The patriot. (Glenmora, La.) 1918-1955, 1919-11-14
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ternine 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 shale strata and about one-quarter as far in
clay in coal. To give some idea of the sensi-
tiveness of the instrument 1t may be said that
pounding with pick on the bltumnous coaNean
be detected for distance of 800 feet, and the
direction determined, and that pounding with a
sledge can be heard as far as 1850 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 oneounce charge
Of dynamite was detected 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
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
disaster. The rests far made in the vicinity
of Pittsburgh show that man pounding on the
coal rib with pick, piece of timber or sedge can
be detected and located from point GU to I.zOU
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 800 feet through the mine cover, depending
upon the quietness of the day outside since any
wind greatly interferes with the successfuI opera
ton of the instruments 1t will at once be seen
that when mines are not too deep they can De
@explored' from the surface and 1t viii thus be
nossihle to And and locate miner who is pound
ing Ait the experimental mine In Bruceton "a,
d man has frequently been located through l4O
feet of cover within 80 feet of the exact point
where he was pounding
study is also being made Of the distances that
pounding on rails and pipes can be heard since
rails are generally buried in the eartn OF aust III
the entries of mine, and since this DUST dampens
the transmission of the sound, the sounds are not
transmitted very we'll The same is true OF pipe
lines However, Ii 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
geophone. 1t 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. # would only
be necessary to 90 into each heading and locate
the direction from which pounding In the other
heading was coming.
Observations made In metal mine recently
showed that direction can be determined nucn
more easily In rock than in coal TINS y Prod
ably due to the fact that there Is some reverbera-
ton to the sound from hammer blow on coal.
sghsle "a stone the sound ii clean cut. Il so hap
pened that IN this mine raise was being driven
ID. about SIX Of eight feet distant from shaft.
Observations we're made n the DRIFT Of the sound