Oonah Road - Updates

Published on 22 July 2024

$7.5 million from the Capital Works Program 2023-24 has been allocated to repair the significant road damage caused by the October 2022 rain event across the multiplicity. Read more about it in Councils Annual Plan and Budget Estimates 2023-24

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UPDATES:

6 November 2024

The residual landslip material has nearly all been removed to a depth of around three meters. 

Clean rock will be punched into the remaining residual landslip material to create a suitable subgrade. 

The project remains on schedule to be completed by the end of 2024, as long as no unexpected issues are discovered before then. 

2 Oct 2024

The work that is ongoing at Oonah Rd is enormous in scale and complex in delivery, with the site engineer forecasting that the road will be closed at least until the end of 2024. 

 

The above photograph shows the section near Guide Road that is ready for sealing once the weather is dry enough. 

 

The section closer to Highclere, which local refer to as ‘the Hill climb section’, is currently being repaired and is about a month away from being finished (if the weather permits).

 

However, during the repairs to the Guide Road end, a third section of road failures was found between the two sites, which also requires a mass bulk out and repair.  

 

With the materials coming from a quarry located at one end of the project, this necessitates works to be confined to one site at a time. 

 

With the best-case scenario being for a completion of work by the end of 2024, the road could be reopened in January 2025, provided the ongoing wet weather does not extend too much longer, and additional locations of failures and landslips do not occur.  

 

Council appreciates that the long time-frame for this project does negatively impact on local residents who would otherwise use the road, but large sums have been invested in the project to ensure that all machinery and workforce required has been available to finish the mammoth project at the earliest possible opportunity.

 

22 July 2024

Four active sites on Oonah Rd

• Oonah Road currently has four active sites with road failures.

• The section near Guide Road (image above) has had the fill embankment removed and replaced with over 27,000 tonnes of rock fill and is close to being finished.

• Another landslip failure was found closer to Highclere and is being repaired (image below).

• The hairpin is the next section to be dug out, with a large amount of material that requires excavating.

• A fourth section will be dug out after this one with similar issues.

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12 April 2024

Oonah Road East (Guide Road)

• The residual landslip material has nearly all been removed. This has been located to a depth of 13m below road level and has required a considerable volume of unsuitable material to be removed in a staged method to ensure no catastrophic embankment failures

• Rock fill is starting to be placed to rebuild the embankment

• Work on Far East is on hold until this section is complete to ensure free truck movements through site

   Above: Unsuitable material at a depth of 13m has been removed 

Oonah Road (Douglas Road)

• Single lane traffic arrangements are in operation
• Digout of soft spots and installation of new culvert has been completed
• Rock buttress fill is nearing completion
• The culvert on the top corner has been found to be collapsed in the middle, so will be dugout and replaced
• Further tree and branch removal will be conducted from Douglas Road to the farm gate where Harding's
  compound is. Most branches in this area will be hitting trucks and there are some trees ready to fall during the next
  major rain event
• Repair works on the road above the culvert at Douglas road will include a 300mm concrete beam on both sides of the failed rock pitching, plus localised road re-shaping to make a low point over the existing pipes, with clean-out of the upstream inlet and new rock pitching and Hardings hotmix reseal
• Gravel resheeting will start from the end of the hotmix to the entry to the Harding's compound
• It is anticipated that all traffic will be able to pass through site from Monday 19 February (weather depending)
• Single Lane, Stop / Slow & 15 min delays will still be in operation until works are completed in March

   Above: Backfilling of the rock buttress is nearly complete

 

Oonah Road East (Guide Road)

• Sheet pile wall has been completed with king posts
• Excavation works are scheduled to begin next week (weather depending)
• Re-sheeting will be completed in this section once backfill is back to current road level

 

Oonah Road Far East

• Rock filling has commenced in the hairpin. Water is still coming through the rock shelf under the road rather than the culverts. The rock buttress is being interfaced with the rock shelf and will allow for free draining of this water.
• The road crossing culverts have been completed on the hill back to Highclere. An additional culvert will be replaced
  due to an obvious depression in the road on the downhill fill.
• There are other sections along Oonah road that have been identified as possible problem areas with obvious signs of the road sagging. A report on these areas  is being prepared to determine what, if any, remedial works are required.

Above: Rock filling has commenced in the hairpin at Oonah Road Far East.

Thank you so much to the community for your patience as we rebuilt this road.

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22 January 2024

Oonah Road (Douglas Road)

• Rock backfilling has begun
• A full road closure is required for 2 days to repair existing soft spots and install the new culvert
  • The road will be closed on Wednesday 31 January and Thursday 01 February.
• Re-sheeting will be completed in this section once backfill is back to current road level

 

Oonah East (Guide Road)

• Bridgepro have begun sheet piling tests with good results
• A 70m sheet pile wall be constructed through the landslip
• This is required to protect the workers during excavations of up to 5m deep and will be removed after the backfill has been completed

Above: Oonah Road East (Guide Road) - Sheet pile wall will be constructed through the landslip area

Oonah East

• Civilscape are currently upgrading the failed culverts down the hill
• In-fill and reshaping of the washed-out V Drain has commenced
• Rock fill in the hairpin has begun

Above: Rock fill in the hair pin has commenced 

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11 December 2023

Oonah Road (Douglas Road)

Harding Hotmix has commenced setting up site for road remediations on Oonah Road - West of Douglas Road. The road will be restricted to one lane, still allowing for vehicle and truck access to continue. As the width of the road will be limited, heavy vehicles are not permitted through the site. For heavy vehicles, please use the detour via Lockwood Creek Road. To ensure the safety of road users and workers, please obey all signage and speed limits.

 

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6 December 2023

Oonah Road Far East 

• Dig out of slip on the bend has exposed a secondary old pipe and the new fill sitting on top of the old road
• Water is disappearing into the ground before reaching the upstream culvert
• The road drain had been filed with loose rock that was washed away during the flood event
• These drains are being reinstated with appropriate backfill and reshaped.
• New culverts and upgrading existing broken culverts will continue

 

New road fill sitting on top of the old road

Dig out on slip end has exposed a secondary old pipe

Oonah Road East

The Sheet pile design is being finalised which will be required prior to the major excavations works. 

Oonah Road (Douglas Road)

Contractor Harding Hotmix will commence on site the third week of December. They will begin replacing the culvert and rebuilding the embankment. 

 

Thank you so much to the community for your patience as we rebuilt this road.

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29 September 2023

Oonah Road West - Completed

Asphalt has been laid with culverts and rock fill drains free flowing with water. 

Civilscape have done an excellent job given the amount of unknowns at the start and working through some very wet weather over winter. 

 

Oonah Road East

Design works have now been completed with major excavation works required to remove the landslip material (see diagram section A-A). Once the material has been removed, the road will be reinstated to the same alignment. 

Corner works will be completed at the same time which includes the fill batter repair, culvert extension and road drainage improvement. 

Civilscapes will commence works in early November. 

 

Thank you so much to the community for your patience as we rebuilt this road.

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21 July 2023

Oonah Road West - OPEN

Civilscape have done remarkably well to have removed so much unsuitable material and place an extraordinary amount of rock in just 5 weeks, especially given the weather conditions.

Oonah Road West will be re opened to the public from 5pm this afternoon (Friday 21 July). Gravel Road and Road Work signage is still in place with maintenance work to continuing next week.

Oonah Road West will re-open at 5pm on Friday 21 July 2023

1600 tones of rock was brought to the site 

 

Thank you so much to the community for your patience as we rebuilt this road.

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14 July 2023

Oonah Road West - Closed

Some small set backs. Oonah Road West will be closed for another week due to delays in laying the final road base. 

Civilscape are currently digging out the last ramp drain, and will be laying the final road base gravel over the current loose rock within the next few days. 

Oonah Road East - Road Remains Closed

Geotechnical investigations are showing that Oonah Road East is still an active landslip. Underground wells and movements are continuingly being monitored. For the publics safety, Oonah Road East will remain closed to all traffic until further notice. Final remediation designs for restoration are ongoing. 

 

Thank you to the community for your understanding as we continue to work hard for you on repairing these roads

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07 July 2023

Oonah Road West - Closed

We're almost there!

Civilscape imported around 1000T of rock yesterday and will have around 600T more by the end of today (Friday 7 July).

Water is freely draining at the bottom of the rock fill per the drainage channels. All going well next week (weather permitting) road gravel will go on and prepped to hopefully open the road next weekend.

 

Oonah Road East - Road Remains Closed

Geotechnical investigations are ongoing.

 

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25 May 2023

Oonah Road West - Closed

During reconstruction works, unsuitable material has been located at the subgrade level.

The road will be closed between Martin Place and Douglas Road for up to four weeks whilst the unsuitable material is removed and the road reconstructed. Council apologise for the delays. 

 

Unsuitable material located at the subgrade level 

 

Oonah Road East - Road Remains Closed

Geotechnical investigations are ongoing.

 

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Thank you to the community for your understanding as we continue to work hard for you on repairing these roads

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14 April 2023

Oonah Road West - Road Open to Single Lane Only

Civil scape contracting are currently placing and compacting sub-base material in preparation for top base material.

About 70% of the remediation works have been completed on Oonah Road.

compacting sub-base material

compacting sub-base material

Oonah Road East - Road Remains Closed

 

Thank you to the community for your understanding as we continue to work hard for you on repairing these roads

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3 April 2023

Oonah Road West - Road Open to Single Lane Only

Consolidation work is near complete on the East Bound lane with drainage work commencing on the west bound lane.

Fun fact to date nearly 2,000tons of ballast material (blue metal) has been imported to site, considering this comes in at the rate of 36tons per truck load - that’s a lot of truck loads!

Consolidation work may be finished within two weeks (weather dependant) then work can start rebuilding the road to final level.

Laying the ballast material 

commencing drainage works on the west bound lane

Oonah Road East - Road Remains Closed

 

 

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Thank you to the community for your understanding as we continue to work hard for you on repairing these roads

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10 March 2023

Oonah Road West - Road Open to Single Lane Only

Repair work to Oonah Road West was affected by 45mm of rain through the week. 

Excavations are continuing in order to establish a firm base for rebuilding the road. Site workers have exposed a number of subterranean drains - as remediation work continues.

 

 

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Thank you to the community for your understanding as we continue to work hard for you on repairing these roads

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3 March 2023

Oonah Road West - Road Open to Single Lane Only

Contactors have removed and stockpiled the existing gravel layer and will mix it with road gravel to reinforce it's strength.

The lower culvert embankment excavation works have commenced, with water beening discovered entering from the uphill side and getting under the culvert. It appears to be old water trapped in the embankment. 

Test holes either side of culvert will be cut to determine the extent of embankment water. This section will be monitored to see if any more water appears.

existing top gravel layer is removed

new drainage being installed 

 

Oonah Road East - Road Remains Closed 

Oonah Road East will remain closed to all traffic until further notice as a final design for restoration is still to be confirmed.

 

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Thank you to the community for your understanding as we continue to work hard for you on repairing these roads

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24 February 2023

Oonah Road West - Road Open to Single Lane Only

Contractors have commenced remediation work on Oonah Road West.

Works to rebuild the road include

• Clearing of trees on northern side of the road as well as any overhanging trees on the southern side.
• Upgrading culverts to dewater existing southern side of road
• Excavating the slip approx. 2.0m to a sound subgrade level
• Reconstruction of the pavement in layers to ensure stability
• Seal the road

(above) Remediation work begins at Oonah Road West clearing overhanging trees

Oonah Road East - Road Remains Closed 

We are still some way off identifying the most suitable solution for this part of Oonah Road, and subsequently Oonah Road will be closed in to the near foreseeable future.

 

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30 January 2023

Oonah Road West - Road Open to Single Lane Only

Repair work to Oonah Road West will commence in the next few weeks and will include:

• Rebuilding the downhill lane
• Creating and upgrading drainage systems to properly direct storm water run off
• Resealing of the road

 

Oonah Road East - Road Closed 

 

Oonah Road East has sustained significant land movement and is still an active slip.

Investigation work in this area is still continuing to identify the best sustainable solution.

Potential options being considered:

• Retaining wall to hold the slip
• Realign road uphill into the less impacted area

Land acquisitions may be required, depending on the solution. 

We are still some way off identifying the most suitable solution for this part of Oonah Road, and subsequently Oonah Road will be closed in to the near foreseeable future.

 

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Thank you to the community for your understanding as we continue to work hard for you on repairing these roads

 

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November 2022

A geotechnical investigation was conducted on the eastern landslide on the 27th of October and the western landslide on the 2nd of November 2022. A public meeting will be scheduled next week for Council Representatives to answer questions regarding the status of the findings to date. Further information will be provide regarding the date and time of the public meeting

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Two landslides have occurred along Oonah Road; one within the western portion of Oonah Road (located approximately 500m east of the East Cam River) and the other towards the eastern end of Oonah Road (located approximately 250m east of the Guide Road intersection).

A geotechnical investigation was conducted on the eastern landslide on the 27th of October and the western landslide on the 2nd of November 2022. A public meeting will be scheduled next week for Council Representatives to answer questions regarding the status of the findings to date. Further information will be provide regarding the date and time of the public meeting.

A summary of the engineering investigation are as follows:

Eastern Landslide

The Road has slumped in a section that is approximately 70m long and contain several large cracks. These cracks extend across the entire width of the road and into the natural soils above and below the road. The observations show that the failed section of road has been subject to a previous landslide, and the current failure is a reactivation of the past landslide.

The engineering investigation will continue over the next two weeks to determine the options for this area.  The road will remain closed until further information is obtained, on the basis that this area remains a significant safety risk to the public. 

 

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Western Landslide

The slumped section of road is approximately 125m long and contain several large cracks. This cracking is significant on the downhill side and extends across the entire width of the road. There is evidence of past landslide activity, however no obvious signs of any recent significant landslide activity was observed.

Most recent engineer tests have indicated that there is no significant structural issue with this portion of the road - the council can now look at initial remediation works as follows:

1:    Installing appropriate drainage, which involves cutting in channels which will be done using minimal earthworks. 

2:    Redirection of existing drainage

3:    Sealing of the open cracks to limit any further water damage.  

Once the above has been undertaken, we will consider the reopening of the uphill lane to traffic.  The downhill lane will need to remain closed  until additional remediation works are undertaken.

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Any individual or business impacted by the flood event, including those effected by these road closures may be eligible to apply for Tasmanian Recovery Funding through the Tasmanian Government.

https://alert.tas.gov.au/recovery/

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Further engineering information can be found below:

Eastern Landslide 

1. The site is underlain by basalt soils and is within a mapped low landslide hazard band
2. The slumped section of road is approximately 70m long and contains several large tension cracks in a typically semi-circle pattern.  The tension cracks within the road typically have vertical displacement of up to 0.4m and a horizontal displacement of up to 0.2m
3. The cracks within the road extend across the entire width of the road and extend into the natural soils above and below the road
4. Directly above the cracked section of road is amphitheatre shaped hill segment with concave slopes, indicative of a past landslide.  The cracks within the road extend out from this feature; and
5. Based on the site observations we consider that the failed section of road is the reactivation of a past landslide.

 

Western Landslide 

1. The slumped section of road is approximately 125m long and contains several large tension cracks in a typically semi-circle pattern.  The tension cracks within the road typically have vertical displacement of up to 0.25m and a horizontal displacement of up to 0.15m.  The cracking is significantly more pronounced on the downhill side of the road 
2. The cracks within the road extend across the entire width of the road and slightly extend into the spoon drain on the upper south eastern side of the road
3. The surrounding natural slopes are typically heavily undulated, consistent with possible past landslide activity, however no obvious signs of any recent significant landslide activity outside the extent of the road and road fill batter slopes was observed
4. Test pits indicate that the failure plane is located at the interface between the fill soils and the natural residual. The failure plane is shallow on the uphill side of the road and increases to 2.0m-2.5m towards the downhill side of the road.  

The intialal remediation works purposed are as follows:

Appropriately drain the depression/gully located above the road.  This will require minimal earthworks, involving cutting a channel from the depression to the upper culvert – approximately 10m long and 1-2m deep;

1. In the area where the tension cracks intersect the spoon drain on the uphill side of the road, redirect the spoon drain channel around this area (slightly cut the drain into the upper slopes); and
2. Seal up the open cracks to limit any further water ingress.