What are geogrids?

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.

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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.

What are the differences?

There is a range of different geogrids available on the market, each suitable for different applications. One of the most obvious differences between types of geogrids is their construction, which can be broadly divided into three categories: 

• Biaxial Geogrids
• Triaxial Geogrids
• Uniaxial Geogrids

Secondly, what are they made from? 

Typical polymers (or plastics) that geogrids are made from include polyester (PET), polypropylene (PP) or High Density Polyethylene (HDPE). The material they are made from determines its construction or manufacturing method. 

Geogrids were first introduced in the s as a way to mechanically stabilise granular fills, and since their inception, they have become more technologically advanced, spawning a range of variants and types that are suited for different purposes. 

Most often used for reinforcing pavements and capping layers in road and railway projects, biaxial and uniaxial geogrids were first to hit the market, with triaxial geogrids following not far behind. 

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Although the triangular apertures of triaxial geogrids were heralded as a more effective way to reinforce soil, various trials have shown that results can vary (refer to the attached report for more information). 

How geogrids work

The main engineering mechanism for pavements reinforced with geogrid is lateral confinement of the granular material. This is achieved by interlocking the granular fill into the openings in the geogrid. The lateral confinement and interlocking forces of the geogrid are critical to holding the pavement in place, so the design of the geogrid has been studied, refined and perfected over the years. 

That is why, rigid, integral geogrid junctions provide the best performance for this mechanism.

Nowadays, there are variations typically available from a geosynthetics supplier. Let&#;s take a look at these in more detail. 

What is a biaxial geogrid?

Biaxial geogrids are designed to handle forces in two lateral directions in the ground, and they are generally designed with square or rectangular apertures. These types of geogrids are ideal for situations where dynamic stress/load is applied in both orthogonal directions, such as in road and railway traffic. 

Designed to contain and stabilise granular material and improve its bearing capacity, they help to reduce select granular material costs due to the reduced thickness of aggregate and subbase material required in a temporary or permanent P-way pavement. 

What is a uniaxial geogrid

One of our most popular uniaxial geogrids is TerraGrid® Uniaxial PET geogrids. This high-performance soil reinforcement solution offers excellent tensile strength in one direction. TerraGrid Geogrid interacts with the soil particles to create a permanent composite soil/geosynthetic structure. 

This type of grid is best suited for walls and slope soil reinforcement applications, as the load transfer is only in one (uniaxial) direction.

Get help and advice on the right geogrid for your project

The Polyfabrics engineering team is here to offer support, advice on product selection and engineering guidance on our range of geosynthetic products. Contact our technical team to find out more. 

If you are looking for more details, kindly visit Geogrid Supplier.