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Submarine
Mining
Cape Breton's coal fields lie close to the coastline and a large
percentage of the fields extend under the ocean. As a result,
Cape Breton's east coast mines, which were among the most extensive
mining operations in the world, faced problems different from
those encountered in other fields.
The biggest challenge in undersea mining is the possibility
that the sea will break into the workings. Until a certain depth
of cover is reached, pillars of a sufficient size to support
the sea bottom must be left intact. Nova Scotia mining law prohibits
coal removal at a depth of less than 180 feet of solid cover
under the sea.
The cover line for most Cape Breton workings is 700 feet, and
until this level was reached, the width of the rooms was restricted
and pillars were left intact. After this level was reached,
the longwall method of mining was usually used as long as 100
feet of solid cover remained for each foot of thickness of the
removed coal.
An advantage of an underground mine working under land rather
than under the ocean is that when the working area is a long
distance from the surface entrance, another shaft can be sunk
to the working face. Obviously this is not an option with submarine
mining and the shaft must continue out under the sea until a
distance has been reached that is not economically feasible
to mine the coal.
How far the mine extends under the sea depends on a number of
factors: the nature and thickness of the seam, the character
of the roof and floor, the rate of dip (determines depth), and
the amount of coal which can be economically removed from the
mine.
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