What is Geogrid?
Geogrid is used in a wide variety of construction applications, but they all fall under two categories; soil stabilisation and reinforcement or slope stabilisation and reinforcement.
They work by preventing the movement of soil or aggregate materials by creating a stronger foundation under pavements, roads, railways and earth embankments. They do this by increasing the bearing capacity and Lateral Restraining Capability.
Reinforcement
The main function of geogrid is ground reinforcement. They are fabricated from polymer materials, typically either polyester, high-density polypropylenes or high-density polyethylene, and may be woven from yarns or knitted from strips of material that are heat-welded together to form a grid. They may also be extruded through a punching pattern into sheets of plastic, then cut to size and stretched into a grid.
The apertures in a geogrid are usually quite large, which allows soil to strike-through the transverse and longitudinal ribs and transmit load from one side to the other. Load transfer through the ribs is enhanced by their stiffness and junction strength (also known as node strength).
These characteristics make uniaxial geogrid particularly useful for wall and slope applications where the primary force is directed towards a wall or down a geogrid slope, rather than away from it. In a properly designed and constructed retaining wall, a uniaxial geogrid will effectively anchor the retained soil body against the wall face.
A layered geogrid-geotextile composite is an excellent choice for deploying in challenging subgrade conditions where subgrade filtration-separation criteria can not be met with a conventional design. The composite acts as an effective filter and separator of the underlying subgrade soils, allowing for the placement of aggregate layer with confidence. The geogrid-geotextile composite also prevents the movement of the underlying subgrade soils that can lead to construction difficulties such as settlement and rutting.
Stabilization
You’ve probably seen some sort of grid or mesh laid down at a public event to stop cars from churning the ground up. While these are similar to geogrid, they’re not designed for the same purpose. They’re mainly used to prevent soil from moving and can be installed underneath roads or foundations.
There are several different types of polymer geogrid, and each offers a unique set of properties. The most common is uniaxial, which is produced by stretching flat ribs of polyester or polypropylene. This type of geogrid is ideal for walls and slopes because it’s designed to resist stress in a single direction. Uniaxial products are also easier to manufacture than biaxial products.
Another option is a biaxial geogrid, which is made by weaving or knitting together flexible junctions that form apertures. This type of product is more versatile than uniaxial geogrids, and it offers the same stability in both directions. Biaxial geogrids are more expensive than uniaxial products, but they offer better performance in a wide range of applications.
Using geogrid under construction sites can increase load-bearing capacity and reduce maintenance needs. It can also help to improve the longevity of a structure by reducing environmental cracking. It can be installed beneath road, railway, and airport projects, as well as in retaining walls and earth embankments.
Separation
A geogrid’s aperture shape significantly influences its mechanical behavior and characteristics. The aperture size affects the interlocking between soil and the geogrid, while the stiffness of the ribs and junctions is affected by their geometry. The oxidation degradation of high-density polyethylene (HDPE) and polyethylene terephthalate (PP) is also affected by the aperture size. However, the long-term degradation of these polymers can be reduced by incorporating additives and developments in polymer chemistry.
Whether used as an alternative to traditional soil stabilization, erosion control, or as reinforcement for roads and other pavements, polymeric geogrids provide effective solutions. However, they are not appropriate for all applications. They are best suited for granular soils, and may not be effective in cohesive or expansive conditions. They can also be expensive, and require special installation techniques to achieve optimal performance.
There are several types of geogrids available on the market, including woven from yarns, heat-welded from strips of material, or laser or ultrasonically bonded together. Regardless of the construction method, each length should be hand-tensioned to ensure that it is taught and that there is no slack. If necessary, additional lengths of the grid can be overlapped to form a continuous matrix. This helps to maintain a uniform strength throughout the entire system and reduces the chance of a weak point developing in the installation.
Drainage
There are several different geogrid designs that have been developed to suit various applications, with some specialised for use in particular soil conditions. The type of grid you choose will depend on factors such as the size of the apertures, the percentage open area and the thickness of the ribs and junctions (also known as nodes).
A biaxial geogrid, for example, has square apertures and offers good composite behaviour when used with a layer of geotextile fabric. It also has excellent in-plane stiffness, which is important when dealing with heavy silt. To further improve performance in such situations, a triaxial geogrid can be used, with its triangle-shaped apertures and added diagonal ribs.
As well as offering a range of Soil Stabiliser Geocell structural advantages, geogrids can provide cost benefits in construction projects. For instance, they can reduce maintenance costs by extending the life of road and pavement structures. They can also be used to overcome design challenges, such as reducing the sub-base thickness of a highway structure without compromising the integrity of the asphalt layer.
Geogrids are polymer materials, typically polyester or polypropylene, that have been stretched into a grid-like shape. They work by allowing soils to penetrate the openings and push against them, distributing any stresses that are applied over a much wider area than would be possible with bare soil. They can also increase the load-bearing capacity of soft soils, helping to reduce asphalt maintenance needs and enabling more economical fill material to be used.
