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ARA Independent Review & Validation:

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

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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 significant time and money 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.

Evaluating Geogrid Equivalence in Subgrade Stabilization

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

What properties matter in a geosynthetic for subgrade stabilization?

Numerous research projects over many years have tried to correlate the physical properties of geogrids with their performance in subgrade stabilization, but no correlation has yet been found. Many manufacturer and supplier sales representatives routinely misrepresent this fact in their efforts to claim equivalence under construction specifications, publishing product data sheets that compare selected physical properties between products.  The situation is further confused because many public agencies do not have performance-based specifications, so they default to specifying products based on physical properties. However, because physical properties do not correlate to performance, the comparison of physical properties between products is effectively an arbitrary comparison.  There are no physical properties of geogrid that are universal inputs into any accepted and validated design procedure for subgrade stabilization.

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.

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How do I know if a product has gone through the proper calibration?

Any manufacturer claiming that its products are calibrated to the Giroud-Han design method should be prepared to provide documentation from the authors of this method (letter or report), verifying that testing and calibration have been properly performed for the specific product(s) being proposed.

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“…a geosynthetic improves an unpaved road through complex mechanisms that mostly do not involve the strength of the geosynthetic…”
(J.P. Giroud and Jie Han 2012)

Comparisons based on physical properties, and/or small-scale tests, are not the same as performance comparisons, nor do they apply to all conditions. Reliance on these comparisons can lead to a false sense of security.

To properly evaluate a product, product testing needs to be performed by a 3rd party. Methodologies derived from that testing need to be calibrated and validated to make sure that the level of performance (usually measured in looking at deformation) is in line with the predicted values.  Simply basing performance on one or two case studies does not constitute a design methodology. 

How should performance be compared? What methodology should be used?

For Subgrade Stabilization, the Giroud-Han design method is the most widely accepted method for evaluating the benefit of geosynthetics. This methodology is outlined in the FHWA Geosynthetics Engineering Manual (NHI-07-092). It is generic and applies to all geosynthetic products. Proper testing and calibration of products are outlined in the reports below. (For geogrids used as a structural component of pavement design, different testing and methodologies apply. Click here for more information.)

The original reports outlining this method were published in the August 2004 ASCE Journal of Geotechnical and Geoenvironmental Engineering.  Subsequent papers outlining appropriate testing and calibration to these methods have been published in recent years. Copies of some of these papers are included here.

Geosynthetics Magazine Article:

Mechanisms governing the performance of unpaved roads incorporating geosynthetics

Geosynthetics Magazine Article:

PART 2: The Giroud-Han design method for geosynthetic-reinforced unpaved roads

Geosynthetics Magazine Article:

PART 1: The Giroud-Han design method for geosynthetic-reinforced unpaved roads

FHWA Reference:

Dr. Giroud, Ph.D., PE & Dr. Jie Han, Ph.D., PE

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