Proper testing requires several steps, as outlined by pavement design experts. The process starts with laboratory testing to better understand how different geogrids interact with different materials. Once this is better understood, geogrids should be tested at full scale to validate the laboratory assumptions under actual wheel loads. Rigorous Quality Assurance and Quality Control procedures are needed to accurately measure and record performance. Changes in asphalt temperature, climatic conditions, pavement materials, loading conditions, layer thicknesses, and other conditions will affect performance, and therefore the measured benefit of the geogrid. The National Cooperative Highway Research Program (NCHRP) has published detailed procedures and requirements for this type of testing in NCHRP Report 512, Accelerated Pavement Testing: Data Guidelines.
Field testing is not as precise as Accelerated Pavement Testing (APT) and, if not conducted properly, can lead to significant inaccuracies regarding performance due to variances in materials, thicknesses, environmental conditions, and subgrade non-uniformity. It requires significant oversight by pavement experts to make sure appropriate data is captured and analyzed correctly. The testing performed by New Hampshire DOT, in 2014-2015, provides a good example of the level of effort required.
"At this time, increasing the layer coefficient is a technique that should only be applied when using Tensar TriAx geogrid, as no other products have had this technique validated through accelerated pavement testing."
Once appropriate testing has been performed, and a methodology for incorporating the test data in design has been developed, the research and design methodology must be reviewed by an independent 3rd party pavement design expert. The review should provide:
This review ensures that values being used for design are sound and results will be reliable and predictable.
The final step in properly incorporating geogrid in pavement design is field validation testing, verifying that the constructued values are in line with the predicted values.
ARA Independent Review & Validation:
Tensar's Modified 1993 ASSHTO Pavement Design Procedure and Verification of SpectraPave4-Pro Software