Construction New stabilizing technique being used to build $60-million interchange
SAINT JOHN - A new stabilizing technique using geo-piers is being employed for the first time in New Brunswick to build the $60-million One Mile House interchange, one of the most expensive ever built in the province.
Marc Thorne stands on what will be the westbound exit of the One Mile House interchange.
Work continues on the One Mile House Interchange on both sides of Highway 1. The $60-million project is one of the most expensive ever built in the province.
Thousands of geo-piers have been installed over the winter on marshland where the new west ramp to the interchange is being built off Allison Road, and they continue to be positioned into the marsh land beside Tim Hortons on Russell Street, where the span will touch down. Tiny flags in the ground mark the location of each geo-pier.
Geo-piers are stiff rock columns drilled deep into the earth's surface, down to a hard, non-yielding depth. They are used to support structures and reinforce the soil when the existing ground is unstable or wet.
Geo-piering is necessary to stabilize the new bridge which, in some spots, is being built on five to nine metres of silt, says Marc Thorne, an engineering technician with the province.
Without them or a similar stabilizer supporting the road, the span would fail, he said.
A huge part of the job's time and cost elements are due to the challenges the marshland presents, Thorne said.
Once built, the bridge, at an average height of 12 metres, will arch over the city from north to east for 600 metres, spanning Highway 1, the CNR railyard, Marsh Creek and Rothesay Avenue, touching down on a stretch of land that runs parallel to Russell Street.
It will be supported by about 17 kilomtres of steel piling.
"It's an enormous structure. I can see it," Thorne said, as he imagines the completed span.
The so-called One Mile House interchange, which is expected to be complete by the fall of 2012, derives its name for the section of land located along the railway, one mile east of the former Union Station.
Directly across from the westbound exit ramp that is being constructed, the eastbound exit is taking shape. Workers don't use geo-piers here because the silt isn't as deep, Thorne said. Instead, workers are using a method called "surcharge," which involves putting additional material atop the soil to compress the silt beneath.
Along the banks of the westbound exit ramp, the silt that has been removed is being spread and readied for hydroseeding, which has already begun in some sections.
Between Tim Hortons on Russell Street and Staples on Rothesay Avenue, Gulf Operator employees use an auger to drill holes six to eight metres deep and remove the silt. The holes are then filled with gravel that is screened to a specific size and mechanically compacted from above with heavy equipment.
As the rock is compacted after every foot of gravel is dumped, it exerts pressure on the walls of the hole and compresses the surrounding soil. The process is repeated all the way to the top of the hole.
To motorists driving by the project, it may not look like much is being accomplished at either site, Thorne says, but the time-consuming process is critical to the project's success. Two dozen operators and technicians work the two sites and, for precision, surveyors use a global positioning system like the one used to build the Confederation Bridge to Prince Edward Island.
As workers install geo-piers at the site of the northern on-ramp, they uncover bits of concrete, old curbs and gutters and other construction material that tell Thorne that, at the time the throughway was constructed about three decades ago, the long-term plan had been to construct what, today, is finally being built.
At the Russell Street site, an auger rips into a piece of old wood, prompting Thorne to speculate about its origin.
"It could be from an old building. There were buildings along here a hundred years ago. Or it could be a very old tree, 1,000 to 5,000 years old," he said.
So far, workers have uncovered nothing of any archeological significance, he said.
The first contract governing work on the new interchange will be done by the end of May, which means that ramps on the north end of the project will be completed to sub-grade and awaiting crushed rock and paving.
By the first of July, Transportation Minister Denis Landry is optimistic that the second phase will begin, which will include building the bridge's foundation: piers, footing and other components.
"It's really important for the municipality of Saint John," Landry said.
"I remember my colleague (Saint John East MLA) Roly MacIntyre advocating for that project so many times."
The One Mile House interchange is being built to route truck traffic away from the uptown and off city streets, straight to the industrial parks on the east side. The structure has become increasingly important with the energy projects that are poised to begin.
The interchange has long been advocated by the Saint John Board of Trade as a crucial piece of transportation infrastructure, allowing the city to better leverage investments and opportunities for new investments to the energy sector and enhance the development and growth of the Green Industrial Park, Bayside Drive properties and both the Grandview and McAllister industrial parks.
With Saint John positioned at the geographic centre of Atlantica, the board has said it is vital that highway infrastructure be improved to allow the region to compete on a global scale.
Published Friday May 1st, 2009 - Telegraph Journal