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ARA Independent Review & Validation:

Tensar's Modifid 1993 AASHTO Pavement Design Procedure and Verification of SpectraPave4-PRO Software

ARA Independent Review & Validation:

Recommended Practice for Incorporating Geogrids in ME Pavement Design

Research Reports:
Tensar TriAx Testing for Pavement Optimization

Full-Scale Accelerated Testing of Multi-axial Geogrid Stabilized Flexible Pavements

Geogrid in M-E Pavement Design

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What Is APT

Structural Condition Assessment of Reinforced Base-Course Pavement

How Geogrids Work

  • Tensar geogrid products are the most rigorously tested geogrids in the world.  Each year, Tensar invests millions of dollars to document the performance of our products, and provide engineers with the best possible solutions for their projects.  Many additional research documents, design tools and software are available.  For more information, please reach out to your Tensar Regional Sales Manager or click the link below.

Frequently Asked Concerns and Questions in Comparing Geogrids for Roadbed Performance

Statements from Giroud and Han Regarding Equivalence Between Products
“Geosynthetic index tests of physical or mechanical properties are not universal indicators…”
“…higher strength geosynthetics do not necessarily perform better…”
“Calibration based on small-scale tests and the index properties of the geosynthetic could lead to a false sense of security…”
“… designers should always verify that geosynthetic specific full scale testing along with case histories, for which a calibrated and validated G-H equation was utilized, resulted in satisfactory performance….”

FAQs When Comparing Geosynthetics for Roadbed Applications

Evaluating Engineered Solutions

Does greater tensile strength correlate to better performance?

Short answer: Geogrids must have a minimum tensile strength to make sure the product is not damaged during the placement and compaction of aggregate. However, no correlation has ever been shown between tensile strength and the performance of geogrids used for roadbed applications.

Design values need to be based on full-scale, highly controlled and monitored testing. Values and design methods should be reviewed by independent authorities with expertise in pavement design and geosynthetics.

Need Assistance in Evaluating Equivalence?DOWNLOAD PAVEMENT CHECKLIST

How am I supposed to be able to evaluate all the testing being presented to me?

Unless you are an expert in pavement design, it may be very difficult to evaluate all of the information that may be submitted to you, and to find time to do so. Unscrupulous suppliers often try to take advantage of this fact by providing large quantities of information, even though it is not sufficient to show equivalency. You can reduce the confusion by writing a specification that includes the information in By using the checklists outlined above – depending on the application (subgrade stabilization or designing a pavement).

Read the Long Answer

What is the difference between a Geogrid and a Geotextile?

Geogrids are synthetic products that have large openings between rib structures and allow for rock to strike from one side of the product to the other side. This allows for rock to become confined within the opening.

Geotextiles are textiles made from synthetic fibers.

What is the Difference between TriAx and Biaxial Geogrid?

Biaxial geogrid was invented by Tensar in the late 1970s. Biaxial geogrids have square or rectangular openings, called apertures. Different types of biaxial geogrids exist on the market, but for roadbed applications, testing has consistently shown that integral geogrids made by a process known as punched and drawn perform best. 

TriAx geogrid has additional diagonal ribs that increase the in-plane stiffness of the product. The triangular pattern is formed into a hexagon to improve how the product absorbs the forces from traffic loading. Ribs in TriAx are designed to provide a high aspect ratio which provides better interlock with the surrounding aggregate.

DOWNLOAD SUBGRADE CHECKLIST

Do all geogrids of the same strength work the same?

No. *This is shown by some of the testing outlined in the long answer of #1 above. Geogrid strength does not correlate to in-ground performance. The ability of the geogrid to interlock and confine the aggregate under wheel loading is important. This can only be measured through full-scale in-ground testing under wheel loads. Property characteristics such as rib shape, aperture shape, rib thickness, in-plane stiffness, junction style, and many other factors are contributors to the amount of interlock and confinement achieved.

Does Triax work and perform the same as BX geogrid?

Short answer: No. Triax has a different geometry, different rib shape and different style types than BX. It works differently than BX geogrid and a design with TX is different than a design with BX.

Read the Long Answer

Is the testing for subgrade stabilization different than the testing needed to quantify the use of a geogrid for a paved road design?

Short answer: Yes. There are different design methods and inputs for each design.  The allowable amount of permanent deformation also differs for both of these applications. They require different testing, and have significantly different failure criteria.

Read the Long Answer

What should I ask for in comparing geogrids for Subgrade Stabilization?

Performance is not based on index properties.  It is determined empirically, using full scale in-ground testing.  Request a copy of the design inputs, using the Giroud-Han method as outlined by FHWA, that were used as the basis of equivalency.  Also ask for the full-scale testing, on the product being submitted (not another “similar product”), and the letter or report from the authors of the Giroud-Han method verifying that the testing and calibration were performed properly.  Once you have this information, you will be able to compare performance related sections and evaluate equivalency.

What should I ask for in comparing geogrids used in pavement design?

Performance is not based on index properties.  It is determined empirically, using precise, full scale in-ground testing.  Require a copy of the 3rd party testing on which the supplier is basing its claim of equivalency.  This testing should include Accelerated Pavement Testing (APT), performed on paved sections, following the procedures defined by NCHRP report 512.   There should be multiple sections tested over different subgrade conditions and different pavement section thicknesses.  Require a 3rd party review, by pavement design experts, verifying that the design values and methodology used are supported by testing for that product, and follow the guidance of AASHTO in R50-09  (“Geosynthetic Reinforcement of the  Aggregate Base Course of Flexible Pavement Structures”).  Also require 3rd party field validation testing, following AASHTO T221-90 (2012), to demonstrate that the results obtained in the field support the assumptions used in the design methodology, and that deformations are in-line with predictions.