Report of the Bureau of Mines of the Department of Internal Affairs of ...

No. 10. MINE INSPECTORS' REPORT. xll
SO llie half of it must take its place on top or in the culm and the
pressure cannot drive the roof lower than 2^ feet, for at this point the
solidity underneath it, equals the solidity of the coal itself. We assume
in the above thalt the pillars represent half the coal. In case
they represent a third only, the roof of a chamber 17| feet high will
drop some 3 feet 8 inches. The following facts should be considered
in connection with the above:
1. Culm cannot be filled as closely in the mines as in the above
mentioned box, but there is a margin as may be seen in No. 2.
2. No squeeze ever compressed the refuse to the density of coal.
8. The waste of mines is supposed to fill only a portion of the
workings that have been made in mining, especially if the mines have
been in operation some time before the flushing begins.
4. Besides, pitch and location of openings have their advantages
and disadvantages in flushing.
Number of Acres Flushed.
The number of acres flushed in our two mines—Dodson and Black
Diamond— as computed b}^ our engineers, Messrs. Aikman & Auman,
is as follows:
Area of space
tilkMl l(> thickness
of vein.
Acres.
Dodson. Old Bennett (Hillman) vein,
Bennett and Baltimore vein,
.
Ross vein
Black Diamond.
Ross vein
Red Ash vein,
Quantity of Coal Saved.
There is no formula by which we can calculate the quantity of
coal that can be saved per acre by flushing. The conclusions are
out of the reach of any theory. It is a matter of judgment and calculation
which vary, of course, according to the changing conditions.
However, the judges in this case, like many others, must be the very
best class of miners—men of experience in
squeezes, caves and explosions.
We are of the opinion that their conclusions would be as follows:
1. That when mining under some 400 feet of strata, flushing will
save the comjiany one-fifth (in the Bennett vein).
2. WIhmi mining 200 feet deeper, in the Ross, it will save a sixth.
3. In the Red Ash, when some 700 feet below the surface, they
might say that flushing will save a seventh. The difference in th-»
amount saved, arises from the fact that the Bennett is under less