The road repair process The road repair process
Auckland Transport is working hard to repair the damage caused by the recent extreme weather events in Tāmaki Makaurau Auckland. Locations that have the highest risk or safety needs are prioritised for attention.
On this page
- Road repairs mahi (work) explained
- Why does it take so long to repair roads?
- What are the steps / works involved?
- What are the reasons for a road being open or closed?
- My road is not on the list, why?
- How much will it cost to fix my road?
- How long is it going to take to repair my road?
- Do you monitor the stability of the road and how often?
- Glossary of slips and repair terminology
Road repairs mahi (work) explained
You may have noticed different repair work around roads near you and wondered what they’re for. We’d like to give you a bit of a run down and explain a bit of the mahi (work) we’re doing
- A barrier, dam or mound used to help channel water from the rain, away from the slip face to improve drainage and soil strength
- These are only temporary fixes and will be removed when the permanent work is started.
Example of bunding on the road surface on Kellys Road, which will channel rainwater on the road past the slip.
- Plastic sheeting over the slip to stop more rain from soaking into the slip or eroding the surface. It's secured tightly so that water running over the ground won’t get under the sheet.
- We need to prevent as much rainwater as possible from soaking into the soil
- It also helps prevent further slips in that area.
- In some areas, we can only cover parts of the slip (due to our team’s safety in being able to place it) and in other area’s simply not safe or possible to cover the slip.
Example of Polythene over slip face, combined with bunding treatment.
Frequently asked questions
Why does it take so long to repair the roads?
Most of the damage to the roads has been caused by the earth under the road being washed out by large volumes of water either above or underground. 90% of slips are caused by saturation and underground water There are several steps that need to be followed to repair the damaged roads.
Each road will need a unique plan for the repair which may include:
- Allowing the soil to dry – whilst the soil is still saturated it is difficult to assess the depth of the damage, and there is the risk of further movement.
- Geotechnical assessment & investigation– engineers will drill into the soil to discover the depth of the damage, followed up with offsite assessment and report. Depending on the severity of the slip it may take weeks to months depending on the testing required or whether the site simply needs to be monitored.
- Planning and design – a plan to rebuild the road is designed. In many cases, this will include rebuilding the earth under the road and constructing retaining walls. These designs then go through safety assessments.
- Procurement and delivery – the resources needed for the rebuild must be ordered and prepared. A contractor is engaged for the physical works, and traffic management plans need to be approved before the work onsite can begin.
- Funding needs to be sourced which can be a lengthy process.
What are the steps / work stages involved?
General steps for the repair process
- Budget approval
- Design approval
- Consents approval
- Procurement approval
- TMP (Traffic Management Plan) approval
What are the reasons for a road being open or closed?
A road is open if it's been assessed by our team as safe to drive on. Roads are closed if there is a risk to safety.
My road is not on the list, why?
If your road is not on the list, it’s because it’s now open with no restrictions and is safe for all to drive on.
The list only mentions sites that are high risk to the public, if significant traffic management is in place or there is a large impact to roads and traffic. Other roads have been identified by our teams and we’re working on ensuring they’re safe and prioritised for further assessment.
How much will it cost to fix my road?
Costs are dependent on the assessment and severity of the damage.
How long is it going to take to repair my road?
This will depend on the assessment, severity of the damage and availability of resources. This includes road crews and equipment that have already been scheduled for BAU road maintenance and redeployment of crews to help in Northland, Hawkes Bay & Te Tairāwhiti. Roads will also be prioritised based on the highest risk or safety needs.
Do you monitor the stability of the road and how often?
Yes we will keep an eye on all slips and monitor the stability of the road on a regular basis especially after heavy rain. How often depends on the location, if it’s on a busy section of road, may impact accessibility for a community or has weight or speed restrictions in place.
Glossary of slips and repair terminology (thanks to Waka Kotahi)
Types of slips
Soil and soft rocks near coastal areas, don’t need much rain to cause a slip, or more commonly known as a landslide.
An overslip is when vegetation, soil or other debris slips down onto the road from a bank or hill.
Overslip in Muriwai
Landslide on private land, Titirangi
Overslip, Wood Bay Road, Titirangi
Underslips occur on the downhill side of the road. They don’t always directly affect the road’s surface but pose a risk if unaddressed. When a section of the road’s surface and foundation has dropped away either from an underslip or other erosion, we call this a dropout.
These issues usually occur in hill country with weak geology, or in areas near the coast or rivers. They often happen suddenly during a storm event, though there are some known sites that we continue to monitor.
When the surface of the ground sinks it’s called subsidence. Sometimes we can’t see that subsidence is happening until it has already created a hazard on the road. Causes include too much water in the ground and weak underlying soil and rock. Subsidence is a major problem in this region.
Subsidence - Scenic Drive, Waiatarua between Forest Hill Road & Elevation Restaurant (*Elevation site)
Flooding occurs when water cannot drain away and spills onto the road. Heavy rain, blocked drains, steep banks, and limited vegetation can contribute to the effects of flooding.
Storm flooding - Kellys Road, Oratia
Treatments to improve resilience
A method used to treat subsidence sites is called Colmix. This involves using a specialised drill rig to mix a small amount of lime and cement into the soil to create a solid column, which improves the strength of the soil. Steel shafts can also sometimes be used to achieve the same goal.
Soft rock and soil like we have on the Western beaches and Waitākere Ranges can absorb a large amount of water and become unstable. By reducing the amount of water reaching the ground and removing water from under the surface, we can improve soil strength so that both overslips and subsidence become less likely.
Candia Road, Swanson – before storm damage
Candia Road, Swanson – after repairs to drainage & culvert
Where a reasonable foundation under the soil exists, a retaining wall can be used to reform an area of road. Retaining walls can be made from various materials: commonly iron or wooden posts and wooden boards, mass blocks of concrete or rocks, or baskets with rock fill inside.
Sometimes the best thing to do is relocate the road away from the issue. This could include moving the road onto more stable ground or away from a river.
Rock protection (known as a rock revetment) is a rock barrier to protect against erosion. Where erosion is occurring, a revetment can remedy the situation by placing fill at the site and then building a thick layer of large rocks to absorb the wave or river energy.
Rock protection on Waiti Bridge, Bethells Beach
There are several site monitoring techniques that can be used such as camera and drone surveillance to monitor slopes.
Low rock fall fences are effective for holding back small quantities of rock and are easy to maintain.
A groyne is a physical barrier that intercepts sediment that would otherwise erode a particular area. It is used to ‘river train’ and deflect flowing water away from high erosion-risk zones.
A gabion wall is a cage or box filled with rocks, concrete or sand and soil used for erosion control. They can be used between the river and the road to prevent underslips.