The Salt Lake tribune. [volume] (Salt Lake City, Utah) 1890-current, 1906-09-16

four TO six inches, according to the
amount Of estimated earth covering.
| The thickness of the walls, as original.
| ly planned, was insufficient to stand
| the side pressure, on account of the fact
| that one side of the excavation is
much higher than the other, as the
conduit is built on the side Of noun
tain, and also because the water would
settle in the spaces left by the forms
tlcularly on the upper side. The forms
referred to are the boards placed in
position to be filed with concrete and
removed when the concrete is com
pleted. The water freezing in tho
spaces left by these forms would pro-
duce pressure which was deemed dan
gerous for six-inch wall, and the walls
we're vn consequently increased from
thickness of six inches to n thickness
OF eight inches TO Withstand this pres
sure and to prevent tho possible de-
struction Of the conduit. As now COM
plcted the walls will successfully resist
the pressure. 1t should be borne in
mind that it would be extremely un-
wise to take the same chances, from
an engineering standpoint, in such an
important matter as conduit 10 sup.
PLY water for a city the size OF Salt
Lake, as might be taken on a private
dwelling. The conduit should be in
existence for a considerable number Of
wears and every care should be taken
to avoid anything which has the re-
motest appearance of insecurity in the
future.
The roof of the conduit was changed
from fiat surface, as designed in the
original plans, to the form of an arch,
IN order to support the vertical pres
sure, both from the back-fllinR and
the drift from the mountains.
The extra concrete necessary for
these. changes made in the original di-
mensions Of the conduit was estimated
at 1852 cubic yards, at tho original con-
tract prlce OF SlO.15 per cubic yard,
$50, ,991.50.
Back-hlling Exposures.
large portion of the conduit is built
either on the surface of the ground or
on piers across ravines, some of these
exposed aqueducts being several hun.
dred feet in length. The original speci-
fcations did not call for the covering Of
these. The rate of expansion of con-
crete under different degrees or temp
eraturc is about one-twolfth of an inch
per 100 feet for every 10 degrees. The
extreme variation of temperature along
the line of the conduit on the surface
or the earth, where exposed TO the di-
rect rays of the sun, is not less than
100 degrees Fahrenheit, which would
produce tension on the conduit sufti-
cient TO rupture the walls. The con-
duit having been constructed in a very
exposed locality. there was also dan.
ger that water flowing at the estimated
velocity through the exposed portion Of
the conduit might freeze and conse.
quently cause the stoppage and even
the possible destruction Of the conduit.
Further, the surface of the concrete,
being rough and porous, would naturally
accumulate sufficient moisture during
the cold wenther to be in danger OF
disintegration through the action of the
frost. This rendered il necessary that
the entire length of the conduit should
be covered with earth Of sufficient depth
to prevent freezing at the surface of
the conduit. This earth covering, in
addition to protecting the conduit
against the action OF the elements. will
maintain the water flowing through il