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AuthorTensar International

DateSep 04 2017

Tensar International’s Spectra M-E software is enabling pavement engineers to analyse the benefits of incorporating stabilisation geogrids in their designs more accurately then ever-before.

“Spectra M-E is unique because, for the first time, engineers can use an mechanistic-empirical (M-E) approach to analyse and predict the service life performance of a pavement when Tensar TriAx geogrids are incorporated in unbound granular layers,” explained Tensar Vice President Global Product Management and Technology Tim Oliver.

A granular layer stabilised with TriAx performs as a composite, due to the interlocking mechanism and particle confinement that develops between the particles and the geogrid. This mechanically stabilised layer provides more effective support to the entire pavement structure than aggregate alone and improves overall performance.

“Empirical methods use stabilisation factors to assess the benefits of incorporating TriAx, which can help reduce pavement thickness, extend service life or a combination of the two,” Oliver said. “The final design can then be assessed for life-cycle costs, including the cost of construction, materials and environmental impact – to ensure the optimal design has been identified.

Mechanistic-empirical (M-E) analysis, on the other hand, uses engineering principles to model stresses and strains in pavement layers caused by traffic loads (the mechanistic part), based upon site-specific conditions, such as founding layers, pavement materials and climate. The perfromance over time is then modelled, based upon the observed behaviour of pavements from field observation and accelerated testing (the empirical part).

“This iterative process allows engineers to optimise their design to meet a project’s specific performance criteria, over the lifetime of the road, much faster and more accurately,” Oliver explained. “However, up until now, it has not been possible to model the positive effect of stabilisation geogrids.”

Spectra M-E calls upon data from more than 30 years of testing and trials, including full-scale accelerated testing of pavements carried out by the UK’s Transport Research Laboratory and the US Corps of Engineers on behalf of Tensar.

“This wealth of empirical data on fatigue, rutting and shearing of road pavements – with and without geogrid – allows engineers using Spectra M-E to see the performance benefits of including TriAx in their designs,” Oliver said.

The software is designed for use with TriAx – other geogrids will perform differently, so analysis using TriAx-specific data would not be accurate, Oliver said – and has been validated independently by leading US pavement specialist Applied Research Associates.

Spectra M-E is used by Tensar’s design teams around the world and is also available to suitably qualified pavement engineers experienced in M-E design; a licence is required for partner users. Contact Tensar at for further information.