PEI's Engineering Marvel

PEI's Engineering Marvel

Islanders had never seen anything quite like it. On July 13, 1995, the world's largest floating crane, known as the Svanen, arrived off the coast of Prince Edward Island for work on the $1-billion bridge that has finally linked the province to mainland Canada. With some refitting, the Dutch-built Svanen stood at 102 m - three times as high as the Prince Edward Hotel, the Island's tallest building. Over the next 17 months, the Svanen methodically transported massive precast piers and girders - some weighing up to 7,500 tonnes - from the shoreline to an appropriate point along the Northumberland Strait. It then delicately raised the pieces in place, at heights of up to 60 m above the waterline. For a time, the Svanen was the talk of the Island, its movements eagerly tracked in hourly radio reports on CBC Charlottetown.

The Svanen, which has since moved on to other assignments, played a critical role in building the 13-km-long Confederation Bridge that now stretches across the Strait between Borden, P.E.I., and Jourimain Island, N.B. One of the world's longest bridges, Confederation is the longest one over waters that choke up with ice during winter months. And, by any standards, it is an engineering marvel, built on a gruelling 44-month schedule that left little room for error. In the process, the project won over many naysayers - people who said the bridge could never be built, at least not in the time frame set by the federal government and Strait Crossing Development Inc., the private consortium hired to construct the bridge. The doubters included many of the 2,400 people - more than 90 per cent of them Atlantic Canadians - employed by Strait Crossing. "We had to make believers out of our own workforce," says project director Paul Giannelia. "It wasn't until the spring of 1996, when all the phases were in full construction, that people started to say, 'Hey, this is really going to happen.' "

Under the contract signed between Ottawa and Strait Crossing in October, 1993, the developer had until June 1, 1997 to finish the bridge project. If it failed to meet that deadline, the company would have to assume the $42-million-a-year cost of operating the ferry service across Northumberland Strait. "From Day 1, we had 1,332 days to go and we had to make each one of those count," says Giannelia. And since winter ice made the Strait impossible to work in for up to five months of each year, the decision was made early on to precast more than 80 per cent of the bridge on land, then move it out in large segments as the waters cleared.

Work began in earnest in November, 1993, with the levelling of a 60-hectare potato farm, purchased by the consortium for more than $1 million - a four-month operation that entailed the removal of some 500,000 cubic metres of fill. This became the main fabrication yard, where an army of 1,500 workers spent the next two years constructing the bridge components. The bridge consists of 44 spans, each marked by a separate pier base, pier shaft and main girder. The pier bases range in height from 13 m to 40 m, depending on the depth of water they stand in. The main girders are 192 m long and weigh 7,500 tonnes - the heft of two modern destroyers.

The most challenging - and controversial - aspect of the project proved to be the pack ice that sometimes piles up in the Strait, forming cliffs up to 10 m high. If the bridge was built on vertical columns, the ice might jam up against it, potentially levelling the structure. Instead, each of the cone-shaped pier bases is capped with a shaft. The shafts feature a bell-shaped, concrete ice shield, half of it above the ice, the other half below. Designed to act like the bow of an icebreaker, the shields force the pack ice to ride up the side of the bridge and break apart.

Some bridge opponents remain skeptical about the ice shields - saying that over the past three winters ice in the Strait has been unusually light and so the piers have not really been tested. But Giannelia says that satellite photos show the shields are doing their job. He also points out that the piers are built to withstand the force of 3,000 tonnes of ice - or about 15 times the force that icebreakers working in the High Arctic ever have to contend with.

As well as ensuring that the bridge is structurally sound, designers had to consider how to make it safe to drive. No passing will be allowed on the two-lane bridge, which has emergency shoulders on both sides. Electronically posted speed limits will be lowered from the maximum of 80 km/h, depending on driving conditions. And a 1.1-m-high concrete barrier along either side will prevent drivers from having a clear view of the water below them - a measure intended to soothe those who suffer from height phobias. The barrier also serves as a partial shield in an area that is among the windiest in Canada and one given to ferocious snowstorms.

Which leads to another common concern among Islanders: will the bridge ever have to be shut down? The answer, according to project designer Ross Gilmour, is simple. "If you can get to the bridge, then it will be open," he says. "The conditions on the bridge will always be better than on the highways leading up to it." Depending on the bridge - as they now must - as their only link to the mainland during the long winter months, Islanders can be expected to hold him to his word.

Maclean's June 2, 1997