June 15, 2023 Ι Landscape Architecture Magazine
A few years ago, if you wanted to visit the site of Cascade Park in Chicago, designed by Claude Cormier + Associés (now CCxA), you’d find yourself near the shores of Lake Michigan at a 50-foot cliff overlooking a vacant pit bordered by a foreboding service road that led to the lakefront trail to the east. “The entire site was one giant hole,” says Matthew Strange, ASLA, a principal at Confluence, the landscape architect of record for the project. (Confluence was preceded by another landscape architecture firm of record, Living Habitats, from the design development phase through construction documents.) Elsewhere in the Lakeshore East high-rise district, there’s a park by OJB and residential skyscrapers by Studio Gang and others, built atop parking and amenity podiums that hoist the developments over the lake. But Cascade Park was the anomaly.
“Everything in Lakeshore East is built up, not down,” says Linda Kozloski, the creative design director of Lendlease, which developed the park and the three high-rises that will surround it. So when the development team committed to centering the project on a park, “there was nothing to excavate; there was nothing to dig.” But that meant the park’s visitors were situated 50 feet above the lake, which was just beyond DuSable Lake Shore Drive. Getting to the lake and its 18-mile lakefront trail meant navigating a dark underpass through the high-rise podiums and following it across an empty lot and under the elevated transit tangle of DuSable Lake Shore Drive. It was enough to stump the many visitors caught on Google Street View by Cormier’s staff. “The site became extremely introverted,” says Claude Cormier, FASLA. “Somehow you feel trapped when you are right in downtown Chicago.”
So, fixing this severed connection to one of Chicago’s greatest landscape amenities took center stage in what was ostensibly another chapter in Lakeshore East’s skyward development. “The landscape was the driving force of the whole site,” Cormier says.
Paul Schroeckenstein, an associate director at bKL Architecture, which designed the Lendlease high-rises and the park’s subsurface structure, agrees. “The thing that came first was generating that connection, and once we had that path, the buildings were [sited] around that path,” he says.
That connection is Cascade Park, a 0.8-acre, 360-foot-long “desire line,” says Kozloski, that steps down 50 feet over its entire length toward the lake with dramatic terracing framed by a pedestrian zigzag path and abundant shrub plantings. This rapid elevation change controls the transition from the elevated podium level to the ground level, revealing views of the lake and a clear path to get there. “We wanted the connection to be accessible and obvious,” says Schroeckenstein.
But that’s easier said than done. To get there, the design team would need approximately 90,000 cubic feet of ultralightweight geofoam to build the undergirding structure; a 40-foot steel decking cantilever to preserve ground-level circulation; and a complex, redundant drainage system to make sure what’s on top of the geofoam doesn’t splash into Lake Michigan.
In the 1990s, the site contained a golf course, but further back in its history, in the 19th century, it was an industrial rail yard. While it’s rare to have a vacant site along the lake anywhere near the city center, separating people from waterfront access with a tangle of transit infrastructure is very common in Chicago and many other cities. The loosely trapezoidal park is hemmed in by towers old and new, narrowing into a wedge as it moves east toward the water.
The entire park is built on a five-level parking podium, and the geofoam fills in the gaps between its structural slabs and the planting soil on top. Without the geofoam, “there’s no way that we could have had soil on that, because the weight would have been too much,” Cormier says. At 0.9 pounds per cubic foot, this filler foam is approximately 72 times lighter than dry soil. And there’s ample precedent for geofoam tectonics in the neighborhood. Maggie Daley Park, where Michael Van Valkenburgh Associates used more than two million cubic feet of geofoam to top a parking structure with play landforms, is one block away (see “We Got Fun. And Foam,” LAM, November 2015).
Topped by sloping concrete decking, the parking structure’s five levels, designed by bKL and structural engineers Thornton Tomasetti, step up in nine-foot increments. The south section of the park cantilevers over a bike and pedestrian path, as well as a service drive for the tower to the south. This section’s 9,000 square feet of steel decking is supported by Y-shaped steel columns. The edge pulls back as it moves eastward, to allow more light to reach down to the trail and service drive. This thin, cantilevered deck turns the circulation west of the park from an ominous, dark tunnel reminiscent of Chicago’s subterranean freeways into a more hospitable, briefly occluded horizon.
A series of nine terraces defines the topography of the site, alternating a 2:1 slope ratio with a nearly level 5 percent slope where visitors can plop down a picnic blanket or throw a Frisbee. (“Nothing is flat in this park,” Schroeckenstein observes.) A paved, zigzag path weaves in and out of the flatter terraces, with shrubs such as horizontal cotoneaster and Celtic Pride Siberian cypress planted in between its triangular wedges. A more direct sloped and staired path runs along the northern edge of the park.
Along the zigzag path, sculptural collections of tree stumps, limestone boulders, and concrete blocks of different heights riff on the topography of the park and provide subtle elements good for a stretch, stairstep, or sit. “They have a ‘play’ quality to them, and kids can certainly play on them, but they don’t read as playgrounds,” Strange says.
The northern edge of the park is dominated by a one-and-a-half-story planted berm that shields a retaining wall. “We tried to make it as steep as possible to hide as much of the concrete [as we could],” Cormier says. Here, bright red dogwood stands out in late fall, echoed by Redpointe maple trees along the northern path. The shorter south retaining wall is screened by Boston ivy, Virginia creeper, and Iowa juniper, which all add much-needed texture to a material palette that’s heavy on lawns and paved circulation. Throughout, it’s a shrub-heavy selection of plants without perennials or grasses, a rarity for contemporary Chicago parks.
Strange says that because of the “stair-stepping effect” of the geofoam under the soil, the range of soil depth varies, from up to four feet for tree plantings to a bit less than a foot in parts of the lawn. To get these desired soil depths, certain plantings called for basins to be beveled out of the top of the geofoam. “We were the ones always pushing for more soil, more soil, more soil,” Cormier says.
The geofoam was slotted in between the landscape parameters established by Confluence and bKL’s structure beneath. “We gave the contractor [BrightView] those two planes with soil depths, and they took that and figured out the geofoam that needs to exist between those two layers,” Schroeckenstein says. The 5 percent slope areas sit on top of geofoam plateaus, which then step down to the next plateau shelf. The smallest pieces of geofoam are wedges no larger than a fist, while others are as large as a go-kart, but when they come together, they create a massive foam ramp, perfect for conveying people—or water. “There was a real concern about drainage,” Strange says. “You can just imagine the amount of water that’s flowing down the 40 feet or so of grade change down that hill.”
Managing rainfall before it could become torrents of stormwater that erode the park and saturate its lawns was one of the project’s most difficult technical challenges. The solution relied on a two-level system with four main elements. The geofoam is topped with a permeable drainage mat, and vertical gaps between geofoam pieces below this mat transmit water downward to another permeable drain mat at the structural slab level, which is protected by a waterproof membrane.
Between the geofoam layers and the soil, perforated drain-tile pipes wrapped in permeable aggregate gravel are located at the low point of terraced slopes, collecting water that permeates the soil. Solid drain-tile pipes collect water from this primary drainage system and move it down the slope to vertical drains, other horizontal drain elements, and a separate subsurface drain system. This second level of perforated subsurface drain-tile pipe offers a “belt and suspenders approach,” says Strange, that moves water that gets trapped at the structural slab layer. Eventually, the stormwater is deposited into the sewer system via a network of vertical drains.
It’s a complex journey masked by the architecture and landscape, but what is no longer hidden is how to navigate to the lakefront. “When you’re there, you know without a sign that you can get to the edge,” Cormier says.
The park is wildly popular with joggers and dog owners (there is a small, fenced-in dog run at the eastern edge), and there’s room for potential commercial space at the toe of the parking garage. The cross-disciplinary collaboration Schroeckenstein encountered on the way to getting people to the lakefront and the successive stacking of engineering, architecture, and landscape were what defined this project for him. “The towers are nice and beautiful and all that, but the park is unique and had its own series of complicated geometric challenges,” he says. “I shouldn’t say this as an architect, but [the park] was the most exciting part of the project.”