Coal and the coal mines

by Homer Greene

The direction in which a gangway, airway, or chamber is to be driven is fixed by the mine boss. His bearings are obtained with a small miner’s compass, and he marks on the roof, near the face of the opening, a chalk line in the direction desired. The miner, sighting back on this line, is thus able to take his course and to keep his opening straight.

Sets of chambers similar to those described are driven up from the gangway along its entire length. This length may be limited by various causes. A boundary line of property, a fault, a thinning out of the coal seam, are some of them. They are usually driven, however, as far as strict principles of economy will allow. A gangway that requires no timbering and is easily kept in good working condition may be driven to a distance of three or four miles. But where these conditions are reversed, a mile may be as great a distance as coal can be hauled through with economy. Beyond that limit it will be cheaper to sink a new shaft or slope than to increase the distance for underground haulage.

As the main gangway progresses inward it may separate into two branches, each following a depression in the coal seam, and these branches may separate into others; so that there may be a number of gangways all keeping the same general level, from each of which sets of chambers are driven. When the chambers tributary to a gangway have reached their limit of length, and there is still an area of coal above them to be mined, a new gangway is opened along the faces of the chambers, or is driven just above them in the solid coal, and from this, which is called a “counter-gangway,” new sets of chambers are driven up the seam. It is often necessary to raise and lower cars passing from one gangway to the other on an inclined plane, on which the loaded cars, descending, and attached to one end of a rope, pull up the light cars, ascending and attached to the other end, the rope itself winding around a revolving drum at the head of the plane. This system can be put into use on any incline where the gradient is one in thirty, or steeper.

By this general system of gangways, counter-gangways, airways, chambers, and planes, the area of coal lying on the upper side of the main gangway and on both sides of the shaft is mined out, hauled by mules to the foot of the shaft, and raised to the surface. On long straight gangways the mule is sometimes replaced by a small mine locomotive, and in these later days the electric engine has been introduced into the mines as a hauling agent.

So far, however, in this mine which we are supposed to be working, not a tap of a drill nor a blow of a pick has been made into the coal on the lower side of the gangway save where the sump was excavated at the foot of the shaft. If this shaft has been sunk nearly to the bottom of the basin or synclinal axis, a short tunnel may be driven from the main gangway through the rock or upper bench of coal across the valley to the rise of the seam on the other side. A new gangway may here be driven right and left, and this area of coal be made tributary to the shaft already sunk. It often happens that a large body of coal lies between the main gangway and the synclinal axis, for these two lines may diverge greatly as they recede from the shaft. But chambers cannot be driven down from the main gangway owing to the difficulties of transportation and drainage. It therefore becomes necessary, in order to work this area, to sink a slope from the main gangway down to or toward the synclinal axis, and from the foot of this slope to drive a new gangway. From this new gangway chambers will be opened extending up the seam to the line of the main gangway, but not generally breaking through into it. The coal is run down to the lower level gangway, hauled to the foot of the slope, and hoisted up it to the main gangway. It is apparent, however, that the inclined plane system cannot work here; the conditions are reversed; the loaded cars are drawn up and the light ones are let down. To do this work it is necessary to bring into use a small steam stationary engine, or one working by compressed air. A common method is to locate the steam engine on the surface vertically above the head of the underground slope, and to carry power to the sheaves below by wire ropes running down through bore holes drilled for that purpose.

The system of slope mining by lifts, which is in common use in the Middle and Southern anthracite districts, has been explained in a preceding chapter. In this system the sump is always made by extending the slope a short distance below the level of the gangway. This gangway is driven from the foot of the slope to the right and left in the same manner as in the Wyoming region, except that, the seam being so greatly inclined, the gangway roof, or a part of it at least, will usually be of coal instead of slate or rock, and in very steep pitching seams the airway will be almost vertically above the gangway. The gangway is not usually so crooked as where the workings are flat, and having been started only three hundred feet down the slope from the surface, it often follows the coal to some low point on the line of outcrop, and is then known as a water level gangway, which is practically the same as a drift.

The system of opening and working breasts differs somewhat from that in use in the Northern field. Beginning at such a distance from the foot of the slope as will leave a good thick slope pillar for its protection, a narrow shute is driven up from the gangway into the coal to a distance of perhaps thirty feet, at a height of six feet, and with a width of from six to nine feet. It is then opened out to its full width as a breast and continued up the seam toward the outcrop, not often breaking through to daylight unless an airway or manway is to be made. Parallel breasts are then laid off and worked out by the usual pillar and breast system. If the dip is less than twelve or fifteen degrees, the coal may be run down from the working face in a buggy, dumped on to a platform or into the shute, and loaded thence into a mine car standing on the gangway. If the dip is more than fifteen degrees the pieces of coal will slide down the breast to the shute, though if it is under twenty-five or thirty degrees the floor of the breast should be laid with sheet iron to lessen the friction and give greater facility in movement. In a steep-pitching breast a plank partition is built across the shute just above the gangway, to hold back the coal until it is desired to load a car with it. This partition is called a “battery,” or, if there is a similar partition to hold the coal in the breast, a “check battery.” In this partition there is an opening through which the coal may be drawn when desired, and through which the men may also go to their work, though a separate manway is often provided. In these steep-pitching breasts the miner works by standing on the coal which he has already mined, and which is held back by the battery, in order to reach the uncut coal above him. There are various systems of shutes, batteries, man ways, etc., in use, but all are based on the same principles.

GROUND PLAN AND LONGITUDINAL SECTION OF CHAMBER.

When the gangway of the first lift has reached its limit in both directions, and the breasts from it have been worked up to their limit, the slope is sunk to another distance of three hundred feet, and the process is repeated. From the gangway of the second lift the breasts are not extended up far enough to break through into the gangway above; a wall of coal is left between that gangway and the faces of the breasts, from fifteen to forty feet in thickness, known as the “chain-pillar.” This is for the protection of the upper gangway against falls and crushes, and is also necessary to hold back water from escaping into the lower level. These lifts will continue, at distances of about three hundred feet apart, until the synclinal valley is reached.