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The Louis Frost Notes 1685 to 1962
Description of Conditions Peculiar to Submarine Mining
Only a negligible proportion of coal is mined from under
the sea in the great coal producing centres, and neither of the
large coal producing countries -- the United States and Russia --
mines submarine coal.
The known submarine areas from which coal is mined at the
present time, are Chili, Japan, the East and West Coast of Northern
England, under the Firth of Forth in Scotland, on Vancouver Island,
in British Columbia on the West Coast and Cape Breton Island,
Nova Scotia on the East Coast of Canada.
Submarine coal has been mined in Great Britain for a great
many years, but the percentage from this source has been very small,
not exceeding 2% to 3%. In contrast to this, nearly 88% of the coal
produced in Nova Scotia comes from the undersea workings in the Sydney
Coal Field, and as 80 per cent of the entire coal resources of Nova
Scotia are submarine, the mining of submarine coal is of tremendous
importance to those engaged in the industry in this province.
The pioneer colliery in submarine mining to any appreciable
extent in Nova Scotia is Princess Colliery of Old Sydney Collieries,
Nova Scotia Steel & Coal Company, where the workings first went
under the sea in 1877. This mine has been in continuous operation
ever since and at the present time the active workings are 3.2 miles
from the shore although the maximum distance penetrated seaward
along the main slope is 3.4 miles, and the maximum cover 1970 feet
under the sea bottom.
Except for three small independent collieries producing a
total of less than 1,000 tons per day, all other operating collieries
in the Sydney Coal Field are submarine. The Dominion Coal Company
operates four collieries in this field and the entire output from
these is submarine.
The workings in these mines extend from a minimum of 0.7
miles to a maximum of 2.2 miles from the shore.
It may be of interest to note that Dominion No. 4 Colliery,
recently closed, had penetrated further seaward than any other colliery in the field, the main deeps having reached a distance of 3.6
miles from the shore. It is also of interest to note that the deepest
submarine mine in Nova Scotia, or probably anywhere, was, prior to
its closure, No. 2 Mine of the Inverness Coal & Railway Company,
where nearly 3,000 feet of cover had been reached.
There is a greater concentration of mines operating in the
submarine coal in the Sydney Coal Field than exists elsewhere, and
the workings extend further seaward than those in the British oversea mines, with the exception of those on the Cumberland Coast, where
a series of upthrow faults makes the winning roadway comparatively
level, allowing of long extension at comparatively moderate depths.
It is necessary in mining submarine coal to take precautions
to prevent flow from the sea, by leaving in pillars of sufficient
size to support the sea bottom until a certain depth has been reached,
at which it is considered prudent to remove the pillars or extract
the whole seam.
Disasters in mining submarine coal have not been unknown
in the past, the most notable being in the north of England in the
early thirties of the last century and in Japan within comparatively
recent years; whilst in Nova Scotia, two mines on the West coast
of Cape Breton Island were flooded by the sea breaking in. In
Mabou in 1909 and Port Hood in 1911, respectively.
The mining laws of Nova Scotia prohibit the extraction of
coal at a depth of less than 180 feet of solid cover under the sea,
although Section 104, Subsection (i)A permits roadways to be driven
to win the undersea coal at a lesser cover than 180 feet, but not
less than 100 feet of solid measures between the roadway and the
sea bottom.
In the Sydney Coal Field it has been the practice to restrict the width of rooms up to the 700 foot cover line to 20 feet
wide and crosscuts 18 feet wide and not to extract pillars under
less than 700 feet of solid measures between the workings and the
sea bottom. In some cases a balanced room and crosscut system is
developed, each place being 16 feet wide, with a maximum extraction
of 59 per cent, 41 per cent being left in pillars to support the
sea bottom.
The method of work and the percentage of coal extracted
in each lift must be approved by the Chief Inspector of Mines for
the Province.
The practice has been to vary the size of pillar from
32 ft. x 48 ft. to 47 ft. x 63 ft., according to the depth of the
workings. These pillars give an extraction of 50% and 41% respectively
Although in past years pillars have been drawn where local conditions
were suitable, the present practice is to revert to longwall when
sufficient cover is gained to permit total extraction.
In the case of mines operating under land, it is always
possible when the workings reach an excessive distance from the
shaft bottom, to sink another shaft near the working faces, if not
for coal hoisting, at least to lessen the distance the miner has to
travel to work. But in submarine mining, when the shafts or slopes
are located on the shore, there can be no such relief and the roadways and workings must progress seaward until a limit is reached at
which it is no longer economically possible to mine coal. The distance it is possible to penetrate seaward will depend on the nature
and thickness of the seam, the character of the roof and floor, the
rate of dip which determines depth, and the amount of water encountered.
These are physical conditions over which there is no control, but
from the economic standpoint the proximity of competing mines under
more favorable conditions must have a material bearing.
Apart from these factors, the life of a submarine mine may
be increased or lessened, dependent on the care and forethought of
the operating company, the points which require particular attention
being:
(1) General layout of workings
(2) Construction of large main haulage roads of as permanent a nature
as possible.
(3) Construction and maintenance of airways of adequate size and the
building of permanent stoppings to reduce air leakage to a minimum.
(4) Provision of roadways over which men may be transported as near
as possible to their working places.
In regard to these points, the submarine mines of the
Dominion Steel & Coal Corporation will stand favorable comparison
with those anywhere in existence.
As regards the layout of workings, the most experienced engineers
in submarine mining have been consulted and reported on the operations
from time to time.
The policy of constructing main roads of as permanent a nature
as feasible has been adopted.
The reconstruction of airways and the adoption of a policy of
providing adequate ventilation for future working which started
following 1920 has been continued and is being vigorously maintained.
Approximately half a million dollars is spent on this work each year
and is probably the most necessary of all expenditures -- one on
which there is no immediate return -- but which safeguards the future
of the industry and the coal resources of the province.
Unless main roads and airways are constructed in a substantial
and fairly permanent manner, the upkeep of these roads as the workings
extend seawards would preclude the possibility of further mining due
to the heavy cumulative maintenance costs, and this is a cost which
submarine mines must bear to a much greater extent than those mining
under land.
All submarine mines of the Corporation, except No. 18 Colliery,
are equipped with special means other than the coal hoisting equipment
to transport the men a considerable part of the way to their working
places. The Corporation transports its workmen a total distance of
15 miles toward their working places, eight miles of roadway being
especially equipped and maintained for this purpose.
The total extraction of the coal seams in the undersea working
is dependent on the nature and the thickness of the superincumbent
strata over coal, the thickness of the seams and the position of
the seams in the order of working.
In this field it is considered prudent to err on the safe side
and to permit total extraction only when the cover over the topmost
seam and the sea bottom is not less than 700 feet.
In general, where the topmost seam is worked first, 700 feet
of cover is considered necessary with the additional thickness of
the intervening strata between subsequent seams to be worked added to
the initial 700 feet.
For example, if total extraction in the Harbour Seam is commenced
at the 700 ft. cover line first, then total extraction of the underlying Phalen Seam would commence at 1100 ft. of cover, depending on
the thickness of the intervening strata between the Phalen and Harbour
seams. In this instance, the combined thickness of the coal as at
Nos. 12 and 16 in the New Waterford district would be 11 ft., or
approximately 100 ft. of strata for every foot of coal extracted.
If, however, the Phalen Seam, a lower seam in the stratigraphical
column, was worked first and total extraction commenced at the 700 ft.
cover line in the Phalen Seam, total extraction of the overlying Harbour
Seam would not commence until the 1100 ft. cover line was reached in
the Harbour Seam.
If the Hub Seam, which overlies the Harbour Seam, was worked
at the same time as the underlying seams, then the minimum cover at
which total extraction in the Hub Seam would commence would not be less
than 1200 ft. and more likely 1500 ft., adopting the general basis
of 100 ft. of solid measures for every foot of coal extraction.
The policy followed by the Corporation in respect to total
extraction under the sea has been substantially approved by expert
advice obtained by the Corporation in 1927.
W. Forster Brown, in his report dated April 1927 on the subject
of total extraction, states on page 5:-
- The general effect of extracting both the Phalen and
Harbour Seams above, upon the system of work proposed to
be employed, in which the roof is free to break in certain
areas and is only partially supported by packs, will probably
result in a subsidence to the bed of the sea amounting to from
50 to 60 per cent of the thickness extracted. Taking the total
thickness of the coal removed in both seams as averaging 12 ft.
6 ins., one might expect a lowering of the bed of the sea by
6 ft. to 7 ft. 6 ins.
- Considering, however, the thickness of intervening strata
between the upper or Harbour Seam workings and the bed of the
sea at the horizon where both this and the Phalen Seam will be
completely extracted, I am decidedly of the opinion that no
risk of any inrush of the seam will be run by adopting the
proposed method of workings, of complete extraction in the
Harbour Seam, where the cover exceeds 700 feet and in the
Phalen Seam where the cover above that seam is 1,000 feet or
more, where the Harbour Seam has been previously extracted.
However, in 1930 when the above wording was questioned, he
replied under date of April 3rd, 1930:-
- I am sorry that the report I made in 1927 on the working
of the sea coal at your Waterford Collieries should have been
ambiguously worded. It was my intention, as you surmise, to
refer to the Harbour Seam, i.e., that when the cover above the
Harbour Seam was 1,000 feet or more there would be no risk in
completely extracting the Phalen Seam under the areas where the
Harbour Seam had also been completely extracted.
It will be noted that the opinions expressed by W. Foster
Brown still leave an ambiguity. Therefore, in practice the comparison in respect to its policy for total extraction in the undersea
area was on the side of safety.
Further, the policy as applied to the total extraction of
contiguous seams simultaneously, as in the Victoria and Lingan Seams
in the New Waterford area, the upper seam is extracted in advance of
the lower seam with a time lag of approximately 6 years, or one
working lift; and where the lower seam is extracted in advance of
the upper seam, a minimum time lag of four years should be the aim,
with all main roadways for haulage and ventilation superimposed in
substantial pillars of solid coal.
Consideration has been given in the past to the replacement of
coal pillars left in at lesser depths, by sand or other debris by
hydraulic stowing, but the increased cost which this method entails
precludes its use.
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