Geogrid – How to Choose the Right Geosynthetic Geogrid for Your Application
Whether you’re building on slopes, or reinforcing a weak soil foundation for heavy equipment roads at construction sites, geogrid is a great way to improve ground stability. This geosynthetic is characterized by parallel sets of tensile ribs with apertures that absorb external forces.
There are three main types of geogrid; extruded, woven, or bonded. Understanding the differences between them is important for selecting the correct one for your project.
Types
There are several different geogrid types. The type that you choose depends on the intended application and site conditions. For instance, uniaxial geogrids have rectangular aperture patterns and provide high tensile strength in just one direction. This makes them ideal for slope reinforcement and wall applications.
Biaxial geogrids, on the other hand, have square or rectangle aperture patterns and offer equal stress resistance in two directions. This makes them better suited to base stabilisation applications where they increase the load distribution angle.
Geogrids are typically made from polymer polymers such as polyester, polyvinyl alcohol, or polyethylene. They can be woven or knitted from yarns, heat-welded from strips of material, or produced by punching a regular pattern of holes in sheets of material that are then stretched into a grid.
The flat ribs of extruded geogrid are usually connected to each other at junctions, which help to distribute stresses across the entire structure. Unlike the fibers of geotextiles, these ribs and junctions are very stiff, which helps to maintain strength even when subject to significant loads.
The predicted lifetimes of these geogrids have been found to exceed 120 geogrid years at a typical site temperature of 20 degC. These results are significantly higher than the 100-year design life of most construction projects. Due to their durability, geogrids are also well-suited to landfill capping systems and slope stabilisation, where they can be used to reduce the need for costly earthworks or stabilize contaminated soils.
Design
There are a few types of geogrid designs available for different applications. The choice will largely come down to whether you require a uniaxial or biaxial type. Uniaxial types are ideal for slope reinforcement or wall applications, as they offer high tensile strength in one direction. These are typically used in slopes, retaining walls and landfill liner systems. Biaxial types are better suited to base reinforcement applications, such as roads. They increase the shearing resistance within soils, which will help to improve load distribution over a road or pavement surface. These are typically used in paved and unpaved road projects carrying rubber-tired traffic.
The main mechanism of how geogrids work is to reduce lateral movement within aggregate layers. This is often caused by wheel loadings or other pressures that push down on the layer. The ribs of the geogrid will resist this pressure by creating a traction force within the layer. This will prevent outward stresses from forming, which would otherwise weaken the overall arrangement of the aggregate and subgrade.
Geogrids also offer a number of other key benefits, including cost savings and speed of construction. They are much cheaper than traditional stabilisation methods, such as earthworks or tarmacadam and allow for lower aggregate layers in unpaved roads without losing performance. They can even reduce the requirement for rail ballast by increasing soil strength, making railway projects safer and less costly to construct.
Installation
When installing a geogrid retaining wall, it is important to use a skilled engineering Soil Stabiliser Geocell consultant and follow the engineer’s design. Depending on the structure, a geogrid may be buried at various depths in order to achieve the desired performance characteristics. It is also a good idea to contact your local utilities before beginning excavation on your project. They will provide free service to mark the locations of any underground facilities which could be impacted by your construction.
Once installed, a geogrid acts to transfer the loads experienced by soils to its ribs. This is a similar concept to placing compacted soil into a mold; the pressures exerted by your hand would compress the soil and keep it from spreading or crumbling outside of the confines of the mold. This is what a geogrid does on a much larger scale.
Biaxial and triaxial geogrids have been developed to offer improved performance in certain soil applications. Using a triangular aperture design instead of squares, these geogrids are able to increase their in-plane stiffness. This increases their ability to resist lateral movement of material and allows for a more uniform distribution of stress over a larger area.
A geogrid can be used in a variety of projects to help reduce the amount of fill material required and increase the load-bearing capacity of soft sub-soils. It can also help with the stabilisation of slopes and improve soil erosion control, as well as enhance the strength of rail ballast and reduce road maintenance.
Maintenance
Using geogrids on embankments that are built over weak soils gives them extra strength by confining the soil to minimise lateral movement, which can otherwise cause settlement, and reduce load bearing capacity. This also improves the longevity of your project by reducing maintenance requirements.
For example, if you take a clump of soil in your hand and press on it with one finger it will lose its shape, either becoming flatter and spread out or crumbling depending on its consistency. If you put the same clump of soil into a square plastic mould, however, it will stay a lot more compacted and will retain its shape much longer. This is what happens when a geogrid is used in road construction.
When you apply a load to the ground, it will be transferred diagonally through the grid layers and into tension that will strengthen the soil mass similar to how reinforcing steel adds strength to concrete. It is this resistance to internal forces that increases the shear strength of the soil and enables you to reduce aggregate layer thicknesses in unpaved roads by up to 50% without any performance loss.
Another advantage of using a geogrid for roadways is that it mechanically stabilises the subgrade soil by evenly distributing traffic loads to prevent excessive rutting and cracking. This makes the paved road surface last longer and helps the government meet its targets of a greener, more sustainable road network.
