Crawford avalanche. (Grayling, Mich.) 1879-19??, 1891-03-19

sgine and boiler house, containing at
present four boilers, four electric light
= engines and dynamos, two ventilatinp
~blows," and the two great pumps for
draining the cut
The great cuttings for tunnel an
proaches were begun on New Years Day
'aOf 1889, says the Chicago Inter Ocean.
The Canadian was begun somewhat N ar
row. AT depth of fifty-eight feet a
landslide deposited about sixteen feet of
soil in this cutting. Work was started
again about ten rods farther back. At
The portal the Canadian great cutting is
sixty feet deep. 1t is 260 feet wide at its
broadest portion. From the portal il
rises one foot in fifty feet for 3, 1872 feet
The American great cutting is fifty-two
feet deep, about 200 feet wide at its
hbroadest part, and rises one foot in fifty
feet for 1888 feet. An inclined track
was laid for flat cars to haul out the tun-
mel soil. In September, 1890, two steam
shovels began work on each side of the
river. Each shovel was attended by
locomotive and train of fat cars Hun
ureds OF men are employed day and
night. When the tunnel proper was
commenced scarcely more than two Law
>eTs OF the soil had been removed. The
;tunnel company grew inpatient, and on
Monday, Feb. o, 1891, took the Canadian
work from the contractors Over 500
men are employed. AS the tunnel will
mot be opened for traffic until after the
approaches are completed the work on
the cutting is being rushed.
Mr.. Alfred f. Beach, an American
engineer, designed and used shield in
the Broadway tunnel, New York City,
In 1868. Since then similar shields have
.hnnn nCn6 m oil Ind
River, London, and other tunnels. This
'excavating shield may be compared to a
cylinder with no head 1t is circle of
steel plates. Inside these plates are
braces, doors, and aids for the workmen.
In the front end are knife-edges to pene-
trate the soil. In the rear portion of the
shield, around the main walls, are hy-
draulic jacks, each supplied with valve,
so that its action may be independent of
Others. The material of the tunnel
walls, masonry, or cast iron, is built in
the rear OF the shield. Pressure is ap-
piled to the hydraulic rams, and thus the
shield is pushed ahead the length of the
jacks pistons. The soil is pushed into
the front of the shield, and the men re-
move it by loading it upon cars, which
arc pushed out to the tramways, on
which they are drawn by mules, or
where they are hoisted to the regular
fiat cars and taken to the dumping
ground. While the men are removing
the soil in front the men in the rear are
busy erecting the walls of the tunnel.
lin case OF iron plates, a revolving crane
lifts the plate by means of counter
balance weight to the desired position,
where it is bolted to the other plates.
When the section of the tunnel Is COM
cpleted, and the pistons of the rams have
been drawn back, the air is applied again,
and the jacks pushed forward for an
other section of the tunnel to be put in.
BY this arrangement the workmen are
always protected from danger above,
around or below. The air pressure
keeps the water back in front, and the
completed tunnel protects the rear.
Two shields were used in the st. Clair
tunnel. Each weighed eighty tons
They were brought I'm sections TO the
north bank of the cutting. where they
were erected. Then came the problem Of
placing the shields in position. Wooden
tracks were laid, huge ropes were placed
around each shield, and they were grad
ualy lowered by men. In eighty min
utes they were In place at the proposed
mouth OF the tunnel Each shield was
16 feet long, and had an outside diameter
of 21L feet The steel plates were 1
inch thick. Each shield had twenty-four
hydraulic rams at equal distances apart.
Each ram had a stroke Of 2 feet and
a diameter of 8 inches. Each
time the pistons were showed ahead the
shield moved enough TO allow a section.
or foot and a half. of the tunnel to be
made. The air could have been forced
20 press 5000 tons on the shield, but the
greatest pressure used was 900 tons. BY
regulating the pressure of any valve the
= direction OF the shield could be varied at
will. An observation Of the shields d.
rectifh was taken every morning, and