The Wallace miner. [volume] (Wallace, Idaho) 1907-current, 1921-02-24
8 HECLA MINE
ITS DEEP OPERATIONS
USE GUNlTE IN LONG TUNNEL IN
PLACE OF TlMsERS-PRE-
VENTS AIR BLASTS.

The Miner is indebted to Z. IL.
Brang. mining engineer OF this city.
Tor "a copy of the Ammnus. published
10y the Alumni association of the
. Michigan school of mines at Hough-
ton. giving IAN account of the Won
derful underground plans now being
carried ont boy the Calumet & Hecla
company. which involve the abandon
ment of incline shafts above Slst level.
the practical duplication of mine
plants ON that level, and driving a
tunnel at that great depth to accom-
modate an electric railway three
miles in length. These however, are
incidental to the main feature of the
article, which is to describe the sue
cessful use of "gunite" in this long
tunnel instead of timbers, fact that
made the great enterprise possible by
reducing the costs. This interesting
Iartcle follows:
Underground Conditions.
The Calumet * Hecla conglomerate
has been mined very largely from the
beginning through inclined shafts, the
inclination being from 50 to 40 de-
grees During the early life of the
mine these shafts were located very
near each other-in some cases only
a few hundred feet intervening. From
time to time some of the intermediate
shafts We're abandoned until at pres
emit there are only five remaining in
active use. But these have reached
depths so great-SOOO feet and more
that it is economically impracticable
TO maintain them in working condl-
ton.
The enormous area stopped out-1ls
miles deep by 2h miles in length
has started movement so vast that no
attempts are made to do more than
provide temporary checks here and
there to maintain passage ways in
the form of drifts and shafts.
The heaviest concrete and mason /
ry crumble as so much clay and mas
sive steel sets are twisted and torn.
Rock and timber cribbing squeeze to- /
gether in time, and openings in part /
of the conglomerate close up to such 1
an extent that after a few years they /
must sometimes be redrlfted i'm order 4
TO be available as passage ways.
Occasional so-caled "air blasts"
occur and sometimes hundreds of /
tons of rock are thrown violently /
from the apparently solid sides of
shaft or drift These phenomena are /
accompanied by terrific gun-like re-
ports and at times have broken 70 /
inch air mains torn mp tracks and /
even filled several hundred feet of /
shaft or drift with debris
The management had then to face .
the following facts: T. The hoists at /
the incline shafts had practically /
reached their working limit i'm depth. /
3 The expense of shaft maintenance /
vas fast becoming prohibitive 3
Millions of tons of high grade ore /
were being indefinitely tied up in the /
form of shaft pillars.
It was. therefore. decided to cut off /
all incline shafts at the S1st level |
about 500 feet from surface on the /
ncline-and to practically duplicate |
the surface layout of a mine at this
depth with the exception Of rock /
crushers and air compressors. It is
planned to erect hosting engines
capable of hosting from an addition
al depth of 5000 feet and to operate
an electric railway whose main line
viii be over three miles in length
Most of the supplies will come down
through No. u shaft which is at the
south end of the Calumet & Hecla
property and the copper rock will all
be hoisted through the Red Jacket
shaft. which is vertical, 5000 feet in
depth, and near the north end of the
mine.
Work on this project began in jan
uary, 1918. and has progressed stead
ily ever since To avoid the disturb
1nces encountered in the cOnglomer-
ate itself. it was decided to drive the
main haulage way and sink the new
shafts in a barren amygda'oid vein
which lies about $50 feet beneath the
This vein had been
found in occasional crosscuts to be
about 20 to 80 feet wide, and it was
believed that lying as it does, back in
the undsturbed foot we would have
a minimum of maintenance cost for
our openings in this area
Danger From slabbing.
Shortly after driving the main tun-
mel had started, however, we were
much disturbed by the fact that
"slabbing' began on a very extensive
scale. There were no air blasts and
no big caves, but ground that had
been carefully barred for loose would
again become dangerous, frequently
in a few days.
This finally became so serious that