THE COLLIERY GUARDIAN

AND ■

JOURNAL OF THE COAL AND IRON TRADES.

Vol. CIX.	. FRIDAY, MARCH 12, 1915.	No. 2828.

Some Notes on Supporting the Roof in Coal Mines.*

By FRANK N. SIDDALL.

Falls of ground havA always been the most prolific
source of accidents in coal mines, and have, therefore,
constantly engaged the serious attention of mining
engineers. Unfortunately, such accidents have not
been diminished by the progress of time in the same
proportion as those of other types. About the year
1900, an official enquiry was made into the question,
with the result that, on May 28, 1902, the Home Office
issued a proposal for new special rules requiring a
system to be adopted in the method of timbering at
each colliery. .	’

A committee was appointed, in 1908, by the late
Royal Commission on Mines to “ enquire into the
causes of and means of preventing accidents from falls
of ground, underground haulage, and in shafts.”f
Many of the committee’s i ecommendations have been
embodied in the Coal Mines Act of 1911, and it may be
said that the sections of that Act dealing with the
question of supporting the roof are the outcome of their
deliberations. .	.

Systematic Timbering.

With regard to the matter of systematic timbering,
it might be a wise plan on the part of the colliery
manager to talk over with his under officials the system
of timbering adopted, and to instruct them in its
application, The manager should also impress on them
the use and necessity of instructing in a like manner the
workmen under their care.

A useful suggestion of the committee was that a plan
or sketch, showing the method to be adopted, should be
posted up where every workman could see it. The
rules when made should be rigidly enforced.

With regard to. the regular and proper application of
the system, the writer has known several cases where
special men, under the supervision of the fireman, have
been employed to do nothing but look after the timbering
and packing in a district, with marked results, both as to
safety and economy.

In considering timbering in general, the writer would
recommend the use of electric safety lamps. He would
advise the colliery manager who has not yet tried the
experiment to carry, when the pit is in full work, an
electric safety lamp of the rescue type;—that is, one that,
throws a strong beam of light forward—when he will, no
doubt, be astonished at the faults which the light will
show in the timbering. The value of such a beam is
especially apparent in thick seams, and in places which
it is not possible to illuminate properly with an ordinary
safety lamp, such as falls of roof on roads, or at the
face.

Supporting the Face.

Coming, now to more particular details, the question
of supporting the face is the most important, owing to
the very large.number of accidents which occur there.
Wooden props are almost universally used for the
purpose ; but, it seems to the writer that frequently the
manner in which they are used does not receive
sufficient attention.

Face props must be set at regular intervals, and ought
to have due support one from the other. Care should
be taken in the setting of props, because it frequently
happens that the true amount of work that a prop
ought to do is not performed, owing to its being badly
set. Experience in highly-inclined seams has shown
the writer that props are often very badly set in seams
with only a moderate dip. Props ought to be set a£
right angles to the dip of the seam, in order to get the
full value out of their strength. If not set in this way,
they will push out at the foot, and are liable to split.

’ No prop ought ever to be set without a lid that is at
least in every way larger than the prop it has to fit.
Thickness of the lid does not matter so much. The

*’ From a paper read before the Manchester Geological
and Mining Society.

1 1909, Cd. 4821.

prop ought to fit the lid tightly all round. The writer
deprecates very much the method adopted at some
collieries of putting in little bits of wood to fill up a
space between the prop and the lid. Props set in
accordance with a definite system ought to be placed in
straight lines in the rows. The roof will cut off much
more evenly where this is done, and so the weight on
the face will be better regulated. At one colliery the
writer knows of, this straight line is provided by the
head stallman marking a line with a chalked string on
the roof. All props set in that row must be on the
chalked line. When coal has been got down ready
for the next row, the proper distance is measured off,
and a new line struck on the roof parallel to the first.

Workmen very frequently neglect the precaution of
setting extra or “ catch ” props at such places as they
are filling coal from. Catch props ought also to be set
at every loose end or corner. This neglect of safety
and extra props is often caused by an imperfect under-
standing of the reasons for systematic timbering. If a
certain number of props have to be set in a certain
space, the workmen think that is quite enough, and
that no more are required. The writer has frequently
seen places in a most dangerous condition, and yet
every prop—nay, more than those required by law—had
been well and truly set.

. The writer strongly advocates the use of tapered
props, on the score both of safety and of economy.
The conditions most favourable to their use are a hard
roof and floor, but they can be used to advantage
wherever the roof is only moderate and the floor is not.
in a state of soft wet clay. The idea of tapering props
is really to make, artificially, a weak place in the prop.
In an ordinary prop, like the mechanic’s beam, the
centre must be the weakest place, as it is farthest from,
its supports. Taper the prop, and the foot becomes
the weakest, but with this difference in practice—the
ordinary prop bends and breaks in the centre, and from
that moment is valueless as a support of the roof. The
tapered prop, on the contrary, gives at the foot, “ burrs ”
up at the end, and, until the tapered part is no longer
the weakest, the prop will remain set and form a sound
support for the roof.

Every roof on a longwall face must, and will, sink
sooner or later, and it is useless to attempt to prevent
it. -Practically, one may say, it begins to sink as soon as
the solid coal is removed. If ordinary props be set, they
will only remain whole until the roof has sunk to such
a point that their breaking strain is reached. But,
with tapered props, the taper allows the roof to sink
gradually without the props breaking. They will
remain firmly set until the tapered end is no longer the
weakest point in the prop. The writer has seen props
6J ft. long, with an 18-in. taper, allow the roof to sink a
foot before they broke. The result of this is that during
the whole operation of holing a web of coal, removing
it, laying the road, and holing again, the same props
wiil remain perfectly sound. The writer has known a
face 400 yds. long, timbered with tapered props, where
there was not a single broken prop anywhere. In his
own experience, the timber cost of a large colliery has
been reduced by more than 50 per cent, by their use,
and, at the same time, the roof of the mine was more
safely timbered than before.

In many systems of timbering the face, the props are
so ai ranged as ,to be set too far apart in the rows.
There is no real economy in this, unless it be the system
to leave all the timber in and recover none of it. But
Surely a face having twice as many props set in it as
another is safer, the conditions being equal. The writer
knows of a case where the props on a longwall face
are set touching one another in the rows. He believes
it to be a fact that for. 60 years no accident of any kind
whatever has occurred from falls of ground at the face.
Yet he understands that the cost of timber there would

compare very favourably with any in the kingdom. The
props in this case are always withdrawn, and are set
time after time in new situations, the simple reason
being that no great weight can ever come on to a single
prop, on account of the support given by those inimme-
diate contact with it.

There are many varieties of props. Some managers
advocate the use of iron or steul props in the form of
light H-section girders, with the web of each end cut
off, and the flanges turned over so as to make a solid
bottom. Others advocate the use of hollow iron props
having a movable rod or bar of iron, sliding in the
hollow part, which can be raised or lowered as required,
and clamped by some device at the required height.
Such props are applicable to a wide range in thickness
of strata;—that is, they can be set under roofs varying
in height. The advantage claimed for these is that
they can be so arranged as to give with the settling of
the roof, and therefore do not cut into it, or become
wedged as a solid iron or steel prop would. Very thick
lids or nogs of wood should be used with either of. these
forms of iron props, so that they may be easily with-
drawn when necessary.

Sufficient use is often not made of bars in timbering
the fac°. These bars may be of various forms,. Props
cut in half make very useful bars. Flat or corrugated
iron strips from J to J inch thick, 3 or 4 inches wide,
and 4 to 5 feet long, have all been used with good results.
Roofs of laminated sandstone, or containing slips dr
pot-holes, are those for which the use of bars is most
useful, as the bars cross all the lines of breaks, and
prevent loose pieces of stone from falling, out, while yet
providing room for the collier to work and his tub to
pass. There is one place in a working-stall at which
bars ought always to be set, and that is at.’the gate-end,
particularly at the edge of the ripping. This is the place
where everyone in the stall is constantly passing ; most
of the work in the stall is done or passes here; it is the
widest part of the place, and yet how often is it
neglected ?

If the system of timbering has been well thought out,
a sufficient number of props used in that system, and
the packing well done, there is no reason why all, or
certainly most of the timber, should not be recovered
and withdrawn from the waste. The great secret in
doing this is not to neglect it. Timber should be with-
drawn as soon , as it has ceased to be of service in
supporting the place at which men are working or
passing, and it should not remain a single day longer.
There is far more danger in withdrawing timber that
has stood a long time, and been neglected, than in
drawing that which is fairly new, and under a compara-
tively good roof.

Regularity in advancing the face-timber should be
accompanied by a like regularity in removing the back
props and timber. A useful rule in this respect is to
insist that, as soon as the packs are built, the back
timber shall be drawn in a line with those packs, or
perhaps one row, and only one row, left behind the
packs. By so doing the weight is regulated on the
face, and the settlement kept at an even rate. In with-
drawing timber the use of temporary or catch props to
protect the men is more* often neglected than such a
precaution ought to be.

Probably the most important operation in working a
coal seam by the longwall method is packing. It is,
however, often sadly neglected. One of the commonest
faults in packing is that it is not made tight enough
Men will leave the pack hollow, particularly if the work
be done by contract, unless they are watched. They may
build fine outside walls, but leave the_inside a hollow
mockery. Timber also is often left in the pack, although
it should not be. Packs are very often not wide enough
for the work that they have to do, and simply act as
pivots for the roof to break over. There is no doubt
that in deep seams it is best to pack the whole face
solid, and often it would pay to do this in shallower
seams. The statement is frequently made that a seam
cannot be worked in a straight line because the face
will come in if this is done, and so it is worked in steps