < 12 sec > 15 secRequirement of relatively small largerhydraulics CM - 05 - 1017 – 19 January 2011, Bangalore, India
  11. 11. International Conference on Underground Space Technology Technical Papers5.0 CASE STUDYPadmavathi khani (PVK) 5 incline is located in Kothagudem area of SCCL,Andhra Pradesh State, India. The mechanized longwall mining technology wasintroduced in August, 1995 with fully mechanized longwall mining equipmentimported from M/s CME, China. Since then, ten longwall panels and two shortlongwall panels have been worked to extract 5.08 Mt of coal by longwall methodof retreating with caving along strike direction with out any major strata controlproblems.5.1 Geo-mining DetailsOf the three coal seams existing in the mine, the Top seam was extensivelyextracted by mechanized powered roof support longwall retreating method. Thethickness of the top seam was varied from 6 to 10m, dipping at about 1 in 9 dueN680E. Top seam was the overlying seam of King and Bottom seams at thismine. The King seam was worked in two sections, the top section by caving andbottom section with stowing. The parting between Top seam and King Seamvaries from 40 to 48m. The longwall face of all the panels in the top seam werelaid out along the dip-rise direction. The middle section of the top seam wasextracted by longwall technology leaving shaly coal in both roof and floor. Thelongwall panels were worked at varying depths ranging from 48m to 297m. Allthe Longwall panels except panel 8 were underlined by king seam extractedpanels, where as panel 8 was overlain by standing pillars of adjacent No. 5BIncline. The details of operating parameters of all longwall panels are given inTable.3.The equipment used in the longwall panel consisted of an AM 500 Double EndedRanging Drum shearer with a extraction height range of 2 to 3.5m, withArmoured face conveyor of 800 t/hr, the beam stage loader 1000 t/hr, and thebelt conveyor 1000 t/hr capacities. The roof was supported with 4x760 tonnes CM - 05 - 1117 – 19 January 2011, Bangalore, India
  12. 12. International Conference on Underground Space Technology Technical PapersIFS chock shield powered roof supports provided with extension bar to supportthe freshly exposed roof at the face. The specifications of the powered roofsupport are given in Table.4 and the diagram of the same is as shown inFigure.6. Table. 3 Details of operating parameters of all Longwall panels of PVK-5 Incline Name Panel Depth Progres Frequenc Period of Maximum of Dimensio Min. & s y of Extractio SubsidenLongwa ns (m) Max. at Periodic n ce (m)ll Panel (m) Main Weightin fall (m) gs (m) 59 &Panel 2 660 x 150 66.5 - 8 Months 2.54 112 76 &Panel 3 675 x 150 80.65 - 7 Months 1.94 128 96 &Panel 4 675 x 150 81.85 - 9 Months 1.88 141 113 & 1 YearPanel 5 830 x 150 61.90 15 to 18 2.20 158 2 Months Panel 135 & 560 x 147 112.0 15 to 18 1 Year 0.74 5A 150 Panel 155 & 1 Year 730 x150 76.75 18 to 20 0.68 5C 184 9 Months Panel 174 & 1 Year 690 x 150 91.50 18 to 20 1.09 5D 203 5 Months Panel 174 & 770 x 150 50.30 15 to 20 2 Years 0.95 22 203 Panel 520 x 62 54 & 96 98.00 18 to 25 4 Months 1.65 1APanel 1 500 x 62 48 & 85 80.00 15 to 20 4 Months 2.60 Panel 203 & 21 420x150 45.00 10 to 12 8 Months 0.835 239 275&29Panel 8 420x150 80.30 15 to 25 - 0.24 7 CM - 05 - 1217 – 19 January 2011, Bangalore, India
  13. 13. International Conference on Underground Space Technology Technical Papers Table 4. Specifications of chock shield support 1. Support height 2.2 to 3.4m 2. Support width 1.5 m 3. Support length 3.87m 4. Canopy ratio 2.5 5. Roof coverage 6.3 sq.m 6. Yield load 760 tonnes 7. Support density 110 t/sq.m 8. Floor specific pressure 3.1 MPa 9. Force to advance conveyor 360KN 10. Force to advance support 633 KN 11. Support weight 20.5 tonnesFig.6. Schematic diagram of Powered Roof Support (4 X 760 t) (Courtesy: SCCL) CM - 05 - 1317 – 19 January 2011, Bangalore, India
  14. 14. International Conference on Underground Space Technology Technical Papers5.2 Field observationsThe experiences of working the longwalls with 4x760t chock shield supportsunder varying contact roofs such as shaly coal and sandstone are studied. Thecompressive strength of the immediate coal roof varies from 9.3 MPa to 11 MPa,where as that of the sandstone varies from 16 MPa to 21 MPa. The roof abovethis level is sandstone predominately, which varies from fine to coarse grainedand consists of a massive strong strata bed of approximately 12-17m thicknesswithin close proximity to the longwall roof. Except the Panel No.21, all otherpanels were worked under coal roof, where as panel 21 had been worked partlyunder stone roof and partly under coal roof due to thinning of the Top seam. Thesupports were set to 65% of the yield load in coal roof and 75% in case of stoneroof conditions. The monitoring of the supports is conducted during the retreat ofthe panel with the help of pressure gauges, continuous chart pressure recordersand tape measurements. The pressure gauges are provided to all four legs of theall the supports placed in the face. Continuous chart recorders are provided tolegs of the strategic chock shields representing various zones in the longwallface.Immediate shaly coal roof caves in as soon as the supports are advanced. Withcoal roof, the main weighting was observed after an area of exposure of 8000 to12,500 sq.m., and periodic weightings at an interval of 15 to 25m. While workingwith sandstone roof, main weighting occurred after 7000 sq.m area of exposureand periodic weightings at an interval of 10 to 12m.From the analysis of strata monitoring data pertaining to longwall faces workedunder coal roof, it can be inferred that;• Setting pressure / increase of resistance showed that front legs were 30 to 40% higher than rear legs. There were variations in leg operating characteristics and variation in pressure distribution on front and rear legs (see Figure.7).• The load ratio of rear legs and the front legs is 0.6:1. CM - 05 - 1417 – 19 January 2011, Bangalore, India
  15. 15. International Conference on Underground Space Technology Technical Papers• Front legs are more loaded than rear legs because of weak immediate roof, which gets crumbled over rear legs due to cyclic loading effect. Due to which, the load exerted during the breakage process of immediate and main roof is transferred to the front legs. During the Breakage and lowering of the upper roof the crumbled roof over rear legs gets compacted and rear legs used to take some of load less than front legs.• In regard to performance of the powered supports, under weak roof rear legs were usually higher than front legs. Pins in rear legs were pulled and bent, consequently, the cave line moved, the coal fractured, head end of the front bar hung down and coal roof failed and coal roof failed above tip bar.• At the time of main and periodic weightings, the front legs used to take more loads than rear legs, due to the crumbled and premature caving nature of immediate shaly coal roof. At the same time, the rear legs are lightly loaded by vertical stress. During some of the major periodic weightings the unsupported roof between canopy tip and face line failed and led to cavity formation.• Front legs can bring their actions into full play compared with rear legs, while the longwall was near the borders of residual pillars and goaves of underlying seam.• In one of the observations, in panel 22, at the time of main weighting, total 32 legs attained bleed pressures of which 23 legs are of front and eight are of rear.• Measured Mean Load Density (MMLD) to Rated Mean Load Density (RMLD) was observed to be around 0.60 to 0.65, meaning thereby that only 60 to 65% of the rated load density of 110 t/sq.m, was utilized, which could be attributed to proper bulking up of caved material increased the goaf compaction resistance.From the field observations and analysis of chock shield leg pressures inlongwall panel with immediate sandstone roof, it can be understood that; CM - 05 - 1517 – 19 January 2011, Bangalore, India
  16. 16. International Conference on Underground Space Technology Technical Papers§ Setting resistance / increase of resistance showed that the front legs were only 8 to 10% higher than rear legs. This means supports were more or less uniformly loaded. During main and periodic weightings some of the rear legs recorded higher pressures than the front legs (see Figures 8 and 9).§ There was a considerable overhang of immediate stone roof observed behind the supports. The rear legs of the chock shields induced break line at the goaf edge.§ During some of the major periodic weightings, all legs of the supports were intensively loaded, due to delineation of large intact blocks led failure of immediate roof between face and canopy tip, caused cavity conditions.§ Front legs as well as rear legs can bring their actions into full play while the longwall face was near borders of residual pillars and goaves of underlying seam.§ The ratio of MMLD to RMLD was found to be around 0.8 to 0.85 or some times even more; implies that almost 80 to 85% of the rated load density was utilized due to delayed caving and poor bulking up of immediate sandstone roof and also mainly due to close proximity of main roof. This indicates that at this geo-mining condition higher rated powered roof supports are desirable.§ During the main weighting in panel No.21, it was observed that out of 62 legs, which attained bleed pressures in the mid face of the longwall panel, 31are of front and 31 are of rear legs. CM - 05 - 1617 – 19 January 2011, Bangalore, India
  17. 17. International Conference on Underground Space Technology Technical Papers 27 Front 25 Rear Leg pressure (MPa) 23 21 19 17 15 34 95 145 212 279 355 429 498 Average face progress (m ) Fig.7. Average pressure distribution between front and rear legs under shaly coal roof in panel No. 1 40 Bleed Pressure Fron t Leg Pressure (MPa) 35 Rear 30 25 Set Pressure 20 1 21 41 61 81 101 s u p p o rts # Fig.8. Pressure distribution between front and rear legs under sandstone roof during periodic weighting in panel No. 21 CM - 05 - 1717 – 19 January 2011, Bangalore, India
  18. 18. International Conference on Underground Space Technology Technical Papers 32 F ro n t R ear 30 28 Leg Pressure(MPa) 26 24 22 20 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 ) Fig.9. Average pressure distribution between front and rear legs under sandstone roof in panel No. 21ConclusionsIt is evident that high rating powered roof supports is a prerequisite for meetinglongwall support requirements under competent strata formations. However, adetailed strata control and face powered support investigations are of paramountimportance for assessing performance of longwall face.From the analysis of the observations under varying contact roofs such as shalycoal and sandstone, the following conclusions and recommendations weredrawn;Ø When selecting a support design, mining engineers should give careful consideration to local conditions and requirements. The desirable type and capacity of the powered roof support must be selected based on the site specific geo-mining conditions.Ø 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 CM - 05 - 1817 – 19 January 2011, Bangalore, India
  19. 19. International Conference on Underground Space Technology Technical Papers researchers and foreign researchers of Australia, china, and Germany, where longwall technology was well proven.Ø Under immediate weak and moderate strong roof conditions, containing overlain massive sandstone beds, high capacity 2- leg shields of same capacity are desirable over 4-leg chock shields.AcknowledgmentsThe authors are thankful to the SCCL management for giving permission topublish this paper. The views expressed in this article are of the authors only andnot necessarily of the organization to which they belong.References1. Zhao Honghu & Venkata Ramaiah M.S., (1996), “Strata Movement on Shallow fully Mechanised Longwall working Face at PVK Mine of SCCL & Option of Powered Support – Strata Control Observation Research at 2# Longwall working face PVK, SCCL”, 2nd National Conference on Ground Control in Mining, CMRI, pp. 123-142.2. Prabhakar Rao C, Veera Reddy B., (1999), "Strata Behaviour with Immediate Forward Support - a Case Study", Proceedings of the National Conference on Rock Engineering Techniques for site characterization, 6-8 December 1999, pp. 413- 420.3. Venkat Ramaiah, M.S and Sudhakar Lolla (2002) “Selection of Powered Roof Supports for Weak coal roof”, Journal of Mines, Metals & Fuels, April, 2002.4. Siva Sankar U, (2005), “Monitoring Strata Behaviour of Shallow Longwall panel – a case Study”, M.Tech. Thesis Unpublished, BHU, Varanasi, India.5. Venkata Ramaiah M.S Sastry V.R, Roshan Nair (2005), “Analysis of the Influence of Contact Roof zone on powered roof supports during extraction by Longwall using F.E.M”, IE(I), MN-335.6. Barczak T.M., (1992), “Examination of Design and operation of powered supports for longwall mining”, Bureau of Mines Information Circular, USA. IC.9320.7. Thomas M. Barczak, “Design considerations for the next generation of longwall shields”, NIOSH, CM - 05 - 1917 – 19 January 2011, Bangalore, India
  20. 20. International Conference on Underground Space Technology Technical Papers8. Barczak-TM (2006), “A Retrospective Assessment of Longwall Roof Support with a Focus on Challenging Accepted Roof Support Concepts and Design Premises”, Proceedings of 25th International Conference on Ground Control in Mining, August 1-3, 2006, Morgantown, West Virginia. pg 232- 24410. T. P. Medhurst (2005) “Practical Considerations in Longwall Support Behaviour and Ground Response” Coal Operators Conference 2005, Pg 49-57.11. Peng S.S., Hsiung S.M. and Jiang Y.M. (1988), “Parameters Affecting the Shield support Efficiency in Longwall Mining”, 21st Century higher Production Coal Mining Systems Symposium, pp.122-13512. Gupta RN and Farmer IW, (1985), “Interaction between roof and support on longwall faces with particular reference to support resistance”, Proceedings of 4th International Conference on Ground Control in Mining, West Virginia, pp. 58-77.13. Zhu D, Qian M, Peng SS (1989), “ A study of Displacement Field on Main Roof in Longwall Mining and its Application”, Proceedings of the 30th US Symposium on Rock Mechanics, Rotterdam, 1989, p.14614. Kidybinski A and Babcock C.O (1973), “Stress Distribution and Rock Fracture Zones on the Roof of Longwall face in Coal Mine”, Rock Mechanics, no.5, 1973, p.1.15. Roberts B.H. (1990), “A review of the performance of various powered support types” Mining Science and Technology, 11 55-69 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands CM - 05 - 2017 – 19 January 2011, Bangalore, India