Geogrid reinforcement and stabilisation is used in roadways in two major applications: base reinforcement/stabilisation and subgrade stabilisation.

In base reinforcement/stabilisation, the geogrid is placed within or at the bottom of a pavement system to improve the load-carrying capacity and reduce the deformation of the pavement under repeated traffic as well as helps control expansive subgrade and environmental movements by managing the associated longitudinal cracks. This function is also known as “stiffening” in some references.

In subgrade stabilisation applications, the geogrids is placed between the soft subgrade and gravel layer and is used to distribute the load to a wider area and reduce the vertical stress on the subgrade and the deformation of the subgrade. In addition, geogrid is used to build a construction platform over weak subgrades to carry equipment and facilitate the construction of the pavement system, without excessive deformations of the subgrade. For such applications, a geogrid-geotextile composite like Combigrid® Geocomposite is used to provide reinforcement and stabilisation as well as separation between fine particles and gravel.

The reinforcement and stabilisation provided by geogrids can be provided through three possible main mechanisms:

1. Lateral restraint of the base and subgrade through friction (geotextiles) and interlock (geogrids) between the aggregate, soil and geosynthetic.

2. An increase in the system bearing capacity can also be achieved by forcing the potential bearing capacity failure surface to develop along alternate, higher shear strength surfaces.

3. Geogrids also provide membrane support for the wheel loads in pavements.

These benefits result in more robust pavements with a thinner gravel layer and/or longer design life and the intrinsic strength to stand up to many years of vehicle movements.

A reinforced unpaved road may be used as is or may serve as a construction platform for a permanent paved road. For permanent road construction, a temporary working platform can be constructed to provide an improved roadbed using geogrid reinforcements with an aggregate layer to provide a form of mechanical stabilisation.

This mechanically stabilised aggregate layer enables contractors to meet minimum compaction and proof rolling specifications for the first two or three aggregate lifts. This is especially true on very soft, wet subgrades, where the use of ordinary compaction equipment is very difficult or even impossible.

How Combigrid® can help

Combigrid® Geocomposite is a robust all in one reinforcement geogrid that is enhanced by an embedded, extremely durable nonwoven geotextile. Bonded together in a single-layer product, these components provide the durability and strength to resist installation damage so that the reinforcement begins its service life in optimal condition. This helps save on aggregate at the time of installation and ensures less maintenance in the future.

This high-quality engineered geogrid performs a significant, multi-functional role in pavement reinforcement and stabilisation – for Combigrid® Geocomposite specifications, contact the engineering team at Global Synthetics.