Modulus Improvement Factor for Geocell-Reinforced Bases, Geosynthetics India 2011, Kief, O., and Rajagopal, K. (2011)

A Modulus Improvement Factor (MIF) of 2.75 was validated for the design of road projects in India and Israel from the contribution of Neoloy Tough-Cell in reinforcement of the base layer.


Geocells were originally used to reinforce base layers over soft cells. But this study, published in Geosynthetics India, provides academic proof that NPA Tough-Cells are also highly effective in upper base layers. Building on studies by Han, Pokharel and others, which demonstrate that NPA Tough-Cell-reinforced bases have a significantly higher performance than unreinforced bases, this study shows that an NPA-Tough-Cell reinforced layer has a modulus improvement factor of 2.75. Field plate load tests and a demonstration project, revealed that NPA Tough-Cells significantly reduce construction and maintenance costs.

Validation – Field plate load testing

A field study was carried out on samples from an access road at the Govind dairy in Phaltan. Plate load tests were carried out in December 2010 to compare the modulus of NPA Tough-Cell reinforced samples and unreinforced samples.

The test found that the NPA Tough-Cell reinforced soil layer has a modulus improvement factor of 2.75, confirming similar results in other research.

In addition, the following visual observations were noted:

  • The unreinforced road sections showed extensive undulations, while the NPA Tough-Cell reinforced road sections had maintained a perfect level surface
  • The unreinforced road sections displayed severe rutting, requiring frequent maintenance

Validation – Demonstration project

A further test was carried out on a 0.5 kilometre demonstration section on the Cross Israel Highway 6, as part of a road widening project. Plate load testing, comparing an NPA Tough-Cell reinforced sample with an unreinforced sample, was designed specifically to investigate reducing the cost of infill and asphalt. The test found a modulus improvement factor of 2.92 on the NPA Tough-Cell reinforced sample

Results – Lower thickness, less maintenance

This study demonstrated that not only do NPA Tough-Cells display high tensile strength, resistance to creep, dimensional stability, but that they can be deployed to great effect in the upper base layers of heavy-duty paved roads. Due to the increased modulus, the following results for the demonstration project were recorded:

  • Asphalt thickness could be reduced from 200 mm to 160 mm
  • High cost crushed stone could be replaced with lower quality, cheaper subbase material
  • Total subbase layer thickness could be reduced by 20 mm
  • One complete deep scraping and overlaying of asphaltic layers could be saved over a 20-year design life

Benefits – Lower costs, better for environment

Using NPA Tough-Cells was found to increase strength and bearing capacity, enabling a reduction in layer thickness of asphalt, base and subbase layers. The demonstration project showed that savings could therefore be made:

  • 8% reduction in construction costs
  • 50% reduction in maintenance costs over a 20-year period
  • Additional savings on manpower, equipment and logistics
  • Greater use of local materials and manpower, reducing the carbon footprint

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