Tom Kuennen, Contributing Editor, Better Roads Magazine
In the May 2014 edition of Better Roads Magazine, Tom Kuennen defines the different types of geosynthetics, describes how they are used to enhance the road construction process, and outlines the results on roadways built with geosynthetics.
Road Science: Down to Earth
Geosynthetics of all types speed construction allowing bridges, highways to be built faster and enhance pavement performance.
Geosynthetics comprise a family of value-added products that allows bridges, highways and roads to be built faster, cheaper and to last longer.
Some geosynthetics enhance pavement longevity by separating good materials from bad, while others promote water flow from pavement structures as they facilitate drainage.
While most geosynthetics are planar or sheet-like in format, 3D geogrids add structural strength to a road section, permitting reduced depths of aggregate bases and bituminous lifts.
Family of geosynthetics
ASTM (2006) D 4439 defines a geosynthetic as a “planar prod-uct manufactured from a polymeric material used with soil, rock, earth or other geotechnical-related material as an integral part of a civil engineering project, structure or system.”
“Geosynthetics are man-made polymeric materials used for geotechnical application,” says the California Department of Transportation (Caltrans) in its Caltrans Geotechnical Manual. “They are used in lieu of conventional materials and often are more cost effective with equal or improved engineering performance.”
“Geosynthetics are materials that are incorporated into layers of rock or soil that can provide stabilization as well as separation of good material from lesser material,” says Aaron Schlessinger, E.I.T., southwest region manager for Tensar In-ternational Corp. “Still, others enhance drainage.”
There are four different types of geosynthetics:
- Geotextiles are either woven or nonwoven and used in civil engineering projects. Their mission is to prevent soils from migrating into drainage aggregate bases or pipes, while maintaining water flow through the system. They are used for filtration, drainage, separation, reinforcement and as a fluid barrier. A subset of geotextiles is paving fabrics used between pavement lifts.
- Geogrids are formed by a network of tensile elements with openings of sufficient size to allow interlock with the surrounding fill materials. They provide reinforce-ment or stabilization, with geogrids oriented such that their principal strength is in one direction (uniaxial), both directions (biaxial geogrids) or in three directions (triaxial).
- Geocomposites are a combination of two or more geo-synthetic materials, such as geotextiles with a core, and are used to enhance drainage, for example as prefabri-cated longitudinal edge drains or a layer feeding those drains.
- Geomembranes are a single, solid sheet of polymeric material, used in construction as an impermeable barrier.