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Pr oject Considerations for Pipe Replacement Methods 257
monitoring of ground movement is advisable. A preconstruction
survey should document all nearby buildings and structures that
have cracks, cosmetic problems, and structural deficiencies. The
elevations of carefully planned settlement points (on nearby build-
ings and on the ground surface) around the insertion and pulling
shafts should be surveyed prior to bursting, during bursting, and
after bursting. These preconstruction surveys and elevations moni-
toring can significantly reduce the risk of law suits to the contractor
and the owner.
6.9.8 Manhole Connections
The thermal elasticity of the PE material causes changes in the pipe
length, for example, 1 in. change in length per 100 ft of pipe for each
10°F temperature change. Therefore, in extreme hot or cold weather
when there is significant difference between the temperature of the
deep soil and the ambient air temperature, it is recommended to
allow the pipe to rest for 12 to 24 hours prior to tie-ins. Also, when
PE pipe has been pulled to a significant portion of its allowable ten-
sile load, it may be prudent to let the pipe rest before connecting to
other pipes, fittings, manholes, and lateral connection. This allows
the pipe to recover from any stretching that may have occurred dur-
ing bursting. For other pipe materials, the manufacturer should be
consulted.
In most pipe bursting applications, the existing pipe is old and
deteriorated, including the manholes along the line. In most cases, it
is therefore economical, on a life-cycle cost basis, to replace the exist-
ing deteriorated manholes and use their locations for pulling or inser-
tion shafts. When existing manholes are replaced with new ones, con-
nections to HDPE pipe can be made using flexible rubber manhole
connectors called “boots.” A pipe clamp is used to tighten the boot
around the HDPE pipe as shown in Fig. 6.11.
If the existing manhole is in reasonable conditions, and it is judged
to be capable of providing adequate future service, the manhole
benching is removed and the pipe opening is enlarged to allow the
passage of the bursting head. Expandable urethane grout and oakum
can be used to create a seal between the existing pipe opening and the
HDPE pipe, as shown in Fig. 6.12. The flexibility of HDPE pipe may
facilitate its movement through this opening.
Frequently, the inlets and outlets of the manhole are damaged
during the bursting operation, such that the resulting inlet or outlet is
no longer round. A low shrink polymer cement grout may then be
used to repair the damage. To obtain a good seal to the HDPE pipe, a
special PVC fitting with bell-end and sand texture outer surface (as
shown in Fig. 6.13) may be used. The grout bonds to the manhole and
the rough sandy surface of the PVC fitting provides a good seal. The
gasket between the PVC fitting and the HDPE pipe allows the HDPE