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In the smaller diameters, the steel casing is usually placed progressively,
following the boring equipment as it tunnels through the obstruction. The
recommended practice is to use plain steel pipe (not corrugated) for the casing
to facilitate movement of the PVC pipe through the casing with a minimum of
resistance. For larger diameters, most of the casing construction is done by
jacking the pipe from excavated pits. Where long casings are involved,
numerous pits for jacking operations are required along the route. Regardless
of the diameter, accuracy in alignment and grade of the casing pipe is very
important in maintaining the established inverts.
2.7.2 PULLING THE PIPE
When PVC pipe is to be installed in casings under highways or railroad tracks,
skids with rounded ends must be used to prevent the pipe and bells from
snagging on the inside of the casing, and to keep the installed line from resting
on the bells of the pipe. Skids shall be thick enough to allow clearance between
the bells and the casing bottom. Normally two to four skids are only placed on
the pipe spaced at 90 degrees as shown in
Figure 5.
For pipe larger than 18
inches, six skids should be placed at 60 degrees apart.
Cable
Strapping
Wood cross piec
Skid
Skids
Figure 5
A cable is passed through the casing and the first pipe length is fastened to
a suitable wood crosspiece at the end of the pipe. The cable is then pulled
steadily by a winch, tractor or other method until about 2 feet of pipe is left
projecting out of the casing for assembly of the next length. (If cable is pulled at
an angle, make sure that the leading pipe end is protected from damage.) The
cable is then passed through the next pipe and the two pipes are assembled.
This operation is continued until the pipe is completely through the casing.
BLUE BRUTE
/BIG BLUE
/ULTRA BLUE
INSTALLATION GUIDE
19
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