The use of geogrids in pavements and foundations is well established now and the benefits would be known by most engineers and roading contractors. However, are you clear on which geogrid type to use, and whether a triaxial or a biaxial geogrid will be best for your application?
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Firstly, let&#;s look at what these terms mean. A uniaxial geogrid is one which has its main strength, or its design strength in one direction, typically the roll direction. It will have some inherent strength in the cross direction as well but this is not generally considered in design. These are mostly used for wall, slope and embankment reinforcement. A biaxial grid has its design strength in two directions, both machine and cross direction. These are the type of grids that have been used for pavement
A biaxial grid has its design strength in two directions, both machine and cross direction. These are the type of grids that have been used for pavement stabilisation and bearing capacity improvement for well over 30 years now with excellent results.
The word triaxial is defined as &#;Having or relating to three axes&#; which in terms of a geogrid would indicate that the design strength or stiffness would be in 3 directions. Strength, or more importantly stiffness at low strain can be measured in 3 or more directions in a radial pattern to give the stiffness of the grid at various points on a radial diagram. Geogrids with square, rectangle and triangle apertures can all achieve radial stiffness and have all been proven to effectively improve an aggregate layer.
It is most likely that what you actually want to achieve is reduced rutting in the pavement, reduced aggregate depth, improved bearing capacity, or all of the above. Therefore, you need performance data and clear guidance on what a specific product can achieve.
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Cirtex has a comprehensive range of grids for many applications, and more importantly, we can assist in practical applications, with tools such as the CAPLab tool. The proven results that Cirtex can demonstrate are probably of more interest to you than any amount of data.
We think practical hands-on assistance and tools you can use, from a passionate locally owned company with global support is the best option for you.
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A geogrid is defined as a geosynthetic material consisting of connected parallel sets of tensile ribs with apertures of sufficient size to allow strike-through of the surrounding soil, stone, or other geotechnical material (Koerner ). Geogrids provide reinforcement, stabilization, and even filtration when used with properly sized aggregate fills. Made from polymers such as polypropylene, polyethylene, or polyester, they are used widely in civil engineering applications.
Geogrids are deployed for three primary applications:
1. Building firm working surfaces over soft ground conditions
2. Enhance a pavement's service life
3. Reduce the structural cross-section of both paved and unpaved roadways for given service life.
Geogrids have also been proven to significantly improve a pavement's susceptibility to environmental cracking common when building over highly expansive subgrade soils. Geogrids work by interlocking with the granular or soil material placed over them. The open apertures of the geogrid allow for the confinement of material within, increasing the shear strength of overlying granular fill.
There are four types of geogrids Uniaxial, Biaxial, Triaxial (Triax®) and Geogrid-Geotextile Composites. Each designed and manufactured for specific construction applications with various geometric and structural index properties.
Uniaxial Geogrid
Certain Uniaxial (UX) geogrids are oriented along the longitudinal, "machine direction" of an extruded sheet of polymer, thus yielding a grid structure consisting of long narrow ribs. Other products
utilize polyester yarns to render extremely high allowable strengths at deficient strains. Given their unique properties, Uniaxial geogrids are ideal for both wall and slope applications such as
retaining walls, landfill liner systems, embankments over soft soils, and very steep earthen slopes.
Biaxial Geogrid
Biaxial (BX) geogrids are stretched in two directions, the longitudinal and transverse, equally distributing stress along both directions. While woven geogrids are still commercially available, extruded punched-and-drawn geogrids
made of polypropylene are the most deployed among biaxial geogrids. Providing the geogrid with the ability to distribute loads over a wider area than usual while increasing its capacity in base
stabilization applications. Biaxial geogrids are best for applications such as foundations for roadbeds, railroad truck beds, permanent unpaved roads, airport runways, construction haul roads,
working platforms on weak subgrades, and parking lots.
Triaxial Geogrid
TriAx® (TX) geogrids, a next-generation enhancement to biaxial geogrids, have additional diagonal ribs that increase the product's in-plane stiffness. The triangular pattern is formed into a hexagon to improve how the product absorbs
traffic loading forces. TriAx® creates a more efficient effect that delivers optimal in-service stress transfer from the aggregate to the geogrid.
Triaxial geogrids have undergone extensive full-scale and field testing and have been calibrated within the more common pavement design methodologies, both for paved and unpaved roads.
Geogrid-Geotextile Composites
Geogrid-Geotextile Composites are comprised of both material types that are heat or sonically welded together to yield an effective reinforcement and separation element for very challenging
subgrade soil conditions. When subgrade filtration-separation criteria cannot be met with adequately graded fill materials, Geogrid-Geotextile Composites are ideal for deploying. Such that
underlying subgrade soils may be appropriately filtered, thus preventing contamination of the overlying granular fill.