Posts Tagged ‘geosynthetics applications’

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.

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Research On Geosynthetic Materials

October 5, 2010

Geosynthetic Applications

Geosynthetics are sheet polymeric materials used in civil engineering.  They have been used since the 1970s in geotechnical (soil) structures for functions such as separation, reinforcement, drainage, filtration, liquid containment and as gas barriers.  In practice this has included applications as diverse as reinforcement in the walls of the Pentagon, reservoir liners, canal liners, road reinforcement, retaining walls, sports fields, dams, landfill liners, embankment stabilization, tree containers, chemical tank liners, and as base and roofing membranes for new buildings.  There is an increasing trend to use recyclates in geosynthetics, particularly PET from bottle recovery.

Geosynthetics often play critical roles in civil engineering and it is important that the materials in use can withstand the physical and chemical pressures of the environment. These range from resistance to leachates from landfill to resistance to root damage in soil liners, as well as standard properties such as resistance to creep, oxidation and UV light, and tensile strength.  This has resulted in sets of test standards being developed by the EU, ISO, BSI and ASTM.

There are several main categories of geosynthetics: geotextiles, geomembranes, geosynthetic clay liners, geogrids and geonets.  This review discusses the polymers used in each type, production methods, test methods and applications.

Geotextiles are permeable fabrics comprising around 75% of all geosynthetics.  Globally, 1,400 million square metres are used each year and the trend in consumption is upwards.  Polypropylene comprises the bulk of this with polyester as the second most commonly used material, Polymer properties and economics decide on material choice. Natural fibers are being used where durability is less important.

Geomembranes are thin flexible sheets with very low permeability.  They are used as barriers to the passage of gases of liquids.  Butyl rubber was the first material used, but now PVC and polyethylene are the most common materials.  Uses include landfill odor control, facing of dams and reservoir liners.

Geosynthetic clay liners are structures containing a clay layer and used as water barriers.  Thus the main component is a clay mineral, bentonite.  They can be used instead of geomembranes or as a second line of defense to geomembranes.

Geogrids are sheets of tensile elements with a regular network of apertures, usually constructed of polyethylene, polypropylene or polyester.  The most common use is for reinforcement of unstable soil and waste masses.

Geonets are composite grid constructions used for drainage capabilities.  Usually a geotextile is used as the drainage core with an upper and lower section of geomembrane.

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.