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consuming,of short life and indefinite strength,and use of timber has involves cutting tress.Therefore they have been replaced by steel supports to a large extent.They are still used in many situations for example: Cogs at goad edges and junction.Two cross bars on cogs at roof ledges.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...