Underground Construction - July 2018 - 37

the creek meets the Fraser
River. Because that was less
than 330 feet away from the
lowest manhole on the project, all means possible were
utilized to protect the waterway. It was decided that the
upper portion of the project
would be completed first and
bursting runs closer to the
creek would be scheduled
for later in the summer, in
anticipation of lower water
levels.
The bursting was divided
into seven runs averaging 350
feet each, for a total of 2,456
feet. The design required replacement of the existing 15inch PVC pipe with three sections of 34-inch DR 17 HDPE
and four sections of 28-inch
DR 17 HDPE. Maintaining the
grade of the pipe was critical
and with such a major upsize,

ground heaving was also a
concern.
The existing 41-inch-diameter manholes had to be
replaced with four 47-inch
and three 53-inch manholes.
Launch and exit pits -10 to
15 feet deep and up to 60 feet
long -were excavated at the
manhole locations to help facilitate removal and replacement of the existing manholes
after pipe bursting was completed.
Crews exposed the sanitary service connections in
order to be ready for re-connection to the new pipe. All
other adjacent services (water, gas) were also exposed
before pipe bursting. Prior to
each pull, the HDPE pipe was
fused onsite and equipped
with a special bursting head
assembly.

Expander heads

O'Sullivan explained the
unique approach: "We used a
three expander bursting head
assembly for this project. The
three expanders increased incrementally in diameter. This
triple expander configuration
provided a staged movement
of the soil, allowing it time to
relax before the next expansion came along."
In addition, PW Trenchless crews used lubrication to
reduce the ground friction,
pumping a mixture of bentonite and polymer through one
pre-fused pipe.
During pipe bursting, some
heaving occurred in the exposed service pits, but none on
the ground surface, just some
cracks along two sections of
34-inch pipe. Crews installed

new inspection chambers for
the re-connected services and
all of the newly installed manholes in Kanaka Creek Park
were sealed for odor control.
The pit locations were restored
and seeded.
And it was all done with
no disturbance to existing
utilities. "The CCTV post pipe
bursting confirmed a successful installation," said O'Sullivan. "Bursting times ranged
between 3 to 4 hours per run,
while removing the different
cones took s6to 8 hours. Set up
and break down was completed
over several days."
FOR MORE INFORMATION:
PW Trenchless Construction Inc.,
(604) 580-0446, pwtrenchless.com
TT Technologies, (800) 533-2078,
tttechnologies.com

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UConOnline.com | JULY 2018

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Underground Construction - July 2018

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