The stabilization of granular layers with geogrids It is one of the most widely used techniques in pavement engineering to improve structural performance. Thanks to the mechanical interlocking mechanism between the aggregate and the open structure of the geogrid, reinforcement is transferred, resulting in the mechanical stabilization of the layer.

Biaxial geogrids are geosynthetic elements designed to provide confinement and restrict the lateral movement of aggregates. This interaction results in the following benefits:

  • Increased stiffness of the granular layers.
  • Optimization of wall thicknesses and construction costs.
  • Better distribution of forces across the subgrade.
  • Reduction of rutting.
  • Greater structural capacity of the pavement.

These benefits make it possible to develop more efficient and sustainable designs, especially for projects with high traffic volumes.

Currently, there are various design coefficients that allow for the quantification of the structural benefits provided by geogrids. Among the most widely recognized are the Traffic Benefit Ratio (TBR), Base Course Reduction (BCR), and Modulus Improvement Factor (MIF). Each serves a different purpose, whether it is to extend the pavement’s service life, reduce the thickness of granular layers, or improve the structure’s equivalent stiffness.

What are biaxial geogrids, and what are their benefits?

Methodologies for the Design of Stabilized Granular Subgrades

TBR (Traffic Benefit Ratio) Methodology

The Traffic Benefit Ratio (TBR) is a coefficient used to quantify the increase in pavement service life resulting from the incorporation of a geogrid. This coefficient is defined as the ratio of the number of load cycles withstood by a reinforced structure to those withstood by a conventional, unreinforced structure. TBR values are always greater than one, indicating an increase in the number of load cycles or equivalent axles due to the geogrid’s mechanical stabilization effect.

BCR (Base Course Reduction) Methodology

Base Course Reduction (BCR) is a factor that determines the reduction in the thickness of the granular layer that can be achieved by incorporating geogrid, while maintaining performance equivalent to that of a conventional structure. In other words, the BCR is always less than 1.0 and allows the stabilization benefits provided by the geogrid to be translated into a reduction in design thicknesses.

MIF (Modulus Improvement Factor) Methodology

The Modulus Improvement Factor (MIF) is a factor that represents the effect of reinforcement by increasing the resilient modulus of the granular layer. This approach is widely used in mechanistic-empirical pavement design methodologies because it allows the benefit of the geogrid to be directly incorporated into the structural analysis.

Differences Between the TBR, BCR, and MIF Methodologies

The following is a comparison of the different methodologies.

Methodology Main objective Profit earned
TBR Extend the service life of the pavement Higher number of repetitions with the load
BCR Reducing Granular Thicknesses Reduction in material consumption
MIF Increase the equivalent stiffness of the structure Increases the mechanical modulus and reduces deformation

The choice of methodology will depend on the specific objectives of the project and the design procedure used.

What types of geogrids are used for the stabilization of granular layers?

Among the available options, woven polyester (PET) geogrids with biaxial behavior are widely used for the stabilization of granular bases and subbases due to:

  • Its high rigidity.
  • The stability of joints.
  • Its ability to form a mechanical bond with the aggregates.
  • The increase in lateral confinement.
  • Reducing permanent deformations.

These characteristics improve the structural response of the pavement and allow for the benefits associated with the TBR, BCR, and MIF methodologies to be leveraged.

Conclusions

  • The Mechanical stabilization of granular layers The use of geogrids is an efficient solution for optimizing the design and performance of pavements.
  • The Traffic Benefit Ratio (TBR), Base Course Reduction (BCR), and Modulus Improvement Factor (MIF) methodologies are the primary approaches used to quantify the structural benefits associated with geogrid reinforcement.
  • While the TBR method is aimed at extending the service life of the pavement, the BCR approach allows for a reduction in the thickness of granular material, and the MIF methodology directly incorporates an improvement in layer stiffness within mechanistic-empirical procedures.
  • Choosing the right design methodology makes it possible to develop pavement structures that are more efficient, sustainable, and offer better long-term performance.