Summary of Extensive Research Program on NPA Conducted at University of Kansas

A summary of extensive research showed that NPA - Novel reduced vertical stresses, permanent and creep deformations, and increased elastic deformation, stiffness, and bearing capacity of base courses.

Summary

This summary of various studies on Neoloy Geocell reinforcement validates that NPA Geocells increase bearing capacity and stiffness, while reducing permanent deformation and vertical stresses. A series of static and cyclic plate loading tests, full-scale moving wheel tests, and numerical modelling was conducted on a variety of infills by the research team at the University of Kansas. In particular, these tests found that Neoloy Geocells can increase stiffness by a factor of up to 3.2x and can reduce vertical stress by approximately 50%. Consequently, Neoloy Geocells can reduce the required base thickness, lowering construction costs.

Challenge – High-quality roads with optimal resources

There is a constant need to optimize natural and financial resources while constructing high-quality roads. Most research has focused on planar geosynthetics such as geogrid and woven geotextile, although Rajagopal and later Mandal and Gupta demonstrated that geocells increase strength and bearing capacity.

Validation – Wide variety of field testing

Staff at the University of Kansas conducted a series of tests in order to investigate the strengths and properties of NPA Geocells. The results were further confirmed by a three-dimensional numerical model developed by Yang:

Static plate-loading tests

Vertical stress was compared in unreinforced, single NPA Geocell reinforced and multi NPA Geocell reinforced samples. The deformation of the base course was recorded at 5-minute intervals with increments adjusted via air pressure. The following results were recorded:

  • Neoloy Geocell confinement significantly increased the bearing capacity of Kansas River sand
  • The stiffness of Kansas River sand and RAP bases was increased significantly by Neoloy Geocell
  • Neoloy Geocell confined bases recorded a stiffness improvement factor of between 1.2x and 3.2x
  • An increase in Neoloy Geocell confinement produced a decrease in creep deformation

Cyclic plate-loading tests

Earth pressure cells and strain gages were used to compare the performance of NPA Geocell-reinforced and unreinforced bases over weak subgrade. The tests found that NPA Geocell-reinforced bases performed like a slab and the following results were recorded:

  • Neoloy Geocell reinforcement reduced permanent deformation and vertical stress
  • In RAP bases, Neoloy Geocell increased elasticity
  • The ratio of the loading cycles for the Neoloy Geocell reinforced section, to that for the unreinforced section was approximately 10x

Full-scale moving wheel tests

Strain gages were used to compare NPA Geocell-reinforced and unreinforced samples over various bases. The following results were recorded:

  • By distributing loads over a wide area, Neoloy Geocells reduced the rut depth and vertical stresses transferred to the subgrade
  • The vertical stress recorded in the Neoloy Geocell-reinforced sample was approximately 50% of that in the unreinforced sample

Benefits – Stronger pavement base, lower cost

The tests summarized in this paper validate that Neoloy Geocell is a cost-effective solution to strengthening pavements, bringing the following benefits:

  • Reduced required thickness of pavement, reducing construction costs
  • Stronger, stiffer pavement
  • Longer life-cycle, reducing maintenance costs

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