Geogrids

Types of Geogrids

There are three types of geogrids: uniaxial, biaxial, and triaxial.

Uniaxial Geogrids

The higher tensile strength of uniaxial geogrids is in the machine direction. Uniaxial geogrids are mainly used for soil reinforcement in a segmental retaining wall or steepened slope. Uniaxial geogrids are usually woven or knitted from polyester yarn into a strong structure with a polymeric or PVC coating, making them resistant to strain, creep, and natural chemicals. Extruded uniaxial geogrids are made from HDPE.

To install uniaxial geogrid in retaining walls, roll the material perpendicular to the wall. The embedment length will be determined by the wall’s height, the conditions of the subgrade and soil, and the supported load and will be specified by the designing engineer.. Always pay attention when rolling the geogrid out, as uniaxial geogrid’s strength is in the machine direction which means the strength is in the length and should be rolled back into the hillside from the wall. Also, make sure not to splice or join 2 pieces of geogrid together trying to reach a certain embedment depth as there should be a single continuous piece of geogrid from the face of the wall to the back of the reinforcement zone.

Biaxial Geogrids

For raised patios, walkways, highways, parking lots, and access roads, biaxial geogrids are the most common type. Using square holes and a more rigid structure, biaxial geogrid increases soil load capacity since they have similar tensile strength in the two directions and have limited creep. These geogrids are used for reinforcing the base and the subgrade. In unpaved or paved applications, they minimize rutting and maintain the cumulative depth.

Unlike uniaxial geogrid, biaxial geogrid carries similar strength in both directions. You’ll want to install biaxial geogrid as deep into the surface as you can with at least 6” overlap between the pieces. This lets the aggregate interlock, preventing the base materials and subgrade from moving under the pavement surface’s load.

Keep in mind, however, that there are diminishing returns after about 12”, wherein you’ll likely need to install an additional layer of geogrid. When using this type of geogrid as a separation layer between the subgrade and the base, non-woven geotextile is recommended to prevent silt from migrating into the base with heavy traffic.

Triaxial Geogrids

With triangular apertures and reinforced ribs, triaxial geogrids may appear differently than biaxial geogrids but generally perform and are installed in a similar way as biaxial geogrids and are used in the same applications as biaxial geogrids.