Culvert headwall system conquers site constraints at Uranium City
by Jim McGeary and
Doug Lowry, Armtec Limited
Both the steel arch and the headwall components were light in weight
compared to alternative solutions.
Highway No. 962 services the
remote northern community
of Uranium City in the
extreme Northwest corner of
Saskatchewan. Uranium City is north
of Lake Athabasca, 30 miles south of
the North West Territories border. The
city was developed and named as a
result of a significant uranium deposit
that was first explored in 1946.
At one point, the highway crosses
the Fredette River. The wood bridge
deck and abutments that had been in
service some 40 years were in serious
distress. The North abutment was sliding
to the south and the deck required
complete replacement. Ground access
to Uranium City is limited and very
expensive, as there are no permanent
roads linking the city with the rest of
Canada. Ice roads are available during
winter, or materials may be hauled via
barge in the early summer.
Project nearing completion.
A number of replacement options
were considered for the bridge. A conventional
girder-on-abutment bridge
would have required that heavy construction
equipment, such as pile drivers,
would need to remain on site for
twelve months. This requirement made
that option prohibitively expensive.
The Saskatoon branch of Armtec
Construction Products was approached
regarding an alternative solution. The
company’s Jim McGeary was invited
to visit the site, along with Department
of Highways personnel to discuss possible
corrugated steel pipe solutions.
Due to environmental and hydraulic
concerns, a full periphery corrugated
steel structure was ruled out.
Following a comprehensive site
meeting, it was determined that a single
radius arch manufactured from
structural plate corrugated steel pipe
seated on footings would be a viable
solution. Existing three-foot square
concrete pilasters that capped wooden
piles would serve as the footings.
A Geoweb® retaining wall reinforced
with T C Mirafi uni-axial polyester
geogrids would be employed for
the headwalls.
Tenders were called requesting the
supply and installation of a 5180 mm
span structural plate arch, mounted to
the existing pilasters, and associated
retaining walls. Normally a supplier,
Armtec chose to bid the project as a
contractor. The scope included:
Demolition, detours, temporary
crossing and environmental protection.
Supply and assembly of the arch.
Supply and installation of the retaining
walls.
Backfilling and compaction of the
arch and retaining walls.
Supply and installation of the
guardrail system.
The contract was awarded to
Armtec in December, 2000. All construction
materials were shipped to site
via the winter ice road. Demolition of
the existing bridge started the following
June. The project was completed in
early August, 2001.
The success of this project was due
to a number of factors. Two of those
factors stood out in particular. Both the
steel arch and the headwall components
were light in weight compared to
alternative solutions. The arch was
shipped as a series of nested plates,
while the cellular Geoweb® fascia
material was shipped in a collapsed
and folded form on pallets. The
geogrid was provided in roll form. The
compact shipping volume, and the relatively
low weight of the primary
bridge and wall components, translated
into significant savings in the cost
of freight.
Both the corrugated steel arch and
the geocell/geogrid retaining walls
were constructed using simple construction
techniques. This feature
allowed local labour, inexperienced
with these products, to complete the
project on time and under budget without
the use of large, expensive and specialised
construction equipment.
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