Studies on geosynthetic-reinforced road pavement structures, K. Rajagopal, et al (2014)

Field and lab trials by Rajagopal demonstrate the higher improvement value of Neoloy Tough-Cells compared to planar geosynthetics.

This field and lab study by Rajagopal, et al (2014) confirms that Neoloy Tough-Cell reinforcement increases the rigidity of pavement structures more than planar geosynthetic products like geotextiles and geogrids. NPA Tough-Cells were shown to be effective in lowering stress on the pavement layers and improving the reinforced layer modulus. The geocell confined soil acts as a semi-rigid mattress distributing loads over a wide area. Finite Analysis of Neoloy Tough-Cells produced an average modulus improvement factor of 2.90.

 Variation of settlement with number of load repetitions

Challenge – Increasing rigidity of pavement structures

Increasing the strength and rigidity of pavement structures, which often fail well before their design life, is the best way to increase pavement life; and geosynthetic-reinforcement is the best method to improve the pavement rigidity.  This study in the International Journal of Geotechnical Engineering, compared the performance of geotextiles, geogrids and NPA Tough-Cells in pavement construction in India, using both field tests and laboratory tests, and back calculations.

Validation – Field and laboratory testing

Field tests were carried out on two pavement sections:

  • Access road to the Govind Dairy Factory in Phaltan, reinforced with Neoloy Tough-Cells
  • Highway under construction near Chennai, reinforced with geogrids

Laboratory tests were carried out on 3 different heights of Neoloy Tough-Cell. Placed on 500 mm thick subgrade using dry sand and GSB, both static and cyclic plate loading tests were conducted in a test box. The cyclic loading tests were carried out at a frequency of 0.7Hz for 50,000 cycles, which according to Pokharel and Han is representative of the traffic loading.

The results of the laboratory tests were verified by back calculations to estimate the equivalent elastic modulus of the unreinforced and reinforced pavement systems.

Results – Modulus improvement, better performance than other geosynthetics

The field tests validated that NPA Tough-Cell reinforcement is “substantial” at both low and high settlements, while geogrids showed “marginal” improvement only at large settlement levels. In the field study, while the unreinforced section required reconstruction 3 times in 9 months, the reinforced section was performing very well 3 years later, prompting the client to reinforce the entire stretch with Neoloy Tough-Cells.

Cyclical loading tests in the laboratory, as indicated in the table below (100 mm height), showed that Neoloy Tough-Cells produce a modulus improvement factor (MIF) of up to 2.90 The MIFs obtained from both static load tests and the cyclic load tests were close to each other

Type of test Geotextile Geogrid + geotextile Tough-Cell + geotextile
MIF from cyclic test 1.67 1.99 2.40
Modulus of elasticity 50,500 61,100 84,500
MIF from finite element results 1.74 2.10 2.90

Subsequent back calculations found that the improvement factors fall within the same range as those estimated using cyclic loading tests.

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The authors concluded that both the strength and stiffness of pavement systems are improved by the use of Neoloy Tough-Cells. This brings the following benefits:

  • Increased life cycle, reducing reconstruction costs
  • Reduced need for maintenance and associated costs
  • Reduced pavement thickness, lower construction costs
  • Fewer aggregate materials required, improved carbon footprint

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