coal trade bulletin - Clpdigital.org

38 THE COAL TRADE BULLETIN.
foremen are obliged to drive their breakthroughs
on the line of a pocket. The object in keeping
the breakline uniform is to
INSURE AGAINST PILLARS
extending back into the gob and acting as a fulcrum,
or the knife edge of a scale beam, upon
which the roof teeter totters and almost invariably
causes additional timber expense and sometimes
losses of coal, both of which could have
been avoided had the breakline been kept uniform.
The general plan of mining advocated by the
Pocahontas Coal & Coke Co. has as its essential
features:
Provisions for tonnage during the development
period, provisions for meeting* the market demand,
large barrier pillars insuring against
squeezes ancl rendering impossible the destruction
of coal over an extended area. Four entry
system for all extensive main entries, using two
as intakes and two as returns with a breakthrough
between only at the points where the cross entries
turn off, rendering unnecessary the building
of expensive masonry brattices every 80 feet and
insuring the maximum quantity of air for ventilation
at a minimum cost for brattices and power
on the air. Cross entries with narrow chain
pillars permitting the rapid advance of the entry.
In general all robbing must be done retreating
with rooms driven after the entry is nearing completion,
insuring against slate falls and rendering
possible the extraction of all tbe coal in the one
operation combining first development and robbing.
The depth of room ancl number of rooms on
an entry vary greatly at different mines depending
on local
CONDITIONS OF THE SEAM;
whether the haulage is by mule or gathering
motor, whether the mining is pick mining or machine
mining, and not infrequently on the personal
equation factor for sometimes the management
of a plant will contend that he obtains best
results when he drives 25 rooms 500 feet deep
to the entry, and another manager working on
Thickness Acres
of
Seam
Of
Entry
Plai it. in Ft. Mined.
1 0.15 3.in;
2 5.65 4.40
9 5.10 2.68
4 4.42 5.88
5 5.94 7.00
6 4.32 2.11
7 5.34 ') 91
8 5.42 3.72
9 4.65 8.10
10 8.03 5.20
Acres
of
Rooms
Mined.
4.57
4.SO
6.52
8.65
10.09
3.64
6.34
6.06
16.80
8.47
Acres
of
Pillars
Mined.
11.03
14.80
15.80
13.09
19.20
9.20
0.00
9.72
2.34
10.09
Total
Acres
Mined.
IS.66
24.00
25.00
27.62
36.29
15.04
9.65
19.50
27.24
23.76
adjoining property under identically the same
physical conditions and with the same type of
equipment on the other side of the property line,
not 1,000 feet away will say that he obtains best
results if his rooms do not exceed 300 feet in
depth and not more than 15 rooms to the entry.
The better policy is to encourage individual iniative
and allow freely such modifications in any
plan ol mining as may be desired, provided that
the modified plan embodies all the principles of
modern methods and sound mining practice.
In the successful operation of any mine some
general scheme of mining must be agreed upon,
subscribed to by all parties in any way concerned
with the matter, including the land owner, if the
property is a leased one. and then no omissions
in, additions to. or deviations from that plan of
mining should be permitted without the written
consent of the lessee ancl lessor.
After the general plan of mining has been
agreed upon and operations begun, its success or
failure will depend very largely upon the degree
of watchfulness exercised. The mine should be
accurately
SURVEYED AND MAPPED
at least once every 90 clays, frequent inspections
should be made of tbe mine, giving minute attention
to the condition of the working faces and the
robbing line. At least once a year tbe theoretical
yield of the property should be balanced
against the actual tonnage delivered at the tipple.
Accurate and complete records of the number of
acres of entry, of rooms, and pillars driven each
year should be kept, the percentage of recovery
per acre and the state of exhaustion of the property.
That the above method of mining will yield the
maximum of recovery is testified by the following
table, the figures of which are typical of the results
obtained by the Pocahontas Coal & Coke Co.
in the Pocahontas field, which so far as the writer
knows are not excelled anywhere. In this connection
it should also be noted that the percentages
of recovery are based on the total seam including
the portion rejected.
Total
Tonnage.
Mined.
165,254
188,391
180.3S6
192,437
334,005
94,427
83,000
144,769
201,044
262,975
Tons Theoretica 1
Portion
Mined Tons Percentage of
per per of Seam
Acre. Acre. Recovery. Rejected.
8,856 9,922 89.3 .24
8,185 9.115 S9.79 .22
7,215 8,325 86.6 .22
6,960 7.131 97.6 .23
9,203 9.582 96.0 .22
6,278 6,969 90.0 .31
8,601 S.614 99.8 .20
8,181 8,777 93.2 .20
7,380 7,534 98.0 .18
11,068 12,923 85.6 .23