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Room
& Pillar Mining
Once the coal was reached by means of a slope or shaft, levels
were driven through the solid coal and headways and deeps branch
out from these to permit the breaking off of rooms. The rooms
ran parallel to the levels and at right angles to the headways.
Crosscuts
were then made joining the rooms as they advanced which formed
the pillars of coal which were so vital to roof support. With
the use of doors and brattice, the air was directed throughout
the working places and kept the mine ventilated and hopefully
free from a dangerous gas build-up.
The
rooms or working faces varied in width (12 feet to 21 feet)
and were responsible for the chief output of coal. A team of
two men who completed hewing, blasting and loading coal into
tubs or boxes drove each room forward. The room was undercut,
most often at the bottom of the seam for a depth of three to
five feet and from side to side of the face.
When
the coal was undercut, it was won by means of a handpick or
sometimes wedging or blasting. When blasting was required, boreholes
were drilled into the coal face, charged with powder and fired.
The system of blasting varied within collieries and depended
upon the thickness of the coal seam and the quality of the coal
and surrounding strata.
The
dimensions of the pillars or blocks of coal that were left intact
between the rooms and crosscuts formed an important part of
room and pillar mining. The width and depth of pillars varied
considerably because they were dependant upon a number of variables.
The depth of the seam from the surface was one of these variables
because with increased depth and pressure of super incumbent
strata, the dimensions of the pillars must be enlarged in order
to give sufficient strength to support the roof and prevent
heavy lifting of the floor.
If the coal was soft or easily broken, the pillars needed to
be larger. Also, if the stone forming the roof was soft or weak,
the superficial area of the pillars was large to distribute
the weight of the strata over a larger surface.
The angle or inclination of the coal seam was another factor
that had to be considered. A larger pillar was required where
the dip of the seam was steep. In many earlier operations, the
pillars left were much too small, sometimes six feet by twelve
feet. This was bad mining practice and often led to roof fractures,
heavy water seepage and crushing.
Eventually, pillar sizes were increased to 20 by 30 feet in
width and later still, under the Dominion Coal Company, pillars
of 100 by 100 feet were left under heavy cover. Needless to
say, it was better to make pillars stronger and larger than
necessary rather than risk the mines and lives of the miners.
One important aspect of laying out a mine was the possibility
of recovering or drawing the valuable coal left in these pillars.
This was usually done when one area of the mine was worked out
or when the life of the colliery was coming to an end.
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