98

THE COLLIERY GUARDIAN.

January 9, 1914.

and the upper side is in a state of compression. That,
in witness’s opinion, was the reason why they had so
many accidents in mines where the roof was strong.
He had seen pieces shot oft from a hard sandstone roof
like a bullet. If the strata were in tension, and there
was a sudden change of strain, it was like releasing a
spring, and the result was bound to be the forcing down
of pieces of under-roof very suddenly. He had seen it
start at the edge of the pack no thicker than paper, and
increase to 9 or 10 inches ; coming oft very suddenly in
between the props where the roof was very hard. The
number of accidents from working where the roof was
very good in thick seams was particularly noticeable.
Witness spent three weeks in Silesia in mines which
were being worked by the ordinary system of hand
packing, 29 ft. coal, and those using hydraulic packing,
and noticed in every case where hand packing was in
use these fractures were quite visible on the face, and
they had a series of slips going back into the workings.
There was quite a series of small-forked planes. Where
part of the coal was left in between those fractures it
was simply a mass of fine particles of dust, due to
grinding. The tremendous noises that took place in
those thick seams in Silesia, where they were working by
hand packing were something fearful. They were not
due at all to the breaking of the strata as much as to
the change of strain in the particles forming the rock,
because when these huge bowks took place there was no
evidence at the face even of the roof coming down.
There was evidence of a very sudden shock in the
particles of dust. Witness believed if they had plenty of
fine coal together, the danger of spontaneous combus-
tion was a great deal less than if they mixed the coal.
The air must get into it.

Hydraulic Stowage in Silesia.

Witness next dealt with hydraulic packing in Silesia.
He said at the largest pit they had pipes going 4,000
yards into the working face. That was at the Louise
mine ; the packing was so complete that where they had
a dip of about 15 degs. there was only about 4 to 5 per
cent, of the thickness of the seam of subsidence shown
on the surface. Previous to that the amount of subsi-
dence was enormous. There was certainly the cure to
prevent the exceedingly rapid crushing on the face to
begin with, and what always accompanies that on a
thick seam, the enormous loss of coal. The fractures
with the hydraulic stowage were absent entirely. The
roof comes down with a bend almost imperceptible to
the eye, so that one can hardly see any break in it at
all. In Westphalia in one or two places some gob fires
had cost £20,000 or £30,000 before they were finally got
rid of. The effect on the face seemed to be to give a
very gradual pressure without any jerking or breaking.
As a matter , of fact it was a most marvellous thing—
the extent of roof that could be exposed at the face on
timbers without showing any severe crush. The system
was applied in longwall working just the same as it was
applied to the bord and pillar system. There was not
a single mine where hydraulic stowage was done in
Silesia on the longwall system. He admitted that it
was always done in panels there, but they were taken
out as longwall faces. It was not a question of
advancing from the shaft and taking all in front.
They could not very well use it for that unless they
were working entirely from the deep. It would neces-
sitate for its proper application an alteration in the
mode of working coal to some extent, and, in witness’s
estimation, a very advisable change.

Shaft Pillars.

Many fires had taken place on the edge of the shaft pillar,
and that was due to the excessive crush. Mr. Rhodes
referred to the method of coming out 500 yards from the
shaft pillar, opening out and working back towards the
shaft pillar, and added that that all turned on whether
headings could be driven. In one case steel girders
have been set time after time in a. road only 10 ft. wide
and in absolutely solid coal. Ho other coal was worked
and these headings had been driven forward for a very
important purpose—that was, to try and get into another
royalty and work in advance where it 'was an utter
impossibility to keep them up and to open out by a
bank system, the process of development would be so
slow that they would really never get their colliery out.
The total thickness of the seam would be roughly 9 ft.,
or 9 ft. 6 in., and about 4 ft. to 6 ft. was worked just
according to the character of the roof, leaving the rest
as support. He (Mr. Rhodes) had been trying a number
of experiments, and tried to take the whole of the seam
out, leaving the top 18 in. and the next 18 in. to see what
the minimum amount of coal was that could be left in
the goaf, and the maximum amount that could be got
out. But it seemed to him that in connection with
hydraulic stowing the question of being able to drive
straight work in flat seams was practically a sine qua non.
Witness said that was so for almost any seam, whether
flat or inclined. There was no difficulty in its applica-
bility to a thick coal that was not inclined except that
there was a slight increase in the barricading to keep
the material in. It could be done by taking out panels
here and there, as.he had seen it done in Westphalia at
the Deutscher Kaiser Mine, where they had taken out
panels about 400 yards square and left coal all round.
The method of working at No. 7 was this. They started
quite near the shaft pillar and took out one panel there.
While they are driving forward they are opening
up and cutting other panels, and they distributed
the extracting of the panels as widely apart as they
could so as to prevent any wide subsiding movement.
A system of hydraulic stowage was worked on the long-
wall principle in the Pas-de-Calais coalfield at Lens,
that is longwall retreating on very big panels. Even in
longwall with long continuous face, witness did not see
that it was at all impossible if they had means of getting
the packing material; only one road need be driven for
a considerable distance—one heading.

The Cost of Stowage.

Sir Arthur Markham seriously questioned the figures
as to cost stated by witness in his papers read before the
Manchester Geological and Mining Society, Witness
explained how these were arrived at.

Sir Arthur said the average cost in Silesia taken
on the Government returns in all the mines was Is. 2d.
a ton with labour at 3s. 6d. a day. Mr. Knox gave his
costs at Manchester at about half that. Witness said
that Krupps’ people told him that they were doing it at
7d. In working the thick seam there it has cost them a
great deal, not so much in taking the material into the
workings as getting the water filtered and getting it
pumped back to the surface. Nor would he suggest
that it could be done here at the same cost. He had a
reply from the assistant engineer at Humboldt’s,* who
said he was afraid some of these costs quoted had been
the costs after deducting the saving in timber and
surface damage or the cost for crushing and packing
only plus interest and depreciation.

Sir Arthur Markham said he was given every possible
information in Silesia; but in Westphalia, naturally, he
was regarded with some suspicion, because that coalfield
is in keen competition with England, and the mining
people told him quite frankly they would not give the
information to English people as to their costs because
they were disclosing a trade secret which they did not
think they were justified in disclosing. On the other
hand, in Silesia, which is not in competition with this
country, they were most courteous, and gave every
possible information as to their costs.

Mr. Rhodes said that in South Yorkshire in the areas
where gob fires had to be contended with they were
working in a purely agricultural country with very
valuable land, and with land which was so constituted
that it was almost impossible to take any of the surface
for hydraulic stowing. There was nowhere within 20
miles where they could get even any rubbish. Witness
said the only solution to his mind was that they would
have to get some arrangement whereby they could get
the steelworks, to which they were sending their coal,
to return the slag and so on. It would have to be
crushed, certainly. But the question of the nature of
the material was a pretty wide one.

Absence of Material for Stowage.

Mr. Rhodes said there was the soil at the top which
could be used; but this is a flat district which extends
from the sea for a distance of about 40 miles, and of
that 40 miles there is a breadth of, approximately,
15 miles, being developed, and the total available head
of drainage is represented by 25 ft. It is all very
valuable agricultural land, which is let to-day at roughly
£2 an acre all round. There is a large group of collieries
where, if this hydraulic stowing could be applied
commercially, there would be very great difficulty. Sir
Arthur Markham added that there was no possible
quantity of debris made in the works that could be
available in comparison with the gigantic output of coal
from a modern colliery. One colliery would take the
whole of the slag made at all the furnaces in the whole
of the district. All these cinders are used, and they
get a very good price for roadmaking. They must pay
the price for them that is paid for roadmaking. Owing
to the high heats used in modern furnaces many of the
cinders are nothing more or less than heaps of lime now.
At Siemens’ furnaces the whole of their slag practically
is being ground and gone over for the purpose of
extracting from it any steel left in it, and the basic is
turned into basic slag for agricultural purposes, for
which they get about £1 a ton after it is ground.

Mr. Rhodes said that 12,000 tons per day within the
next six years would be something like 24,000 tons if
the present developments went on, and that was a
conservative estimate.

Sir Arthur Markham said he had visited all the mines
where hydraulic stowing was being carried on, and there
were no mines where they were using argillaceous
material. The chief inspector of mines in Westphalia
told him that half the mines in Westphalia could not
adopt hydraulic stowage because they had not the
material, and the only case where the slag was being
used was in the town of Dusseldorf itself, where they
were working under furnaces, and the furnaces supplied
the slag to the collieries for nothing, and ground it up
for nothing, and gave it to them free for the purpose of
enabling the coal to be extracted under the town. So
that they must not take that slag which was used at the
Deutscher Kaiser Mine as an illustration, because the
colliery company paid nothing for the material, and the
ironworks branch of the company’s business paid for
the whole of the cost of grinding and of conveying to
the colliery, charging nothing for it. Witness said the
same applied to the prices at Krupp’s. As a matter of
fact, it was a saving to the firm, because they were paying
rent for the tip. So far as the actual costs side is
concerned, the difficulties here were very much greater
than they would be in either Germany or in France
even, because they had many facilities granted by the
railway companies, and so on, for the transit of material.
In various parts of Westphalia they were providing the
material very cheaply on account of the fact that a great
deal of the benefit goes to themselves in supporting the
railway. Previously the railway was supported by
pillars, and now the material is being carried they are
getting it carried, probably, below the ordinary rates
for the purpose of packing. Sir Arthur Markham put
it that the only way in which hydraulic stowing can be
worked is for the State to work these mines—putting
the economic question aside—and bringing the material
on a State railway. Witness agreed that under the
conditions described by Mr. Rhodes, it certainly seemed

* The Humboldt Engineering Company make a speciality
of hvdraulic stowing plants, and their estimate for stowing
only is 2|d. to 4|d. per ton of coal raised, according to the
amount of crushing required.

to be impossible for anyone to compete in an open
market to produce coal at a profit where such a heavy
cost would be entailed in getting the coal. The district
seemed to be an exceptionally unfortunate one for
hydraulic stowing. He would still maintain that there
are a number of collieries subject to spontaneous
combustion which, as things are, could be carried on
successfully with hydraulic stowage, and this difficulty
be overcome.

The Effect of Moisture.

Mr. Rigby mentioned one special case where they
carried the face forward at as regular a rate as they
could. That was a most important point, because they
made use of the weight over the coal face to enable
them to get that coal where they could not blast.
Hydraulic stowage in a case of that sort would put a
very considerable increased cost on the coal-getting.
Another point was the effect of water in certain seams.
Witness said that if they took the water in pipes,
without leakage, they could collect the water and bring
it back again in the same way. They used the old roads
behind as the drainage area.

As to the effect of a saturated and warm atmosphere
excluded from light on the lungs and liver of the men
in connection with ankylostomiasis and any of the
scheduled diseases, witness said that was one of the
things he enquired into in Westphalia at every colliery
he went into, because many of the mines are very deep
and the temperature fairly high, from. 75 to 78 degrees.
Of course, every official assured him that it had no dele-
terious effect at all on the workmen. He discussed the
question with one or two of the representatives of the
trade union, and they seemed to think in some of the
deeper mines it had had a bad effect on the health of
the miners, although they could not state any specific
cases where it had been very noticeable, except that it
was the general opinion. Witness noticed, however,
that two or three weeks afterwards the trade union body
had been laying down some claims for alterations in
hours, and they wanted a shorter working day in those
deep mines where the percentage of moisture in the air
was increased; but he did not think the percentage of
moisture in the atmosphere was so much greater where
they had hydraulic stowing if they piped the water there
and back. There was only a very small part of the
surface exposed to the air current, and the reduction in
the temperature in those mines, through preventing
that grinding action, more than compensated for any
added moisture there might be put into the air.

Mr. Knox thought a great deal too much weight was
put on the question of water and creep. It seemed to
him the whole thing was a question of translating the
particles underneath by the pressure on the pillar. It
was not merely the question of the occlusion of water;
there must be some other change going on. He had
seen creep exceedingly bad on a roadway where it was
perfectly dry, and in the same seam where it was wet
there was absolutely no sign of creep at all. If in some
cases hydraulic stowing has, as apparently it would
have, the effect of causing these clays to swell by some
means unknown, for every one of those cases where it
would cause swelling of that description, it would save
others which are merely the result of pressure. The
retreating system, after all, was the one that solved the
difficulty.

The Maintenance of Pipelines.

Witness said the maintenance of the pipeline was
very costly to start with; but the cost had now been
reduced to a minimum, first of all by getting rid of the
excessive amount of wear in order to keep the pipeline
intact. The trouble at first was that, in using ordinary
pipes, in about three months’ time the pipe got worn to
such dimensions on the underside that it either had to
be taken out or arrangements made to turn io, and at
first they used to turn it every three months, and every
twelve months they had to put a new pipe in. But at
Krupp’s Works one of the heads of one of the depart-
ments who had carried out a series of experiments and
who had a laboratory filled with pipes of various
descriptions, tried all kinds of things, and ultimately
came to the conclusion that the porcelain pipes were
the best. To prevent the leakage at the joints, they
had a sort of spigot and faucet arrangement with
clamps. In one case he carried 1,100,000 cubic yards
for 1 in. of wear in porcelain-lined pipes. The lining
was 2 in. thick, so that it had been worn half way
through. It was a pipeline where they were attempting
to force stowing uphill.

Application in North and South Staffordshire.

Mr. Rigby referred to the rearer mines in North
Staffordshire, and in the steep measures in Warwick-
shire where they are working a mile to the rise to a
height of 140 yards, witness suggested that they would
have to drive tunnels high up in the shaft to take in the
pipe-line as they did on the Continent in all their steep
working.

Sir Arthur Markham disagreed with witness that it
was possible to approximate the pressure by the depth
at any one point, taking the specific gravity which they
were using. As a matter of fact, they never had more
than 150 lb. pressure even in the deepest shaft at the
bottom part. They never filled the pipes, and therefore
there was never a solid head which gave them a total
pressure due to the static head. In fact, at some of
these deep mines they had relief valves to let the
pressure out when it gets over 150 on account of the
difficulties with the joints. Sir Arthur added that they
had given up the oval pipe in the Government mines,
and were going in for some kind of steel lining made
under a special process which is harder than the china,
and they were getting better results from that than
from the china pipes—in fact, they were using them in
all the Government mines in Silesia. They had these
special steel lined pipes in which they got more than