The comparative “Roadeo” field test, evaluated the different engineering properties of 4 geosynthetics in poorly-graded sand embankments of new highway construction, including NPA (Novel Polymeric Alloy – Neoloy) Geocells, as part of the SHRP 2 (US Strategic Highway Research Program) conducted at the Center for Earthworks Engineering Research (CEER), Iowa State University. 8 conventional QC and QA methods testing methods were used to evaluate the results, which were conclusive – Cyclical plate loading tests showed that the Neoloy Geocells had the lowest permanent deformation (4.1 mm vs. 5.6 mm for geogrid) and the highest modulus of all the geosynthetics. The study validated that Neoloy Geocells are more effective at increasing the stiffness and lifespan of highways than any other geosynthetic solution.

Validation – Comparative in-situ testing

Four geosynthetics were installed in poorly graded sand embankments on State Road 98 under construction in Jacksonville, Florida – NPA Geocells, biaxial geogrids, geogrid/geotextile geocomposites and polypropylene woven fabrics. Four test beds were constructed, with the geosynthetic placed on top of an existing sand base layer.

Earth pressure cells were installed in soil layers to monitor total horizontal and vertical stresses before, during, and after vibratory compaction.

In-situ tests were conducted on the 4 samples – They included cyclic plate load test to determine elastic initial/reload modulus and permanent deformation characteristics, plus LWD (Light weight deflectometer) to determine elastic modulus.

Highway test section with geocell reinforced sand base 

Results – Neoloy Geocells have highest modulus, lowest deformation

The report on the tests, by White and others, concluded that “Sand and gravel are improved more with NPA Geocells than any other geosynthetic.”

Cyclical plate loading tests showed that Neoloy Geocells had the lowest permanent deformation (4.1 mm as opposed to 5.6 mm for geogrid) and the highest modulus of all geosynthetics tested.

The modulus improvement factor (MIF) of the sand as a result of NPA Geocell confinement was consistent with the results of other field tests in the US, India, Holland and Germany, which produced a MIF of 2.5-4.0, validating the use of sand for structural infill for highway pavements.

Layout of PRS Neoloy Geocells on site with sand infill

Benefits – Increased stiffness, increased lifespan, reduced costs

The authors noted several benefits of Neoloy Geocells – lateral confinement increases stiffness and shear strength of the soils, which distributes wheel loads more widely and reduces rutting, making it applicable to a wide variety of highway construction. In particular, NPA Geocells allow the following:

  • Stronger pavements, sustain greater loads for longer
  • Reduced pavement deformation, costs saved on maintenance
  • Reliable construction over unstable soils, reducing reliance on expensive imported soils