Innovative Planter Design
adds Green Space to Chicago Plaza
By John Albanese, Dan Salsinger, Patricia Stetler
The Plaza at One North Wacker Drive includes nine domes (below) that line the sidewalk. Three additional domes (right) are at the building entrance. The three domes at the entrance are each designed with a raised planter sphere and two encircling rings. The outer ring contains eight trees and the inner ring is a reflection pool.
One man’s conceptual vision can become another man’s construction challenge. Chicago-based landscape contractor, Walsh Landscape Construction was given the opportunity recently to partner with Chicago-based John Buck Company and Peter Walker and Partners, Berkley, California, distinguished landscape architectural consultants, on a recent beautification project in downtown Chicago at the new One North Wacker Drive, an award-winning building designed by Lohan, Caprile, Goettsch Architects. Walsh Landscape was both honored and challenged by the opportunity.
The green-leafed sedum kamchaticum can be seen covering the finished structure. Below, the green leaves of the plant are displayed. However, to the right, are sedum’s yellow flowers, which bloom in the spring and turn red in the fall.
The renowned Peter Walker and Partners has earned a reputation for challenging traditional design by producing landscapes that are both unique and timeless. The company’s distinctive signature is transforming landscapes by exploring relationships between art, culture and context. The firm has collaborated on many prominent projects worldwide, including the Harima Science Garden City and Town Park in Japan and the Millennium Park for the 2000 Olympics in Australia.
Peter Walker’s unique vision was recently revealed in the design of One North Wacker Plaza in the city of Chicago. The conceptual plan for the new Plaza would include sphere-shaped raised planters integrated with a series of granite seating areas and water features. The repetitive use of the spherical shaped domes was chosen to create green aesthetics and add dimension and interest to the overall Plaza atmosphere. Columnar shade trees would provide the centerpiece to the large raised circular planters. At the base of the trees, half spheres were included to create mound-like planting beds filled with a low-growing manicured ground cover. At the front of the Plaza building, three smaller domed planters were designed with two encircling rings – an interior reflection pool and exterior planter containing small trees.
The Concept Challenge
Building the project, however, would prove to be no small task. Walsh Landscape Construction was hired to assist with the research and development required to bring this concept to life. Partnering with a number of suppliers and manufacturers, the company explored a variety of products on the market with which to construct these unique planting environments.
Nine crewmembers finished the construction of the twelve planter spheres in six weeks.
John Albanese, Project Manager for Walsh Landscape, identified a number of issues and requirements addressed by the research:
- The need to engineer a fabricated structure that could be reproduced to achieve the exact size, shape and dimension for each planter while having the stability and strength to support the weight of cell-like material filled with planting medium and ground cover.
- The structure needed to be constructed of material that could be dissembled to allow accessibility for tree care and maintenance. Also, once this planting environment was achieved, horticultural considerations had to be addressed for the columnar shade tree in terms of moisture, oxygen and the ability to properly respirate gas in an urban setting.
- Plant selection was critical in order to choose material hardy to this area, and durable enough to survive this unique urban situation. Irrigation and drainage needs were also addressed to ensure a healthy plant environment.
These were just some of the issues that needed to be addressed in creating the successful landscape.
The Construction Challenge
While Walker’s firm provided the conceptual design for the planters, developing the actual construction design, prototype and the construction logistics were left to Walsh Landscape Construction. Integration of contractor details with the plaza construction was performed by Steve Nilles of Lohan, Caprile, Goetsch. Albanese contacted Dan Salsinger, Ero-Tex, an erosion control and textile material specialist, for ideas on fabricating the planter structures so they could sustain the soil and ground cover. Albanese inquired about utilizing the perforated Geoweb® cellular confinement system (geocell) to stabilize the infill material over each sphere. The geocell system is a plastic honeycomb-like structure that stabilizes infill material in its network of interconnected cells.
The repetitious spherical shape of the domes was chosen to add dimension and points of interest throughout the plaza.
The geocell system has been utilized in the landscape architecture and civil engineering markets since the early 1980’s for stabilizing soils in load support, slope and channel protection and earth retention applications. Emerging environmental concerns and regulations have led to the increased use of the geocell system for living solutions.
“The specific pattern of perforations in the geocell material will allow the ground cover to lockup within the cell walls for a more stable, vegetated system,” explains Salsinger. “The cell wall holes let water drain laterally, which should help to reduce any runoff. The system’s flexibility is ideal for conforming to the dome’s contour without losing any confinement ability or structural strength.”
The cell holes pictured here drain laterally and inward. This design helps to reduce runoff and gives the system flexibility for conforming to the contour of the dome without compromising structural strength.
Albanese experimented with a variety of construction materials to mock-up a full-scale prototype. The final prototype was fabricated with stainless steel frames with removable sections so the interior tree could be replaced if needed.
“When constructing the prototype model, several difficulties were encountered,” recounts Albanese. “The irrigation layout needed to be configured so that the valves were buried in the cage, but would still be accessible for maintenance or repair if required. The centerpiece columnar trees would need to be anchored without the anchoring getting in the way. A combination of stainless steel chains, cables, and stainless steel angle iron was finally used to accomplish this task.”
Quarter-inch stainless steel was used to create the quarter sections of the spheres, each sphere weighing 175 lbs. After the quarter sections were fastened together with 3/8 inch bolts, the spheres were covered with a Kintex SF40 spun-bonded nonwoven geotextile to help hold the soil in the cells and allow water flow through the plane of the fabric. The fabric type is also heat bonded which provides additional backing of the cells.
The geocell system is a plastic honeycomb-like structure that stabilizes infill material in its network of interconnected cells.
A 100 mm (4 inch) deep geocell section was placed over the geotextile and attached to the sphere’s frame with pull ties inserted through the perforations and around the cage members. The model was ideally planned so that one standard geocell panel would cover the perimeter of each small sphere. Next, a drip irrigation system was installed for the center trees and pop-up misters for the plantings outside the sphere. After installing the irrigation systems, soil was brought in and the interior of the sphere was hand filled to the top of the tree root ball. Stone back fill was placed over the soil from the top of the tree ball, to almost the top of the sphere.
“There was a good deal of research done to determine what plant material could withstand the conditions of the urban environment of downtown Chicago,” states Albanese. “Prolonged exposure to building shade, wind, pollution, and extremes in climate and moisture conditions were important factors in determining the suitability and ultimate sustainability of the plants and trees.”
The centerpiece trees were anchored with a combination of stainless steel chains, cables and angle iron.
After evaluating the aesthetics of a variety of plantings in the prototype, Walsh Landscape; Lohan , Caprile , Goettsch Architects and developer, John Buck, decided on the ground cover Sedum Kamchaticum. This fast growing, glossy green-leafed plant produces yellow flowers in the spring and turns red in the fall. The growing medium was placed by hand in the individual cells of the geocell section and then sedum plants added. To insulate and protect the ground cover through the winter, evergreen boughs were placed over the planter and secured with wiring. Once vegetation begins the germination process in early spring, the boughs are removed.
The completed Plaza at One North Wacker Drive includes nine large planters and three small planters at the building entrance. The three small planters are designed which each planter sphere raised and centered in the middle of an interior pool. An exterior planter containing eight smaller trees surrounds the pool. A granite pedestrian seating area provided by the W.R. Weis Company encircles the planters and completes the space.
Workers near completion of one of the three entrance planters. The rings encircling the dome can clearly be identified. Additionally, a granite pedestrian seating area encircles the planter and completes the space.
These planters were specifically designed with a unique, aesthetic element,” explains Albanese. “Each planter is surrounded by a pool of water, creating a mirror effect that reflects the half sphere. As you look into the water, the reflection creates the image of a completely round sphere.”
Working with nine crewmembers from Walsh Landscape, construction of the twelve planter spheres was completed in about 4-6 weeks. The vision and design concept were conceived by the illustrious Peter Walker and Partners firm. Implementation of that design was accomplished with integrity by the Walsh Landscape Construction team. At the end of the project, Walsh Landscape received a most gratifying message from the notable landscape architectural firm – “thanks for making our concept a reality.”
Authored by John Albanese, Walsh Landscape Construction, Daniel Salsinger, Ero-Tex and Patricia Stelter, Presto Products Company. Information used with permission from Walsh Landscape Construction.