New trafficking test rig up and running at USASK, Canada

Subbase comparison testing with Tensar InterAx geogrid is underway. 

A laboratory-based full-scale trafficking rig has completed its commissioning at the University of Saskatchewan (USASK). Trafficking tests are underway comparing the performance of subbase layers with and without Tensar InterAx geogrid. The data will be used to further validate Tensar’s LAAMS method (see below) for the design of unpaved roads. 

The USASK Trafficking Test Facility

The test facility consists of a large test box, wide enough to allow four test lanes to be constructed side by side. A manufactured subgrade material is placed and compacted in the box. On top of this, a selected unbound aggregate material is placed and compacted to the specified layer thickness and density. 

Trafficking takes place using a rig with dual wheels and pneumatic tyres, applying a 40kN load. This tracks back and forth over the lane undergoing test.

As the testing progresses, rutting develops. The longitudinal surface deformation profile is measured continually by monitoring of the vertical displacement of the axle. Transverse rut profile measurements are taken periodically. In addition, high speed accelerometers have been installed to enable a newly developed multi-channel analysis of surface waves (MCASW) technique to determine the stiffness of the aggregate layer during the test. 

In this episode of Ask Andrew, Andrew Lees takes a trip to the University of Saskatchewan (USASK) Trafficking Test Facility 

Why build a trafficking test rig in a laboratory rather than test in the field?  

Field testing can provide invaluable validation of a design for a specific construction method in a unique combination of location, site conditions and environment. However, it does not allow control of construction variables and environmental variables such as soil moisture content, rainfall, and temperature.

The benefit of laboratory-based full-scale testing is that it allows control of all variables. By enabling variables to be kept constant or within specified tolerance levels, the effect of a single variable can be explored and quantified. For example, the effect of inclusion of a specific geogrid. In this way true comparisons can be made, and design parameters developed.

The Tensar trafficking test program at USASK. 

For the test program commissioned by Tensar, a subbase layer of high quality crushed aggregate overlays a soft clay subgrade. The clay is maintained at a CBR of around 1%.

Some test lanes have Tensar InterAx geogrid installed below the subbase, creating a mechanically stabilised layer. A true comparison of the trafficking performance of the different sections can be made.

The data obtained will be used to further validate the LAAMS method for the design of unpaved roads.

Tensar has a long history of testing geogrid performance by trafficking tests. 

Tensar has long been a strong advocate for the use of laboratory-based trafficking testing to validate the performance of mechanically stabilised layers. Tensar has its own small scale trafficking test rig at their research facility in Blackburn, UK. This is used for product development and comparative studies. For performance validation and the development of design parameters, full-scale testing is preferred. The first full-scale trafficking tests were conducted at the UK Transport Research Laboratory (TRL) in the early eighties. Since then, multiple trafficking test programmes have been carried out at the TRL facility, the Engineering Research & Development Facility (ERDF) of the US Corps of Engineers (USCoE) in Vicksburg USA, and other facilities. 

The data from these test programmes has been used to develop and validate the LAAMS Method for the design of unpaved roads and to determine design parameters for each grade of Tensar geogrid.

What is the LAAMS method? 

The Lees Approach to Applied Mechanical Stabilisation (LAAMS) provides a scientifically rigorous and fully validated method for the design of unpaved roads incorporating stabilisation geogrids. Previous design methods for unpaved roads have been based on a narrow set of observations, requiring major assumptions that restrict their range of application. LAAMS overcomes these limitations by using the data obtained from laboratory testing and both small-scale and full-scale trafficking testing, to characterise the problem in terms of its true mechanics. It is the first method to accurately incorporate the beneficial effects of mechanical stabilisation using geogrids. Further information on the LAAMS method can be downloaded from here.

Software for the design of unpaved roads  

The LAAMS method for the design of unpaved roads has been incorporated into Tensar+ software.  
If you would like to obtain your free copy of Tensar +, visit:

www.tensarplus.com