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Application Specialist – Roads & Rail, Nilex Inc.

In 2004, Dr. J.P. Giroud and Dr. Jie Han advanced the field of geosynthetics when they published their methodology for applying geosynthetics in unpaved structures in the ASCE Journal of Geotechnical and Geoenvironmental Engineering. The methodology has since been adopted by the Federal Highway Administration in 2008, and is considered at the forefront among industry professionals.

Karan Jalota, an applications specialist with Nilex Inc., is one of those professionals. For a better understanding of the doctors' original research, and the current geosynthetic practices, we reached out for his perspective.

What did Dr. J.P. Giroud and Dr. Jie Han's research bring to the field of geosynthetics?

When Dr. Giroud and his previous colleague Dr. Noiray started research with geotextiles, they devised equations which indicated that if you used a specific type of geosynthetic fabric, you could potentially provide an enhancement to the subgrade bearing capacity. Therefore, one could look at reducing the thickness of an unpaved structure.

Dr. Han came in on the next phase of this research, which was extremely important. They published the Giroud-Han Method for applying geosynthetics on unpaved roads in 2004, which helped engineers better understand the extent of their work and what would need to be done to calibrate products to the G-H equation.

For example, if I have geogrid “X” from one company, and someone else has geogrid “Y” from another, they may say it's the same, but my question to them would be: Have you done the testing and validated it with multiple subgrade and loading conditions? Have you calibrated and provided a calibration factor to put into an equation like the G-H equation? That is why Dr. Giroud and Dr. Han's research is so important, and why it's been at the forefront of the industry for 30 years.

How has that methodology been interpreted since?

The original research is typically misunderstood because one of the key boundary conditions was based on 10,000 axel passes. Today, unpaved structures certainly carry more, so when somebody says they're going to go up to 100,000 axel passes – or even 10 million – they forget the original methodology was based on 10,000. To go higher, you need to conduct testing. It is also recommended to have a third-party review of the data and results, and for the reviewer to provide conclusions.

Also, the original methodology was capped at a specific axel load. Similar to the AASHO Road Test (circa 1960), their testing was with vehicles with much lesser weights than the vehicles we have currently. That’s one example of factors people occasionally do not take into consideration. You really need to be extremely cognizant of what the original methodology was based upon.

Overall, why is the design aspect paramount when incorporating geosynthetics into unpaved roadways?

It's important for several reasons. Geosynthetics have been around in Canada for 35-40 years. Traditionally, back in the late 1970s and early 1980s – and even to this day – geosynthetics were just put in the ground for stabilization purposes. Now, as the research has developed, it's important to understand the boundary conditions of where geosynthetics would be effective and the types of geosynthetics that would be effective in specific conditions. That makes the design aspect crucial, especially when it comes to engineers specifying materials and reducing thicknesses of structures. 

What are the key mechanisms that impact unpaved road performance?

The key mechanisms depend on the types of geosynthetics that are used. Wovens can have higher strength and lower elongation, and non-wovens can extend up to 50% once you put aggregate on them, which is also dependent on how stiff or dense the subgrade is below. Then, if you think of a high-strength woven, it may still extend up to about 2-5%. Once these products extend, they are essentially like a hammock acting in tension and holding up the load of the trafficked structure.

When you are looking at grids, they are the most effective product when using granular material because the fractured aggregate interlocks with the apertures/holes of the geogrid. Also, geogrids can provide an enhancement of the load distribution, effectively enhancing the bearing capacity of the subgrade soils from what they would have been by a certain factor, which is dependent on the type of geogrid chosen.

How can the industry improve when it comes to using this methodology correctly?

It's all about knowledge transfer. That's why I write articles for our newsletter, conduct workshops for industry, share research and encourage my colleagues to do so as well.

For more information, visit www.nilex.com.

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