Environmental Science & Engineering - www.esemag.com - March 2003
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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: 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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