a quick turnaround on technical RFIs, site installation issues
or situations where there were geotechnical anomalies that
didn’t accurately line up with predicted conditions. The use
of field PDAs to confirm design adherence as well as on site
QA/QC by engineering helped to ensure the final product
met all specifications.
The decision was made to pinpoint critical towers with
higher loading, such as the heavy angle or dead-end struc-tures,
for caisson construction and develop a simpler, smaller
driven pipe pile design for tangent and angle structures. Since
tangent and angle towers made up a substantial portion of
the required work, the simplified design allowed consistent
and low impact daily completion of foundations to keep the
project moving at an aggressive pace.
To facilitate this pace, Northstar Sharp’s used an impres-sive
fleet of owned equipment, including eight Junttan units
for the driven piles, six excavator-mounted units for the heli-cal
piles and five Soilmec and two Watson drilling rigs for
the drilled shafts. In addition, two pull-test frames for PDA
testing and two Marl AR80 tracked units were used for the
program’s geotechnical investigation.
Construction problems and creative solutions
Some of the unique project challenges included river cross-ings
along the path of the powerline. There were three river
crossings that needed to be considered: the Athabasca River,
Pembina River and North Saskatchewan River. For these
crossings, drilled shaft piles with diameters of 3.65 m by 17 m
deep were chosen as the preferred foundation type. There
were also other existing powerlines to contend with and
often the power could only be interrupted for a short dura-tion
– in some cases, not at all.
“The dedicated effort from
Northstar Sharp’s, coupled
with an innovative design and
work process, has been a key
component to the WFMAC
project’s overall success.”
– Brett Smit, P.Eng., Valard Construction
For the large diameter concrete pours, high temperature
was a concern in the summer months for the concrete curing
process. Therefore, the crew’s start time and end time were
changed to be earlier in the morning when temperatures
were cooler. Concrete truck routes were also timed to be pre-cise
with test drives being performed to discover the most
effective and quickest route. This allowed Northstar Sharp’s
to maximize all possible options for concrete delivery includ-ing
using the Klondike ferry to cross the Athabasca River
while performing a continuous 170 m3 pour.
Another ongoing test for the team was the various ROW
surface conditions experienced along the full route of the
project. From wetlands, fine sand and steep terrain, to the
river, various pipeline and powerline crossings, structure
access by crews and equipment were a continual challenge.
The various foundation designs were optimized through
the standardization of material. Regardless of the design
selected for an individual site, wherever possible all mate-rial
and sizes were made to be identical. This streamlined
the procurement and execution phases by making it very
Helical piles being installed by Northstar Sharp’s Exca-Driver
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