Vernon Parish Democrat. (Leesville, La.) 1917-193?, 1919-11-22
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termine the distances at which the shock waves
resulting from the discharge of various explosives
could be heard. A brief investigation Of the
factors influencing the transfer of energy from
mining tool to the clay and coal were also made in
order that recommendations could be made as to
the type of mining machine which could be used
to accomplish the most work with the least noise.
In this connection it found that sounds
were transmitted only about half as far in clay
as in shae strata and about one-quarter as far in
clay as in coal. To give some idea Of the sensi-
dveness Of the instrument 1t may be said that
pounding with pick on the bituminous coal can
be detected for a distance of 900 feet, and the
direction determined, and that pounding with a
sledge be heard as far as 1,150 feet These
measurements were made in the Pittsburgh coal
seam in the vicinity of Pittsburgh where the coal
is somewhat harder than in most other bituminous
coal beds. The explosion Of a one-ounce charge
of dynamite was detected a distance Of over 1000
feet through the shale strata.
Sound Tells the Implement
One interesting feature of the instrument is
that the sound transmitted to the ear is charac-
teristiC of the implement producing the sound. To
illustrate: Twelve mining and carpentering
operations were carried out on the coal rib. An
engineer of the bureau of mines who had never
used the geophone and who did not know what
tools were to be operated was able to recognize
and name nine of the implements at distance of
several hundred feet through the strata The
other three sounds were accurately described, but
the tools were not identified.
Now that the war is over, the bureau has turned
to the development of the instruments for peace
time uses. For one thing, it is believed that they
will be Of great value to mine-rescue crews who
may be entering mines for exploration and to
locate miners who may have been entombed after
a disaster. The tests so far made in the vicinity
Of Pittsburgh show that man pounding on the
coal rib with pick piece of timber or sledge can
i T,a
feet distant. This distance depends greatly on the
character of coal upon which the man is pounding,
and intervening rooms and entries seem to have
surprisingly little effect upon the distance the
determination of direction.
Pounding with sledge be heard from 200
to 300 feet through the mine cover, depending
upon the quetness of the day outside, since any
wind greatly interferes with the successful opera
ton of the instruments. 1t will at once be seen
that when mines are not too deep they can be
explored" from the surface and 1t win thus be
possible to find and locate miner who is pound
ing. At the experimental mine in Bruceton Pa,
q man has frequently been located through 140
feet of cover within 80 feet of the exact point
where he pounding.
A study is also being made Of the distances that
pounding on rails and pipes can be heard Since
rails are generally buried in the earth dust in
the entries of a mine, and since this dust dampens
the transmission Of the sound, the sounds are not
lines However, If the pipe lines are not buried,
but are laid on blocks and ties the pounding can
be heard great distances. So far lines have
been found long enough to show the limit Of the
geophone It is known, however, that the naked
ear can get sounds farther than 1000 feet.
Used to Guide Tunnel Work
In metal mines expensive surveys have some
times to be made in order that the approaching
tunnel headings may be brought together &C
curately. Since direction can be determined so
well with the geophones, it is thought that they
can be used to guide such work. 1t would only
be necessary to go into each heading and locate
the direction from which pounding in the other
heading was coming.
Observations made in a metal mine recently
showed that direction can be determined much
more easily in rock than in coal. This is prob
ably due to the fact that there is some reverbera-
ton to the sound from hammer blow coal,
while on stone the sound is clean cut. It 50 hap
pened that In this mine raise was being driven
up, about six or eight feet distant from a shaft.
Observations were made In the drift OF the sound