What is the function of a geogrid in a pavement?
Geogrids are a type of geosynthetic material used for mechanical stabilization and soil reinforcement in construction. These large, flexible rolls of polymers follow a grid-like pattern with intersecting openings called apertures. Depending on the application, geogrids are inserted either within the subgrade material or as a layer between the subgrade and base, depending on the California Bearing Value of the soil on-site.
Geogrids mechanically strengthen the unbound layers of aggregate and other subgrade materials by confining them within the apertures, creating a mechanically stabilized layer. This layer manages differential settlement, decreases necessary fill depths, caps weak deposits, and enhances dynamic traffic loading and bearing capacity, ultimately leading to a more stable pavement structure.
The use of geogrids improves the performance and durability of the pavement system. Their inherent material stiffness and flexural rigidity enhance the subgrade’s load-bearing capacity by reducing lateral soil movement through the interlocking mechanism of apertures with the material.
At times, we also recommend adding a layer of geotextiles to ensure adequate separation between layers to avoid migration of soils, reducing the risk of rutting, cracking, and other forms of distress. It’s worth noting that the use of geotextiles and geogrids should not be confused.
Let us explore why geogrids are a good choice for pavement designs, and the benefits they offer when included in a project.
Significance of geogrids for subgrade stabilization
Subgrade stabilization enhances the properties of the subgrade – the natural soil or aggregate layer beneath roadways, highways, or railway tracks. The subgrade is akin to the foundation of the structure. The purpose behind subgrade stabilization is to reduce or minimize rutting, increase the stiffness of the subgrade, and distribute loads more evenly to prevent differential settlement.
Whether a geogrid is necessary or not is determined by the subgrade being reinforced. An overlooked factor is the quality of the subgrade itself, which, although it may have soil with a robust Resilient Modulus (MR), can lose strength when saturated with water or subjected to iterative dynamic loads. This can also occur due to the presence of low-plasticity fines or fine sands in the subgrade, causing its contamination. By distributing the load at junctures and leveraging tensile strength, the soil’s shear strength increases by up to 50%. The benefits of geogrids for stabilization therefore can be in the following ways:
Improving subgrade stability:
The primary role of geogrids in pavements is to provide mechanical stability to weak subgrade soils. By locking the subgrade into apertures, the confined movement minimizes lateral pressure, enabling a more uniform load distribution from the top. As the paved road ages, this is key because the subgrade will undergo temperature changes and other fluctuations, which must be addressed to avoid failures, cracking, rutting, and other maintenance challenges.
Lesser aggregate fill needed:
Geogrids reduce the amount of aggregate required in the pavement structure by 15-20%. This makes it an economical choice and offers a more sustainable construction process. By improving the shear strength, we no longer need thick layer upon layer of aggregate material. Instead, a thinner layer effectively distributes loads.
Easy installation:
Geogrids are easy to install when compared to other subgrade stabilization methods. Geogrids installation doesn’t require skilled labor or specialized equipment. This is another lever which helps bring down the overall cost of the project.
Extended pavement life:
The use of geogrids in subgrade stabilization can help extend pavement life structure by providing a strong and durable foundation. With reduced maintenance costs, minimized degradation of the paved structure, and longer maintenance cycles, we see longer lifespans for pavements using geogrids.
Sustainable alternative to traditional mechanical methods:
By reducing the amount of aggregate needed for the project, geogrids also reduce quarrying activity required to create subgrade, as well as the logistical costs of transporting materials from the quarry site to the project site. This not only affects the project’s net carbon footprint but is also an important consideration for ecologically sensitive regions where extensive excavation is not feasible. Additionally, it can reduce the extent of deep mixing required in certain cases. This is particularly valuable for mountainous regions prone to landslides and water saturation, as well as coastal areas with unique soil challenges.
Factors to consider while selecting geogrids for stabilization
For pavement design, various factors that impact pavement lifespan must be considered at the design stage. Factors such as traffic volume, traffic load, CBR value, and environmental conditions must be taken into account when developing project plans. This is where Strata Geosystems’ extensive experience in global projects becomes valuable. Our manufacturing and application experience provide unique insights into projects that may pose unforeseen challenges. When choosing the right manufacturer and partner for your project, we help you determine what is needed for the site, from design to final implementation. We partner with you and guide you through the following aspects:
- Help you understand lab- and site-tested ultimate tensile strength values, low creep factors, and stiffness properties that reduce the amount of subgrade material needed by up to 20%.
- Aperture sizes and shapes that suit various terrains and soil types, with customization options.
- Compatibility with soil, accounting for chemical, environmental, and mechanical degradation, while remaining inert due to the use of a trademarked coating material.
- Installation guides to ensure the process is understood, even with unskilled labor, resulting in double cost savings.
- Conducting a cost-benefit analysis to identify the optimal mix of products for reducing lifetime costs.
- Strata Geosystems’ design recommendations are tailored to your unique needs.
Geogrids for pavement enhancement
Geogrids have three key benefits: improve the trafficking performance, longevity and cost of a given project. These benefits are essentially interlinked. In subgrades which would typically need high levels of mechanical stabilization, today geogrids deliver high value over the life of a project. For example, for the Kohima-Bypass Road in Nagaland, there were project goals which needed to be met. Essentially, design that supports the dynamic load, and also reduced maintenance cycles given the remoteness of the site itself.
The initial parameters included a subgrade California Bearing Ratio (CBR) of 10% and a traffic intensity of 50 MSA. The optimized design ultimately featured two layers of SGB Grid –our biaxial geogrid: one within the Wet Mix Macadam (WMM) and the other within the granular sub-base. The design approach followed the LCR method. The inclusion of SGB Grid had a confining effect that minimized both vertical and lateral aggregate movement, resulting in superior stability under traffic loads compared to unreinforced sections. This is where one can compare the superior difference in introducing geogrids.
Our solution allowed for easy installation using unskilled labor (another cost saving measure), reduced layer thickness to conserve natural materials, and decreased maintenance needs. The flexibility of SGB Grid promoted better interaction with aggregates in the pavement, enhancing fatigue and rutting design life, and facilitating economical and rapid construction.
In summary, geogrids play a crucial role in optimizing pavement performance and durability by providing reinforcement, separation, improved physical properties, reduced base layer thickness, enhanced load distribution, and cost-effective construction practices within the pavement system. Choose Strata Geosystems for a best-in-class experience in end-to-end project management for all your geotechnical challenges. With certifications from ASTM, ISO, NTPEP, ISI, BBA, we’re poised to meet your requirements with independently tested lab reports and three decades history of experience.