Year: 1869

it,"


The Omaha Bridge.


The Atlantic cable and the Union Pa
cific railroad made one epoch; the build
ing of the Darien ship canal and the
erection Of the Missouri river railroad
bridge another. The skepticai, those
who dream Of the Big Muddy, as flow
ing in n channel of sand infinite in
depth, may smile at the project. But
J the same men who said they could build
- railroad frnr. thiss III 10 SAN I'r.,,ois-
CO. long before rich localities made the
preliminary surveys for ten mile
plug spent $4,000 in soundings, to
ascertain whether uuicksands could rest
on nothing. Steel bars, the ordinary
implement for sounding, disclosed u
foundation at less than discouraging
depths, and with such accuracy as to en-
able them to make protiIes OF the dips
of the bed rocks. The superstructure


will be of wrought iron, and will be
| 200 feet long. The piers are built of
hollow cast iron cylinders in sections of
from ten to twelve feet long, and 81 feet
in diameter, with thickness of iron Of
II inch. The site is half a nile below
the ferry landing on the Iowa side. The
natural approaches are by three terraces,
the last declivity being bank of sand,
and finely grained soil. The following
may be taken as an example of the mode
ofreaching the bed rock 10y sinking the
tubes. The first section having no bot
tom !!ange for hoiting to its counterpart,
is lowered to its position by huge der
rick, and an air tight cap is bolted on
the top. The air within is exhausted
by double air pump, moved by "A steam
nnpi,,n anI Stnl, It.h
feet from the site of the pier. The
weight of the external atmosphere, let
fall into the cap, forces the cylinder
downwards depth depending upon
either the compactneSs or looscness Of
the soil. When the top of the first see
ton reaches the level of the water sur
face, the metal cap is removed, and an
other section boted on, the bolts pass
ing through corresponding iianges on
the inside. The process of eNhausting
the air, and forcing the cylinders to
their place 10y the force Of gravity in
the weight of the metal, and in the
pressure of the atmosphere on the cap,
Is continued until the foundation be-
comes too firm for this mode OF operat-
ing. This being the case, an air cham
Der made OF strong boiler iron in size to
match the circumference ofthe cylinder,
is bolted on top of the section, and
Workmen are sent inside of the column
to eXcavate the hard earth while the
water is kept out by forcing strong
current of air into the hollow pier by
the same pump used for eXhaLsting in
the first operation. When the soil and
sand are loosened they are forced out of
the inside by an invention made and
used only by Gen. Smith. 1t is done
by sending in u column of compressed
air and bringing it in contact with the
loosened earth. The velocity and force
ofthe current sendthe debris up through
nozzle in the eair-chamber in il stream
20 feet high in the air, making it Curl
Gus fountain of sand which casts its
rainbowless spray for rods around the
neigh hbOrhood. The process Of forcing
he earth upward by compressed air,
develops and confirms, Oh Il grand scale.
n scientific fact. The air pas>cs to the
chamber through u ca-t-iron pipe, five
inches in diameter. The air is received
in its natural atmospheric temperature,
but by compression it becomes hot
enough to render the pipe through


which 1t is passing too hot to allow one
to rest ones hand Oh it. The efficiency
Of this mode of excavation may be
judged by the fact that IA cubic yards of
sand and earth have been removed in
- minutes. In heavy clay, workmen
dig it loose, and it is carried up through
the column TO the cap, which is the
bottom Of the air chamber, hy winilass
| and bucket, the windlass being worked
by 4 donkey engine attached to the out
side of the chamber. 1t is then dis
charged through depressed hollow arms


ut the sides closed with valves. \ col
| umn of hollow metal for the first pier
has already been sunk b meath the sur


face So feet, and within five feet of the
| rock bed. \ hard pan Of clay has been
! reached, firm enough in itself with the


aid of the lateral pressure Of sand, and
! the base surface composed Of the con-
crete filing, to make Il good iuundalion;
/ but Gen. Smith has determined to 20 to
| the rock. BargcS lave also been built,
| and machinery of the same kind as


that used Oh shore pat on them to work
! in water.