Gilpin observer., 1913-07-03

his boots and leaving them clogged
i'm the flood OF ooze.
I'D. w. Brunton relates that i'm
driving the Cowenhoven tunnel ait AS
pen, it was net unusual to have the
tunIel filled with mud for hundreds
of feet back from the breast and that
the miners saved themselves by all
Joining hands and rushing out to-
gether. In passing l wdsh to say that
there never was completed in all the
world a harder job of tunnel driv-
ing in soft and swelling ground, with
nothing but timber supports, than
Aspen.
"If the ground lis soft, water-soak-
ed clay, then the method CT an aud
vancing iron shield must be employ
ed, such as was used in the North
river tunnels of New York City. The
working compartment of the shield
is kept under a pneumatic pressure
of several atmospheres to hinder
the thrush of the water7soaked mud.
The installment and operation of
movable shield is extremely expen-
sive and dn addition the lining re-
quired to hold the soft ground is
great expense.
ITO illustrate the relative disad-
vantages of very soft or very hard
rock, let us assume an ideal rock
for tunnel building as a basis and,
for the purpose of Illustration, as
sumo that 1t will cost $50 per foot to
drive a given tunnel through it. Then
1t is evident that very hard rock can
run the price up relatively small
amount, say to $75 per foot, while
very soft rock may run the bill up
to almost any figure, say to $500 per
foot.
''One of the important considera-
tons in boring deep into the earth's
crust is the matter OF heat. 1t is
known that in some formations, the
y
3,300-foot level of the Consolidated
California & Virginia mime at Virgin
ia City, New, the rock temperature
was 1SO degrees Fahrenheit. 1t has
been proven that in all formations
there is an increase of temperature
with depth. Part of the heat is the
latent heat of the rock, but where
excessive temperatures have been
encountered, the excess Of hat was
found to be due either to the expos
ure Of minerals which were acted
upon by the air or to local volcanic
heat.
Soft lime is rock which Is apt
to generate a let of heat when the
stone at great depths is exposed to
the action of the air. The Alpine
tunnels had this difficulty to over
come. Some of the feldspars also
decrepitate ON exposure to the air,
with swelling and the generation of
heat.
''The tunnel section of the main
range has been carefully studied for
formations that might cause unusual
rises of temperature but none have
been found.
From data gathered in the mines
of Saxony, Hungary. France, Lake
Superior copper field, Virginia City,
Bendigo, Australia, the Rand. South
Africa Java, Westphalia and from 164
we'll borings of the United States
where temperature records were kept
Tin all about $4,000 records), l. find
that the average increase In temper
ature may be taken as 1 degree, Fahr
enheit for every 20 feet OF depth. A
depth OF $500 feet will then induce
a rise of temperature of 40 degrees
F. As the average temperature at
am altitude of 5000 feet in Colorado
rs 43 degrees F., and as ordinary ven
tilation will reduce the abr temperate
ure about degrees F. below the
rock temperature. we see that a tenn
perature OF only IS degrees F. need
be anticipated, which Is only comfor-
tably warm. This reasoning agrees
with the actual experience in the
deep shafts Of Central City. where
no troublesome temperatures were
encountered down to a depth Of 1900
feet.
by thds ddgressdon, hope have
been able to show the important
bearing geology has on estimating
the cost OF boring the Moffat tun-
mel. OF course, there are many who
say that no mans eyes, however
we'll trained. can see any further into
the ground than amother's. This is