Tensar Uniaxial geogrids can carry high tensile loads applied in one direction (along the roll length). Their open aperture structure interlocks with fill material to provide superior load transfer from the soil to the geogrid. Tensar's HDPE geogrids achieve their strength by punching and drawing a homogenous polymer sheet to provide a uniform, consistent product that does not require weaving, coating, or welding to maintain the product's integrity. This unique process provides superior junction strength, allowing high-strength connections to other geogrid rolls or facing components.
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Tensar's Uniaxial (UX) Geogrids offer a soil reinforcement solution ideal for wall and slope applications. With over 400 million square feet installed globally, these geogrids feature high-density polyethylene (HDPE) construction for superior load transfer and long-term resistance to degradation. Suitable for various market applications, including residential, public roads, and commercial projects.
Geogrids provide stabilisation or reinforcement to enhance the performance of soils, as well as separation between soil and aggregate layers. There are four main types of geogrid, each with different physical properties or characteristics. The most suitable type of geogrid in any given application will depend on both these physical properties along with the compatibility of the aggregate and soil.
In this guide, we’ll be looking at the physical properties of geogrids and how they impact suitability, before looking more closely at the key properties of Tensar geogrids in particular.
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Tensar geogrids can be used to solve civil and geotechnical engineering problems in or on the ground. They help design engineers to achieve substantial time- and cost-savings across a range of applications, from roads and railways to working platforms and foundations. If this could be of use for your upcoming project, speak to our team today.
Geogrid strength can refer to a number of different properties, including:
While the design strength of geogrids for the function of reinforcement is a critical property, for the function of stabilisation, other physical characteristics should be considered when assessing their potential performance, such as junction efficiency, rib height, and radial stiffness. We will go into each characteristic in more detail below.
Ultimate tensile strength (UTS) is the maximum amount of load a geogrid can handle before performance is compromised.
This is established through tensile testing, where the geogrid is stretched until it breaks.
Many geogrid specifications focus on tensile strength, equating high UTS with better performance. In reality, however, UTS is irrelevant, particularly when a geogrid is used in the design of roads or temporary working platforms.
In these cases, the ultimate tensile strength of a geogrid alone is actually a poor indicator of performance. This is because the ‘tensioned membrane’ effect—the strength that a geogrid offer when stretched or strained—does not offer appropriate support for the layers above it.To work, the geogrid has to be stretched. But when a load is placed on it, the geogrid will curve to accommodate this load, similar to what happens when a person sits on a hammock.
Consequently, the pavement will suffer deformation at the level where the reinforcement geogrid is placed. Deformation will also likely appear at the road surface level in the form of rutting, cracks and potholes, reducing its operational life.
Learn more about Why tensile strength is not a good measure of stabilising geogrid performance.
The physical property of geogrids known as junction efficiency is the measure of the strength of the node compared to the strength of the rib, expressed as a percentage and indicates the ability of the geogrid to transfer loads from one rib to other ribs in different directions:
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Junction efficiency—and not junction strength—is a parameter the European Assessment Document (EAD) characterises and associates with stabilisation geogrid performance.
The EAD sets out parameters the European Organisation for Technical Assessment (EOTA) confirms are specific to the distinct function of stabilisation. No such link has been made between any junction parameters and reinforcement geogrids.
Where stabilisation geogrids are used to take advantage of the ‘confinement effect’, junction efficiency is the more important physical property in relation to performance in road and temporary working platforms than tensile strength.
The confinement effect—where the aggregate is locked into the apertures of the geogrid and pushes up against its ribs, preventing the material from rotating or moving.
Load is put against the ribs, which are held in place by the junctions. As a result, the efficiency of the junctions compared to the rib is one characteristic that will influence the performance of a stabilisation geogrid.
The next physical property of geogrids, known as radial stiffness, is in-plane stiffness measured in a single direction across the geogrid. The mean radial stiffness is the average stiffness measured in multiple directions, while the radial stiffness ration is an indication of the uniformity (isotropy) of radial stiffness. These two characteristics provide indicators of the ability of a stabilisation geogrid to evenly distribute a load through 360 degrees, without deforming elastically.
Mean radial stiffness and radial stiffness ratio are characteristics of stabilisation geogrids associated with the stabilisation function, with the geogrid acting as a component of a mechanically stabilised layer in road applications. The overlapping hexagonal structure of Tensar’s TriAx and Tensar InterAx geogrids provides a more uniform response to the load traffic imposed on the road than geogrids with square or rectangular apertures.
Elastic modulus is another physical property of geogrids related to stiffness, but not related to performance in ‘normal’ applications.
Finite element analysis (FEA) sometimes requires a geogrid’s elastic modulus. However, Tensar’s own research has confirmed that the effect of a geogrid should not be modelled on individual product parameters. We have developed an FEA module—for more information, contact the Tensar Technology team.
Long-term design strength (LTDS) is a relevant property of geogrids in reinforced soil applications—including retaining walls and slope reinforcement—where layers of geosynthetic materials (such as geogrids) are placed within the fill used to form the finished structure.
Unlike roads, which bear a constantly changing load, reinforced soil carries a permanent load throughout its operational life, which could be up to 120 years. Consequently, the design of the structure and load-bearing components (including the geogrids) should reflect this.
Polymers are viscoelastic, meaning their strength and stiffness are affected by temperature and how frequently or long they bear a load. Under a constant load, polymer geogrids will stretch very gradually as their physical properties change.
Creep strength can be assessed by subjecting geogrids to long-term loading. This involves suspending different-sized weights from the geogrid in temperature-controlled conditions and measuring and recording the strain for a standard duration of 10,000 hours, just over a year.
Partial reduction factors—such as environmental effects and the effect of damage caused during installation—should be applied before using creep strength in LTDS calculations.
Uniaxial geogrids are also available in different grades, but their geometry is similar across the range.