IN THE BITUMINOUS COAL MINES.
A brief history of the discovery and introduction into use of the
bituminous coals of Pennsylvania has already been given; but only
casual reference has been made to the methods of mining in the
bituminous regions. It is true that of the one hundred and twenty
thousand square miles of workable coal beds in the United States less
than five hundred square miles are of anthracite coal. It is true,
also, that more than two thirds of the coal produced in the United
States during the year 1887 was of the bituminous variety, and that
the income from bituminous coal during that year was nearly twice as
much as the income from anthracite. Yet it is obvious that in any
description of coal mining methods the anthracite mines should be
used as the chief examples. This is not only because of the greater
commercial importance of anthracite, and of its greater familiarity
as a domestic fuel, but it is principally because of the far greater
skill, judgment, and ingenuity required in mining it and preparing it
for market. In the bituminous regions the coal is soft, lies flat and
near the surface, and is mined by the simplest methods. The reader
is already familiar with some of the complications, obstacles, and
problems that meet and beset the operator in the anthracite regions,
and with the great labor, vast expenditures, and high degree of skill
necessary to reach, take out, and prepare the anthracite coal. In
view of these facts no excuse is necessary for attaching the greater
importance to the description of methods in the anthracite region. But
a brief outline of the systems in vogue at the bituminous mines will
not be uninteresting, so far at least as they differ from those in use
at the anthracite mines.
In the year 1887 a little more than one third of the bituminous
coal output of the United States came from the Pennsylvania mines.
Pittsburgh is the centre of the soft coal trade of that state, and
the principal coal seam of the region is known as the “Pittsburgh
bed.” It is included in an area about fifty miles square, and varies
in thickness from two or three feet in the northwestern part, and six
feet at Pittsburgh, to ten feet up the Monongahela River, and twelve
feet up the Youghiogeny. The exhaustion of so vast a coal bed is a
practical impossibility, and the questions that engage the attention of
the mining engineer in these regions are not so much questions of the
economy of coal as they are questions of the economy of labor. The coal
lies near the surface, and the outcrops on the flanks of the hills and
banks of the rivers are so numerous that most of the mining can be,
and is, done by drift above water level. The outlay of capital required
in opening a mine is therefore very small, marketable coal being
obtained at almost the first blow of the pick.
Before mining operations are begun a complete survey is made of all
outcroppings, and their differences in level are obtained. From this
data a comparatively accurate knowledge may be had of the position of
the coal bed under ground, as the dip of the seams is very moderate and
uniform, and but few faults and other irregularities are encountered.
It is then decided where to locate the mouth of the drift so that the
entry can be driven in on the rise of the coal and the mine become
self-draining. It is important, however, to have the opening at a
convenient point near the river or railroad, and it is usually so made
if possible, even though the dip should be away from the opening.
The inclination is always so slight as not to interfere greatly with
the hauling of cars, and it is not much of a task to make a separate
opening for drainage. The coal seam is divided by vertical cleavage
planes, running at right angles to each other, one of which is known
as the _butt_ cleavage and the other as the _face_ cleavage. The
main entries are driven in, if possible, on the face cleavage, as
are also the chambers, or “rooms” as they are called here; while the
entries from which the rooms are turned are always driven on the butt
cleavage. The drift, or main entry, has an airway running parallel
with it; sometimes it has one on each side of it. It is driven eight
or nine feet in width, except where two tracks are necessary, in which
case it is made from twelve to fifteen feet wide. These double or
treble entries are parallel to each other, and are separated by a wall
of coal from twenty-five to forty feet in width. Through this wall,
at about every thirty yards, entrances, or, as they are called here,
“break-throughs,” are made, having the same width as the entry. The
height of roof in the entries of the Pittsburgh seam is usually five
and one half or six feet in the clear. At right angles to the main
entry butt entries are driven in pairs, parallel to each other and
about thirty or forty feet apart, with break-throughs or cross-cuts
for the passage of air, as on the main entries. From each of these
butt entries, at right angles to them, and in opposite directions,
the rooms are driven. They are made about twenty-one feet wide, with
pillars between them twelve feet thick, and are not often more than
eighty yards in length. They are usually driven to meet the faces of
the rooms which are being worked from the next parallel butt entry, or
are extended to that butt entry itself. At the point where the room
turns off from the butt entry it is made only seven feet wide for a
distance of from fifteen to twenty-one feet, then the room is widened
out to its full width of twenty-one feet. The track on which the mine
wagon runs is laid straight up the side of the room from the opening
at the entry, occupying a clear space about seven feet wide. The rest
of the room is well filled with the refuse which has been separated
from the coal as mining has progressed, and the roof is supported by an
abundance of props, or “posts” as they are here called. In one room,
with an ordinary roof, about six hundred and fifteen posts would be
necessary. The pillars are long, the distances between break-throughs
averaging thirty yards. This is known as the “double entry” system,
to distinguish it from the single entry system which was formerly in
general use. The method by single entry consisted in driving the butt
entries singly, about one hundred and sixty yards apart, and the face
entries the same distance apart, at right angles to the butt entries,
thus laying off the mine in large square blocks which were then mined
out. The difficulty with this system was that from twenty-five to fifty
per cent. of the pillars were necessarily lost, while by the double
entry system, which now prevails, all or nearly all the pillars can be
taken out.
Of course the features in the plan of each mine vary according to the
special necessities of that mine, but in general they do not differ
greatly from those that have been described.
[Illustration: PLAN OF A BITUMINOUS COAL MINE.]
The method of cutting coal here is also peculiar to the soft coal
mines. The miner has a pick with sharp, pointed ends, and with this
he cuts a horizontal groove or channel, from two and a half to three
and a half feet deep across the entire width of the entry or room.
This groove is cut in that horizontal section of the face known as the
bearing-in section. It may be in the bottom layer of coal, or it may
be one or two feet above the bottom. The process itself is known as
“bearing in,” “under cutting,” “holing,” or “undermining.” While he
is at this work the miner must lie on the floor of the room, partly
on his side, but with hands and arms free. When the horizontal groove
has been completed a vertical groove similar to it in size and shape
is made at one side of the face. These channels are sometimes cut
with mining machines having compressed air for a motive power. This
machine is small but powerful. It is placed on a low inclined platform
at the face of coal, and is operated by a man called a “runner.” The
inclination of the platform causes the machine, which is on wheels, to
gravitate constantly toward, and to press against, the face of coal.
The compressed air cylinder drives a piston-rod to which is attached
a steel bit two inches in diameter projecting from the front of the
machine. This bit strikes the coal with sharp, swift blows, chipping
it out in small fragments, and eats its way rapidly into the seam.
The compressed air is carried to the machine in an iron pipe from the
compressing engine, which is located at the mouth of the mine. When
a machine is used, seven men usually work three rooms. Three of these
men are contractors or partners, three of them are laborers employed
by the contractors, and one of them, called the “scraper,” is a
laborer employed by the coal company. When the channel has been cut a
sufficient depth and distance the coal above it is brought down either
by wedging or blasting. If blasting is to be resorted to it will be
unnecessary to cut the vertical groove. If the bearing-in channel was
cut above the floor, the bottom coal is then lifted by wedging, and
broken up. The miners do the cutting and blasting, the laborers break
up the coal and load it into the mine wagons, and the scraper is kept
busy cleaning the cuttings away from the channels and attending to the
lamps.
The mine car track that is extended up into the room is of wooden
rails, and the empty wagon is pushed in to the face by the laborers,
and loaded and run out by them to the entry. Each wagon will hold a
little more than a ton, and a mule will draw four wagons to the mouth
of the drift. The wheels of the mine car are set close to each other,
near the middle of the car, to facilitate its movement around sharp
curves; the doors at the ends of the car are swung from a bar hinge at
the top, and the cars are dumped in the same manner as those in the
anthracite region. In some of the bituminous mines a small locomotive
is used to draw the trains of mine wagons from the working parts of
the mine to the opening. It will draw from twelve to sixteen wagons
at a time, and will do the work of twenty mules. There is usually a
separate split of the air current to supply the locomotive road in
order to keep the smoke out of the working rooms.
When a set of rooms has been driven to its limit the miners then
“draw back the rib;” that is, take out the pillars between the rooms,
beginning at the face and working back. Posts must be used freely to
support the roof while this work is in progress, about sixty or seventy
being necessary in drawing a rib.
Ventilation here is obtained by both the fan and the furnace systems.
In mines that are worked below water level fire damp often accumulates,
but where the coal does not descend at any point below the water-level
line, there is no probability that mine gases will be found.
As has already been said, the usual method of entry into the bituminous
mines has been, and still is, by drift. But as the working faces of the
mines recede farther and farther from the general lines of outcrop, it
often becomes necessary to resort to the method of entry by shaft, and
this latter method will doubtless in time supersede the former almost
entirely. The main shaft, as it is now constructed, is usually about
twenty feet long by nine feet wide, and has three compartments, two for
hoisting and one for ventilation and pumping. It rarely exceeds two
hundred feet in depth. The hoisting apparatus is much like that in use
in the anthracite districts. Air shafts from fifty to one hundred feet
deep, sunk for purposes of ventilation and drainage, are frequent, and
stair shafts in which are fixed ladders for the purpose of ascent and
descent, and which may be used as air shafts also, are not uncommon.
Slopes, like those in the anthracite regions, are not usual here; the
coal seams do not dip sufficiently to make them practicable. Narrow
rock slopes are sometimes driven diagonally through the strata, at an
inclination of twenty degrees or less, to strike the coal bed, but they
are used only as air ways, as traveling ways for men and mules, and to
serve as the “second opening” required by the mine law.
In the bituminous regions coal breakers are unnecessary and are
unknown. As the vertical planes of cleavage of the coal are at right
angles to each other, and as the stratification is nearly horizontal,
the coal when broken takes a cubical form, large blocks of it being
made up of smaller cubes, and these of still smaller, to an almost
microscopic limit. All slate is separated from the coal as it is mined,
and the refuse is piled up in the room.
The mine wagon is loaded only with good coal, and is taken directly
from the mine to a building which, with its appliances, is called a
“tipple.” It is here dumped into a screen, it runs from the screen
into a car or boat, and is then ready to be hauled or floated to market.
If the opening of the mine is practically on the same level as the
tipple the arrangements are very simple, as no extra motive power is
required to get the cars to the dumping place. It is usual, however, to
find the opening at a higher point than the tipple, since the latter
must always be at the railroad track or on the bank of a river. It
becomes necessary, therefore, in this case, to raise and lower the cars
between the opening of the mine and the tipple. This is usually done by
the inclined plane system, in which the loaded cars descending draw the
light ones up. The same system is much used in the anthracite mines,
and has already been explained.
The railroad tipple consists simply of a frame building from forty to
sixty feet long, fifteen feet high, and from eighteen to thirty feet
wide. This structure is set upon four or five plain timber bents,
and its floor is usually twenty-seven feet higher than the top of
the track rails which run beneath the outer end of it. A platform on
this floor is so adjusted by a single shaft that, when a loaded car
is pushed on it, it tips forward to an angle of about thirty degrees.
The end gate of the wagon is then opened and the coal runs out on to
the screen. This screen is simply a set of longitudinal iron bars
inclined outwardly at distances apart of one and one half inches. All
coal that passes over these bars is called “lump coal” and is run
into a sheet-iron pan suspended from the scales platform, where it is
weighed, and it is then dropped directly into a car standing on the
track below it. The coal which passed through the first set of bars
has, in the mean time, fallen on to a second screen with bars only
three quarters of an inch apart. The coal that passes over these bars
is called nut coal, and is also weighed and dropped into the cars,
while the coal that passes through the bars is called “slack.” This is
dropped into a shute, is carried by it into a car on the slack track,
and is run thence to the dumping ground. When all three kinds of coal
are loaded together it is called “run of mine,” while lump and nut coal
together make “three quarter coal.” These tipples may, of course, be
built with two sets of screens and platforms, and thus be made to do
double work, and some of them are so built. Under the projecting end
of the tipple there are usually four tracks; the first or outside one
for box-cars, the next for lump-coal cars, the next for nut-coal cars,
and the last for cars for slack. Four men operate a single railroad
tipple; two dump and weigh the coal above, while the others trim and
move the railroad cars on the track below. To this number a helper is
often added, both above and below. Besides these men a boy is usually
employed to rake the nut coal from the lower screening bars where it
sticks and prevents the slack from passing through. Sometimes it takes
two boys to do this work properly. Boys are also employed to push the
slack with a scraper down the shutes into the car on the slack track
when the elevation of the tipple above the rails is not sufficient to
afford the necessary grade. Bars are being largely superseded now by
revolving screens for separating slack from nut coal; they do the work
far better, and make the employment of a raking boy unnecessary.
The river tipple is operated in much the same way as the railroad
tipple, except that its apparatus must be so arranged as to accommodate
itself to high or low water. The floor of the river tipple is usually
placed from forty to fifty feet above low-water mark, and the weighing
pan is held in position by a counter-weight, which may be raised or
lowered at pleasure. A small stationary engine, or a hand windlass,
draws the empty boat or barge into position under that end of the
tipple which projects over the water. About twice as many men are
required to operate a river tipple as are necessary to operate a
railroad tipple, and while the railroad tipple costs but from two
thousand to four thousand dollars the river tipple is built at an
expense of from four thousand to ten thousand dollars. But even this
latter figure is small when compared with the cost of an anthracite
breaker, which may run anywhere from twenty thousand to one hundred
thousand dollars.