January 30, 1914.

THE COLLIERY GUARDIAN.

243

return airway of any ventilating district of the mine
on any one occasion^ :—

(а)	When smoke or other signs indicative of a fire
occur in any such mine the whole of the workmen
should be withdrawn from the ventilating district
affected, and before they are re-admitted the
manager and two representatives of the workmen
(if the workmen elect to appoint two such repre-
sentatives) should make an inspection, the result of
which should be entered in a book to be kept at the
mine for the purpose, and should be signed by the
parties making the inspection. The men should
not be re-admitted to that part of the mine unless
such report (jointly if the men’s representatives
take part in such inspection) states that it is safe
to do so.f

(б)	When the presence of fire has been definitely
determined, that is to say, when actual fire has been
located or is known to exist, the whole of the men
working in the seam in which the fire has occurred,
and in other seams worked from the same level,
should be withdrawn from the mine, except those
engaged in combatting the fire, unless the seam is
naturally wet throughout, or unless such other
districts in the seam or seams worked from the
same level are naturally wet throughout or are
adequately protected by some means which in the
opinion of the Secretary of State is effective in
stopping the progress of an explosion of coal
dust.I

* There is a memorandum, signed by Mr. R. A. S.
Redmayne, Sir Arthur B. Markhom, Mr. C. E Rhodes and
Mr. Herbert Smith, expressing the opinion that on the
outbreak of a fire in a mine wheie safety lamps are not
required by the Coal Mines Act, 1911, or any Regulation or
Order under that Act, to be used in the ordinary course of
working, or the return air of which has never been found to
contain as much as £ per cent, of inflammable gas, those
persons who are engaged at work upon the return side of
the fire, should be withdrawn from that part of the mine.
They suggest also that a similar inspection to that
described in the Report, should be made with a view to
determining whether any of the persons on the intake side
should be allowed to continue work or not. See also note f.

t There is a memorandum signed by Sir Arthur B. Mark-
ham, Mr. C. E. Rhodes, and Mr. Herbert Smith, urging that
an inspector of mines should be associated with the manage-
ment and representatives of the workmen in making the
inspection, and that the record of the inspection should be
signed by all the parties concerned. Mr. Frank Rigby puts in
a memorandum in which he says he agrees with the second
memorandum in so far as it applies to mines in which
safety lamps are used, whether in pursuance of the Act or
the Regulations and Orders under the Act, or in mines in
which one quarter per cent, of inflammable gas has been
found in the return airway of any ventilating district of the
mine on any one occasion, but he does not agree that it
should apply to other mines under the Coal Mines Act.
There are many mines, for instance, in the South Stafford-
shire and other coalfields, in which fires or heating are
constantly occurring, and where there is no necessity that
the men should be withdrawn, even from the return side of
such a fire or heating, or that the inspector need be called
upon to make an inspection together with the management
of the mine. If such a regulation were made, the inspector
of the division might bo occupied in doing nothing but
making inspections in such mines, in many cases where prac-
tically no danger existed, to the detriment of his work in the
division generally. Ig would be no uncommon occurrence
for an inspector to be required in several mines on the same
day, and it might be that the men would have to be with-
drawn from a mine or part of a mine and not readmitted for
some days before an inspector had visited the mine. Were
it made a legal obligation to keep the men out of such mines
pending his arrival, considerable economic disturbance and
great and unnecessary hardship, both to workmen and
employers, would result.

J There is a memorandum to which Mr. R. A. S. Rd-
mayne, Sir Arthur B. Markham, Mr. C. E. Rhodes, and Mr.
Frank Rigby are the signatories, on the use of incombustible
dust in a mine subject to gob fires. They are of opinion
that in the interests of safety it is desirable that the
following words should be added to paragraph 4 (&) ;—
“We are of opinion that, one of the means which might and
should be adopted as effective in stopping an explosion of
coaldust, is the use of incombustible dust, and we are in
agreement in thinking that the necessity for the withdrawal
of the workmen from the ventilating districts other than
that in which the fire occurs, would cease to exist if such
other districts in the seam or seams worked from the same
level were adequately protected by incombustible dust on
the roads of such districts, the dusting being in the propor-
tion of at least two parts of incombustible dust to one of
coaldust; and we are further of opinion that in whatever
part of the mine a fire occurs all accessible parts of the
mine immediately contiguous to the fife should be dusted
in the proportion of at least four parts of incombustible
dust to one of coaldust. Our reason for suggesting a higher
proportion of incombustible dust than that put forward as
a minimum in the Fifth R^p^rt of the Explosions in Mines
Committee is that, having regard to the fact that mines
subject to spontaneous combustion are more prone to
dangerous conditions, a higher scale should be insisted
upon.” In a further memorandum the same Commissioners
state:—“Although this subject is not immediately included
within the scope of our enquiry, yet we desire to give a
strong expression of opinion, on the evidence which has
been submitted to us, as to the very great desirability in
all mines liable to spontaneous combustion, of all timber
being withdrawn from wastes and from roads about to be
abandoned. It has been very clearly demonstrated to us
that timber so left is a very fruitful source of danger.”
On these points there are also memoranda by Mr. Herbert
Smith as to the use of incombustible dust in mines ; he
expresses the opinion that more experience should be avail-
able in the use of incombustible dust in mines before any
rule s are adopted making its use compulsory. “ I am
anxious to prevent loss of life and destruction of property
by explosions, but, before adopting any rules making it
compulsory to use dust in mines, I favour the Committee
appointed to enquire into this problem continuing their

(c) In the event of a fire being dammed off the
whole of the men should be withdrawn from the
mine until the work is completed, and should not be
re-admitted until an inspection, has been made in
the manner recommended above, and the conditions
reported safe.

The above suggestions should be incorporated by the
Home Office in the General Regulations.

work more searchingly and clearing away, if possible, any
doubt as to the wisdom of using dust of the
character named or any dust injurious to health.”
With reference to the withdrawal of timber from wastes
and roads about to be abandoned, he states that he is in
agreement with the fifth memorandum as to the “ great
desirability, in all mines liable to spontaneous combustion,
of all timber being withdrawn from wastes and from roads
about to be abandoned.” He is, however, of opinion that
the leaving of small pillars of coal in the goafs is an equal
if not a more fruitful source of danger than the leaving of
timber. And he further thinks that the question of with-
drawal of timber, and also the getting out of pillars of coal,
should be dealt with in the general report on the question
as to the best method of preventing gob fires.

A PROPOSED HEW METHOD OF MKIHG
LARGE ARCHES MIHES.*

By John Roberts, Wigan.

It is generally admitted that the work of constructing
large arches for pit-bottoms, engine rooms, and stables
is an operation bristling with difficulties and attended
with no little danger. This is due chiefly to the fact
that very large excavations have to be made in the first
place, and these have to be well timbered temporarily to
protect the men engaged in the work. The securing of
the roof and sides temporarily is perhaps the most
difficult part of the work, because not only have the
supports to be of a substantial character, but in the
best practice they must be set in such a manner that
they may be completely removed, portions at a time, as
the walling is being built, so that the arch may be
thoroughly well packed in order that the pressure of the
strata will be uniformly distributed over the entire
structure.

The object of this paper is to put forward a method
that, as far as the writer is aware, has not previously
been adopted or suggested, and which will, to a great
extent, tend to overcome the difficulties and reduce the
danger connected with the work.

Members are well acquainted with the methods
hitherto adopted in practice, and it has not been thought
advisable, therefore, to include a description of them in
this paper. Suffice it to state that there are two
methods of removing the ground. In the first, the
excavation is commenced at the top and proceeds down-
wards ; in the other, the preliminary drivage is made at
the bottom and the rock removed upwards. The former
method is the more generally adopted in this country.

Several different methods of timbering have from
time to time been carried out, and in some of these
large quantities of timber are used, as not only have
the roof and sides to be secured, but in excavations
having a sectional area of 1,000 square feet or more
the face of tbe heading must also be timbered. An
enormous amount of labour is entailed in setting
temporary props, removing these, and setting semi-
permanent supports. Even when this work has been
well executed, there still remains an air of insecurity
about the structure. Also, there is yet the difficulty
of removing all these timbers piecemeal, after they have
been standing some considerable time and the weight of
the roof and sides has come upon them. Numerous
cases could be cited in which engineers have been
compelled to leave considerable quantities of timber,
especially the longer pieces, and even steel girders,
above and behind the arch.

The writer purposes to reduce the amount of
temporary timbering almost to a minimum. The first
operation consists in driving a heading about 8 ft. wide
and 7 ft. high at the top of the site of the arch. This
would be timbered in the usual manner, as shown in
fig. 1. The only special point to note is that the lags a,
near the middle of the “ collar,” are of substantial
dimensions, and preferably rectangular, or nearly so, in
section. The object of this is to allow of their being
readily supported by temporary props, as indicated in
dotted lines, before withdrawing the “pair” of timber
as the walling is being built up. The heading is then
widened out on both sides, as shown in fig. 2. Further
supports are put in, either in the manner shown at b or
as at c, care being taken that each prop and “ arm ” has
a firm hold in the floor. The distance between the
“pairs” of timber might be 4ft. or less as required;
longer lengths might cause too great an area of roof to
be exposed at one time when the timbers are being
withdrawn. This forms practically the whole of the
temporary timbering required, no timber being placed
against the fence.

This part of the work having been completed, the
upper section of the arch is now begun at d. The first
thing would be to fix in the supports for the centres f,
fig. 3. These may be set back in the side for about a
foot or so. The centres would be specially designed for
this section of the arch. On the centre supports planks
about 6 in. thick would be placed parallel with the
axis of the road, and these would form the base g of this
portion of the arch. The work of building the arch e is
now proceeded with in the usual manner, taking out the

* A paper read before tbe S mth Wales Institute of
Engineers and published in the Proceedings.

timber little by little, and well packing the back of the
arch with sand or boiler ashes h. Tbe props shown
dotted in the previous figures would support the portion
of the roof above the centre of the road, and thus allow
the arch to be built up to the “ crown ” after taking out
the double timber. When about to putin the “ crown”
these props and lids are removed.

It will at once be apparent that the timbers, being of
comparatively short lengths, may be removed much
more readily and with greater safety than when long
bars are used. Moreover, owing to the fact that the
timbers have not to remain in for any length of time,
lighter pieces may be used, and are withdrawn practi-
cally before the weight has had time to settle upon
them. The arch now forms a substantial protection for
the workmen, and the excavation may be proceeded with
downwards in comparative safety. In this work care is
taken not to disturb the arch, and it would be necessary
to leave strong ledges of rock k to support it, much in
the same way as in a sinking pit. In ordinary ground
these ledges would be carried down such a distance as
would allow the invert to be put in. After constructing
the invert in the ordinary way, preparations are made
for building the side walls. For this purpose the ledges
would be removed bit by bit and the walling put in in
sections, the arch being supported in the meantime on

Fig 1

the planks g, and as a further precaution the centre
rests would also be supported by means of props n..
Having got sections of the side walls built tightly
against the planks, further portions of the ledges are
taken out in a similar manner.

An objection may be raised against the use of the
thick planks used in the first section of arch on the
ground that such planks have in some cases been
responsible for wrecking arches. This liability may be
reduced somewhat by inserting in the walls occasional
courses of wooden bricks of comparatively soft wood.
These would yield as the weight came on and thus allow
the arch to take the “ squeeze ” without disastrous results.
Where the ground is likely to be troublesome and the
pressure considerable, a special base for the upper
portion of tbe arch might be made. The method
suggested is to use H-iron supports, about 6 ft. apart,
for the centres, and these are set well back in the solid
ground, as shown at f, fig. 4. Girders are then placed
parallel with the road as at m. Concrete g is run in so-
as to surround these longitudinal girders. A skewback
ferro-concrete base is thus formed on which to build the
arch. It might be advisable not to run this concrete
right back to the side, otherwise unequal resistance
would be offered to the pressure, and the structure may
consequently be prematurely crushed. Transverse
bars o would be used for supporting the sides below the
arch. On removing sections of the ledges k the concrete
would be in tension, and it is for this reason that the
girders or old rails m are used. The dotted lines n
show the positions of the supports for the centre rests
or needles, /. There should not be much difficulty in
removing these needles when portions of the arch have