May 25, 2007

Battling the Elements

Contractors rely on frozen tundra base

PETER KENTER

correspondent

The popular RollerCoaster Tycoon computer game involves building amusement park rides all over the world. One module even allows players to build a coaster on top of ice floes. That may sound outrageous to game players, but for a few months each year, some contractors in Canada’s north rely on local ice as a firm footing for building projects.

Construction of the 400-metre Suncor Bridge across Alberta’s Athabasca River in 1996, for example, was accelerated through the use of an ice bridge — an artificially thickened ice surface that extended the construction season through the winter.

“Theories about the capacity of ice to carry construction loads aren’t very new,” says David Andres, an engineer with Northwest Hydraulic Consultants Ltd. in Edmonton. “However, until recently we’ve never really established ways of identifying the risk of what happens on an ice sheet.”

Andres and engineer Dr. Samanaidu Balakrishnan of Associated Engineering Alberta Ltd., also of Edmonton, published a study entitled Use of Ice Platforms for Bridge Construction in 2002. Part of the study was based on the construction of the Suncor Bridge. During construction, the river ice sheet sustained construction loads of approximately 200 tonnes. Not only did the ice platform help contractor Kiewit Management Company build the structure ahead of schedule, it also offered the environmental advantage of protecting fish habitats below.

“If you let nature take its course, you develop only so much ice by a certain point in the winter,” says Andres. “If you get proactive, you can thicken the ice by flooding it and having that ice freeze.”

NORTHWIND INDUSTRIES

A snow plow maintains an ice road near Inuvik, NWT

But all ice is not alike, and thickness alone doesn’t determine the suitability of ice for supporting a piece of equipment the size of a construction crane or a drilling rig. “The average contractor likes to use a handbook that would show that a certain thickness of ice is acceptable,” says Andres. “That isn’t enough. We need to know about the internal characteristics of the ice sheet before we can say explicitly that the ice is suitable for a heavy load.”

Northern contractors also specialize in building ice roads, temporary winter highways that connect remote communities.

“We drill beneath the existing ice for water and flood the intended road area at various stages a number of times to increase its thickness and strength,” says Dave Patrick, controller of Northwind Industries, a construction firm located in Inuvik, NT. “If you had to wait for the ice to thicken naturally, you’d use up a great deal of the transportation season. There are many loads — oil rigs or heavy derricks for example — that wait specifically for the construction of ice roads. These loads would otherwise have to be brought up on the Mackenzie River or through the Beaufort Sea.”

Some of the company’s contracts involve building “lease pads” for the oil industry, thickening ice wherever a company has a lease on a particular area, whether over ocean water or a muddy plain on the Beaufort Delta.

One of Northwind’s smaller divisions specializes in ice profiling. “We’re pretty damned good at it,” says Patrick. “The work is very sophisticated and involves the use of ground penetrating radar to create ice profile maps.”

However, the company rarely relies on maps alone. “The people who live here know how the water and the tides move. There’s no replacement for local knowledge.”

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