Geogrid Mechanisms Explained: Lateral Restraint & Bearing Capacity

by Bryan Gee, P.E., on February 20, 2020

In 2003, the U.S. Army Corps of Engineers defined three primary mechanisms for how geogrids work to stabilize paved and unpaved roads. In an engineering technical letter (ETL), the Corps identified the three primary mechanisms as: lateral restraint, improved bearing capacity, and tensioned membrane effect. Here, we explain the two most important mechanisms, lateral restraint and improved bearing capacity, and demonstrate their effects. (These videos are designed to help you visualize the mechanisms: design is more complex, but based on these ideas.)

Lateral Restraint

For geogrids, lateral restraint is the primary mechanism of the three discussed in the ETL. So, what is it exactly and why is it so important? Lateral restraint is the ability to confine aggregate particles within the plane of the geogrid. Once the aggregate strikes through the apertures of the geogrid, its movement is limited. This increases the stiffness of the stabilized aggregate layer. In other words, when geogrid is used in the design of your paved or unpaved structure, your structure becomes much more efficient at managing the stress imposed by heavy loads because the aggregate moves very little. 

This box-of-rocks video offers a simple demonstration of the lateral restraint mechanism at work. You'll see how an unstablized section responds when compared to a section benefiting from the introduction of TriAx Geogrid in an aggregate layer.


Improved Bearing Capacity

Improved bearing capacity, also known as the snowshoe effect, becomes an important mechanism as subgrade soils get weaker. Just as a snowshoe distributes your weight over soft snow, a stiff layer of aggregate and geogrid better distributes loads over soft subgrades.

Improved bearing capacity of the subgrade results from pressure dissipation at the geogrid-subgrade interface. Generally, this mechanism applies to unpaved applications where stabilization is required to yield a stable working surface. However, it also applies to pavement structures, particularly flexible pavements stabilized with a geogrid at the aggregate-subgrade interface.

Sand Box Demonstration with TriAx Geogrid: Using soft foam, a weak subgrade condition is simulated to demonstrate the improved bearing capacity realized using Tensar TriAx geogrid. Note how the participant’s weight is not supported in the unstabilized condition, but is easily carried by the stabilized composite of sand and TriAx Geogrid.


How can TriAx Geogrid Help Your Next Project?

Tensar has developed online resource centers so that engineers and contractors can learn how to build more efficiently using TriAx Geogrid technology. Here you'll find free design tools, webinars, project profiles and more. Click the links below to get started.  

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