MINING METHOD

  Longwall advancing and longwall retreating: There are 2 variants of long wall method- Long wall Advancing and Long wall Retreating.                                                        Long wall Advancing - In longwall advancing,extraction of coal commences from the vicinity of shaft and advance towards the boundary of the mine or panel.Approach to the face is by parallel roads formed at a specified distance apart,which is equal to length of face.The roof over the extracted area(goaf)is packed by sand(or packwalls of stone)or allowed to cave in.The method has the advantage that coal extraction can be started soon after reaching the coal seam by shaft or inclines.But maintenance of the approach roadways is costly and difficult.           Long wall Retreating - In longwall retreating,pairs of heading are driven in sol...

Timber supports   Timber support are heavy,bulky,costly,time consuming,of short life and indefinite strength,and use of timber has involves cutting tress.Therefore they have been replaced by steel supports to a large extent.They are still used in many situations for example: Cogs at goad edges and junction.Two cross bars on cogs at roof ledges. Vertical props with lagging at pillar sides having tendency to spall.Inclined stay props to support overhangs. Support of faults,slips,breaks in roof by cogs on either side with cross bars across them. Support of isolated spots in roadways by props,cross bars or cogs as required.As temporary supports.    Statutory requirements for timber supports    Props:diameter atleast 15cm,set on sound foundation and kept tight against the roof.Lid width not less than prop dia,thickness at least 8cm,length at least 50cm,When set on sand shall be on flat base piece not less than 5cm thick,50cm wide,75cm long.Set normal to floor in...

Dangers in blasting in hot strata                          * Danger of   premature blasting of explosives. *Danger of misfire                          Precautions : DGMS permission shall be obtained.Only slurry or emulsion shall be used. Blasting shall be done with detonating fuse down the hole, Detonator shall not be placed in the hole. Temperature at bottom of blast holes shall be measured and recorded after drilling and every shift thereafter .If temperature of hole exceeds 80° C,it shall not be charged.All holes shall be kept filled with water.A hole traversed by cracks and fissures shall not be charged unless it is lined with an asbestos pipe and the hole filled with water.In addition,bentonite shall be used for sealing cracks at the bottom of holes. Before loading explosives,the detonating fuse shall be cut from the reel.Stemming shall be commenced...

METHOD OF SUPPORTING WEAK SHALE ROOF                  When shale roof can be supported by special type of roof stitching recently designed by CMRI, Dhanbad.Two holes 1.5m deep shall be drilled on two sides at the roof level at an angel of 45° using ordinary coal drills.Three more holes of the same depth shall be drilled vertically in the roof at equal intervals in the same alignment.A piece of old haulage rope 20-22mm dia shall be cut with a length=depth of two holes+width of gallery.One end of the rope shall be fixed in one of the side holes with cement   grout and a wooden plug shall be hammered to prevent the rope shall be fixed in corresponding inclined hole with the cement grout.Now there j-bolts shall be fixed with cement capsule and wooden plugs in the three vertical holes.While fixing j-bolts,there lower end shall be anchored to the rope.When cement is set, wooden sleepers shall be placed between two adjacent rope as ...

  After a slice or stook has been extracted,stowing shall be done as soon as possible.The entire area shall be stowed,no gaps shall be left.Stowing shall be tight upto the roof.As stowing progresses,only one stowing pipe shall be opened at a time.The pipe shall be kept supported and it's end shall not be allowed to get buried in sand.At the end a flexible hose shall be used to fill gaps near the roof.If work is done by level slicing,at intervals barricades of half height shall be erected.Boxing shall be made strong so that it does not burst.Frequent starting/stopping shall be avoided.Stowing Shall be commenced only after ensuring adequate stock of sand and water in the sand bunker,water tank respectively. Support shall be withdrawn timely and any odd material lying inside the boxing shall be removed.Proper arrangment shall be made for drainage of stowing water.Pipe range shall be cleaned by runing only water for 5-7minutes at the beginning and end of stowing.Goad edge shall be kept...