700

THE COLLIERY GUARDIAN.

April 4, 1913.

The Discussion.

The President said the subject was of special
interest to the members of the institute. The working
of rearer seams was, of course, by no means a new
thing there, and in other districts as well, highly
inclined seams—equally highly inclined to those in
North Staffordshire—had been been working for a long
series of years. But, so far as he was aware, this case
of the Podmore Hall Collieries was the first instance
where these highly inclined or rearer seams had been
worked under a thick deposit of alluvium charged with
water. Mr. Barber had pointed out that a broad
pillar of coal was left at the outcrop of the seam—that
was to say^ immediately under the alluvium. He (the
president) wished to point out that the breadth of the
pillar was always more or less a matter of uncertainty-
The floor of denudation was not a regular' plane ; and
if one could strip the alluvium off, one would find
valleys of all sorts running across. Consequently, the
pillar of coal might be 40 yards in breadth at one place>
and only 10 yards at another ; and it was essential, there-
fore, to have a pillar of such width as would make
allowance for those valleys. Then, further, if the
alluvium were perfectly dry, the engineering difficulties
would practically vanish. The difficulty here was that
the alluvium was saturated with water, and further, it
was largely mixed with clay. When the gob was shot,
naturally the clay was precipitated into the gob, and in
some cases appeared under the influence of the roof
weight to form a solid pack or seal, holding up
accumulations of water until by-and-by these solid
packs were weakened by the running of the gob lower
down until the water, so stored up, was discharged into
the gob. If the gob consisted simply of dry sand, or of
coal slack or dry debris of any kind, the running of it
would be a simple matter, but when they considered the
risk of running it with deposits of water somewhere in
it, they could easily understand that the risk was
enormously increased. The problem of working these
rearei- seams was an exceedingly difficult one, and he
had no doubt Mr. Barber would be indebted to anyone
who had had experience of them if they would give the
benefit of their experience. This was one of the most
difficult problems that had ever had to be faced in
North Staffordshire.

Mr. J. Gregory said this was the first real
description he had heard of the working of these
Staffordshire rearers; the paper would add to the
Transactions a very useful record of the work.

Mr. J. T. Stobbs said the alluvium in that part of the
district was a glacial deposit. If he had caught Mr.
Johnstone's idea accurately, it was thatthe solid surface
on which the sand rested was a very irregular surface,
such as might be formed by, say, water erosion. Water
erosion was very irregular, and could not be calculated,
But from the conditions of the alluvium deposit he
should expect that the solid bottom on which the glacial

nearing the top of the coal it was found to be very tender
and inferior—in fact, it had the appearance of old workings.
It was then decided to drive one j tckhole through to the
surface, and it was during this operation, after passing
through the inferior coal, that the alluvium was met with,
and found to be of such a light, loose character, that it ran
through at this point to the surface. The jackhole had,
therefore, to be abandoned, and no further attempts were
made to pierce the strata. The difficulty of dealing with
the alluvium in the drifts was, however, at once anticipated,
and the top heading from the cage dip was driven, leaving a
pillar of coal underneath the alluvium. When the first
drift was opened out, special care and attention were
directed towards ensuring safety in working and towards
getting the goaf broken in and under control This opera-
tion was successfully accomplished—indeed, the drifts had
been going for 12 months, and the third drift had been
worked back 60 yards before any complication or serious
trouble arose, when in this latter drift, immediately
following the shooting of the goaf, an inrush of water took
place. A similar accident occurred 16 months later.

These accidents occurred in the third and fifth drifts off
the first dip wcrked in this breadth, and in the first 200 yards
length of face. As a consequence, blocks of coal were left
in the most convenient positions then available; these
blocks extended upwards through the recovery and reduced
the workings to one set of driftings, operating from the far
end of the level. This method, although adopted in what
were not exactly the most favourable circumstances, proved
effectual, and the experiment was fully justified, as the
remaining 600 yards of drifting face was worked without
any serious trouble or recurrence of such accidents.

Mr. Barber exhibited a plan and section, respectively
illustrating the recovery of the seams lying in the area
beyond the Ten-feet seam, including the Seven feet,
Eight-feet Banbury and Bullhurst seams. He also
explained by section and sectional elevation the system
of working the latter seam. From these, he said it would
be seen that the alluvium would not extend throughout
the whole length of the area, but the ground to the
northern boundary rose rapidly above the alluvium, the
seam coming up with it into the open practically with-
out any surface cover. This was proved by the old shaft
previously referred to. In this area the seam would be
won out by levels driven in a northerly and southerly
direction off the recovery crut, with three rise dips,
from which the coal would be worked downwards.

The dips are arranged, Mr. Barber continued, so as to
divide the seam into six separate panels, formed by
leaving blocks of coal extending from the main level
upwards through the seam ; at the top of the breadth,
directly above and along the whole length of the
district, there will also be left a solid pillar of coal
40 yards thick. The coal will then be worked outwards
from the boundaries in Nos. 1 and 2 dips, the work being
confined in each case to drifting on one side of the dips
only. When these sides are exhausted, drifting will
commence on the opposite side of the dips. The same
method of procedure applies to No. 3 dip, the coal on
the northern side being worked first, and in the southern
district last.

deposits rested would not be irregular—that it would
be more or less a surface planed by the ice sheet—and,

pillars had ever been attempted. If not, he wondered
why, because it seemed a natural way—taking a long
face and avoiding all those corners, and airways packed
with posts and so on. By taking out the lower pillars
first they would have an even face through the whole
length of goaf from top to bottom. Speaking entirely
as an amateur in those matters, he wondered how far
such a face line might tend to larger production of
round coal and to a more easy handling of the gob, and
general safety.

Mr. F. H. Wynne asked if they had much difficulty
in forming the first goaf in the place that was started
under the surface rib.

Mr. Barber said they had none. Proceeding to reply
to Mr. Johnstone’s and Mr. Stobbs’ observations, Mr.
Barber showed, by a sectional elevation of the working
of the 10 ft. rearers, the point where they first proved
the alluvium. This was right in the base of the belt of
coal and it rose from this point on either side. He
thought they might take it for granted that the alluvium,
whatever it might be elsewhere, was deepest at that point.
There it was 35 yards deep, and it was that point that
they had estimated upon. Mr. Wynne’s point also
affected Mr. Wain’s question as to hydraulic stowing.
When they ran through to the surface at the point indi-
cated they abandoned any idea of maintaining the road
through it. A thin pillar of coal was left in to start
with and the first drift broke in very nicely. The sand
came in and filled the goaf, so that the goaf was exceed-
ingly well formed. They congratulated themselves upon
having attained such a perfect goaf and did not antici-
pate any further difficulty. They thought, as Mr. Wain
said, it was an ideal place for hydraulic stowage. But
the difficulty did not arise from the falling in of the
goaf. The goaf had come in well in every place; it had
come in too well. But this alluvium being partly clay
and partly sand, it had no doubt formed ponds or pools
of water on the goaf, although there had been nothing
at the face to give indications of it. The water had,
however, accumulated at some point back in the goaf and
then, at some unexpected time, had rushed forward and
filled in the workings. The leaving of the pillar referred
to had been to avoid that and to prevent any breakage
of the alluvium. Replying to Mr. Wain’s suggestion as
to taking out the lower pillars in advance of the upper
Mr. Barber remarked that the result would be they
would never get to the top pillar. If they took the foot
out the coal would come down and they would lose the
whole seam.

A vote of thanks was accorded to Mr. Barber, on the
motion of Mr. E. B. Wain, seconded by Mr. J. R. L.
Allott, and the discussion was adjourned.

AN ADJUSTABLE ECCENTRIC.

The accompanying illustration shows an adjustable
eccentric, an article which John Jardine, Nottingham,
is now offering. The eccentric has been used in con-
nection with the various classes of machinery made by

Where small openings are made in the panel pillars for
convenience of working, such openings will in each instance
be chocked, packed or stowed with dirt as the work proceeds
downwards. By this method each cage dip will be utilised
for drifting an area of coal in both the north and south
directions, whilst the utmost safety will be ensured by
working the coal on each side separately and alternately.

Tbe blocks forming the panels are also arranged to
support surface drains and roadways, as in the case of the
Ten-feet seam, and it is estimated that the pillars left are
of sufficient size to admit of exhaustion before any serious
damage to tbe surface cover can ensue, for in practice it
does not necessarily follow that where a rearer seam is
worked on a long line of face, even near to the surface, that
subsidence takes place along the whole length of such line.

The gcaf first formed at the point where the drifting
commences, consisting of loose debris, rapidly fills in the
ground following the working face, and thus forms asupport
to the pillar or cover above, and tends to prevent it from
slipping or breaking away to any extent, so that the area of
surface damage, where it does take place, is generally
confined to a few yards on each side of a vertical line
directly above the line of the dip of the seam.

The method here sketched out is being adopted in these
seams as being the principle best calculated to deal with
the problem involved, and to ensure the utmost safety in
working. At the same time, the circumstances are of such
a character that it is impossible to set out in every detail
either this or any other method of procedure, for in mining,
as in other subjects—and perhaps even more so—there is
always the exception to the rule, and the unexpected
happens. Modifications, such as actual conditions and
experience alone can suggest, have therefore frequently to
be introduced, and may be advantageous in the present
instance.

Mr. Barber added that he did not claim to have dealt
exhaustively with the subject, but had introduced it on
the basis of his experience with a view to discussion.

threfore, he could not anticipate that irregularity of , Jardines for over 20 years, but has never been offered
surface that Mr. Johnstone seemed to fear. He con- as a separate item by them. Through several enquiries
sidered it an exceedingly useful paper.	I and orders for same they have decided to place it on the

Mr. E. B. Wain said most of those present were ' market. Any throw can be obtained, from zero to the
thanking Heaven that they had not had anything to do i dimensions for various sizes, and adjusted to a nicety by
with rearer workings, and those who had were probably i set screw. It will be seen at once by the illustration
thankful that the area of rearer workings in North that the eccentric will be a useful piece of mechanism

Staffs was distinctly limited. One idea that struck
him was that the seam in question seemed to be an ideal
place for the hydraulic stowing they had heard so much
about; in fact, Nature seemed to have provided
hydraulic stowing in readiness for them. There was one
other point; he was not quite sure whether at any time
taking out the lower pillars in advance of the upper

and will meet the requirements for innumerable jobs.

Institution of Civil Engineers.—At students’ meetings,
to be held on Mondays, April 7 and 21, lectures on “Produc-
tion of Steel Sections and their Application in Engineering
Structures” will be given by Mr. A. T. Walmisley
MJnstC.E.