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Uneven Road Surfaces on the Hauraki Plains – FAQs

In Hauraki, a large proportion (44%, about 230km) of the Hauraki District Council (HDC) road network lies on soft, moisture sensitive organic (peat) and gley soils. These are predominantly on the Hauraki Plains.

*INTERESTING FACT - Almost half of all peatlands in New Zealand are located in the Waikato region. These peatlands have taken over 18,000 years to form and can be tens of metres deep.1

What does this mean for our Plains' roads?
What can we can do long term to prevent this issue from repeating itself? 
What are gley soils?
How do drought conditions amplify soil shrinkage in peat and gley soils?
Are the condition of these roads a hazard to driver safety?
What are we doing to rectify this issue?
When will speed restrictions and warning signs be in place and where? 
How long will speed restrictions be in place?
What roads are Council responsible for?
Repair failure – drought or workmanship?
I have noticed a road that seems dangerous. What should I do?
To report an issue on a state highway 
References

 

What does this mean for our Plains’ roads?

These founding soils are difficult for road construction due to low bearing strength, and are typically unsuitable for building roads using traditional design principles.

As well as the issues with bearing strength, organic and gley soils are also moisture sensitive, making them prone to movement when the soil’s moisture levels change. For example, shrinking in dry weather.

This shrinkage can cause road surfaces to settle unevenly, creating bumps, cracks, and ruts in the road.

This is a common issue around the Waikato region and is more pronounced following dryer than usual summer and autumn seasons.

Because issues are primarily caused by environmental factors (as opposed to load related), such as the underlying soils’ bearing strength, movement with seasonal wetting and drying, and recent ‘shock events’ such as the 2020 drought causing widespread pavement (road surface) distress, it is difficult to achieve a traditional design life of 25-30 years for these roads.

What can we can do long term to prevent this issue from repeating itself?

Peat and gley soil layers on the Hauraki Plains are very deep and cover a wide area, making it uneconomical to excavate and replace them with more suitable road foundation materials or improved pavement layers. We manage the situation by budgeting to reshape the surface of peat & gley roads every 5-20 years, but exceptionally dry years mean more repair work.

It is no simple task catching up on ‘shock event’ repairs - we expect the 2020 drought repair programme will be completed over three years – in addition to our ‘business as usual’ pavement repair programmes.

It appears that weather patterns are changing, with more frequent drought events experienced in the Hauraki in recent years as evidence of this.

As part of our response to the 2020 drought, we are researching road embankment configuration and materials. This has involved collecting materials from a number of sites across the Hauraki Plains so they could be laboratory tested. This will give us further understanding of the soils properties and triggers to road pavement distress, helping us to tailor treatment types and strategies moving forward.

What are gley soils?

Gley soils are poorly or very poorly-drained in their natural state. Saturation occurs during prolonged periods, oxygen becomes limited, and reducing conditions occur.

They are essentially older wet mineral soils derived from a variety of parent materials including alluvium, colluvium and wind-blown coastal sands. They occur in valley floors, on the upper part of coastal terraces and coastal and river back swamps or former back swamps. 2

How do drought conditions amplify soil shrinkage in peat and gley soils?

The result of soil shrinkage is more easily observed during drought conditions – this is because these ‘shock events’ amplify pavement distresses in a short timeframe.

The double whammy of the extreme drought of 2019/2020 and the delays to our usual maintenance work due to Covid-19, means that some of our roads on the Plains are still showing signs of cracking, slumping, rutting and settling, from when the underlying soils dried out and contracted.

Are the condition of these roads a hazard to driver safety?

Differential settlement leading to the localised loss of the normal road shape can be a hazard, particularly for motorcycles, truck and trailers with a high load or vehicles travelling at speed. The most important thing is for drivers to slow their speeds and drive to the conditions over the winter period.

What are we doing to rectify this issue?

Council staff and contractors are monitoring roads and intervening where required to erect warning signs and temporary speed restrictions and/or to smooth the surface with asphalt when needed.

The combined impacts of drought and Covid-19 delays mean our contractors are working through a reseal and repair programme that is 4-5 times their usual workload.

We have had to prioritise work and resort to temporary fixes in some instances until we can tackle them again in the 2021/2022 summer construction season.

We don’t generally like to build roads in the wetter winter months, and like to delay repairs where possible to allow soils to return to ‘normal’ moisture levels. However, we also decided not to leave failures too long as water ingress from rain can cause the roads to fail too so the pavement failures that presented a safety risk have been repaired.

When will speed restrictions and warning signs be in place and where?

Drivers will see signs and speed restrictions in place on many of our roads already so please be aware of road crews out and about, slow down for the temporary speed limits in place and drive to the conditions.

How long will speed restrictions be in place?

Until longer term pavement repairs can be completed. Repairs are generally undertaken within the drier construction months of October – April.

What roads are Council responsible for?

We manage and maintain the urban and rural local road network in our district. Waka Kotahi NZ Transport Agency manages and maintains the three state highways in our district – State Highway 2, State Highway 25, and State Highway 26.

Repair failure – drought or workmanship?

When the repairs fail, we have to establish if this is due to the underlying drought conditions or workmanship. If we establish that it is workmanship, this is reworked at the contractor’s expense.

I have noticed a road that seems dangerous. What should I do?

Please call our customer service team on 0800 734 834 or 07 862 8609 and report it. While our staff may be aware of the location and issue, at times cracks and bumps can appear quickly over a few days so we need to hear about any issues as drivers come across them.

Please drive to the conditions, be vigilant and report any URGENT issues to us 24/7 on 0800 734 834 or 07 862 8609. For non-urgent service requests, you can also message us on Facebook or complete a service request online.

To report an issue on a state highway

Ring 0800 4 HIGHWAYS (0800 44 44 49)

References

  1. Waikato Regional Council - Managing Peat.  Sourced 8 July 2021 
  2. Description of gley soils sourced from Bay of Plenty Regional Council Enviro Report. Sourced 19 May 2021

For a larger view of the image below, download the pdf - HDC local roads network organic and gley soils [PDF, 969 KB] PDF document

Organic and Gley soils in the Hauraki roading network