Roanoke Rapids herald. [volume] (Roanoke Rapids, N.C.) 1914-192?, 1919-11-14
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lelminc the distances M which the shock waves
resulting from the discharge Of various explosives
could be heard. 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 us to
the type Of mining machine which could be used
10 accomplish the most work with the least noise
In this connection 1t was found that sounds
were transmitted only about half ms far in clay
rs in shale strata and about onequarter ms far in
clay MS in conl. To give some idea of the sens-
tiveneSs Of the instrument 1t may be said that
pounding with pick on the bumInous coal can
be detected for distance of 800 feet. and the
direction determined, and that pounding with
sledge can be heard MS far as 11jO feet These
measurements were made in the Pittsburgh coal
seam in the vicinity of Pittsburgh where the coal
IS somewh@t harder than In most other bitumnous
coal beds. The explosion Of 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 car is charac-
terstic of the implement producing the sound To
illustrate: Twelve mining and carpenterng
operations were carried oul on the coal rib An
engineer Of the bureau Of mines who had never
used ;he geophone and who did not know what
tools were to be operated was able to recognize
and name nine of the implements ut Il distance OF
several hundred feet through the strata. The
other three sounds were accurately described but
the tools not identified.
Now that the war Is over, the bureau has turned
TO the development of the Instruments for peace
time uses. For thing, II 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
q disaster. The tests so far made In the vicinity
of Pittsburgh show that n man pounding on the
coal rib with n pick. piece of timber or sedge can
be detected and located from II point 600 to 1000
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 or the
determination of direction.
Pounding with sledge can be heard from 200
to 300 feet through the mine cover, depending
upon the quletness of the day outside, since any
wind greatly nterferes with the successful opera
ton of the instruments. II will at once be seen
that when mines are not too deep they can be
explored from the surface and II will thus be
possible to find and locate Il miner who Is pound
ing Al the experimental mine in Bruceton, Pa.
n man has frequently been located through l4O
feet Of cover within so feet of the exact point
where he was nOunulnE.
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 or dust In
the entries Of mine and since this dust dampens
the transmission of the sound the sounds are not
transmitted very well. The same is true Of pipe
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 no lines have
been found long enough to show the limit of the
gcophone It is known, however that the naked
ear can get sounds farther than 1000 feet
Used to Guide Tunnel Work.
Tn metal mines expensive surveys have some
times to be made in order that the approaching
tunnel headings may be brought together ac-
curateIy 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 20 into each heading and locate
the direction from which pounding In the other
heading coming
Observations made in metal mine recently
showed that direction can be determined much
more easy in rock than in coal. This Is prob
ably due TO the fact that there is some reverbera-
tlon to the sound from n hammer blow on coal
while on stone the sound is clean cut II hap
pened that In this mine n raise was being driven
up, about six or eight feet distant from shaft
Observations were made in the drift of the sound