by Ian Elliot
Northern News Services

NNSL (Oct 13/97) - When the rivers in the North no longer flow, the ice roads do.

The territorial transportation department will be opening its winter roads system again as soon as the weather allows, which is usually early December.

It builds and maintains 1,300 kilometres of winter roads, 400 km that run across frozen lakes and rivers.

Private contractors will build hundreds of kilometres of their own, and, depending how many contracts the company holds, they will move huge volumes of their own. RTL-Robinson, for example, which has been building ice roads since 1968, will employ as many as 680 people and haul as much as 90 million litres of fuel and 4,000 truckloads of dry supplies in a winter, said company spokesman Marvin Robinson.

Winter roads are built as much by intuition and experience as by design manuals. Those who work on the roads often find themselves describing ice the same way one describes a living thing.

"I knew an oldtimer who spent a lot of years building roads, and he always said, 'The more you understand about ice, the more afraid you are of it,'" said Art Barnes of the transportation department.

Ice has one major feature which makes it very different from other materials used to build roads: it is very elastic and is constantly changing its shape and thickness.

"Ice is an elastic membrane stretched over a body of water," Barnes said.

Its mechanics are predictable, but they lead to all sorts of complications you don't get with asphalt. Heavy trucks actually ride in their own depression as they travel along an ice road, pushing a bow wave ahead of them. Their weight can cause cracks; they can drop through the ice if they drive over their own wave, and ice at the shore can actually explode if the truck is going too fast and pushes the wave into the shore too hard.

Ice naturally cracks as vehicles drive over it and undergoes a kind of fatigue if too many vehicles go over it too quickly. Given time to rest, the ice will heal itself, but too many heavy trucks going too fast can lead to a sudden failure of the surface. And when ice cracks, it isn't the lead driver who goes through.

"That's the irony of it," said Mike Elgie, a department highway maintenance foreman based out of Yellowknife.

"You can have a bunch of cowboy truckers driving too fast and thinking that they got away with it, then the next poor bugger that comes along following the rules goes into a hole."

One of the major factors that affects ice is temperature. It is hard and brittle on extremely cold days, yet flexible and strong on warm ones.

"The higher the temperature, the stronger the

ice," said Elgie.

"On a warm spring day, when the temperature is about plus 5, it's almost impossible to break ice."

Constructing the roads involves more than simply ploughing the snow off lakes and rivers in a straight line and waving on the transports.

The science of ice-road building has improved from years ago, when truck drivers kept one hand on the door handle in case they had to jump out of a sinking transport. Now the instincts of experienced road builders are backed up by calculations that estimate the carrying capacity of ice, although every road builder does it slightly differently.

On the ice road from Yellowknife to Dettah, which is a short but typical example, workers wearing flotation suits will go out for the first time around Dec. 8, and begin edging towards the community, drilling holes every 100 metres to test ice thickness. Ice 10 centimetres thick can support a person; 25 centimetres can carry a car or light truck; ice one metre thick can carry 40 tonnes safely.

Workers drill holes every hundred metres or so to gauge the thickness of the ice -- 63 holes between Yellowknife and Dettah -- and the shallowest of those holes are monitored weekly to ensure that underwater currents are not eating away the ice.

Thin ice can be thickened by auguring through the ice and pumping water up to freeze on the surface; important bridge points like Fort Providence get a water cannon that sprays slush into the air and it freezes on top of the river ice.

The best place to build any ice road is across deep, still water.

"If you are out on a lake, you have better ice conditions," noted Barnes, because the water has fewer currents and offers more stable ice.

"You also don't want to follow the shore a great deal, which goes against people's natural instincts a bit."

Ice roads are laid down in largely the same places each year as builders figure out where the best route is, although varying water levels can change the currents.

Roads are also plowed as soon after snow falls as possible, Elgie noted, because a layer of snow acts "like a roll of pink insulation", preventing the Arctic air from cooling the surface.

The reverse happens when roads cross land. There crews first lay down a pillow of snow to protect the fragile muskeg and to smooth out the naturally occurring humps.

"We generally do build a cap over the land so we disturb very, very little of the soil," said Robinson.

That snow blanket that starts the winter road also announces its end. When the snow melts so that the black soil shows, the road is closed.

"When we close down, the ice is still thick enough to drive on but it's the land portions that go to hell," said Elgie.

The day the ice road arrives can be compared to a cork coming out of a champagne bottle, especially in isolated communities where people are eager to drive out during the short time they are allowed.

Traffic is so heavy, he notes, that crews often stop 10km from a village until all sections of the road are thick enough before breaking the trail to town.to town.