We interviewed Landscape Architect Jeffrey Bruce, consultant to Michael Vergason Landscape Architects, Ltd., to get the scoop on the specialty soil he has formulated for Tisch Park. But first, a crash course on what’s happened so far below the (future) surface of the park.
If you’re closely following the East End Transformation’s progress, either in person or via the webcams, it’s evident that change happens on the site every day.
Over the summer, for example, the underground parking garage took shape with its exposed, white concrete lid:
And that mysterious black square that appeared on the garage lid in late July? No, not the start of a skating rink. A test sample of the waterproofing system that eventually would cover the entire lid surface:
Next came the “choker grit” — i.e the gravel — an essential component for proper water drainage:
Then came the sand. For a brief, glorious moment, we had our own “Brookings Beach.”
And soon will come the soil. That’s engineered, scientific soil, not dirt. Make no mistake — they’re not the same thing. Just ask a soil scientist.
“Dirt is stuff that lands on your floor that you need to sweep up,” said Bruce, whose firm Jeffrey L. Bruce & Co., specializes in green infrastructure. “The technical term for what we’re talking about is soil. And the right soil can make every difference. It can overcome manmade and natural stressors and contribute to the landscape and the environment.”
Below are some excerpts from our conversation with Bruce regarding Tisch Park’s engineered soil.
Tisch Park will be an expansive landscape of lawns, trees and rain gardens. As the university’s “front yard,” it will be a high-profile, high-traffic area. What about your soil mix ensures it will thrive?
We considered many factors when thinking about the soil and how it should perform. We wanted a soil to support large trees. We also needed a soil that could handle a lot of wear from special events and day-to-day activities. Naturally occurring soils aren’t up to that task. They’re highly variable and easily degraded by intense use. So we created a blend that is a mix of sand and organic matter. The organics provide nutrients so plants can grow. The organic matter also influences soil moisture. In soil design, we are trying to accomplish two different objectives. You want the soil to be free-draining so excess water moves out and away. But we want to maintain enough water for plant growth.
Organic matter? As in composting? What kind of compost do you use?
Compost can be made from a number of waste products such as animal waste, food waste, clippings and leaves, filter cakes from wastewater treatment. Each type of compost has different contaminants and challenges — from too much nitrogen to not enough of the right organic matter. It’s a challenge to get the right mix.
Your soil mix for WashU will live on top of a parking garage. Are there other unconventional places where you’ve been challenged to help things grow?
I can think of two projects. We recently completed the renovation of Navy Pier in Chicago, where soil for shade trees was on top of the pier running over a half-mile into Lake Michigan. And we’ve put soil on top of a cruise ship to create a natural grass sundeck. It was a challenge because if you put much weight on top of a cruise ship it will increase the chance of it rolling over. So there, the soil was only one-half of an inch. For most high-use situations, like the campus here, we’ll put down five to 12 inches of soil. The tree beds are deeper, about 24 inches. And the trees in the allées will have 36 to 42 inches. That’s over 20,000 cubic yards of soil.