Rolling out the —€˜green—€™ carpet

October 2009 » Products » GEOSYNTHETICS
From subsurface support to rooftop gardens, geosynthetics are proving versatile and cost-effective solutions to civil engineering problems.
Bob Drake

Geosynthetics comprise one of the broadest product categories increasingly used in civil engineering projects. Applications include erosion control; drainage; soil stabilization and retention; roadway pavement, base, and subgrade reinforcement; water containment; and green roof systems.

“Geosynthetics are increasingly being used successfully due to their ability to solve design problems at a cost savings to the owner,” said Steve Lothspeich, president, and Greg Kiggins, product manager, for Huesker. “Increased speed of construction and decreased cost provided by the specification of geosynthetics are preferred over conventional design solutions and materials.”

Lance Carter, P.E., technical director for Strata Systems, Inc., suggested three reasons for the increased use of geosynthetics. “First, there seems to be a greater awareness by the civil engineering community, both in design and specification,” he said. This is in part due to the effort undertaken by industry through education and awareness, but it also has a lot to do with the greater exposure to geosynthetics that young engineers receive during their college education.

“Secondly, cost plays a significant role in the specification of any product, and geosynthetics are often the most cost-effective solution. This is driven by an ever-increasing competitive market. There are just more geosynthetics suppliers today than in the past, and the customer is seeking the best solution at the best price. Geosynthetics can not only provide best price, but they often provide the best price with the fastest delivery and construction time.

“Lastly,” Carter said, “there is a continued focus on environmental and green issues. Geosynthetics can be inexpensive to transport, can often accommodate the use of local or onsite materials, and are durable products that provide a significant design life or extend the design life of the structure.”

The Presto Geoweb system stabilizes soft soils for vehicle access during wind farm construction. The system can be quickly deployed for immediate access, reduces material base requirements in half, and can sustain repeated heavy loads typical of construction vehicles, the company said.

Green solutions
Manufacturers attribute the growing market for geosynthetics, at least in part, to an emphasis on environmental issues. “The stormwater and green building sectors are the fastest growing areas in the past two years,” said Bill Handlos, P.E., CPESC, director of Presto Geosystems. “The Leadership in Energy and Environmental Design (LEED) and low-impact development (LID) influences are having a great impact upon projects, and that is growing the need for geosynthetics to solve the need for green elements in design. Porous pavements of all types (grass, aggregate, and even hard-surfaced) are growing in demand, even during the economic downturn. The benefit and cost-savings realized through reduction in stormwater collection systems and reduction in the need for stormwater ponds are tangible.”

Green initiatives often emphasize vegetation, where possible, for erosion control and slope stability, Carter said. But vegetation alone may not be enough. “The renewed interest in vegetated, steepened slopes is creating a similar renewed interest in a multitude of geosynthetic products,” Carter said, “including geogrid, erosion protection, geocell, filter fabric, and other geo-products related to vegetation growth or support.”

Accordingly, Strata Systems expanded its product line beyond its traditional geosynthetic products — Stratagrid geogrid reinforcement, StrataTex non-woven and woven geotextiles, and StrataDrain drainage composites — to include StrataSlope, StrataWall, Sleeve-It, and Strata/PRS Neoweb Geocell.

Handlos noted that although cellular confinement products such as Presto Geosystems’ Geoweb have been available to the marketplace for 30 years, the company is seeing a great increase in its use because it offers green solutions for slope and channel protection, earth retention, and load support. “We believe the growth is tied to a ‘discovery’ by the marketplace that geosynthetics can save money even as green building goals are met,” he said.

With increased emphasis on LEED certification for buildings, geosynthetics such as moisture barriers, moisture adsorption composites, drainage nets, nonwovens, and geogrids can provide key components in greenroof systems, adding as many as six LEED credits, according to Lothspeich and Kiggins. Huesker manufactures many of these products specifically designed for greenroof structures.

(left) Interest in vegetated, steepened slopes is increasing interest in geosynthetic products such as Strata Systems’ StrataSlope. (right) Fortrac geogrids from Huesker are PVC-coated, high-tenacity, polyester yarns constructed into a grid pattern and used to reinforce retaining walls, steepened slopes, and landfill liner systems.

“In many cases, it is impossible to create green solutions using legacy design approaches,” said Handlos. “Well-engineered solutions using properly tested and manufactured geosynthetics [products] allow for opportunities to cut project costs while meeting Clean Water Act-driven mandates, LEED, and LID project goals. It is a good idea for engineers and architects to familiarize themselves with alternative methods because a savvy, well-informed firm can better differentiate itself when competing for work.”

Design resources
Fortunately, there is help for civil engineers who lack familiarity or experience designing with geosynthetics. All three companies interviewed for this article provide online resources such as product data and project case studies, as well as design aids such as the following:

  • Strata Systems (www.geogrid.com) provides its StrataSlope design software to advance the use of geogrid reinforcement in steepened slope applications.
  • Huesker (www.huesker.com) offers two software programs for quick analysis of reinforced soil structures — ForWall for retaining walls and ForSlope for steepened slopes — and its engineering staff can provide design recommendations.
  • Presto Geosystems (www.prestogeo.com) offers a free design service for its products to introduce engineers to the use of geosynthetics.

But design resources alone are not sufficient for a successful project, according to Presto Geosystems’ Handlos. “The market always attracts fast followers who cannot meet quality standards but who often times simply copy standards publications and have not tested nor can offer proof of quality. It is essential that geosynthetics specifiers demand consistent quality and demand proof of testing and manufacturing quality,” he said.

“In the end,” Strata Systems’ Carter said, “geosynthetics are proving to be what they have always been promoted as — a cost-effective, sound engineering solution to conventional civil engineering problems.”


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