April 13, 1917.

THE COLLIERY GUARDIAN.

717

The representatives of the various districts of the
kingdom on the executive council having been
appointed, the call for the current year was fixed.

On the motion of Mr. J. T. Browne, a resolution of
thanks was passed to the hon. treasurer and the hon.
auditors for their services, coupled with a request that
they would favoui’ the association by continuing to act
in the capacities named; which Sir William Barrett,
in acknowledging the resolution on behalf of his
colleagues and himself, was good enough to indicats
they would be prepared to do.

The Parliamentary and other committees having
been re-appointed, the proceedings closed with a
hearty vote of thanks to the chairman, which he
acknowledged.

COLLIERY WORKERS AND DAYLIGHT
SAVING ACT.

An important conference was held at the Wigan
office of Sir Thomas R. Ratcliffe-Ellis, secretary to the
Coal Owners’ Association, on Saturday, between
representatives of the Lancashire and Cheshire
Coal Owners’ Association and the representatives
of the joint council of colliery workers outside
the Miners’ Federation, consisting of Lancashire
and Cheshire enginemen and boilermen, Lanca-
shire and Cheshire colliery firemen, and other
organised colliery workers, there being present, in
addition to the representatives of the coal owners,
Messrs. W. T. Roberts (president), T. Watson (secre-
tary), and W. Forshaw (assistant secretary), repre-
senting the Enginemen’s and Boilermen’s Federation ;
W. T. Miller (president), Peter Derbyshire (general
secretary), and T. E. Clark, Lancashire and Cheshire
Colliery Firemen’s Association; W. Burrows, N. Fair-
hurst, and J. Lancaster (secretary), Colliery Trades-
men’s Association. The question for consideration
was the effect which the arrangement come to between
the coal owners and the Miners’ Federation in regard
to the operation of the Daylight Saving Act would have
upon the organised colliery workers outside the Miners’
Federation. The arrangements as agreed upon
between the representatives constituting the Lanca-
shire and Cheshire Joint Committee, are as follow: —

(1)	After the coming into operation of the Daylight
Saving Act (April 9, 1917), and during its continuance,
the hours of work on each day of the week, except Friday
and Saturday, shall be from 7 a.m. to 3 p.m.; on Friday,
from 7 a.m. to 4 p.m.; and on Saturday, from 7 a.m. to
1 p.m.

(2)	At collieries where in any week the Saturday is not
a working day at the pit, the extra hour, if worked, on
Friday shall be paid for as one-seventh of a day.

(3)	Where Saturday is a working day at the pit, a work-
man who is absent from work on the preceding Friday, but
works on Saturday, shall only be entitled to be paid six-
sevenths of a day for such Saturday.

(4)	In cases where work now commences at 7 a.m., and
the majority of the workmen employed at the colliery
desire the present hours of work and conditions to con-
tinue, no alteration in the existing hours and conditions
shall be made.

(5)	The management and a majority of the workmen
employed at any colliery may, in lieu of the above arrange-
ment, adopt the practice and conditions now prevailing at
collieries where the hour of the commencement of work is
7 a.m., and not 6 a.m.

After a lengthy discussion, an agreement was arrived
at by the conference in regard to the organised colliery
workers outside the Miners’ Federation and the opera-
tion of the Daylight Saving Act, on the accepted prin-
ciple that any arrangement come to by the organised
coal owners and the Miners’ Federation, if it affected
the organised colliery workers outside the Miners’
Federation, could not take effect unless by agreement
between the representatives of such organised colliery
workers as were affected and the coal owners. In
regard to enginemen and boilermen, the terms agreed
upon by the conference were : —

(1)	All winders and other enginemen working on the
loose and tie system to change shifts as hitherto; excep-
tional cases to be considered by the management and the
enginemen’s representatives.

(2)	All two or single shift winding enginemen to alter
their time of coming on duty according to the new time
arrangements between the Coal Owners’ Association and
Miners’ Federation for April 9, 1917; all other cases of
enginemen, including also locomotive men; exceptional
cases to be considered by the management and engine-
men’s agents.

(3)	All stokers working on the loose and tie system
where there is the same number of stokers on each shift to
change shifts as hitherto; but where there is a larger
number of stokers employed on day shift than on either
of the other two shifts, then the time of changing shifts to
be altered according to the new time arrangements as
stipulated for enginemen in clause 2; exceptional cases to
be considered by the management and the enginemen’s
agents.

It was agreed that the arrangements with the
Miners’ Federation and other workmen did not
involve any change in colliery tradesmen’s hours.

The representatives of the Lancashire and Cheshire
Colliery Firemen’s Association agreed to conform
with the change in hours, providing the agreement did
not affect the wages of colliery firemen, and this condi-
tion was accepted.

American Coal for Allies.—The Federal grand jury has
indicted 21 coal companies on charges of combining to fix
unreasonably high prices for coal sold to ships belonging
to the Allies which coaled in New York harbour, whereby,
it is alleged, the vessels have been charged an excess esti-
mated at 4,000,000 dols. in the year.

SUBSIDENCE RESULTING FROM
MINING.*

By L. A. Young and H. H. Stock.

The removal of solid minerals from the earth’s crust
produces cavities, and thus the equilibrium which has
previously existed is disturbed. If the cavities caused
by the mining operations are not of great extent,- or,
even if long, are narrow, this disturbance may be
apparent only as a local movement, and may cause
only occasional falls of rock from the roof. If the
excavation is wide as well as long, the unsupported
strata above the excavation will tend to sag under
their own weight, and, if their texture will not permit
the bending movement necessary for the strata to
become adapted to the new conditions, cracks and
fissures resulting in extensive falls of roof will occur.
Successively, the overlying beds may break and fall
until the disturbance extends to the surface.

If the overlying measures bend without breaking
and sag until finally they are supported by the floor of
the excavation, the strata at greater height may sag
successively and in a corresponding manner. Eventu-
ally, this movement may extend to the surface, the
disturbance generally being less extensive as the
vertical distance from the excavation increases.

In estimating the weight upon any coal seam or other
mineral deposit due to the overlying rock, it is custo-
mary to assume that this weight is distributed more or
less uniformly over the entire deposit. When a por-
tion of a bed of mineral is removed, the burden carried
per unit of area by the unmined portion becomes
greater than the burden carried before any portion of
the deposit was mined, because the weight formerly
distributed over the deposit is now concentrated upon
the pillars. The extent of the increase of burden on
the pillars depends upon the extent of removal of the
material of the bed, assuming that the overlying rock
does not break in such a way as to relieve the stress on
the pillars. If the pillars are not strong enough to
support the increased load, or if the underlying bed
does not have sufficient bearing power to resist the
increased pressure, a movement will begin which is
commonly called a “squeeze ”f or a “ creep.” Depend-
ing upon the depth of the mining operations and the
geological conditions, the “ squeeze ” may cause an
extensive vertical movement which may reach to the
surface. The removal of coal or other bedded minerals
from any considerable area, therefore, at once develops
the problem of the support of the surface, which
involves certain factors requiring careful attention by
the mine operator before extensive excavations are
made. If the operator, for commercial reasons,
meets these problems in a manner that is not in har-
mony with the prevailing ideas of conservation, a
remedy should be sought which will secure for the
public the greatest continuing benefit.

Upon the opening of a new mine, the following
questions may well be asked: —

(1)	Is the owner of the surface, if other than the owner
of the mine or mining rights, legally entitled to surface
support?

(2)	Is the material to be mined at such a depth that
mining of all of it will not disturb the surface ?

(3)	If the removal of all the deposit will cause surface
subsidence, what percentage of the deposit left in pillars
will prevent subsidence ?

(4)	What is the ratio between the value of the material
in the pillars necessary to prevent surface subsidence and
the value of the surface ? What would be the charge per
ton against this pillar material if the surface were bought
outright ?

(5)	What amount and what extent of subsidence may be
expected under the conditions of operation most econo-
mical at the time?

(6)	Upon what basis will it be possible to adjust claims
for damages?

(7)	What will it cost to restore the surface for agricul-
tural uses after all the deposit has been removed ?

There are certain questions which the public and
the State should answer at an early date: —

(1)	Shall the coal or other mineral now in the ground be
brought to the surface and used, or shall it be left in the
ground, serving like worthless rock, only to support the
surface ?

(2)	Assuming that the removal of all the material will
temporarily prevent use of that part of the surface over-
lying the area being mined, will it be better policy for the
State to see to it that all the merchantable material is
mined, and then have the surface restored, or will it be
wiser to permit nearly one-half the material to be lost
permanently in the effort to avoid temporary injury to
the surface ?

(3)	If the mine operator is required by law to protect
the surface, shall anything be done to prevent his leaving
a large percentage of the deposit in the ground, never to
be recovered, and simply to support the surface ?

Scientists who have investigated the national
resources have emphasised the fact that the supply of
minerals is not inexhaustible, and that at the present
rate of increase in production the exhaustion of the
supply of some of the most important ones is not far
off, as time is measured in the life of a nation. In the
case of coal, one of the means by which the life of our
supply may be extended is by recovering all, or at
least a much greater percentage than is recovered at
present, of the coal in the ground. If the extent of
the entire area underlaid with workable coal beds be

* From University of Illinois Engineering Experiment
Station Bulletin No. 91.

t The Pennsylvania Mine Cave Commission gave the
following definition: “A ‘squeeze’ is caused by the
general subsidence of the strata overlying the coal bed, due
to a partial failure of the pillars; when this subsidence
radiates from origin it is called a ‘creep.’” Another
meaning of “ creep ” is movement of the floor, due to
pressure of pillars.

compared with the extent of tillable land not under-
laid with coal, it will be noted that the actual area
that might be affected by surface subsidence is rela-
tively small. When it is realised that land affected
by subsidence may in most cases be restored to service
for agriculture after all the deposit has been removed,
it may be rightly urged that the mine operators
remove much more of the coal than is taken under
present conditions, when preservation of the surface is
frequently the determining factor in deciding the
amount to be mined. Since mineral once lost by
improper mining or left in pillars in abandoned mines
is lost for ever, the maximum recovery consistent with
safe mining is of prime importance, and is funda-
mental. The problems, therefore, are to discover
what effect mining under the existing physical condi-
tions will have upon the surface, to anticipate and to
reduce to a minimum possible surface subsidence, and
finally to discover the best means of harmonising and
co-ordinating the various industrial and commercial
interests involved.

Records of Damage to Surface.

While the technical Press contains many reports of
surface subsidence attributed to mining operations,
there are in America only a few reliable records avail-
able for study showing the exact amount of subsidence
of the surface after the mineral deposit has been
mined. However, there are a number of instances in
which European engineers have kept records of sur-
face levels extending through long periods of years.

Surface movements have in many instances been
disastrous; records of damage to property being avail-
able both in Europe and in America. In the following
section a number of the most important instances of
damage to property resulting from mining operations
are presented. These instances show that the problem
is,of widespread interest, and is not a local one.

Belgium.—Although serious subsidence adjacent to
salt mines was noted in England in I860, and instances
of damage by coal mining are recorded in British tech-
nical literature, the problem of surface subsidence due
to mining operations seems to have been studied first
in Belgium. In the early part of the 19th century it
was claimed that coal mining about Liege, Belgium,
was causing damage to buildings, and in the year 1839
complaints were filed with the city officials on account
of damages to property. As a direct result of these
complaints, the city appointed a committee to report
upon the problem, and in filing its report the com-
mittee established the necessary restrictions required
for the safety of the city, and determined the size of
adequate safety pillars.

The Belgian engineer, Gonot, formulated a theory of
subsidence in 1839, and some years later published a
pamphlet dealing with the damage to a row of houses
adjacent to the mine of the D’Avroy Bovene Company,
claiming the mining, company was responsible for the
damage done. The mining company published a reply
to Gonot in 1858. The Provincial Government
appointed two engineers to investigate the cause of
the damage to the houses, and they reported that the
houses were not damaged by coal mining.

By a Decree of May 31, 1858, the Minister of Public
Works appointed a special committee to report on the
influence of mining upon the surface, and also to
review the rules of the committee appointed in 1839.
The committee of 1858 endorsed the recommendations
of the committee of 1839.

The disturbance of the surface about Liege con-
tinued, and G. Dumont was appointed to investigate
the matter. In his report he supported the funda-
mental principle of Gonot’s theory, but made certain
reservations in its application. He placed the respon-
sibility for the surface disturbances upon the mining
companies. The Colliery Owners’ Association pub-
lished a statement pointing out the fallibility of
Gonot’s theory, but admitted the applicability of the
theory to relatively flat seams.

Since 1875 considerable attention has been given to
the problem in Belgium, and the situation has been
complicated by the mining of coal from superimposed
beds.

England, Scotland, and Wales.—Considerable atten-
tion has been given to the subsidence problem in
England, Scotland, and Wales, owing to the extent of
the coal and salt measures, to the importance of the
coal industry, and to the proximity of the mines to
centres of population. In the early days of coal
mining in Great Britain it was customary to leave
pillars, but as mining practice improved, a portion
of the coal in the pillars was removed. In discussing
early methods of working coal, Bulman and Redmayne
refer to surface subsidence resulting from the removal
of pillar coal as follows—

The date at which it became customary to remove
pillars formed by a previous "working has been a point of
some importance in determining claims for damage to the
surface, and many such claims in which the point arose
have led to legal proceedings. That damage of this ,kind
was done at an early date is proved by the records of the
Halmote court for the county of Durham. Early in the
15th century there was an enquiry before that court about
a case which had occurred in the parish of Whickham, in
which it is recorded : “It is found by the jury that John
de Penrith is injured by a coal mine of Rogers de Thorton
so that the house of the said John is almost thrown down,
to the damage of the said John of 200 pounds, assessed by
the jury, therefore it is considered that the said Roger
repair the said house to the value aforesaid, or satisfy the
said sum.”

Since the year 1860 a number of British mining
engineers and operators have written upon the general
subject of subsidence and support of excavations.
Subsidence has resulted from salt mining operations,
as well as from coal mining, and owing td the nature
and extent of the salt deposits, the effect upon the