The imagination of the designer and the skills of the engineer combine for unique geosynthetics applications, from subsurface to rooftop.
By Andrew Aho
Geosynthetic materials entered the marketplace during the last third of the 20th century, and since then have increasingly become a staple for landscape architects and designers. By incorporating the creative use of geosynthetics, landscape projects are limited only by the imagination of the designer and the application skills of the engineer. Gravity and other physical laws notwithstanding, the designer’s scope has expanded greatly through the use of geosynthetics.
Whether the project involves the simple elegance of a sculpted river bank or the attractive, but highly functional, aesthetics of natural barriers of protection for federal buildings … from the hobbit village-like effect of a green roof to cleverly constructed temporary parking facilities, geosynthetic materials allow engineers, designers, and landscape architects to do things that would simply not be possible using only natural materials.
Geosynthetics and landscape design
Geosynthetics are made of the same synthetic polymers that are so much a part of our everyday consumption and comfort—in fact, the general public may refer to them as plastics. But when these polymers are combined with the imagination of a designer and the skills of an engineer, we can literally reshape the earth to accommodate our needs. Generally, the function of geosynthetic materials is to separate, reinforce, filter, drain, and contain earth and water.
More than $4 billion were spent on geosynthetics worldwide in 2003, according to Robert M. Koerner in Designing with Geosynthetics (Prentice-Hall, 2005). He estimated that geosynthetics are growing at a rate of 5% annually when used in transportation and environmental applications. Use in the geotechnical sector is growing by 10% per year, and by 15% per year in hydraulics and private development. It is also estimated that only 20% of the marketplace has been tapped for geosynthetics applications, Koerner noted.
That sculptured river bank, the building protection barriers, a temporary parking facility, and a green roof were all projects that were expertly presented at the 2005 IFAI Expo Educational Track, “Geosynthetic Materials for Landscape Architecture.” The eclectic collection of presentations and wide variety of applications represented just a small slice of the market potential for the use of geosynthetics in the landscaping and construction industries.
Todd Croke of North American Green in Evansville, Ind., highlighted the use of geosynthetic reinforcement materials in erosion-control projects. The aesthetically acclaimed White River project in Indiana included erosion-control mats that combine natural fibers and a geonet that allows vegetation to be established on the relatively steep slope. The geonet keeps that vegetation in place; the roots grow through the geonet and form a stabilized erosion-control blanket. The reinforcement was needed because of hydraulic pressures from both runoff into the river and the occasional flooding onto its banks. According to Croke, the geonet helps keep the vegetation root system in place and also creates a green, park-like appearance along the riverbank.
The casual observer is not generally aware of the presence of geosynthetics because they are usually buried in the earth. We simply see a grassy hillside next to the walking path by the river. Or, in the case of the Federal Building and U.S. Courthouse in Minneapolis, we observe some curious green mounds in front of the building.
The mounds in front of the Federal Building in downtown Minneapolis were put in place in response to new security measures required in the design of federal buildings since the bombing of the Oklahoma City Federal Building in 1995. Steve Gale of Gale-Tec Engineering Inc., Wayzata, Minn., was the engineer on this novel design that used geosynthetic material as part of a project aimed at helping to protect a building from a possible terrorist act. Gale noted that the intent of this project was to create a visual obstacle and security barrier to the front of the building. The mounds appear to be solid, grassy knobs protruding from the concrete deck. They are, however, actually made with a core of geofoam, a lightweight geosynthetic material, with a sand fill held in place with geogrids. The sod is attached to the geosynthetic materials with wire, and small trees are set in a planter in the 5- to 8-ft. mounds to create a visual impression of a tree-studded hillside.
Another project presents a less natural finished appearance but addresses a growing problem: Imagine having 9,000 new cars and no place to park them. This was the challenge that Ford Motor Co.-Canada presented to Ian Peggs of I-Corp International of Ocean Ridge, Fla.
Dr. Peggs came up with a productive, reuseable, geosynthetic answer for Ford’s situation: Instead of paving paradise and putting up a parking lot, his solution was to roll out 57 acres of geosynthetics to produce a temporary parking site. He chose a geocomposite, a geosynthetic material of more than one component; in this case, a biaxial geonet sandwiched between polypropylene geotextiles. This material provided one large, clean, stable, fire-retardant surface that was UV-resistant and also permeable, so there was no change in the natural water runoff.
After minor scraping of topsoil in a field near the Ford plant in Oakville, Ontario, lengths of the geocomposites were welded, stretched, and anchored. Parking stalls and traffic lines were painted on the surface, and Ford had its 9,000-vehicle, temporary parking facility. After three months of duty in Canada, the “parking lot” was rolled up, transported, and installed in a field by another Ford plant near Chicago.
Moving from bottom to top, one of the more unusual applications of geosynthetics is in the building of green roofs for residential and commercial structures. A green roof is planted with vegetation to increase the value of a structure by extending the service life of the roof; not only do green roofs produce energy savings, they can mitigate stormwater damage by serving as a natural barrier that allows rainwater to percolate through the vegetation, much as it does on the ground.
Charlie Miller of Roofscapes Inc. in Philadelphia explained that geosynthetics are an important component of green-roof construction. Geonets are used as drainage devices on green roofs; geomembranes serve as waterproofing liners and barriers to contain plant roots; geotextiles are used for separation of soil materials and for water transmission; geogrids provide support and reinforcement on green roofs with slopes. Geocomposites are also used, and provide multiple functions, including drainage, separation and protection.
Although relatively common in Europe, green roofs have yet to gain much popularity in the North American marketplace. However, some successful North American green-roof projects include Chicago City Hall, the World Trade Center in Boston, the Heinz 57 Center in Pittsburgh, and the Central Library in Kansas City, Mo.
From riverbank to rooftop, homeland security to portable parking lots, geosynthetics are providing 21st century answers.
Andrew Aho is managing director of the Geosynthetic Materials Association, a division of the Industrial Fabrics Association International.
North American Green Inc., Evansville, Ind., +1 812 867 6632, 800 772 2040; fax +1 812 867 0247, Web site: www.nagreen.com
Roofscapes Inc., Philadelphia, Pa., +1 215 247 8784, fax +1 215 247 4659 Web site: www.roofscapes.com