Trailer Magazine

ARRB paves way for improved road surface testing

  • Posted on Tuesday 29th, October 2019.

Austroads has published a report describing the findings of a project undertaken by the Australian Road Research Board (ARRB) in the interests of improving pavement rehabilitation design.

The study has centred around finding more cost-effective ways of assessing the strength of existing pavements based on surface deflection measurements.

With more vehicles, especially heavy vehicles, on the road network, road maintenance and rehabilitation are large and growing components of Local, State and Commonwealth government budgets.

“There were two parts to this project,” said ARRB Principal Professional Leader, Future Transport Infrastructure, and principal author of this report, Dr Didier Bodin.

“These were to assess the feasibility of using traffic speed deflectometer data to improve pavement rehabilitation treatment design; and improve the back-calculation algorithm that determines the pavement layer moduli from pavement surface deflection.”

Over time procedures have been developed using different deflection technologies including the Benkelman Beam and the falling weight deflectometer (FWD). The traffic speed deflectometer (TSD), recently introduced in Australia and New Zealand, provides at-speed, repeatable pavement deflection measurements under a rolling wheel load, but its data had not been previously used in project level rehabilitation design.

The relationship between FWD and TSD data was evaluated using paired databases provided by road agencies, and a linear regression analysis method was developed.

The findings allowed a deflection standardisation factor to be developed to predict the FWD maximum deflection from the TSD data. This factor was then used to predict Benkelman Beam maximum deflections from measured TSD data for incorporation in the empirical design methods.

“Based on the results, we calculated a deflection standardisation factor to be used for pavement treatment design, with a factor of 1.2 proposed for the empirical thickness design of granular overlays,” said Bodin.

“This report also presents the process for estimating the modulus of existing pavement layers and subgrade from measured surface deflections. These moduli can be back-calculated from FWD data, but practitioners use different processes and software which can lead to different design outcomes.

“As a result, we developed a detailed back-calculation algorithm based on previous Austroads methods and included two additional enhancements to reduce variability of back-calculated pavement layer moduli. One method calculates the seed modulus value for the subgrade, and the second method enables an embedded multilayering procedure for granular materials to be used.”

The report describes the algorithm, including instructions and detailed mathematical equations, and the two case studies used to validate the data.

“These findings promote innovation and will help standardise processes for estimating the strength of the existing road assets,” said Bodin.

“Overall, better design methods will improve durability and quality of pavement rehabilitation treatments, helping save road agencies time and money.”

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