Nyirripi Road ch22km polycom trial

By Central Desert Regional Council

The Northern Territory’s Central Desert Regional Council (CDRC) manages 2,030km of local roads over an area of 282,000km² located in the centre of Australia. As most of the connecting roads between CDRC’s nine main communities are unsealed, maintenance and grading works are common and time consuming – leading Council to trial an exciting new road stabilisation technique.

As the CDRC’s traffic volume is relatively low, obtaining funding can be difficult – especially when road sealing requires large upfront and maintenance costs. Due to this, the CDRC Roads Team is trialling a technique that could see the region’s roads last longer, require less upkeep and provide a smoother journey for residents.

CDRC CEO, Leslie Manda, said,“The road stabiliser material trial demonstrates Council’s solid steps towards innovation to build road resilience in remote areas where there are funding restrictions.”

How does the trial work?

The trial involved a stabilising aid, which is used to improve the engineering properties of gravels and soils for road construction, thereby reducing maintenance requirements on unsealed roads.

CDRC decided to trial a Polycom Stabilising Aid on Nyirripi Road – which connects the remote community of Nyirripi with Alice Springs, and is over 440km long. Due to the project’s size, it took several months to line up all the requirements, equipment and timelines to prepare for the trial.

The stabilising aid was applied to a 1km section of formed sand clay, and a second 1km section was constructed with no stabiliser aid immediately after for comparison purposes. The two sections will be monitored for around two years, and regular tri-monthly levels will be taken with digital survey equipment to record any differences in wear of the sections.

This was the first time the CDRC crew had experienced the work of applying, mixing and compacting a stabilised road base. A crew from ID in Adelaide gave effective support and training into the method and handling of the stabilising aid throughout the two days of the trial.

Dispersing the stabilising aid.

The project’s journey

For the stabilising aid to be most effective, managing the material at optimal moisture content (OMC) and mixing it in thoroughly is critical to the whole process.

The graders turned over the first 500m section of wetted sand clay base course material, in order to get the material evenly mixed to OMC. Water was added as required during the mixing process and the material had to be turned over three times before it was ready for the stabiliser aid, with the whole process taking a few hours.

Prior to adding the stabiliser the sand clay base course was laid out 7m wide, ripped with the scarifyer to the 150mm depth of the base course, and after given a steady watering – water is required to activate the stabiliser.

A spreader was attached to the tow-bar hitch on a Toyota Hilux. The stabiliser, a fine granulated blue powder, is poured into the small bin and fed into a spinning device underneath, much like a fertiliser spreader.

The device spread the stabiliser two metres wide as the ute travelled at 16km/h along the prepared surface. This gave a spread rate of approximately 28kg per kilometre and appeared as very small blue specs on the sand clay surface after spreading. Finally the stabilised base course material is laid out and compacted with a multi roller.

Can the trial take the heat (and rain)?

Summer is the usual time of rain in the desert, with the summer of 2022-23 affected by extreme rain and flooding. Since the trial began, there has been torrential rain in parts of CDRC and the region was even declared a disaster site.

Due to the weather, the trial consultant conducted an early assessment to collect information, reporting that the road had survived the events without any ruts or wheel marks, which bodes well for the rest of the trial.

Mr Manda said that the trial showcases “the growing need for local government responsiveness to the impact of natural disasters”. A cost-benefit analysis will be completed once the trial is finished, and if the results are still positive, driving to and from remote communities in CDRC could be smooth sailing in the future.

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