Validation of Tough-Cell Design for Unpaved Roads, Geosynthetics 2015, Portland, Oregon, Pokharel, et al (2015)

Eight pavements constructed in challenging conditions validated the design methodology for NPA Tough-Cells for reinforcement, showing minimal rutting, requiring no additional gravel and performance exceeded design criteria


Over 100 unpaved roads have been constructed with Neoloy Tough-Cells using the Pokharel design methodology. Eight of these were evaluated to validate the design methodology and performance of NPA Tough-Cells reinforcement in built projects.

The pavements constructed were all situated in the Canadian provinces of Northern Alberta and British Columbia. Severe cold weather and freeze-thaw cycles, plus poor subgrade and high loading demand, posed a particular challenge to building long-lasting pavements requiring minimal maintenance.

The comparison between estimated and measured rut depth shows the road performance exceeds the rut design criteria. The roads were in good serviceability conditions and none required additional gravel. The design method was validated, exceeded theoretical values determined in lab testing in some cases and has a slight margin of safety factor.

Challenge – Real time testing for Neoloy Tough-Cells

Studies by Pokharel, Han and Giroud have all demonstrated the benefits of Neoloy Tough-Cell reinforcement, in terms of permanent deformation, settlements and failure criteria. Kief (2011) showed that Neoloy Tough-Cells can improve the modulus of pavement layers x3, while Thakur (2012) demonstrated that they increase pavement life x10. However, few real-time post-project evaluations have been conducted on NPA Tough-Cells to validate these findings. The design methodology was based on Pokharel’s modification of the Giroud and Han (2004) design for geosynthetic reinforcement, by changing the geosynthetics dependents according to calibrated test results.

Access Road over Swamp, Canada


Validation – Pavement construction in hostile conditions

Eight pavements were constructed using Pokharel’s design methodology. The roads were characterized by similar conditions and exposed to: A freezing and thawing cycles, poor subgrade and the demands of high loading associated with the oil, sand and forestry industries.

  1. MEG Energy:  Temporary access road: A 3.2 km x 8m access road to drilling areas carrying heavy loads over soft Muskeg soil was reinforced with NPA Tough-Cells and constructed within 6 weeks. Designed for 250,000 ESALs and rut of 62 mm, the road rut measurement was less than 25 mm after a full year of service. No gravel material was added after two years of heavy loading. Client satisfaction was demonstrated by their expansion of the solution to other access roads.
  2. MEG Energy:  Main access road: An existing 7 km long, 8m x 10m road was widened and reinforced with Neoloy Tough-Cell to make it strong enough for all-weather use. Although constructed during winter, almost no subsequent maintenance was required. Rut measurement after ~20,000 ESALs was less than 10 mm and after 100,000 ESAL was less than 30 mm on average. The road structure was firm and no sign of failure after two severe winters and heavy use.
  3. MEG Energy:  J-Hook road: A 700m long temporary curved section was constructed, designed for just 3 months of operation and 16,000 ESALs. However, the actual road loading was over 25,000 ESALs in the first month alone far beyond the project design limits, resulting in significant rutting and road failure.
  4. CANFOR:  Access road to logging yard: A road subject to ~100 fully loaded double trailer trucks daily was reinforced with Neoloy Tough-Cell. After two severe winters the road structure stood firm, with average rutting measured at just 25 mm and no grading or additional gravel was required.

logging yard (sawmill canada)

Canfor Access Roads and Log Yard Ground Improvement, Canada

  1. CANFOR:  Access within logging yard: The yard experiences about 20 passes of heavy CAT loaders each hour over the same path. Eight months after Neoloy reinforcement, average rutting reached 66% of its design criteria (75 mm) after 60% of its ESAL capacity (500,000 passes).
  2. County Road:  Lac St Anne: Road approaches to a bridge required almost weekly maintenance during the spring thaws. A new design for this bridge approach included crushed gravel reinforced with NPA Tough-Cells. It performed excellently, with no visible rutting, requiring no additional gravel and grading only twice after one year.
  3. County Road:  Long Run Exploration: A 3 km long major access road to a drilling site, was reinforced with Neoloy Tough-Cells. An average of less than 10 mm rut was measured after 4 weeks after traffic of about 8,000 ESAL.
  4. Cause Way Grizzly Oil Sand: Designed for one pass of a hydraulic trailer with 112 wheels on 14 axles, 100,000 ESALs. Rutting was minimal and the road remained serviceable 3 months after the pass of the extreme load.

Benefits – Strong pavement, reduced maintenance

Pokharel concluded that the design formula worked well beyond previous laboratory and moving wheel test limits and in some cases the design seemed to perform better than that predicted. The base reinforcement of unpaved roads with Neoloy Tough-Cells proved valid and reliable, with the following benefits:

  • Stronger and longer lasting pavement even over poor subgrade
  • Less maintenance required, lowering maintenance costs
  • Use of poorly graded, local subgrade, reducing hauling costs.

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