coal trade bulletin - Clpdigital.org

must be used to ward the fall off, which timber
later interferes with a satisfactory fall at the
time it is desired.
Fig. I is a cut of a pillar which is being robbed
back by splitting. "A" shows the
SPLIT IN THE PILLAR,
with the wings "B"-"B" remaining, "C" shows a
portion of the right wing removed by attacking
the pillar at the point "D." The shaded area
"E" represents the fall which occurs cutting one
off from the extreme inside portion of the left
wing "Z," or if this fall is warded off, good sound
timber will have to be used freely as shown.
What more frequently happens is that the split
in the pillar is driven as at "A" and the pillar is
attacked at "D," but all of the coal is not mined
and a good sized stump of coal is left behind, the
quantity of good coal lost depending on the thickness
of the seam, to support the roof as at "E,"
and so on all the way back to the entry or the
coal is mined at "A" leaving a shell of coal on
both wings all the way back to the entry. The
miner loading the coal from the wings is very
often apt to leave a larger shell than he supposes
as a result of poor alignment of the split or of the
room and this large quantity of coal acts as a
fulcrum or pivotal point, preventing a good clean
fall of tbe roof, throwing the weight which should
be on the bottom onto some nearby pillar causing
it to be unduly strained, and if the number of
pillars working is great and the losses of coal
occur too frequently within a limited area there
may result a squeeze which will cause very serious
losses of coal.
A better method is to rob back the pillars immediately
upon the completion of tne rooms and
to stump off the pillars by turning the room track
into the pillar as at "A", Fig. II.
In this way the miner is always protected by
solid coal and the
LOSSES ARE A MINIMUM.
Room No. 6 shows the pillar stumped off and the
stumps removed; room No. 5 shows the pocket
just starting in : room No. 4 shows the pocket
finished and the stump partly drawn back; room
No. 3 shows the pocket finished and work just
starting on the stump; room No. 2 shows the
pocket driving followed by a second pocket which
is only driven as far as a man can conveniently
load the coal without a track turn, in order to
avoid the necessity for frogs ancl switch points.
Room No. 1 shows the pocket just starting. The
width of pocket and thickness of stump depend
very largely on the nature of the roof and the
mine equipment, with poor roof that falls unsuspectingly,
or within a few hours after the removal
of the coal, the thickness of the stump
should be such that a miner can reach all of the
coal safely and easily without venturing too far
THE COAL TRADE BULLETIN. 37
beyond the rib line of the pocket, or if the roof
is good and does not fall soon after the removal
of the stump, the thickness of the stump may be
increased and the number of track turns required
per pillar may be reduced.
In the application of mining machines to the
robbing of pillars the distance centre to centre
of pockets should be such that the thickness of
stump left will form one machine cut, under bad
roof, or two machine cuts under good roof.
The more common practice where the roof falls
soon after the extraction of the stump, is to leave
a small
SHELL OF COAL
as at "A" Fig. II, to protect the miner from the
gob and also prevent his loading fine slate into
the car of coal. This results in a loss of coal
that can be avoided at a timber expense, under
ordinary circumstances, that is less than the value
of the coal. A practice whic-h has been advocated
and has proven successful, is to place a row of
Figure 2
props on tbe lower rib of the pocket, before the
removal of the pillar stump has begun. When
the next pocket is driven below it will be found
that practically the entire stump may be loaded
out without any admixture of gob and that a
greater percentage of lump coal will be obtained
from the stump. This precautionary row of timbers
is especially desirable where machines are
used on the pillars.
In regard to the maximum number of pillars
that can be successfully robbed in one robbing
line it is the writer's observation that the roof
over a robbing line, in excess of 2,400 feet in
length, sometimes begins to sag in the middle and
renders difficult the removal of the pillars in that
immediate section.
The breakline should be kept as uniform as possible
at all times.
The engineers are they take their monthly measurements
mark the distance centre to centre of
pockets on the robbing rib of the room and the