Geogrid and geotextile. Two common products and two common terms thrown around in construction plans, meetings, and on site conversations. But what are they? Does anyone ever explain the difference? Not usually – people just expect you to know – or they use the terms interchangeably, which causes even more confusion!
Read on below where we explain in detail what geotextile, what geogrid is, and the differences between geogrid and geotextile.
What is Geotextile?
Geotextiles are a type of synthetic fabric used in construction that contain solids, but allow liquid to travel freely through. They are generally used to provide separation between different materials – usually between soils that shouldn’t be allowed to touch or mix together. The term geotextile is sometimes used interchangeably with “filter fabric”.
A common use for geotextile is a French drain or drainage blanket, where a free draining material like washed gravel is installed in a nonpermeable material such as clay. The free draining material typically has a drainage pipe installed within it and is intended to allow water to be rapidly shed from the area in which it is installed. In such a system, the free draining gravel is completely wrapped with a layer of geotextile to prevent the clay from migrating over time into the voids within the gravel. Preventing the migration of clay into the free draining gravel with a geotextile gives the drainage system a much longer lifetime.
Below, we will cover the four most common types of geotextile.
1. Non Woven Geotextile
Non woven geotextiles are the most commonly speced (specified) form of geotextile in both large and small construction projects. They come in many forms and products but are generally categorized by their thickness which influences their tensile and puncture strengths.
Non woven geotextile is recommended for residential sized projects such as gravel driveways, retaining walls, and other drainage sensitive work. For these applications, Super Geotextile is a fantastic brand that offers many rolls sizes and thicknesses.
In general, the 6 oz thickness will be sufficient for residential sized projects. If you’re going to have heavy equipment travelling over the geotextile you should consider the 8 oz size, and consult with a qualified, local geotechnical engineer.
If you’re purchasing non woven geotextile for your project, you should make sure you pick up some landscaping staples to fasten it in place, and some heavy duty fabric scissors.
2. Woven Geotextile
Woven geotextiles are less common as they are significantly less permeable than non woven geotextiles so much that they might as well not allow any water to pass through them. While they do make up for their lack of permeability with an increase in their tensile strength (ability to reinforce), they are overshadowed by geogrid, a product made specifically for reinforcement.
Except for specific projects where you are advised by an expert, woven geotextiles can generally be avoided.
3. Polyspun and Spunbond Geotextiles
Although these two types of geotextile are produced with different processes, the end products are largely the same. Polyspun and spunbond geotextiles are generally very thin and weak and should not be used in construction of any kind. They are typically used only in landscaping projects or gardening as a weed barrier only.
What is Geogrid?
Geogrid typically consists of polyester or polypropylene plastics and is produced in such a way so that it looks like a grid or net when laid flat. Geogrids are very strong in tension and work by allowing soils to penetrate through the openings in the grid and then allowing them to push against the grid. As the grid is significantly stronger than the soils, it allows the soil to distribute any load applied to it over a much wider area than it would be able to without geogrid being present. See our article on How Geogrid Works if you are interested in a more in depth explanation.
Geogrids are used in a wide variety of projects from retaining walls to roadway stabilization and foundation improvements. Geogrids are produced in uniaxial (one-way) and biaxial (two-way) forms, with each being used for different applications.
1. Uniaxial Geogrid
Uniaxial geogrids, also sometimes referred to as “one-way” or “one-directional” geogrids are geogrids that are only strong in one direction, even though they may look very similar to a biaxial geogrid. Uniaxial geogrids are typically used in scenarios where soils only require reinforcement in one direction – almost always in retaining walls or slope reinforcement scenarios.
If using a uniaxial geogrid for a retaining wall, it is essential that you cut the geogrid to your desired reinforcement length and lay the geogrid so that the strong axis of the grid is perpendicular to the retaining wall face. Rolling the geogrid out along your retaining wall seems like the smart way to install it, but it wont do anything if it is installed with its strong axis running parallel to the wall face.
2. Biaxial Geogrid
Biaxial geogrids are sometimes referred to as “two-way” or “bi-directional” geogrids and are equally strong in two directions. This type of grid can be used in retaining wall construction, and CAN be rolled out along the retaining wall blocks, provided the roll width is wide enough to cover the geogrid design width. It’s typical use however, is in roadway construction (including gravel driveways) and foundation improvement applications.
So, What Are The Differences?
As you can see from the information outlined in this post, there are many differences between geotextiles and geogrids. As summarized below
Geotextile: Used primarily for soil separation to promote drainage. Generally allows very little to no soils to travel through, but does allow water to move freely.
Geogrid: Used primarily for soil reinforcement. Does not impede water or soils from travelling.
We hope that this article has answered any questions you had. Feel free to contact us if you’ve got any questions.
