By Ron Bygness
In the October/November 2011 issue of Geosynthetics, we looked at how a popular section of Toronto was being redeveloped, thanks to the drainage power of the mighty little wick drain.
The article “On the waterfront (in Toronto)” specifically featured the West Don Lands, an 80-acre area situated just inland from what developers call East Bayfront, home of the new George Brown Waterfront Health Sciences Campus.
This section of waterfront and near-waterfront in Toronto is best described as “geotechnically unsound.” A river used to run through the land where the new George Brown campus now sits, and more than 30% of that building’s substructure is below the water level of adjacent Lake Ontario.
Furthermore, much of the area’s soil had been saturated with the worst-of-the-worst kind of contamination: tanneries, a polychlorinated biphenyl (PCB) storage facility, and underground fuel tanks. After removing the contaminated soil, construction crews capped the site with 5ft. (1.5m) of clean fill, then installed 27,000 nonwoven geotextile-wrapped wick drains that provided geotechnical soil consolidation for the entire redevelopment area.
Then a layer of sand was placed to bury the tops of the wicks, followed by a layer of soil to the elevation needed for flood control—about 4m (13ft) higher than existing grade. Portions of the site got another layer of soil—a surcharge as much as 7m (23ft) thick—placed there for its weight. The surcharge presses down on the underground pockets of old marsh.
“It’s like taking the sponge and squeezing out the water,” said a program manager on the project. To continue the analogy, the water is squeezed out through the 27,000 straws (the wicks) and is naturally forced into the sand layer, where it can dissipate into the surrounding soil. That process took place quickly—about eight weeks—and it made the subterranean soils dry and receptive for development.
Today the wicks are completely buried and the surcharge soil is still there too. Through the innovative use of geotextile-clad perforated pipe, the swampiest portion of this former industrial site is now transformed into a home for play areas, trails, housing, and office and retail buildings serving residents in Toronto’s newest urban neighborhood.
The 330,000-square-foot, $175-million George Brown campus opened for business last September after only 17 months of construction.