Posts Tagged ‘geosynthetics’

Geosynthetic Applications

October 19, 2010

Primary Functions Of Geosynthetics

Geosynthetics are generally designed for a particular application by considering the primary function that can be provided.  As seen in the accompanying table there are five primary functions given, but some groups suggest even more.

Separation is the placement of a flexible geosynthetic material, like a porous geotextile, between dissimilar materials so that the integrity and functioning of both materials can remain intact or even be improved.  Paved roads, unpaved roads, and railroad bases are common applications.  Also, the use of thick nonwoven geotextiles for cushioning and protection of geomembranes is in this category.  In addition, for most applications of geofoam, separation is the major function.

Reinforcement is the synergistic improvement of a total system’s strength created by the introduction of a geotextile, geogrid or geocell (all of which are good in tension) into a soil (that is good in compression, but poor in tension) or other disjointed and separated material.  Applications of this function are in mechanically stabilized and retained earth walls and steep soil slopes; they can be combined with masonry facings to create vertical retaining walls.  Also involved is the application of basal reinforcement over soft soils and over deep foundations for embankments and heavy surface loadings.  Stiff polymer geogrids and geocells do not have to be held in tension to provide soil reinforcement, unlike geotextiles.  Stiff 2D geogrid and 3D geocells interlock with the aggregate particles and the reinforcement mechanism is one of confinement of the aggregate.  The resulting mechanically stabilized aggregate layer exhibits improved load bearing performance.  Stiff polymer geogrids, with rectangular or triangular apertures, in addition to three-dimensional geocells made from new polymeric alloys are also increasingly specified in unpaved and paved roadways, load platforms and railway ballast, where the improved load bearing characteristics significantly reduce the requirements for high quality, imported aggregate fills, thus reducing the carbon footprint of the construction.

 

Identification of the Usual Primary Function for Each Type of Geosynthetic

 

Filtration is the equilibrium soil-to-geotextile interaction that allows for adequate liquid flow without soil loss, across the plane of the geotextile over a service lifetime compatible with the application under consideration.  Filtration applications are highway underdrain systems, retaining wall drainage, landfill leachate collection systems, as silt fences and curtains, and as flexible forms for bags, tubes and containers.

Drainage is the equilibrium soil-to-geosynthetic system that allows for adequate liquid flow without soil loss, within the plane of the geosynthetic over a service lifetime compatible with the application under consideration.  Geopipe highlights this function, and also geonets, geocomposites and (to a lesser extent) geotextiles.  Drainage applications for these different geosynthetics are retaining walls, sport fields, dams, canals, reservoirs, and capillary breaks. Also to be noted is that sheet, edge and wick drains are geocomposites used for various soil and rock drainage situations.

Containment involves geomembranes, geosynthetic clay liners, or some geocomposites which function as liquid or gas barriers.  Landfill liners and covers make critical use of these geosynthetics.  All hydraulic applications (tunnels, dams, canals, reservoir liners, and floating covers) use these geosynthetics as well.

Geosynthetics In Agricultural Applications

August 3, 2010

Agricultural Use Of Geosynthetics

Agricultural use of geosynthetics is one of the fastest growing market segments worldwide.  The earliest geosynthetics applications were for on farm use and some of the earliest specifications were directed at agricultural use of pond linings.  These early uses included the lining of ditches to help save valuable water as well as the lining of farm ponds and water harvesting catchments in the arid regions of the world.

Today, there is a wide variety of applications ranging from covered and uncovered ditch linings and ponds to protection of the groundwater and surface waters that are being polluted by animal waste.  The use of geosynthetics and in particular geomembranes on the farm has come a long way and has grown significantly in recent years, especially with more stringent governmental legislation as well as public awareness through programs such as those developed by the USDA/NRCS, U.S. EPA and governmental agencies in other countries.

Containment As A Requirement

Potable water sources are becoming more and more scarce and water is becoming more costly.  The requirement to provide a barrier against high rates of water seepage loss is already a reality in many more areas than just the arid and semiarid regions of the world.  And, just as water is important to conserve, it is even more important to environmentally protect surface and groundwater sources from pollution due to animal waste and the air we breathe from noxious gases and odors.  Again, containment with a reliable time proven method is a requirement, not just an option due to  environmental legislation in many parts of the world.

Shown here: Anaerobic digesters with waste lagoon

Geosynthetics will provide a reliable cost effective alternative to traditional compacted soil and clay liners that provide much less in seepage control, are highly variable in quality and may not be acceptable for design and regulatory compliance.  Although geomembranes are the primary type for use as a barrier or odor control cover, other geosynthetics are used in conjunction with geomembranes and include geotextiles, geo-composites, and geonets.

Animal Waste Lagoon Liners

Animal waste lagoons contribute to the pollution of ground and surface waters worldwide.  To control waste seepage, compacted earth linings as well as geosynthetics are utilized.  However, with the increasing concern over pollution and governmental legislation, the use of geosynthetics has been increasing very rapidly.  In particular, exposed geo-membranes, geo-membranes with soil cover and GCL’s with soil cover are currently being used.  In addition, geo-textiles and geo-net composites are utilized for protection / gas transmission.

Animal Waste Odor Control Covers

A growing number of scientists and public health officials have traced a variety of health problems to vast amounts of concentrated animal waste which emit toxic gases such as hydrogen sulfide and ammonia.  Odor control covers can be a low cost geomembrane or coated fabric or they can be a more expensive engineered floating geo-composite cover system dependent on the design and criticality of the containment.

Shown here: Irrigation canal

Water Conveyance
Geosynthetics and most notably geomembranes have been used for decades in preserving and transporting clean water for on farm use.  The conveyance of water in ditches, laterals and main canals for delivery to crops is as common as on farm water storage tanks and ponds.  However, water is becoming more and more scarce and more costly especially with the drought conditions in many parts of the World.  Seepage loss in canals and ditches can approach 30 to 50% but loss of valuable water can be eliminated with the use of geosynthetics as lining systems.  Both soil covered and exposed geomembranes are used extensively in the lining of both new and old canals that require rehabilitation.

In addition, old cracked concrete lined canals have lost their effectiveness over the years and are being replaced or repaired with geomembranes.  Water conveyance systems utilize other geosynthetics in conjunction with geomembranes such as protection geo-textiles, geocomposites and geo-grids.

Water Containment
Water containment in ponds and concrete tanks for on farm use is just as important as water conveyance in that seepage and loss of valuable water should be minimized, especially for remote ponds and tanks.  Soil covered geomembranes and GCL’s are used for the construction of new or the rehabilitation of old ponds.  Exposed geomembranes are used to re-line old stock water concrete tanks or to line

Anaerobic Digesters
Anaerobic digesters are used to rapidly decompose animal waste in a controlled environment thus allowing the recovery and use of methane-rich low Btu biogas.  Biogas is used to fuel combined heat and power (CHP) generators that produce on farm electricity, process heat and domestic hot water.  They are also a viable method of waste management due to the fact that both bottom lining systems as described above and flexible cover systems are used.  With every digester constructed, geosynthetics are used to either line the anaerobic lagoon or cover the lagoon for collection of biogas. The number of operating digesters is rapidly increasing worldwide as government funding is becoming available for farm installations.

Data provided with compliments http://www.geosyntheticssociety.org and R. Frobel.

Types of Geosynthetic Materials

May 20, 2010

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 liners.

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.  The category is ‘temporary housing,’ if you will, for any new products.  When it is determined the appropriate family, it is moved to “permanent housing.'”