Page 382 - Trenchless Technology Piping Installation and Inspection

332 Cha pte r Ei g h t

The boring pits must be located at a safe distance from existing struc-
tures to avoid any hazard to the structure or the public. The distance of
the pit from the roadway must be adequate to allow sloping of the pit
if necessary. If sufficient sloping cannot be accomplished due to space
constraints, an earth support system of pit walls must be considered.
Enough room for safe loading and unloading of equipment, and for
spoil removal must be provided. Accidents are less likely to occur at
sites that are open and kept clear of debris.
Typically steel pipes are used for casing in order to prevent the
potential damage caused by the rotating augers. The casing must
be of good quality and well prepared. Machine-cut beveled ends
assure casing alignment, joint end squarness and exact lengths keep
the head at the correct location relative to the casing, and smooth
walls reduce the required jacking force and the tendency of the casing
to rotate during the boring process.
After successful installation of casing pipe, the carrier pipe (also
called product pipe) can be installed. Carrier pipe is installed by first
attaching wooden skids or premanufactured casing spacers to the
carrier pipe before assembly. The carrier pipe is then installed, one
piece at a time, from either the entry or exit pit. It can be installed by
pushing by hand or with a boring/jacking machine, or by pulling
with a winch or other methods. The use of premanufactured casing
spacers are not recommended for gravity sewers installations as they
do not allow for differential blocking of the sewer inside the casing.
Postinstallation and installation monitoring includes the following:
• Preparing an as-built drawing.
• Amount of spoil removal must be checked for possible voids
outside of the casing. Any voids needs to be grouted with
approved grouting materials and methods.
• In sandy or unstable soil conditions, there is a possibility of
void formation in the line of bore, and in this condition grout-
ing of outside of casing is strongly recommended.

8.4.2 Materials

Pipe
Pipe used in this method includes an external casing pipe (also called
jacking pipe) and may include an interior carrier or product pipe.

Allowable Forces
Considerable jacking forces may be required to install pipe using this
method.

• Casing pipe must be obtained from one manufacturer.
• The allowable jacking strength capacity of casing pipe must
be capable of withstanding the maximum jacking forces