56 MINING CONDITIONS UNDER CITY OE SCRANTON, PA.
DRY FILLING.
Although we recognize that the flushing process is the most substantial method for artificially supporting the roof of coal mines, and that it is also universally suitable for thin or thick beds and deep or shallow beds, nevertheless the method is not always applicable or convenient. There are many localities in the coal mines where it may be either preferable or permissible to resort to some of the other less efficient or less costly methods of roof support, which for one reason or another are more adaptable to a particular locality. Therefore we refer to the improvements that may be made in the different methods of dry filling.
IMPROVED METHODS OF GOB STOWAGE.
Formerly the gob of coal mines was disposed indiscriminately over the chamber at the side of the roadway, mainly for the purpose of getting rid of it at as little cost as possible. A casual inspection of the comparative table of tests on page 55 will show that well-constructed gob piers are much stronger than those indifferently built. It is also evident that in supporting the roof of coal mines, as well as in other matters, “an ounce of prevention is worth a pound of cure.” The effort, therefore, should be to prevent the first small settlement, and the way in which to accomplish this effort as far as possible in the matter of stowage will be to pack the rock fragments carefully and tightly against the sides of the pillars from floor to roof, irrespective of the horizontal area occupied, and to use the fine refuse, so far as may be, to fill the voids. If the gob now contained in the thinner seams under the city of Scranton had been carefully packed so as to completely fill the space from floor to roof it would not only reinforce and preserve the strength of the coal pillars, but would present very much greater resistance to pressure and would be a much more efficient roof support than is afforded by the usual present stowage with 1 to 2 feet of space between the top of the stowed gob and the mine roof.
In some beds now working there is a surplus of mine rock which can not be stowed in the chambers and must be hauled out into other parts of the mines. If it is determined to continue thus to stow this material instead of hauling it to the surface and grinding it for flushing purposes, as has been previously mentioned (see p. 55), the purpose of roof support would be better served if the places for depositing this surplus stowage were selected with reference to the weak parts of the mines, or with reference to the support of the ground under some particularly valuable surface improvement.
Commendable work is being done along this line at the Cayuga mine of the Delaware, Lackawanna & Western Railroad; the pillars