718

THE COLLIERY GUARDIAN.

April 13, 1917.

surface has been even more disastrous than the effect
of coal mining. Salt mining has been carried on in
the vicinity of Northwich, Cheshire, for many years.
In a depth of 390 ft. there is a total thickness of
almost 200 ft. of salt in four beds, the thinnest being
5 ft. thick, and two being each approximately 90 ft.
The shallowest bed is covered by 32 ft. of soil and by
92 ft. of salt marl. Shafts were sunk to the upper bed
shortly after 1670, and the pillar-and-room system was
used. Pillars from 12 to 21 ft. square were left to
support the surface, but these pillars were weakened
in time by the dissolving action of the water, which
seeped through the roof, and was pumped out as
brine. Surface breaks occurred which were generally
marked by brine pools. In 1750 the first serious
breaks occurred near the main street of Northwich.
These old breaks have been filled, and buildings have
been erected directly over them. Since 1750 numerous
breaks have occurred throughout the salt district.
After 1781 all new shafts were sunk to the second bed,
which is nearly 92 ft. thick, and is separated from the
upper bed by about 28 ft. of hard marl. The most
serious subsidence occurred in 1880, and the locality
is now covered by a lake about 30 acres in area and of
considerable depth. The drilling of brine wells has
increased the rapidity with which the pillars have
become weakened, and has hastened subsidence in the
vicinity of the old mines. Brine streams or channels
have been formed underground between the wells and
old shafts, and subsidence is greatest near these under-
ground streams. ,	\

The examples of surface subsidence due to coal
mining in England and Wales are very numerous.
Much agricultural land has been damaged and also
various improvements, including buildings, railroads,
bridges, railroad tunnels, canals, reservoirs, and
streets and highways.

In one district the Great Western Railway had to
fill 60,000 to 70,000 cu. yds. annually. A canal in
South Staffordshire has been raised 20 ft. Coal
mining under the Merthyr Tunnel, miles long, pro-
duced a total subsidence of 10 ft. in part of the tunnel.
The settlement throughout the length of the tunnel
was not uniform, and part of the line had to be cut
down to make the grade uniform.

In the South Staffordshire district there has been
considerable difficulty in securing suitable reservoir
sites owing to the fact that coal mining has extended
under most of the land, and owing also to the fact
that the bed is thick, and nearly all the coal has been
removed. A 3,500,000-gal. reservoir was built on a
site which had been undermined 34 years before.
When the reservoir was filled, the subsidence
amounted to 1| to 2 in. The cracks were filled with
cement, and the reservoir has since given no trouble.
Another 43,000,000-gal. reservoir was constructed in
the coal district in which there are three workable
beds, of coal, one being 8 ft. 3 in. thick, and lying at a
depth of 1,200 ft., while 66 ft. below it is a 6 ft. 3 in.
seam, and 80 ft. above it is a 6 ft. seam. These have
been worked, and one end of the reservoir has lowered
4 ft. more than the other, the great difference in
elevation between the ends being attributed to a fault.
In order to reduce the damage to water mains, the
practice in the English mining districts is to use lead
joints instead of the cc turned and bored” pipes. In
the Midland and South Yorkshire coal fields the
measures overlying the coal are principally shales, and
mining at a depth as great as 2,000 ft. has caused
some subsidence.

In his address as president of the Institution of
Mining Engineers, W. T. Lewis called attention to the
seriousness of subsidence in Wales, stating that the
surface sinks from 10 to 15 ft. on account of mining
at 1,800 to 2,400 ft. The removal of 4 ft. 9 in. of coal
and underclay, constituting a shaft pillar, at a depth
of 2,108 ft. is reported to have caused surface sub-
sidence of 3 ft. 6 in. at the South Kirby Colliery. This
amount of subsidence is unusual in the district, and
was attributed to the crushing of a shaft pillar in the
overlying Barnsley bed. A maximum subsidence of
1-74 ft. resulted from longwall mining of 5 ft. of coal
at a depth of 1,595 ft. in Derbyshire. Mr. James
Barrow cited an instance of mining coal 5 ft. 6 in. to
6 ft. 6 in. at a depth of 2,400 ft. The longwall method
was used, and the debris resulting from the working
of the seam and the brushing of the roof was stowed
underground. Subsidence caused buildings on the
surface to crack, water and gas mains to be broken,
and bridges to be squeezed and distorted. Mr. J.
Kirkup reported that the mining by longwall of a
seam 22 in. thick produced cracks in walls, and caused
damage in pipes in workings in a seam 279 ft. above.
Moreover, a careful survey showed that the movement
in the upper seam extended in advance of the work-
ings in the lower seam. Mr. I. T. Rees has reported
on subsidence resulting from longwall mining in the
coal field in South Wales. The lower seam worked
was from 3 to 4 ft. thick, and was well stowed. “ Three
hundred and sixty feet above this seam, workings had
been prosecuted in another seam in advance of the
seam below, and although there were 360 ft. of inter-
vening strata, and the openings caused by working the
seams were well stowed, yet the workings of the seam
above were affected a distance of 150 ft. in advance of
the workings of the seam below.” In 1912 the Wear-
mouth Coal Company Limited (Sunderland) was forced
to stop working the Hulton seam, which employed 400
men, on account of the heavy charges for surface
damage resulting from subsidence. In one case the
charge was 500,000 dols.

France.—In France subsidence has been noted in
the salt mining district as well as in the coal fields.
In French Lorraine the salt measures extend, under
an area approximately 9 by 19 miles. The thick-
ness of the beds varies from 33 to 230 ft., and the beds

lie at a depth of 300 ft. or more. The salt has been
removed in part by solution methods, which produce
large chambers, and, owing to the great size of these
chambers, and to the character of the roof, extensive
falls of roof rock have occurred. The subsidence has
generally taken place slowly, but where the covering
is limestone there have been sudden breaks which have
caused extensive damage. Among the serious surface
movements reported are one in 1879 at St. Nicholas
and one at Ars-sur-Meurthe in 1876.

Fayol made a number of observations of subsidence
at the Commentry Mines, as well as laboratory experi-
ments, and published the results of his observations,
including the levels taken at these mines from August
1879 to May 1885. He advanced a theory of subsi-
dence which was essentially different from that formu-
lated by the Belgian engineer, Gonot.

Germany.—Probably the first important German
publication on surface subsidence in connection with
mining was by A. Schulz in 1867. He investigated
the dimensions of safety pillars and the angle of break
in the Saarbruck field. The problem was considered
so important that in 1868 the Prussian Government
appointed a commission of four engineers to investi-
gate the effect upon the surface of mining operations
in the coal fields of Belgium, England, France, and
Rhenish Prussia. In 1869 von Dechen wrote upon the
subsidence in and about the city of Essen. He had
previously (in 1866) emphasised the importance of
studying the part played by the heavy marl beds over-
lying the coal measures.

In 1867 von Sparre contributed a paper upon the
“ afterbreak.” In 1894 the project of a canal between
Herne and Ruhrort aroused a discussion in regard to
the stability of the surface over which the proposed
canal was to run. The Board of Mines of Dortmund
conducted observations in the Dortmund district, and
the results were published in 1897. In the Dortmund
district there have been a number of accidents due to
thrust movements, and in the Ruhr coal fields minia-
ture earthquakes, supposed to have been due to coal
mining, have caused considerable damage. . Methods
of reducing surface subsidence by hydraulic stowing
have received much attention from mining operators of
Upper Silesia and Westphalia. The coal beds under
Zwickau, Saxony, are situated at a depth of 600 to
2,500 ft. Beginning in 1885, observations were made
at 82 points to determine the surface movement result-
ing from mining operations. After 12 years, it was
noted that subsidence amounted to 85*2 in., due to
mining at 600 to 900 ft. At 1,500 ft. the subsidence
was only 9T7 in.

The town of Eisleben, in the Mansfeld mining dis-
trict, was seriously damaged by earth shocks, fissures,
and subsidence during the years from 1892 to 1896.
Various theories were advanced concerning the cause
of these disturbances. Some held that they were due
to the dissolving of various salt deposits by under-
ground water, thus producing caverns, and that as
these caverns became of great extent, large falls of
overlying rock caused the shocks and the subsidence.
Others held that, in addition to the solution of the
salt, carbonated waters were leaching the deeper lying
dolomitic formations, and when these became honey-
combed they were unable to support the load concen-
trated on the natural pillars resulting from the solu-
tion of part of the overlying salt beds. At the Mans-
feld copper mine copper bearing shale from 12 to
20 in. thick was being mined by a longwall method at
a depth of from 900 to 1,800 ft. Public opinion
blamed the mining company, and, as a result of arbi-
tration, the company paid 125,000 dols. damages.

Potash mining at Stassfurt in beds 50 ft. thick and
dipping 40 degs. has caused serious subsidence. Stone
buildings have sunk as much as 20 ft., rows of houses
have been removed to firm ground, and chimneys and
towers are standing 5 degs. from the vertical.

On June 10, 1910, surface subsidence, described as
a local earthquake, occurred at the Consolidation
Mine. 11 The part of the coal measures most affected
formed part of an undulation or 1 saddle.’ The forces
at work were of such intensity, and so irregular in
their action, that steel rails were twisted into cork-
screw-like shapes, and in a section of the saddle 10 ft.
in length, two lines of rails, water pipes, signal wires,
and ropeway were found crushed together into a
bundle of about 12 to 16 in. thick.

Austria.—The review of the theories of subsidence
presented by Austrian engineers, as given by Gold-
reich, indicates that as early as 1859 there were regula-
tions controlling the mining of coal under railways in
Austria. Director W. Jicinsky published a treatise
on ‘1 The Subsidences and Breaks of the Surface in
Consequence of Coal Mining.” The publication by
Rziha was the first contribution by an Austrian engi-
neer to the theories of subsidence. Most of the
Austrian writings on subsidence have been on the pro-
blems of the Ostrau-Karwin coal district. Goldreich
has studied the problem principally through years of
observation in railway engineering.

One of the most serious disasters in Austria result-
ing from surface subsidence occurred on July 19,
1895, at Brux, Bohemia, where the brown coal seams
lie nearly horizontal at a depth of 325 ft., covered by
clay shale interspersed with quicksand from 10 to

65	ft. thick. There are in all four seams, having an
average total thickness of 80 ft. Some filling had been
used, but sand broke into the mine, and it is estimated
that 2,000,000 cu. ft. of sand entered the workings.
Numerous holes were formed on the surface, rendering

66	houses uninhabitable, and making 2,000 people
homeless.

Another serious disaster occurred at Raibi,
Bohemia, at a lead mine, where an attempt was
being made to secure an adequate water supply
through underground workings. Two short drifts

were being driven through the rock toward water-
bearing sands, and though a borehole was kept ahead
of each drift, a blast so weakened the cover that the
roof broke, and a rush of sand followed. ' A large hole
was made on the surface, and without warning a
small municipal hospital dropped 40 ft., causing the
death of seven of the inmates.

India.—Coal mining in the Bengal field has caused
disturbance of the surface along the outcrop. At the
Khoira Colliery tne mining of 10 ft. 6 in. of coal
dipping 30 degs. has caused complete subsidence of the
surface where the workings are shallow. At the
Barrea Colliery, owing to the value of the rice land,
stowing has been used to reduce the amount of subsi-
dence. In the same field mining of thick coal over-
laid by thick beds of sandstone has been attended by
extensive falls of roof which have produced fatal air
blasts.

(To be continued.')

CHILD MORTALITY IN THE COAL
FIELDS.

Report by the Medical Officer of the Local Government
Board on Child Mortality at Ages 0—5 in England
and Wales.

In the present report a further analysis is made of
the incidence and causation of deaths occurring in
England and Wales during infancy and in the next
four years of life, with special reference to the deaths
at these ages in the 245 chief provincial towns and in
the 29 • Metropolitan boroughs.

During the four years 1911-14, 575,078 deaths
occurred in England and Wales at ages under five, or
more than a quarter (28-2 per cent.) of the total
deaths at all ages during these years. In some of the
274 urban areas specially considered in this report the
death rate was three times as high as in some others.
There is evidently a large mass of preventable mor-
tality.

’NORTH;

South 7/777/77

Zf'ECClESTON,

150 ts 800 to 300 to 350 and

200. 250. 350. over.

St. Helens : Infant Death Rates in various
Wards (up to 5 years old).

The city is the seat of several important industries.
There are coal mines within the borough, the miners
living chiefly in the West Sutton Ward.

It should be added that even in the most backward
of the towns and boroughs in the following lists much
saving of child life has already been secured. This
saving implies for the whole country that if the average
experience of the decennium 19U1-10 had continued,
the number of deaths at ages 0—5 in the four years
1911-14 would have been nearly 719,000, or 144,00’J
more than the 575,078 deaths which actually occurred.

A considerable section of this report is occupied by a
detailed comparison of towns with the highest and
lowest death rates 0—1, 1—2, and 2—5, and from
various causes of death. This comparison will be
valuable chiefly to members of local authorities and
their public health officers, to the medical staff of the
Local Government Board, and to all who are con-
cerned with ascertaining the chief centres of excessive
child mortality as the necessary first step to its further
investigation and to administrative action for its
reduction.

The one outstanding fact is that the centres of
excessive child mortality are those in which the chief
industries of the country are carried on. That this
association in the main is not inevitable is shown by
the great reduction in child mortality already secured
in these centres, and by the great variations in present
child mortality in towns having the same or closely
allied industries.

The chapter dealing with some of the circumstances
of environment favouring excessive child mortality
gives only a preliminary sketch of the subject. The
problems raised in this chapter and allied subjects need
study in every large sanitary area, as the component
factors producing excessive loss of child life vary