MINING CONDITIONS UNDER CITY OF SCRANTON, PA.
60
SUGGESTIONS FOR IMPROVEMENT IN MINING METHODS AND PIULAR SUPPORT.
The solid coal remaining to be mined under the city of Scranton is mainly in the Dunmore beds Nos. 1, 2, and 3. These beds are from 200 to 600 feet below the surface under the greater portion of the city.
Future mining plans, we think, should provide for leaving at least 50 per cent of the coal in these beds on first mining, and the columni-zation of the pillars throughout all new mining as far as possible.
FLUSHING.
Keference has been made to the practice, now quite general, of flushing culm into the mines. This is being done at nearly all of the collieries within the city limits, and the method and effectiveness of this kind of support was observed by personal inspection underground (see PI. 26).
With reference to the tests made at Lehigh University of the compressibility of the several kinds of support now in use or suggested, we are of the opinion that a practicable method for the support of the overburden, utility and cost being considered, is flushing the openings with culm, ashes, sand, broken stone, material excavated from cellars, and other stuff of similar nature that can be reduced to a size small enough to be carried in pipes with water.
As before referred to, the flushing of mines for the support of the overburden has been adopted in Europe with marked success, both in the matter of support and recovery of all the mineral, the material used for filling being sand, loam, crushed slag, and crushed stone.
It is manifest that the quantity of culm available for flushing the extensive mine openings is insufficient, even if all of that now on the surface within the city limits, together with that produced in the preparation of the present output of coal were put into the mines.
According to figures we have assembled and supplemented with estimates, it appears that there has been extracted from the beds underlying the city, approximately 221,000,000 tons of coal and other material.
The workings under the city are, of course, not all open, large areas having been closed by general caves and squeezes. It is not possible to determine the proportion of openings that have been thus closed or filled, but a conservative estimate of the space now open would be that it probably does not exceed 50 per cent of the original.
The positive protection of all of the surface would appear to require the filling with some supporting material of all of the open spaces as rapidly as the coal is extracted; but such a scheme is, of course, impracticable. It therefore remains to determine about what