Geosynthetics in Stormwater Management
Types of Geosynthetic Materials
Geotextiles - Textiles
in the traditional sense, they consist of synthetic fibers so that
biodegradation is not a problem. They make up one of the two largest
groups of geosynthetics. These synthetic fibers are made into a flexible
fabric by standard weaving machinery or are matted together in a
random, or nonwoven, manner. The fabric is porous to water flow across
its manufactured plane and within its plane. There are at least 80
specific applications for geotextiles, but the fabric always performs at
least one of five discrete functions: separation, reinforcement,
filtration, drainage, or barrier to moisture.
Geomembranes - These
are the other largest group of geosynthetics. In sheer sales volume,
they are probably larger than geotextiles because their growth has been
stimulated by government regulations enacted in 1982. The materials
themselves are impervious thin sheets of rubber or plastic material used
primarily for linings and covers of liquid- or solid-storage
facilities. Thus, the primary function is always as a liquid or vapor
barrier. The range of applications, however, is very great, and at least
30 applications in civil engineering have been developed.
Geogrids - Plastics
formed into very open, gridlike configurations, geogrids have at least
25 applications, but they function almost exclusively as reinforcement
materials. They represent a rapidly growing segment within the
geosynthetics family, says Drexel University Professor Grace Hsuan.
Geonets - Also called "geospacers," these products are
usually formed by a continuous extrusion of parallel sets of polymeric
ribs at acute angles to one another. When the ribs are opened,
relatively large apertures are formed into a netlike configuration.
Their design function is completely within the drainage area, where they
have been used to convey fluids of all types, explains Hsuan.
Geosynthetic Clay Liners - Rolls
of thinly layered bentonite clay sandwiched between two geotextiles or
bonded to a geomembrane, these products are seeing use as a composite
component beneath a geomembrane or by themselves as primary or secondary
Geopipe - Perhaps
the original geosynthetic material still available today is buried
plastic pipe. Plastic pipe is being used in all aspects of geotechnical,
transportation, and environmental engineering with little design and
testing awareness, probably because of a general lack of formalized
training. The critical nature of leachate collection pipes coupled with
high compressive loads makes geopipe a bona fide member of the
geosynthetics family. Its function is clearly drainage.
Geocomposites - Combinations
of geotextile and geogrid; geogrid and geomembrane; geotextile,
geogrid, and geomembrane; or any one of these three materials with
another material (e.g., deformed plastic sheets, steel cables, or steel
anchors) are geocomposites. This exciting area brings out the best
creative efforts of the engineer, manufacturer, and contractor. The
application areas are numerous and growing steadily, and they encompass
the entire range of functions for geosynthetics: separation,
reinforcement, filtration, drainage, and liquid barrier.
"Geo-Others" - Innovations
in geosynthetics have created products that defy categorization. These
"geo-others" include such products as threaded soil masses, polymeric
anchors, and encapsulated soil cells. The geo-other name is not one
specific area, although similar to geocomposites, its primary function
is product-dependent and can be any of the five major functions of
geosynthetics, Hsuan explains. "The category is 'temporary housing,' if
you will, for any new products. When we determine the appropriate
family, we move it to 'permanent housing.'"
- Information provided by Geosynthetic Research Institute (www.drexel.edu/gri)